Energy flux correlators are powerful observables that have been widely studied in both formal and phenomenological contexts. However, much of our current understanding is restricted to states close to the vacuum. In this talk, I will explain why energy correlators provide a natural and robust framework for probing systems with a large number of quanta, such as the quark–gluon plasma or highly excited states with large scaling dimension in conformal field theories (CFTs).
I will focus in particular on energy correlators evaluated on states carrying large global U(1) charge, a regime in which the conventional perturbative expansion around the vacuum ceases to be applicable. In the CFT context, these observables can instead be computed semiclassically using the effective field theory (EFT) of a conformal superfluid. I will discuss the novel features that arise in this large-charge regime and clarify the conditions under which the EFT description remains valid—or breaks down—when applied to these intrinsically nonlocal probes.