Physical insights from imaginary-time density–density correlation functions

An accurate theoretical description of the dynamic properties correlated quantum many-body systems, such as structure factor S(q, ω), is important in many fields. Unfortunately, highly Monte Carlo methods are usually restricted to imaginary time domain, and analytic continuation imaginary-time density–density correlation function F(q, τ) real frequencies a notoriously hard problem. Here, it argued that often no required because by definition, contains same physical information does only represented unfamiliarly. Specifically, shown how one can directly extract key temperature or quasi-particle excitation energies from τ which relevant for equation-of-state measurements matter under extreme conditions [T. Dornheim et al., Nat. Commun. 13, 7911 (2022)]. As practical example, ab initio path-integral results uniform electron gas (UEG) considered, even nontrivial processes roton feature UEG at low density Phys. 5, 304 (2022)] manifested straightforwardly τ). A comprehensive overview given various useful relates usual factor. In fact, working domain advantageous reasons opens up multiple avenues future applications.