Theoretical High Energy Particle Physics Group

String Theory Seminars

Place: Potter Room (first floor, Pavilion B of the CMS)
Time: Thursdays, 1pm
Organiser: Dr Daniele Dorigoni, Dr Sungjay Lee

Easter 2013

11-Apr-2013: Landau levels and incompressible states in dense holographic matter

Gordon Semenoff (British Columbia) [Transparencies]
Abstract:

Past Seminars

• 2013:
  Lent
  Lent

  • 17-Jan-2013: Holomorphic blocks in 3 dimensions
    Sara Pasquetti (Surrey) [Transparencies]
    Abstract: We show that sphere partition functions and indices of 3 dimensional, N = 2, gauge theories can be decomposed into a sum of products of a universal set of holomorphic blocks. The blocks count BPS states of a theory on R2 x S1 and are in one-to-one correspondence with the theory's massive vacua. The blocks turn out to have a wealth of surprising properties such as a Stokes phenomenon and have interesting dual interpretations in analytically continued Chern-Simons theory and open topological strings.
  • 24-Jan-2013: On the physical meaning and consequences of the loop IR divergences in global dS
    Emil Akhmedov (ITEP) [Transparencies]
    Abstract: The tak is based on arXiv:1209.4448, arXiv:1202.1202 and arXiv:1110.2257. We show that in global de Sitter space its isometry is broken by the loop IR divergences for any invariant vacuum state of the massive scalars. We derive kinetic equation in global de Sitter space. It follows from the Dyson-Schwinger equation of the Schwinger-Keldysh diagrammatic technique in IR limit and allows to understand the physical meaning and consequences of the loop IR divergences. In many respects the isometry breaking in global dS is similar to the one in the contracting Poincare patch of de Sitter space. Hence, as a warm up exercise we study the kinetic equation and properties of its solutions in the expanding and contracting Poincare patches of de Sitter space. Quite unexpectedly we find that under some initial conditions there is an explosive production of massive particles in the expanding Poincare patch.
  • 31-Jan-2013: Dynamical simulations of holographic matrix models
    Curtis Asplund (Leuven) [Transparencies]
    Abstract: The holographic AdS/CFT duality of string theory lets you study quantum black holes indirectly via their dual field theory states. Most existing studies have focused on equilibrium or static quantities, such as entropies, temperatures, etc., or near-equilibrium quantities such as thermal Green's functions, linear transport coefficients and quasinormal modes. We wanted to learn about the real time, non-equilibrium dynamics of the field theory states and so made numerical simulations of some holographic matrix models [including flat space (BFSS) and plane wave (BMN) versions]. More precisely, these are simulations of the classical dynamics of the bosonic sectors of these models, which should be appropriate for high temperatures. This is in the same spirit as a molecular dynamics simulation of a fluid. I'll present the current results from our ongoing analysis of these simulations, in which we observe thermalization, fluctuations and other behavior. I'll then discuss and invite your comments on the relations to supergravity black holes and other future work. The talk is based on the papers arXiv:1104.5469 and arXiv:1211.3425.
  • 07-Feb-2013: Supersymmetric Field Theories on Three-Manifolds and Applications
    Cyril Closset (Weizmann Institute) [Transparencies]
    Abstract: In the first part of my talk, I will present a general classification of Riemannian three-manifolds on which one can put 3d N=2 supersymmetric field theories while preserving some amount of supersymmetry. This formalism clarifies the relationship between the extra couplings necessary to preserve supersymmetry in curved space, on the one hand, and various operators of the flat space theory, on the other hand. In the second part of the talk I will present some simple applications of this formalism. In particular I will present exact results for various two-point functions of N=2 SCFTs which were hitherto out of reach.
  • 12-Feb-2013: Higher spin symmetry and its breaking in CFTs
    Alexander Zhiboedov (Princeton) [Transparencies]
    Abstract: I will review the use of higher spin symmetry in conformal field theories (CFTs). First, I will demonstrate that the theory is essentially free when the higher spin symmetry is present. Then I will discuss different ways of breaking the higher spin symmetry. This will lead to the idea of 3d bosonization and prediction of certain critical exponents in the 3d Ising model.
  • 14-Feb-2013: Polylogarithms in tree-level open string calculations
    Johannes Broedel (Zurich ETH) [Transparencies]
    Abstract: Recent investigations have revealed a beautiful structure in open string tree-level amplitudes: they can be organized in terms of classes of multiple zeta values, which in turn provide the link to a related Hopf-algebra structure. While the open string tree-level function can be written in an extraordinarily simple form, the actual calculation was subject to difficulties and thus confined to low multiplicities and low orders in the inverse string tension. In this talk I will describe how to employ polylogarithms in order to algebraically obtain results for any multiplicity efficiently. Those results can be used to test the underlying algebra for previously unaccessible scenarios.
  • 28-Feb-2013: Landau Levels and Holography
    Mike Blake (DAMTP) [Transparencies]
    Abstract: One of the outstanding problems facing applied holography is the development of a complete understanding of how the traditional Fermi surfaces of condensed matter physics are realized in the bulk. Whilst the general problem is very hard, in this talk I shall describe a regime in which progress can be made. In the presence of a strong magnetic field the dynamics of fermions undergoes a dimensional reduction and we are able to use Coleman's classic technique of bosonization. This allows us to obtain a description of the Landau level physics of the boundary theory in terms of a `star' of gravitating sine-Gordon kinks in the bulk.
  • 5-Mar-2013: New transport properties of holographic superfluids
    Daniel Fernandez (University of Barcelona) [Transparencies]
    Abstract: In the context of holography applied to condensed matter theory, I will present an analysis of transport properties of p-wave superfluids by means of a gravity dual. Fluctuation modes in the SU(2) Einstein-Yang-Mills theory are considered, and phenomenological implications are derived. Due to the spatial anisotropy of the system, a non-universal shear viscosity is obtained, along with a new coefficient associated to normal stress differences. I will also discuss how the transport phenomena in this model is related to the thermoelectric, flexoelectric and piezoelectric effects (mixing of electric current, heat flux and mechanical stress).
  • 07-Mar-2013: Harmonic R-matrices for Scattering Amplitudes and Spectral Regularization
    Jan Plefka (Humboldt) [Transparencies]
    Abstract: Planar N=4 super Yang-Mills appears to be integrable. While this allows to find this theory's exact spectrum, integrability has hitherto been of no direct use for scattering amplitudes. To remedy this, we deform all scattering amplitudes by a spectral parameter. The deformed tree-level four-point function turns out to be essentially the one-loop R-matrix of the integrable N=4 spin chain satisfying the Yang-Baxter equation. Deformed on-shell three-point functions yield novel three-leg R-matrices satisfying bootstrap equations. Finally, we supply initial evidence that the spectral parameter might find its use as a novel symmetry-respecting regulator replacing dimensional regularization. Its physical meaning is a local deformation of particle helicity, a fact which might be useful for a much larger class of non-integrable four-dimensional field theories.
  • 14-Mar-2013: Holography without translational symmetry
    David Vegh (CERN) [Transparencies]
    Abstract: We propose massive gravity as a holographic framework for describing a class of strongly interacting quantum field theories with broken translational symmetry. At finite chemical potential, the gravity duals are charged black holes in asymptotically anti-de Sitter spacetime. The conductivity in these systems generally exhibits a Drude peak that approaches a delta function in the massless gravity limit, while the optical conductivity shows an emergent scaling law.
• 2012:
  Lent
  Lent

  • 19-Jan-2012: Moduli Stabilisation for Chiral Global Models
    Michele Cicoli (ICTP)
    [Transparencies]
    Abstract: I shall show how to combine moduli stabilisation and SU(5)- or MSSM -like chiral models in a fully consistent global set-up in Type IIB /F-theory by considering compactifications on Calabi-Yau orientifolds which admit an explicit description in terms of toric geometry. I shall present explicit choices of brane set-ups and fluxes which lead to three different phenomenological scenarios: the first with GUT -scale strings and TeV-scale SUSY ; the second with an exponentially large value of the internal volume and TeV-scale SUSY without fine-tuning the background fluxes; and the third with a very anisotropic configuration that leads to TeV-scale strings and two micron-sized extra dimensions. The fibred structure of the Calabi-Yau three-fold is also particularly suitable for cosmological purposes.
  • 28-Jan-2012: Singularity structure and massless dyons of pure N=2, d=4 theories with SU(r+1) and Sp(2r) gauge groups
    Jihye Seo (McGill University)
    [Transparencies]
    Notice: special place Seminar Room 1, Isaac Newton Institute
    Abstract: We study pure Seiberg-Witten theories with SU(r+1) and Sp(2r) gauge groups with no flavors. We study singularity loci of moduli space of the Seiberg-Witten curve. Using exterior derivative and discriminant operators, we can find Argyres-Douglas loci of the SW theory. We also compute BPS charges of the massless dyons of SU and Sp SW theory. In a detailed example of C_2=Sp(4), we find 6 points in the moduli space where we have 2 massless BPS dyons, and 3 of them give Argyres-Douglas loci. We show that BPS charges of the massless dyons jump as we go across Argyres-Douglas loci, giving an explicit example of Argyres-Douglas loci living inside the wall of marginal stability.
  • 01-Mar-2012: Fluid-Gravity Duality at a Cutoff Surface
    Cindy Keeler (U. Michigan)
    [Transparencies]
    Notice: special place Seminar Room 1, Isaac Newton Institute
    Abstract: We show by explicit construction that for every solution of the incompressible Navier-Stokes equation in $p+1$ dimensions, there is a uniquely associated "dual" solution of the vacuum Einstein equations in $p+2$ dimensions. We consider both a "near-horizon" limit in which $\Sigma_c$ becomes highly accelerated, and a long-wavelength hydrodynamic limit. We show that the near-horizon expansion in gravity is mathematically equivalent to the hydrodynamic expansion in fluid dynamics, and the Einstein equation reduces to the incompressible Navier-Stokes equation.
  • 08-Mar-2012: TBA
    Kyriakos Papadodimas (CERN)
    [Transparencies]
    Abstract: TBA.
  • 22-Mar-2012: The Harmony of Superstring Disk Amplitudes
    Oliver Schlotterer (MPI Munich)
    [Transparencies]
    Abstract: I will present the open string tree level amplitude of massless states to any number of external legs. It turns out that the kinematic factor of disk amplitudes is entirely captured by the underlying SYM field theory, i.e. that all the dependence on polarization vectors enters through color ordered SYM amplitudes. Moreover, the structure of the N point string theory amplitude exploits the minimal basis of (N-3)! SYM subamplitudes and adjoins a dual basis of (N-3)! hypergeometric functions encoding the alpha' corrections. These patterns within disk amplitudes exhibit rich implications from and to field theory.The pure spinor formalism is the crucial tool to identify SYM amplitudes within the string computation. That is why I introduce a compact representation for N point SYM amplitudes in pure spinor superspace. It reflects the decomposition into cubic diagrams a la Bern, Carrasco, Johansson and generalizes Berends Giele recursion relations.
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  Easter
  Easter

  • 26-Apr-2012: Time Evolution of Entanglement Entropy
    Matthew Roberts (New York University)
    [Transparencies]
    Abstract: We calculate the time evolution of the entanglement entropy in a 1+1 CFT with a holographic dual when there is a localized left-moving packet of energy density. We find the gravity result agrees with a field theory result derived from the transformation properties of Renyi entropy. We are able to reproduce behavior which qualitatively agrees with CFT results of entanglement entropy of a system subjected to a local quench. In doing so we construct a finite diffeomorphism which tales three-dimensional anti-de Sitter space in the Poincare patch to a general solution, generalizing the diffeomorphism that takes the Poincare patch a BTZ black hole. We briefly discuss the calculation of correlation functions in these backgrounds and give results at large operator dimension.
  • 17-May-2012: Cusp Anomalous Dimension in N=4 Super Yang-Mills from Integrability
    Diego Correa (IFLP, Universidad Nacional de La Plata)
    [Transparencies]
    Abstract:
  • 31-May-2012: One-Loop Renormalization and the S-matrix
    David Mcgady (Princeton University)
    [Transparencies]
    Abstract: In this talk, I will discuss the proportionality between tree amplitudes and the ultraviolet divergences in their one-loop corrections in Yang-Mills and (N < 4) Super Yang-Mills theories in four-dimensions. From the point of view of local perturbative quantum field theory, i.e. Feynman diagrams, this proportionality is straightforward: ultraviolet divergences at loop-level are absorbed into coefficients of local operators/interaction vertices in the original tree-amplitude. Ultraviolet divergences in loop amplitudes are also calculable through on-shell methods. These methods ensure manifest gauge-invariance, even at loop-level (no ghosts), at the expense of manifest locality. From an on-shell perspective, the proportionality between the ultraviolet divergences the tree amplitudes is thus not guaranteed. I describe systematic structures which ensure proportionality, and their possible connections to other recent developments in the field.
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  Michaelmas
  Michaelmas

  • 04-Oct-2012: The ABCDEFG of Instantons
    Jaewon Song (Caltech) [Transparencies]
    Abstract: We will discuss methods of computing instanton partition functions for arbitrary gauge groups including the exceptional ones. Even though there is no explicit algebraic construction of instanton moduli space available for the exceptional groups, we're able to evaluate the partition function using the blow-up recursion relations derived by Nakajima and Yoshioka. We compare this result with the proposal based on the superconformal index of SCFTs with E6, E7 global symmetry. We also compare our result with the norm of certain coherent states of W-algebras and thereby extending the AGT correspondence for pure YM theory to all gauge groups.
  • 11-Oct-2012: Scale Without Conformal Invariance
    Jeff Fortin (CERN) [Transparencies]
    Abstract: We investigate the theoretical implications of scale without conformal invariance in quantum field theory. We argue that the RG flows of such theories correspond to recurrent behaviors, i.e. limit cycles or ergodicity. We discuss the implications for the a-theorem and show how dilatation generators do generate dilatations.
  • 18-Oct-2012: Quarkonium dissociation by anisotropy in a strongly coupled CFT
    Mariano Chernicoff (DAMTP, U. Cambridge) [Transparencies]
    Abstract: We compute the screening length for heavy mesons moving through an anisotropic, strongly coupled N=4 super Yang-Mills plasma by means of its gravity dual. We present the results for arbitrary velocities and orientations of the mesons, as well as for arbitrary values of the anisotropy. For generic motion we find that: (i) mesons dissociate above a certain critical value of the anisotropy, even at zero temperature; (ii) there is a limiting velocity for mesons in the plasma, even at zero temperature; (iii) in the ultra-relativistic limit the screening length scales as $(1-v²⁾{\epsilon}$ with $\epsilon =1/2$, in contrast with the isotropic result $\epsilon =1/4$.
  • 25-Oct-2012: SCAPEZILLA: the backreaction of antibranes in flux compactifications
    Iosif Bena (Saclay) [Transparencies]
    Abstract: I will discuss the backreaction of anti-D3 branes in geometries with D3 brane charge dissolved in fluxes, and I will show that these solutions must have a certain singularity in the infrared. Since singular solutions must normally be discarded unless there is a compelling physical reason to accept the singularity, I will discuss possible mechanisms for its resolutions, and show that none work. If this singularity is not physical this will imply that the mechanism for uplifting AdS vacua (which are ubiquitous in flux compactifications of string theory) to dS vacua by placing antibranes does not work, and hence string theory does not have a landscape of dS vacua.
  • 01-Nov-2012: Partition function of N=(2,2) gauge theories on S^2 and vortices
    Stefano Cremonesi (Imperial College, London) [Transparencies]
    Abstract: I will review the basics of rigid supersymmetry on curved spacetimes and of supersymmetric localisation and apply these methods to 2d N=(2,2) supersymmetric field theories of vector and chiral multiplets with a vector U(1) R-symmetry on the round 2-sphere. I will explain two different localisation schemes, leading to the ``Coulomb branch'' and ``Higgs branch'' representations of the partition function. Finally, I will briefly overview the potential of these exact results for the study of type II string compactifications, geometry and supersymmetric gauge theories in various dimensions.
  • 08-Nov-2012: New Skins for an Old Ceremony: The Conformal Bootstrap and the Ising Model
    Sheer El-Showk (Saclay) [Transparencies]
    Abstract: The existence of a positive linear functional acting on the space of (differences between) conformal blocks has been shown to rule out regions in the parameter space of conformal field theories (CFTs). We argue that at the boundary of the allowed region the extremal functional contains, in principle, enough information to determine the dimensions and OPE coefficients of an infinite number of operators appearing in the correlator under analysis. Based on this idea we develop the Extremal Functional Method (EFM), a numerical procedure for deriving the spectrum and OPE coefficients of CFTs lying on the boundary (of solution space). We test the EFM by using it to rederive the low lying spectrum and OPE coefficients of the 2d Ising model based solely on the dimension of a single scalar quasi-primary ? no Virasoro algebra required. Our work serves as a benchmark for applications to more interesting, less known CFTs (such as the 3d Ising model) in the near future.
  • 15-Nov-2012: Probing higher spin black holes
    Eric Perlmutter (DAMTP, U. Cambridge)[Transparencies]
    Abstract: I will discuss recent progress in understanding higher spin black holes and their interactions with scalar fields, in the context of Vasiliev's 3d theory of higher spin gravity. This is relevant for the holographic duality with a certain class of 2d minimal model CFTs, proposed by Gaberdiel and Gopakumar. Despite unusual aspects of causality in higher spin gravity, the behavior of scalar boundary correlators in the black hole background appears consistent with a conventional black hole interpretation.
  • 22-Nov-2012: Stars, black holes and superconductors
    Simon Gentle (Durham U.) [Transparencies]
    Abstract: Charged black holes in planar AdS can be unstable to the formation of charged scalar hair. Through holography, one hopes to use this fact to uncover general principles governing unconventional superconductors. It has been shown however that the behaviour of `holographic superconductors' depends strongly on their embedding into string/M-theory. In this talk I will discuss two aspects of this issue in which progress can be made. First I will demonstrate how the ground states of these systems may be found by blowing up stars in global AdS, then I will hunt for the instability of highest temperature in a wider consistent truncation of supergravity. Both aspects raise concerns that a new approach to the problem is needed.
  • 29-Nov-2012: Unitarity and fuzzball complementarity: Alice fuzzes but may not even know it!
    Borun Chowdhury (Amsterdam U.) [Transparencies]
    Abstract: We investigate the recent black hole firewall argument. We argue that unitarity requires every quantum of radiation leaving the black hole to carry information about the initial state. Unitary evaporation is thus inconsistent with an information-free horizon at every step of the evaporation process. The required horizon-scale structure is manifest in the fuzzball proposal. To address the experience of an infalling observer, we argue for fuzzball complementarity. Unlike black hole complementarity and observer complementarity which postulate asymptotic observers experience a hot membrane while infalling ones pass freely through the horizon, fuzzball complementarity postulates that fine-grained operators experience the details of the fuzzball microstate and coarse-grained operators experience the black hole. In particular, this implies that an infalling detector tuned to energy E \sim TH, where TH is the asymptotic Hawking temperature, does not experience free infall while one tuned to E \gg TH does.
• 2011:
  Lent
  Lent

  • 20-Jan-2011: Invariants, symmetries and divergences
    Paul Howe (King's College London)
    [Transparencies]
    Abstract: "Supersymmetric invariants, their symmetries and various approaches to contructing them are discussed. Their role in the investigation of the onset of UV divergences is outlined. In particular, it is argued that D=4 N=8 supergravity is finite up to, and including, 6 loops."
  • 27-Jan-2011: Dense matter at strong coupling and hedgehog black holes
    Prem Kumar (Swansea University)
    [Transparencies]
    Abstract: "The thermodynamic properties of field theories at large-N with an equally large number of flavours are explored, focussing attention on the regime of low temperature and high density. At strong coupling, in the context of the D3-D7 system, it is argued that in a certain limit such states could be described by "hedgehog" black hole solutions."
  • 03-Feb-2011: Effective holographic theories for low-temperature condensed matter systems
    Elias Kiritsis (University of Crete and APC, Paris)
    [Transparencies]
    Abstract: "The IR dynamics of effective holographic theories capturing the interplay between charge density and the leading relevant scalar operator at strong coupling are analyzed. Such theories are parameterized by two real exponents (γ,δ) that control the IR dynamics. By studying the thermodynamics, spectra and conductivities of several classes of charged dilatonic black hole solutions that include the charge density back reaction fully, the landscape of such theories in view of condensed matter applications is characterized. Several regions of the (γ,δ) plane can be excluded as the extremal solutions have unacceptable singularities. The classical solutions have generically zero entropy at zero temperature, except when γ=δ where the entropy at extremality is finite. The general scaling of DC resistivity with temperature at low temperature, and AC conductivity at low frequency and temperature across the whole (γ,δ) plane, is found. There is a codimension-one region where the DC resistivity is linear in the temperature. For massive carriers, it is shown that when the scalar operator is not the dilaton, the DC resistivity scales as the heat capacity (and entropy) for planar (3d) systems. Regions are identified where the theory at finite density is a Mott-like insulator at T=0. We also find that at low enough temperatures the entropy due to the charge carriers is generically larger than at zero charge density. The extremal solutions found are the most general scaling solutions in the IR generalizing the AdS and Liftshitz backrounds."
  • 10-Feb-2011: String theory and the Velo-Zwanziger problem
    Rakibur Rahman (Scuola Normale Superiore, Pisa)
    [Transparencies]
    Abstract: "The Velo-Zwanziger problem is the loss of (causal) propagation of a charged massive field with spin greater than one, when minimally coupled to a constant electromagnetic background. String theory, originally proposed as a theory of massive high-spin particles, should spell out appropriate non-minimal terms to give a consistent description of such a system. We show that while string theory does achieve this feat, only the leading Regge trajectory fields can be exposed in isolation. We comment on the critical dimensionality, on the gyromagnetic ratio, and on some consistent dimensional reduction that can produce interesting models."
  • 17-Feb-2011: Mesons as open strings in holographic QCD
    Shigeki Sugimoto (IPMU, University of Tokyo)
    [Transparencies]
    Abstract: "We present our attempt to obtain meson spectrum from open strings in a top down approach of holographic QCD. Our main focus in this talk is on those obtained from the first and second excited massive open string modes. For example, we argue that a₂(1320), b₁(1235), π(1300), a₀(1450), etc., are identified as the first excited massive open string states and ρ₃(1690), π₂(1670), etc., are identified as the second excited states. Ref: arXiv:1005.0655 (Done in collaboration with Toshiya Imoto and Tadakatsu Sakai)"
  • 24-Feb-2011: The classical integrable structure of AdS/CFT
    Benoit Vicedo (DESY, Hamburg)
    [Transparencies]
    Abstract: "The classical integrability of Green-Schwarz superstrings on AdS backgrounds relevant for the AdS/CFT correspondence relies on the existence of a Lax connection whose flatness is equivalent to the classical equations of motion. I will explain how a careful derivation of this Lax connection within the Hamiltonian framework leads to a modification of the well known Bena-Polchinski-Roiban connection. Surprisingly, this new Lax connection coincides with the matter part of the pure spinor superstring Lax connection of Vallilo. We then show that the associated underlying integrable structure has a very natural description within the R-matrix formalism. In particular, we identify the classical R-matrix and give a simple algebraic meaning to the Zhukovksy map which plays a central role in the AdS/CFT correspondence."
  • 03-Mar-2011: The F-ate of GUTs
    Sakura Schäfer-Nameki (King's College London)
    [Transparencies]
    Abstract: "I will discuss, what constraints SUSY GUTs have to satisfy in order to arise from generic F-theory compactifications to 4d. Surprisingly, a lot can be said quite generally, with fateful implications ..."
  • 10-Mar-2011: Geometry of double field theory
    Olaf Hohm (MIT, Cambridge)
    [Transparencies]
    Abstract: "I discuss the recently constructed so-called double field theory, which introduces in addition to the usual coordinates new "winding-type" coordinates in order to make the T-duality property of string theory manifest at the level of the low-energy effective space-time action. The new geometrical features which extend the Riemannian geometry underlying pure Einstein gravity are discussed."
  • 17-Mar-2011: Framed BPS states, moduli dynamics, and wall-crossing
    Sungjay Lee (University of Cambridge)
    [Transparencies]
    Abstract: "I will discuss supersymmetric low energy dynamics for BPS dyons in strongly-coupled N=2 Seiberg-Witten theories, and derive wall-crossing formulae thereof. For BPS states made up of a heavy core state and n probe (halo) dyons around it, I will derive a reliable supersymmetric moduli dynamics with 3n bosonic coordinates and 4n fermionic superpartners. The small parameters that control the approximation are not electric couplings but the mass ratio between the core and the probe, as well as the distance to the marginal stability wall where the central charges of the probe and of the core align. Quantizing the dynamics, we construct BPS bound states and derive the primitive and the semi-primitive wall-crossing formulae, conjectured by Denef and Moore from the first principle. I will also speculate on applications to line operators and Darboux coordinates, and also about extension to supergravity setting."
  • 24-Mar-2011: Physical properties of p-wave holographic superconductors
    Johanna Erdmenger (Werner Heisenberg Institute, Munich)
    [Transparencies not available]
    Abstract: "Recently, considerable progress has been achieved in using gauge/gravity duality for describing strongly coupled systems of relevance for condensed matter physics. In this context, I discuss both top-down approaches and bottom-up approaches to holographic superconductors where the order parameter has p-wave symmetry. In the top-down approaches, the holographic superconductors are realized in a probe brane construction involving a probe of two D-branes at finite isospin density. The dual field theory is known explicitly. We obtain the thermodynamics and the Fermi surface for these systems. Moreover, we consider bottom-up approaches for p-wave superconductors in which we study the back-reaction of the required SU(2) gauge field on the geometry. We find the phase diagram. A particularly interesting feature of this model is that the shear viscosity over entropy ratio displays non-universal behaviour, it is temperature-dependent at leading order in N and lambda."
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  Easter
  Easter

  • 05-May-2011: Describing M5-branes using loop spaces
    Christian Sämann (Heriot-Watt University, Edinburgh)
    [Transparencies]
    Abstract: "I will start by discussing a lift of the ADHM construction of monopoles, which can be interpreted in terms of a D1-D3-brane configuration, to a construction of self-dual strings, which is related to an M2-M5-brane configuration. This construction involves a loop space description of the abelian M5-brane theory. I will then show that the nonabelian loop space equations correspond to a recently found set of supersymmetric equations for the (2,0) tensor multiplet in six dimensions. Therefore, they might indeed capture some aspects of the effective dymanics of multiple M5-branes."
  • 12-May-2011: Holographic phase space: c-functions and black holes as renormalization group flows
    Miguel Paulos (LPTHE, Paris)
    [Transparencies]
    Abstract: "We consider domain-wall and AdS-black hole backgrounds in Lovelock theories of gravity. We construct a "c-function" N(r) for these, which we argue counts the number of effective fields at a given scale - on AdS spaces it is related to the Euler anomaly, and at a black hole horizon it is proportional to the entropy. The monotonicity properties of N are controlled by the "gravitational field" which has opposite signs in the domain-wall and black hole backgrounds, due to the presence of negative (positive) energy in the former (latter). We show how N can be written as the ratio of the Wald entropy to a quantity resembling an effective phase space volume."
  • 19-May-2011: Holographic hydrodynamics on non-conformal field theories
    Giuseppe Policastro (Ecole Normale Superieure, Paris)
    [Blackboard talk]
    Abstract: "In recent years the description of the transport properties of non-conformal field theories has attracted much attention. I will discuss some of these results, in particular concerning the phenomenological models of "improved holographic QCD" based on Einstein-dilaton gravity with a potential."
  • 26-May-2011: Anomaly-induced charges from Skyrme model
    Takaaki Ishii (University of Cambridge)
    [Transparencies not available]
    Abstract: "We investigate baryons under external electromagnetic fields. We show a novel charge structure of baryons in electromagnetic field due to the chiral anomaly. Here baryons are treated as solitons of mesons, and we use Skyrmions to calculate the charge distributions in a single baryon and find an additional charge. We discuss the nonlinear pion clouds the baryons wear. Amusing charge distributions for classical multi-baryons with B=2, 3,...,8 and 17 are also shown."
  • 02-Jun-2011: Lessons from holography: the shear viscosity bound and UV/IR decoupling
    Sera Cremonini (University of Cambridge and Texas A&M University, College Station)
    [Transparencies]
    Abstract: "The gauge gravity duality has proven to be a valuable tool for probing the dynamics of strongly coupled field theories. Within this program, much of the focus is now on systems which exhibit rather different UV and IR behaviors. In this talk I will discuss the role played by the gauge/gravity duality on understanding properties of the shear viscosity to entropy ratio. In particular, I will focus on theories where there is a decoupling of UV from IR physics."
  • 09-Jun-2011: The complete n-point superstring disk amplitude in pure spinor superspace
    Carlos Mafra (Albert Einstein Institute, Potsdam)
    [Transparencies not available]
    Abstract: "In this talk I'll show how the pure spinor formalism can be used to obtain a surprinsingly simple closed-formula solution to all n-point superstring disk amplitudes."
  • 16-Jun-2011: Holography of mass-deformed M2-branes
    Seok Kim (Seoul National University, Seoul)
    [Transparencies]
    Abstract: "We study holographic aspects of M2-brane CFT with mass deformations. We first show how the geometry of Lin, Lunin, Maldacena is related to the supersymmetric vacua of the field theory. We also find the holographic RG flow of a mass-deformed CFT and find the Schrodinger geometry in the IR."
  • 23-Jun-2011: N³ and junctions in 6-dimensional (2,0) theories
    Kimyeong Lee (Korea Institute for Advanced Study, Seoul)
    [Transparencies]
    Abstract: "We count the number of 1/4 BPS objects in the Coulomb phase of 6d (2,0) theories and find it is identical to one-third of their anomaly coefficient c_G which is product of the dimension and dual Coxeter number of the corresponding group."
  • 12-Jul-2011: Differential geometry for string theory, beyond Riemann
    Imtak Jeon (Sogang University, Seoul)
    [Transparencies]
    Notice: special date and time Tuesday, 12-Jul-2011, 2:15pm
    Abstract: "While the fundamental object in Riemannian geometry is the metric, closed string theories put a two-form gauge field and a dilaton on the same footing as the metric. In this talk we introduce a novel differential geometry which treats those three objects in a unified manner, and manifest not only the gauge symmetries (diffeomorphism plus one-form gauge symmetry) but also the O(D,D) T-duality. We also discuss how to couple to Yang-Mills theory."
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  Michaelmas
  Michaelmas

  • 06-Oct-2011: Holographic Fermi Surfaces: The view from the top down
    Julian Sonner (Imperial College London & University of Cambridge)
    [Transparencies]
    Abstract: Strongly interacting fermions at finite density are infamously hard to treat. Gauge/gravity duality gives a way of studying them in a controlled environment. For such studies to be reliable it is important that the models are eventually embedded in M-theory (or string theory). In this talk I will describe how to look for some of the most basic features of fermionic finite-density states in M-theory, such as the occurrence of Fermi surfaces, and describe the wider implications of our recent intriguing results on these objects.
  • 13-Oct-2011: On Renormalization Group Flows in Four Dimensions
    Zohar Komargodski (IAS & Weizmann Institute of Science)
    [Transparencies]
    Abstract: We discuss some general aspects of renormalization group flows in four dimensions. Every such flow can be reinterpreted in terms of a spontaneously broken conformal symmetry. We analyze in detail the consequences of trace anomalies for the effective action of the Nambu-Goldstone boson of broken conformal symmetry. While the c-anomaly is algebraically trivial, the a-anomaly is "non-Abelian," and leads to a positive-definite universal contribution to the S-matrix of 2->2 dilaton scattering. Unitarity of the S-matrix results in a monotonically decreasing function that interpolates between the Euler anomalies in the ultraviolet and the infrared, thereby establishing the a-theorem.
  • 20-Oct-2011: Aspects of Holographic Fermions
    Joao Laia (University of Cambridge)
    [Transparencies]
    Abstract: We show how to compute beta functions for double trace fermionic operators in the dual conformal field theory. We also describe a novel implementation of non-relativistic fermions in AdS/CFT by imposing Lorentz violating boundary terms for a Dirac spinor in AdS4. The dual boundary theory is scale invariant, and can be reached by an RG flow started by a Lorentz violating double trace perturbation. This new CFT exhibits a number of interesting properties, including a dispersionless flat band of gapless excitations.
  • 24-Oct-2011: Instantons from Branes and Higgs Vacua in N=1 Theories
    Anatoly Dymarsky (IAS)
    [Transparencies]
    Notice: special date and time Monday, 24-Oct-2011, 4:00pm
    Abstract: We study vacua of N=1 SUSY gauge theory using conventional field theory tools and a dual supergravity background. The Higgs vacua are dual to mobile D3-branes which dissolve into flavor D7-branes. Hence the moduli space of the world-volume gauge instantons on D7-branes should match the Higgs branch of the field theory. In case of N=2 theories this relation was readily provided by the ADHM construction. In the N=1 case both sides of the duality are more complicated because of quantum corrections. We carefully analyze the case of the cascading N=1 SU(N+M)xSU(N) theory and find agreement between field theory and gravity.
  • 27-Oct-2011: Fluid/gravity at finite "r"
    Daniel Brattan (Durham University)
    [Transparencies]
    Abstract: In this talk I will review my recent paper, arXiv:1106.2577, which gives the dual field theory formulation of the Dirichlet problem for gravity in the bulk. I will highlight some rather surprising results and the still open questions they pose.
  • 03-Nov-2011: Matrix models, duality and spontaneous SUSY breaking in 3D QFT
    Vasilis Niarchos (University of Crete)
    [Transparencies]
    Abstract: I will discuss recent developments in three-dimensional superconformal field theories based on the use of localization techniques. Special emphasis will be given to a particular example of three-dimensional Seiberg-like duality and the proposal of a new non-perturbative constraint on spontaneous supersymmetry breaking based on matrix models.
  • 10-Nov-2011: Holographic three-point functions for short operators
    Joseph Minahan (Uppsala University)
    [Transparencies]
    Abstract: "TBA."
  • 17-Nov-2011: On the Taxonomy of Holographic Fermi/Non-Fermi Liquids
    Norihiro Iizuka (CERN)
    [Transparencies]
    Abstract: The existence of Non-Fermi liquids which are not described by Landau?s Fermi liquids is a fascinating puzzle in theoretical physics. In this talk, I will show universal field theories where we can go around the Landau?s Fermi-liquids and obtain Non-Fermi-Liquid behavior. These field theories contain dynamical singlet fermions which couple through fermion bilinear terms to strongly coupled sectors which are characterized by its dynamical scaling. Suppose these strongly coupled sectors have gravity dual (which is not necessarily anti-de Sitter space), then by using powerful gauge/gravity duality, I will argue how these dynamical scaling parameters determine the natures of the dynamical singlet fermions in a very universal way; These natures include the existence of Fermi-/Non-Fermi liquids, sharp Fermi-surface, the decay rates and breakdown of the quasi-particles description. I will end with discussion for generalization of our work to include the lattice effects and impurities for more interesting condensed matter system.
  • 24-Nov-2011: Holography of Einstein-Maxwell-Dilaton theories and applications to Condensed Matter Systems
    Blaise Gouteraux (Universite Paris 7)
    [Transparencies]
    Abstract: Recently, holographic techniques have been applied to Condensed Matter Systems (CMS) with strongly-coupled electrons. Einstein-Maxwell-Dilaton (EMD) theories provide an interesting setup for such endeavours, as they allow non-trivial, non-conformal Infra-Red fixed points, which are postulated to be Quantum Critical (QC) points describing the physics near extremality. First, we shall describe the black hole solutions of EMD theories and review earlier results on their transport coefficients. Then, we shall address the issue of how to set holography up for these theories, using 'generalised' dimensional reduction. Finally, we shall apply this to the previously mentionned QC points.
  • 01-Dec-2011: k-String Tension from Eguchi-Kawai Reduction
    Daniele Dorigoni (University of Cambridge)
    [Transparencies]
    Abstract: The k-string can be thought of as a bound state of k fundamental QCD-strings. Its tension has been vastly discussed in the literature. In particular, most analytic approaches in the case of theories with adjoint fermions suggest that the k-string tension respect the Sine scaling. After having introduced some basic facts about k-string I will discuss how the use of Eguchi-Kawai dimensional reduction can help us in computing the tension. As an explicit example I will discuss in details the reduction of adjoint-QCD from 3 to 2 dimensions in which the k-string tension can be computed under some assumptions, whose validity I will analyse.
  • 08-Dec-2011: Spinning Conformal Correlators and Blocks
    Slava Rychkov (Ecole Normale Superieure)
    [Transparencies]
    Abstract: We will talk about recent progress in using embedding space formalism to describe conformally invariant correlation function of operators with spin.
  • 15-Dec-2011: Bosonic Excitations in Holographic Quantum Liquids
    Richard Davidson (University of Oxford)
    [Transparencies]
    Abstract: I will discuss the bosonic excitations present in certin strongly-interacting holographic field theory states with a large density of matter. Particular attention will be paid to the properties of the sound modes of these theories and how they compare with the properties of the sound mode of a Landau-Fermi liquid.
• 2010:
  Lent
  Lent

  • 14-Jan-2010: Surprising symmetry of scattering amplitudes in gauge theories
    Gregory Korchemsky (CEA Saclay)
    [Transparencies]
    Abstract: "I will review a recent progress in computing scattering amplitudes in gauge theories - a fascinating subject which has been recently boosted by the formulation of the gauge/string duality in maximally supersymmetric Yang-Mills theory. In addition to the conventional symmetry of the underlying Lagrangian, the scattering amplitudes in this theory exhibit a new, dual superconformal symmetry. This symmetry is powerful enough to completely determine the scattering amplitudes for arbitrary coupling in a suitably defined limit."
  • 21-Jan-2010: Inching towards strange metallic holography
    David Tong (University of Cambridge)
    [Transparencies]
    Abstract: "Strange metals are materials with numerous anomalous properties. The flow of electricity within these materials cannot be explained in the familiar language of a fluid of individual electrons, but instead requires a new strongly interacting description. In this talk, I will review some basic facts about these materials. With this as motivation, I will explain how to compute conductivity in certain strongly interacting, non-relativistic field theories which are defined holographically by gravity in Lifshitz backgrounds."
  • 28-Jan-2010: T-duality invariant string theory at the quantum level
    Daniel Thompson (Queen Mary, University of London)
    [Transparencies]
    Abstract: "In this talk I will be discussing some reformulations of string theory which promote T-duality to the level of a manifest symmetry namely Hull's Doubled Formalism and Klimcik and Severa's Poisson-Lie T-duality. Such formalisms double the number of fields but also incorporate some chirality-like constraint. Invoking this constraint leads one to consider sigma-models which though duality invariant do not possess manifest Lorentz Invariance. Whilst such formalisms make sense at a classical level their quantum validity is less obvious. I address this issue by examining the renormalization of these duality invariant sigma models. This talk is based upon both forthcoming work and recent work: arXiv:0910.1345 [hep-th] and its antecedents arXiv:0708.2267 [hep-th], arXiv:0712.1121 [hep-th]."
  • 04-Feb-2010: Gradient formula for the beta function of 2d quantum field theory
    Anatoly Konechny (Heriot-Watt University, Edinburgh)
    [Transparencies]
    Abstract: "A gradient formula is proven of the form ∂_ic = -(g_ij + Δg_ij-b_ij)β^j where β^j are the beta functions, c and g_ij are the Zamolodchikov c-function and metric, b_ij is an antisymmetric tensor introduced by H. Osborn and Δg_ij is a certain metric correction. The formula is derived under the assumption of stress-energy conservation and certain conditions on the infrared behaviour. Being specialized to non-linear sigma models this formula implies a one-to-one correspondence between renormalization group fixed points and critical points of c."
  • 11-Feb-2010: Towards exact quantum entropy of black holes
    Atish Dabholkar (LPTHE, Paris)
    [Transparencies]
    Abstract: "I will report on some recent progress on defining and computing finite size effects in the entropy of black holes with highly nontrivial agreements between thermodynamics and statistical mechanics. I will describe a number of puzzles and their resolutions along with some exact computations, and then briefly discuss the role of mock modular forms and Borcherds-Kac-Moody superalgebras in this context."
  • 18-Feb-2010: Magnetic bags and black holes
    Stefano Bolognesi (University of Cambridge)
    [Blackboard talk]
    Abstract: "We begin with a review of magnetic bags, which are macroscopic limit of multi-monopoles with large magnetic flux. We focus on some of their common properties with black holes. We then add gravity to the system, and study the transition from monopole to black hole."
  • 25-Feb-2010: Viscosity and conductivity in general theories of gravity
    Miguel Paulos (University of Cambridge)
    [Transparencies]
    Abstract: "Recently there has been great interest in calculating transport coefficients for field theories at large coupling, using AdS/CFT. In this talk I will discuss recent work showing how to use the membrane paradigm to easily compute the shear viscosity and conductivity in arbitrary gravity theories. In a certain sense these can be thought of as effective couplings at the black hole horizon dual to the field theory plasma. An explicit Wald-like formula for these couplings is given for a large class of generalized gravity theories."
  • 04-Mar-2010: Brane tilings, M2-branes and Chern-Simons theories
    Noppadol Mekareeya (Imperial College London)
    [Transparencies]
    Abstract: "Brane tilings are known to describe the largest known class of SCFTs in 3+1 dimensions. There is a well established formalism to find AdS₅ x SE₅ duals to these SCFTs and to compare results on both sides. This talk extends this formalism to 2+1 dimensional SCFTs, living on the worldvolume of M2-branes, which are dual to AdS₄ x SE₇ backgrounds of M-theory. The SCFTs are quiver gauge theories with 4 supercharges (N=2 in 2+1 dimensions) and Chern-Simons couplings. They admit a moduli space of vacuum configurations which is a CY₄ cone over SE₇. The talk will go over the formalism and look at several examples in detail."
  • 11-Mar-2010: Connections between dualities of string theory and the ultraviolet properties of maximal supergravity
    Michael Green (University of Cambridge)
    [Transparencies]
    Abstract: "This talk will present a forensic analysis of the first few terms in the low energy expansion of the type II superstring four graviton amplitude in dimensions 3≤D≤10. Terms in this expansion are automorphic functions of the moduli that are invariant under the duality groups in the E_n series (1≤n≤8). In particular, they are expressed in terms of Langlands Eisenstein series and generalisations that possess some very surprising properties. The coefficients of logarithmic ultraviolet divergences of maximal supergravity are encoded in the structure of these functions and emerge as a consequence of the dualities. This suggests that there is a seven-loop divergence in N=8 supergravity in four dimensions."
  • 18-Mar-2010: 3d N=2 CFTs with chiral flavours from M2-branes at toric CY₄ singularities
    Stefano Cremonesi (Tel-Aviv University)
    [Transparencies]
    Abstract: "Following the work of Aharony, Bergman, Jafferis and Maldacena, a great effort has been made to understand the 3d conformal gauge theories describing M2-branes at conical singularities. Special attention has been directed to N=2 supersymmetric AdS₄/CFT₃ pairs arising from M2-branes at toric CY 4-folds, where powerful algebraic techniques are available. After reviewing known results concerning brane tilings, the relation between the toric CY₃ and CY₄ moduli spaces of 4d and 3d toric quiver gauge theories, and M-theory/type IIA duality, I will explain how fundamental flavours naturally arise in this framework, and how their matter content and superpotential couplings to bifundamental fields are encoded in geometric data. Quantum effects are crucial in determining the moduli spaces of such flavoured quiver gauge theories. Quiver Chern-Simons (CS) theory of the kind considered in the AdS₄/CFT₃ literature so far can be obtained by coupling a 3d gauge theory with the same quiver diagram but no CS terms to chiral flavours, and integrating the latter out via a real mass term."
  -
  Easter
  Easter

  • 22-Apr-2010: Phenomenology of D-branes at toric singularities
    Sven Krippendorf (University of Cambridge)
    [Transparencies]
    Abstract: "In this talk I will discuss aspects of D-brane model building at toric singularities. After reviewing dimer techniques, I will apply these tools to show an upper bound on the number of families and discuss why the lightest quark is massless in this infinite class of models. We compute the CKM matrix for explicit models in this setting and find the singularities possess sufficient structure to allow for realistic mixing between generations and CP violation. This talk is based on arXiv:1002.1790."
  • 29-Apr-2010: Pohlmeyer reduction for AdS₅ x S⁵ superstring
    Arkady Tseytlin (Imperial College London)
    [Transparencies]
    Abstract: "We shall review several aspects of Pohlmeyer reduction applied to AdS₅ x S⁵ superstring. We shall discuss the tree-level S-matrix for the elementary excitations of the reduced theory and compare it to the S-matrix of the superstring theory."
  • 06-May-2010: Fluxes, geometries and non-geometries
    Savdeep Sethi (University of Chicago)
    [Transparencies]
    Abstract: Not available
  • 13-May-2010: N=8 and N=6 superspace constraints for three-dimensional gauge theories
    Robert Wimmer (Ecole Normale Superieure, Lyon)
    [Transparencies]
    Abstract: "We present a systematic analysis of the N=8 and N=6 superspace constraints in three space-time dimensions. The general coupling between vector and scalar supermultiplets is encoded in an SO(8) tensor for the N=8 and an SU(4) tensor for the N=6 case. These tensors are functions of the matter superfields and are subject to a set of algebraic and super-differential relations. We show how conformal BLG- and ABJM models, which describe the dynamics of M2 branes in M-theory, as well as the three-dimensional super Yang-Mills theory provide solutions to these constraints and can both be formulated in this universal framework. We also discuss the supersymmetry enhancement from N=6 to N=8 via monopole operators."
  • 20-May-2010: SUSY gauge theories and quantum many body systems
    Samson Shatashvili (Trinity College, Dublin and IHES, Bures-sur-Yvette)
    [Transparencies]
    Abstract: "I review recent results on the relation between supersymmetric vacua and quantum integrability."
  • 27-May-2010: Heterotic moduli space via linear sigma models
    Ilarion Melnikov (Albert Einstein Institute, Potsdam)
    [Blackboard talk]
    Abstract: "The linear sigma model is particularly adept at describing an interesting subset of heterotic moduli. Recently these deformations were studied for mirror pairs of Calabi-Yau hypersurfaces in toric varieties. This led to an identification of mirror symmetric (0,2) linear sigma models, as well as a construction of an explicit mirror map. I will discuss these developments and their significance for our understanding of the heterotic string."
  • 03-Jun-2010: Amplitudes using pure spinors
    Jonas Bjornsson (University of Cambridge)
    [Transparencies]
    Abstract: "A first quantised approach to loop amplitudes based on the pure spinor particle is applied to the systematics of four-graviton amplitudes in theories with maximal supersymmetry. Counting of fermionic zero modes allows the identification of momentum factors multiplying R⁴ in the low energy limit thereby making manifest their ultraviolet properties as a function of dimension, D. For L=2,3,4 loops the leading divergence is in D=4+6/L dimensions and proportional to d^2L R⁴, in line with earlier field theory calculations. However, at 5 loops there is a radical change in the systematics, suggesting the presence of a contribution with an explicit logarithmic ultraviolet divergence when D=24/5 that is proportional to d⁸ R⁴. We further argue that d⁸ R⁴ should receive contributions from all loops, which would imply that N=8 supergravity (with D=4) is not protected by supersymmetry from a seven-loop divergence."
  • 08-Jun-2010: Black hole microstate counting and its macroscopic counterpart
    Ashoke Sen (Harish-Chandra Research Institute, Allahabad)
    [Transparencies]
    Notice: special date and time Tuesday, 08-Jun-2010, 4:00pm
    Abstract: "In this talk we shall describe how the near horizon geometry of an extremal black hole contains precise information about the ensemble of quantum states the black hole represents. This includes not only the total number of states in the ensemble, but also distribution of global charges among the members of the ensemble."
  • 10-Jun-2010: Supersymmetry, localization and quantum entropy function
    Ipsita Mandal (Harish-Chandra Research Institute, Allahabad)
    [Transparencies]
    Abstract: "AdS₂/CFT₁ correspondence leads to a prescription for computing the degeneracy of black hole states in terms of path integral over string fields living on the near horizon geometry of the black hole. In this talk, I will discuss about how to make use of the enhanced supersymmetries of the near horizon geometry and localization techniques to argue that the path integral receives contribution only from a special class of string field configurations which are invariant under a subgroup of the supersymmetrytransformations. I will identify saddle points which are invariant under this subgroup. I will also use this analysis to show that the integration over infinite number of zero modes generated by the asymptotic symmetries of AdS₂ generate a finite contribution to the path integral."
  -
  Michaelmas
  Michaelmas

  • 07-Oct-2010: From correlation functions to Wilson loops and amplitudes
    Burkhard Eden (Durham University)
    [Transparencies]
    Abstract: "We discuss a class of n-point correlation functions of 1/2 BPS operators in N=4 super Yang-Mills theory in four dimensions. Since this is a massless theory the question is best discussed in configuration space. For generic positions of the operators these correlation functions are finite. We give a summary of recent work on the leading singular behaviour in a limit in which the positions are taken to be successively light-like separated. In dimensional regularisation or with a mass regulator the correlation functions reduce to polygonal Wilson loops with light-like edges. A useful technical tool is to compute the correlators by insertions of the N=2 Yang-Mills Lagrangian, in which case it is particularly simple to take the light-like limit. If in a non-standard version of dimensional regularisation only the dimension of the integration measure at the insertion points is modified, we reproduce scattering amplitudes instead. The integrand obtained in this way exactly agrees with a recent proposal by Arkani-Hamed et al."
  • 14-Oct-2010: Scaling and integrability from AdS₅ x S⁵
    Riccardo Ricci (Imperial College London)
    [Transparencies]
    Abstract: "According to AdS/CFT a remarkable correspondence exists between strings in AdS₅ x S⁵ and operators in N=4 SYM. A particularly important case is that of fast-spinning folded closed strings and the so called twist-operators in the gauge theory. This is a remarkable tool for uncovering and checking the detailed structure of the AdS/CFT correspondence and its integrability properties. In this talk I will show how to match the expression of the anomalous dimension of twist operators as computed from the quantum superstring with the result obtained from the Bethe ansatz of SYM. This agreement resolves a long-standing disagreement between gauge and string sides of the AdS/CFT duality and provides a highly nontrivial strong coupling test of SYM integrability."
  • 21-Oct-2010: The classical geometry of quantum integrability
    Nikita Nekrasov (IHES, Bures-sur-Yvette)
    [Transparencies]
    Abstract: "Supersymmetric gauge theories give rise to a plethora of quantum integrable systems, and to a construction of the spectra of the latter. In some cases the gauge theory construction is equivalent to the Bethe ansatz techniques, in the form of the Bethe equations written in terms of the Yang-Yang functional. We explain the meaning of this functional (which puzzled the experts in the field for the last forty years) using the branes in the gauge theory. An important ingredient of our construction in the case of Hitchin system is the new set of Darboux coordinates on the moduli space of flat SL(2,C) connections."
  • 28-Oct-2010: Mesons in the (Dymarsky-)Kuperstein-Sonnenschein holographic models
    Matthias Ihl (Universidade Federal do Rio de Janeiro)
    [Transparencies]
    Abstract: "I will first discuss some new results concerning the phenomenology of pions and vector mesons in a model of flavor chiral symmetry breaking in the Klebanov-Witten background, recently introduced by Kuperstein and Sonnenschein. I will outline the calculation of electromagnetic form factors in this model. Here, our main result is the pion form factor, which matches available experimental data surprisingly well. In the second part of the talk, I will present our results and discuss ongoing research relating to the spectra of scalar and vector mesons in the Dymarsky-Kuperstein-Sonnenschein model, which geometrically realizes flavor chiral symmetry breaking in the Klebanov-Strassler model, i.e. a non-conformal deformation of the Klebanov-Witten background. Interestingly, the lightest scalar meson, associated with fluctuations of the background gauge field, is lighter than the lightest vector meson in this model, which potentially has interesting implications for holographic nuclear physics."
  • 04-Nov-2010: Double field theory and the geometry of duality
    Chris Hull (Imperial College London)
    [Transparencies]
    Abstract: "String theory on a torus requires the introduction of dual coordinates conjugate to string winding number. For a d-torus, string theory can be formulated in terms of an infinite tower of fields depending on both the d torus coordinates and the d dual coordinates. This talk focuses on a finite subsector consisting of a metric and b-field (both d x d matrices) and a dilaton all depending on the 2d doubled torus coordinates. The double field theory is constructed and found to have a novel symmetry that reduces to diffeomorphisms and anti-symmetric tensor gauge transformations in certain circumstances. It also has manifest T-duality symmetry which provides a generalisation of the usual Buscher rules to backgrounds without isometries. The theory has a real dependence on the full doubled geometry: the dual dimensions are not auxiliary. It is concluded that the doubled geometry is physical and dynamical."
  • 11-Nov-2010: From weak to strong coupling in ABJM theory
    Marcos Marino (Geneva University)
    [Transparencies]
    Abstract: "It has been recently pointed out that the partition function and Wilson loop vevs in ABJM theory can be computed by a matrix model. By relating it to a topological string theory, we solve this matrix model at all orders in the 1/N expansion. We show that the planar limit gives explicit, exact interpolating functions of the 't Hooft coupling which make it possible to test various gravity predictions for the strong coupling behavior of ABJM theory. We give in particular the first gauge theory derivation of the N^3/2 growth in the degrees of freedom typical of N M2-branes. We also use the explicit results on the all-genus expansion of the partition function to address non-perturbative aspects of the type IIA superstring in AdS₄ backgrounds, like Borel summability and the role of D-brane instantons."
  • 18-Nov-2010: Generalized geometry and M-theory
    David Berman (Queen Mary, University of London)
    [Transparencies not available]
    Abstract: "We will show how one can naturally reformulate (the bosonic part of) eleven dimensional supergravity using generalized geometry so that the duality group becomes a manifest symmetry. The relation to T-duality for Membranes is discussed along with futher details on the symmetries of M-theory."
  • 25-Nov-2010: Quantum Riemann surfaces
    Tudor Dimofte (University of Cambridge)
    [Blackboard talk]
    Abstract: "Quantized complex curves (Riemann surfaces) play a central role in many areas of mathematical physics, including topological string theory, Chern-Simons theory with noncompact gauge group, and irrational conformal field theory (as relevant, in particular, for the AGT correspondence). In all these cases, the quantum curves yield operators that annihilate partition functions. However, for the most part, the actual quantization of these curves has only been understood indirectly. I will discuss a geometric, intrinsic quantization scheme in the context of Chern-Simons theory that has promise of extending to full generality."
  • 02-Dec-2010: Elliptic hypergeometric integrals, superconformal indices and duality
    Viacheslav Spiridonov (LTP JINR, Dubna)
    [Transparencies]
    Abstract: "Around ten years ago the speaker has introduced a new class of special functions of mathematical physics -- the elliptic hypergeometric integrals. Some of these integrals are either exactly computable or have highly nontrivial symmetry transformations. In 2008, Dolan and Osborn have discovered that superconformal indices of supersymmetric field theories are expressed in terms of such integrals. Equalities of the indices in a number of Seiberg dual field theories follow from the properties of the integrals which were rigorously established earlier. In a joint work with G. Vartanov we have conjectured many new mathematical identities following from known dual field theories and, vice versa, many new supersymmetric dualities were suggested from known relations for elliptic hypergeometric integrals. In this talk the structure of the indices and corresponding integrals will be described and a brief summary of our results will be given."
  • 09-Dec-2010: Fermionic T-duality from a spacetime perspective
    Hadi Godazgar (University of Cambridge)
    [Transparencies]
    Abstract: "We consider the low-energy target space theory and show that the type II supergravity equations admit a symmetry that transforms the Ramond-Ramond fields and the dilaton. The transformations given by this symmetry involve Killing spinors and include the transformations of fermionic T-duality. However, we show that they also allow real transformations."
  • 16-Dec-2010: Travelling front of the decaying brane
    Debashis Ghosal (Jawaharlal Nehru University)
    [Transparencies]
    Abstract: "Some of the perturbative vacua of open string theory are known to be unstable. They decay to other (meta-)stable vacua. We will consider the dynamics of this relaxation process (decay). In particular, the equation that describes an inhomogeneous decay turns out to be a variant of a non-linear partial differential equation that appears in many other areas. We will point out their similarities and differences."
• 2009:
  Lent
  Lent

  • 15-Jan-2009: Black hole microstate geometries and the information paradox
    Iosif Bena (CEA, Saclay)
  • 22-Jan-2009: Wilson loops in N=6 supersymmetric Chern Simons theory
    Donovan Young (Humboldt University, Berlin)
  • 29-Jan-2009: 4-loop perturbative gauge theory results from AdS/CFT
    Romuald Janik (Jagiellonian University, Krakow)
  • 05-Feb-2009: Jet quenching in heavy ion collisions from AdS/CFT
    Jose Edelstein (University of Santiago de Compostela)
  • 12-Feb-2009: Non-Abelian vortices in N=1* theory and its gravity dual
    Prem Kumar (University of Swansea)
  • 19-Feb-2009: Superprotected n-point functions in N=4 super Yang-Mills
    Jan Plefka (Humboldt University, Berlin)
  • 26-Feb-2009: Temperature versus acceleration: The Unruh effect for holographic models
    Kasper Peeters (University of Durham)
  • 05-May-2009: Computing Hermitian Yang-Mills connections
    Volker Braun (Dublin Institute for Advanced Studies)
  • 12-May-2009: Scattering amplitudes in supersymmetric Chern-Simons theory
    Tristan McLoughlin (Albert Einstein Institute, Potsdam)
  -
  Easter
  Easter

  • 23-Apr-2009: Simplifications of unordered amplitudes in gravity and QED
    N. Emil J. Bjerrum-Bohr (Niels Bohr Institute, University of Copenhagen)
  • 30-Apr-2009: The Kerr/CFT correspondence
    Monica Guica (LPTHE, University Pierre et Marie Curie)
  • 07-May-2009: Twistor methods for scattering amplitudes
    David Skinner (University of Oxford)
  • 14-May-2009: Integrability for the full planar spectrum of AdS/CFT
    Pedro Vieira (Albert Einstein Institute, Potsdam)
  • 21-May-2009: SU(N) flux tubes as Nambu-Goto strings
    Andreas Athenodorou (University of Oxford)
  • 28-May-2009: Holographic superconductors
    Julian Sonner (Imperial College London and Trinity College Cambridge)
  • 04-Jun-2009: Supersymmetry breaking in local string/F-theory models
    Sven Krippendorf (University of Cambridge)
  • 11-Jun-2009: Spiky strings and spin chains
    Manuel Losi (University of Cambridge)
  -
  Michaelmas
  Michaelmas

  • 08-Oct-2009: Gauge threshold corrections for local string models
    Joseph Conlon (University of Oxford)
    [Blackboard talk; Transparencies of a CERN seminar]
    Abstract: "Local string models are those where Standard Model degrees of freedom arise on a small region inside a large bulk volume. I study threshold effects on gauge coupling running for such models. The Kaplunovsky-Louis formula for locally supersymmetric gauge theories predicts the unification scale should be the bulk winding mode scale, parametrically large than the string scale where divergences are naively cut off. Analysis of explicit string models on orbifold/orientifold geometries confirms this; the winding mode scale arises from the presence of tadpoles uncancelled in the local model. I briefly discuss phenomenological applications to supersymmetry breaking and gauge coupling unification."
  • 15-Oct-2009: Universal phenomena in strongly coupled gauge theories and gravity
    Ayan Mukhopadhyay (Harish-Chandra Research Institute, Allahabad)
    [Transparencies]
    Abstract: "The AdS/CFT correspondence defines a sector with universal strongly coupled dynamics in the field theory as the dual of pure gravity in AdS described by Einstein's equation with a negative cosmological constant. We will explain, from the field-theoretic viewpoint how the dynamics in this sector gets determined by the expectation value of the energy-momentum tensor alone. We will first show that the Boltzmann equation has very special solutions which could be functionally completely determined in terms of the energy-momentum tensor alone. We will call these solutions 'conservative' solutions. We will indicate why conservative solutions should also exist when we refine this kinetic description to go closer to the exact microscopic theory or even move away from the regime of weak coupling so that no kinetic description could be employed. We will argue that these 'conservative solutions' form the universal sector dual to pure gravity at strong coupling and large N. Based on this observation, we will propose a 'regularity conditon' on the energy-momentum tensor so that the dual solution in pure gravity has a smooth future horizon. We will also study if irreversibility emerges only at long time scales of observation, unlike the case of the Boltzmann equation."
  • 22-Oct-2009: Making contact with supersymmetric AdS₅ solutions
    Jerome Gauntlett (Imperial College London)
    [Transparencies]
    Abstract: "We discuss the most general class of supersymmetric conformal field theories in four spacetime dimensions that have a D=5 anti-de-Sitter (AdS) dual in type IIB supergravity. We discuss the underlying geometry and show that there is a canonical contact structure which can be used to calculate quantities of physical interest, such as the central charge of the conformal field theory, without full knowledge of the solution."
  • 29-Oct-2009: Dynamical vacuum selection in string theory
    Jock McOrist (University of Cambridge)
    [Transparencies]
    Abstract: "Intersecting brane models in string theory are known to exhibit a rich landscape of vacua. Within a particular class of models, I will describe how early universe cosmology generically drives the system to a particular long lived metastable vacuum. These results are of relevance to the landscape problem in string theory."
  • 05-Nov-2009: Transport in QGP and non-critical holography
    Umut Gürsoy (University of Utrecht)
    [Transparencies]
    Abstract: "I will present a phenomenological model of the quark-gluon plasma that stems from 5-dimensional holography. The model is superior to the previous 5D models as it incorporates the running of the gauge coupling. It is constructed by requirements from QCD and a few lattice data. I will describe the transport properties of the quark-gluon plasma such as the bulk viscosity, energy loss of heavy quarks etc and their effects on the observables."
  • 12-Nov-2009: Wilson loops: From pseudo-holomorphic surfaces to 2d Yang-Mills
    Riccardo Ricci (Imperial College London)
    [Transparencies]
    Abstract: "In this talk, I will discuss a new family of supersymmetric Wilson loop operators in N=4 SYM. These operators can be defined for any loop on a three-sphere in space-time and generically preserve two super-conformal charges. On the string side, via AdS/CFT duality, these loops map to surfaces which are 'pseudo-holomorphic' with respect to a novel almost-complex structure defined on a suitable subspace of AdS₅xS⁵. Of particular interest is the subclass of loops lying on a two-sphere in space-time whose expectation value is conjectured to be computed exactly in terms of the analogous observables in bosonic 2d Yang-Mills on S². Several evidences for this conjecture, both on the gauge theory and on the string theory side will be discussed."
  • 19-Nov-2009: Twisted tori and flux backgrounds of type II and heterotic string theory
    David Andriot (LPTHE, Paris)
    [Transparencies]
    Abstract: "Solvmanifolds, in particular nilmanifolds, commonly known as twisted tori, provide several examples of internal manifolds in flux compactifications towards de Sitter, Minkowski or Anti de Sitter. The properties of these manifolds, their relation to the six-dimensional torus, and the string vacua obtained on them are the main interests of this talk. We will first present some properties of these manifolds. We will give a generic construction of their Maurer-Cartan forms out of the six-dimensional torus, via a transformation called the twist. This transformation actually encodes most the properties of these manifolds, in particular their compactness. We will then describe several Minkowski flux backgrounds of type II supergravity obtained on these manifolds. Thanks to the generalized complex geometry approach, we will show that one can obtain those solutions from solutions on the torus, via the twist transformation. The latter is then able to relate backgrounds which are not T-duals. Finally, we will apply this twist transformation technique to relate Kähler/non-Kähler solutions of the heterotic string. This talk is based on a work with Enrico Goi, Ruben Minasian and Michela Petrini, 0903.0633 and to appear soon."
  • 26-Nov-2009: Structure of gauge and gravity amplitudes in string and field theory
    Pierre Vanhove (IHES, Bures-sur-Yvette and CEA/Saclay, Gif-sur-Yvette)
    [Transparencies]
    Abstract: "Recently, there have been remarkable progresses on the analysis of the multi-loop amplitudes in supergravity in various dimensions using string theory and in field theory methods. There are strong indications that four-dimensional maximal supergravity theories have a better ultraviolet behaviour than expected from a conservative implementation of on-shell superspace, and is a intricate consequence of gauge invariance and supersymmetry. As well the N=8 supergravity amplitudes have a much more simple structure than guessed from a traditional approach based on a Lagrangian and Feynman graphs formalism, and display striking similarities with N=4 super-Yang-Mills amplitudes. In this talk we will analyze the constraints from supersymmetry, gauge invariance on the ultraviolet behaviour of maximally supergravity gauge theories in various dimensions. We will compare the ultraviolet behaviour of N=4 super-Yang-Mills amplitudes at higher-loop order in the leading and subleading color factor and compare with the expectations for N=8 supergravity amplitude in various dimensions."
  • 03-Dec-2009: Probing strongly coupled gauge theories with AdS/CFT: The violation of the shear viscosity to entropy bound
    Sera Cremonini (University of Cambridge)
    [Transparencies]
    Abstract: "The gauge gravity duality has proven to be a powerful tool for probing thermal and hydrodynamic properties of strongly coupled field theories, with possible applications to the realm of RHIC and QCD-like theories. In this talk I will discuss some of the recent applications of AdS/CFT to the ratio of the shear viscosity to entropy density. In particular, I will focus on the role played by higher derivative corrections at finite chemical potential. I will also touch on possible fundamental constraints that gravity might be imposing on the set of allowed dual CFTs, in the context of the weak gravity conjecture."
  • 09-Dec-2009: Holographic flavor transport
    Andrew O'Bannon (Max Planck Institute, Munich)
    [Blackboard talk]
    Abstract: "Gauge-gravity duality is an extremely useful tool for studying strongly-coupled gauge theories, and has many applications to real-world systems, such as the quark-gluon plasma and quantum critical points. It is especially useful for studying the hydrodynamics of strongly-coupled non-Abelian gauge theories. For example, gauge-gravity duality is currently the only reliable way to compute transport coefficients for many theories. In this talk I will describe a calculation of a transport coefficient, a conductivity, associated with flavor fields in a strongly-coupled plasma. From the result for the conductivity, I will show how gauge-gravity duality captures a lot of real-world physics, such as momentum dissipation, Schwinger pair production, and more."
• 2008:
  Lent
  Lent

  • 24-Jan-2008: Type II small stringy black holes, probe branes and higher derivative corrections
    Linda Uruchurtu-Gomez (University of Cambridge)
  • 31-Jan-2008: Higher derivative corrections in IIB string theory on T²
    Anirban Basu (Institute for Advanced Study, Princeton)
  • 07-Feb-2008: Non-perturbative superpotentials across lines of marginal stability
    Inaki Garcia-Extebarria (CERN)
  • 14-Feb-2008: Supergravitons from one-loop perturbative N=4 SYM
    Maciej Trzetrzelewski (University of Stockholm)
  • 21-Feb-2008: Axion inflation in type II string theory
    Thomas Grimm (University of Bonn and Wisconsin University, Madison)
  • 28-Feb-2008: Twistor strings with flavour
    James Bedford (Imperial College London)
  • 06-Mar-2008: Finding vacua in string phenomenology
    James Gray (University of Oxford)
  • 13-Mar-2008: TBA
    Benjamin Zwiebel (University of Cambridge)
  -
  Easter
  Easter

  • TBI
  -
  Michaelmas
  Michaelmas

  • 09-Oct-2008: Stringy corrections to holographic hydrodynamics
    Miguel Paulos (University of Cambridge)
  • 16-Oct-2008: Generating stationary axisymmetric solutions of Einstein's vacuum equations in 5d and a black ring in Taub-NUT
    Pau Figueras (University of Durham)
  • 23-Oct-2008: Compactification of higher derivative corrections and automorphic forms
    Daniel Persson (Universite Libre de Bruxelles)
  • 30-Oct-2008: Chern-Simons quivers and Sasaki-Einstein manifolds
    James Sparks (University of Oxford)
  • 06-Nov-2008: Sigma model dualities and dual superconformal symmetry
    Martin Wolf (University of Cambridge)
  • 13-Nov-2008: The chiral ring of AdS₃/CFT₂ and the attractor mechanism
    Kyriakos Papadodimas (University of Amsterdam)
  • 20-Nov-2008: Summing the instantons in the heterotic string
    Jock McOrist (University of Chicago)
  • 27-Nov-2008: Free fermions on quantum curves
    Lotte Hollands (University of Amsterdam)
  • 04-Dec-2008: External fields and the dynamics of flavours in holographic duals of large N gauge theories
    Arnab Kundu (University of Southern California, Los Angeles)
• 2007:
  Lent
  Lent

  • 18-Jan-2007: Moduli stabilisation and de sitter string vacua from magnetised D7 branes
    Kerim Suruliz (University of Cambridge)
  • 25-Jan-2007: Non-geometric flux compactifications
    Brian Wecht (MIT, Boston)
  • 01-Feb-2007: Holographic QCD and perfection
    Nick Evans (University of Southampton)
  • 08-Feb-2007: Cancelled
  • 15-Feb-2007: Aspects of non-Abelian 2d gauge theories and mirror symmetry
    David Tong (University of Cambridge)
  • 22-Feb-2007: Superparticles in AdS
    Michael Chesterman (CEA, Saclay)
  • 01-Mar-2007: A scattering phase for AdS₅ x S⁵ strings
    Rafael Hernandez (CERN)
  • 08-Mar-2007: A magical mystery tour around some spots in the Landscape
    Florian Gmeiner (NIKHEF, Amsterdam)
  • 15-Mar-2007: Cancelled
  • 22-Mar-2007: TBA
    Sean Hartnoll (KITP, Santa Barbara)
  -
  Easter
  Easter

  • 26-Apr-2007: Bubbling geometries from gauge theory
    Diego Correa (University of Cambridge)
  • 03-May-2007: Charges from attractors
    Nemani Suryanarayana (Imperial College London)
  • 10-May-2007: How many giants live near a black hole?
    Aninda Sinha (University of Cambdridge)
  • 17-May-2007: Connecting giant magnons to the pp-wave: An Interpolating limit of AdS₅ x S⁵
    Ian Swanson (Institute for Advanced Study, Princeton)
  • 24-May-2007: AdS₅ black holes and supersymmetry
    James Lucietti (University of Durham)
  • 31-May-2007: D-brane instanton effects in IIA string vacua and their phenomenological implications
    Timo Weigand (University of Pennsylvania)
  • 07-Jun-2007: Breathing magnons
    Keisuke Okamura (University of Tokyo)
  • 14-Jun-2007: Marginal stability and dyon spectrum in N=4 supersymmetric string theories
    Ashoke Sen (Harish-Chandra Research Institute, Allahabad)
  • 21-Jun-2007: Rigid limit in N=2 supergravity and weak-gravity conjecture
    Yuji Tachikawa (Institute for Advanced Studies, Princeton)
  -
  Michaelmas
  Michaelmas

  • 27-Sep-2007: Thermal derivation of the Coleman-de Luccia tunnellig prescription
    Adam Brown (Columbia University, New York)
  • 04-Oct-2007: TBA
    Yang-Hui He (University of Oxford)
  • 11-Oct-2007: Backreacting flavours in the Klebanov-Strassler Background: A new cascade
    Francesco Benini (SISSA, Trieste)
  • 18-Oct-2007: Supersymmetric AdS black holes
    Harvey Reall (University of Cambridge)
  • 25-Oct-2007: Polytopes and the landscape of hidden dimensions
    Max Kreuzer (University of Vienna)
  • 01-Nov-2007: This seminar is joint with the Isaac Newton Institute
    Tristan McLoughlin (Penn State University)
  • 08-Nov-2007: This seminar is joint with the Isaac Newton Institute
    Kostas Skenderis (University of Amsterdam)
  • 15-Nov-2007: TBA
  • 22-Nov-2007: Quantum corrections and the large volume scenario
    Michael Haack (Ludwig-Maximilians University, Munich)
  • 29-Nov-2007: TBA

Past Seminars

Lent 2013

Lent 2012

Easter 2012

Michaelmas 2012

Lent 2011

Easter 2011

Michaelmas 2011

Lent 2010

Easter 2010

Michaelmas 2010

Lent 2009

Easter 2009

Michaelmas 2009

Lent 2008

Easter 2008

Michaelmas 2008

Easter 2007

Lent 2007

Michaelmas 2007