Speaker
Description
QCD with a real chemical potential suffers from a sign problem in numerical calculations of Euclidean space path integrals. A novel approach exploits the fact that an imaginary chemical potential avoids the sign-problem and can be interpreted as a real Lagrange multiplier enforcing a current density rather than a number density. At zero temperature, Lorentz symmetry then allows rigorous upper and lower bounds on the equation of state (EoS) $ \epsilon ( n ) $ (where $ \epsilon $ is the energy density and $ n $ the baryon number density) to be inferred from sign-problem-free current-density calculations alone.
This talk presents this novel approach and its first application to an interacting quantum field theory, namely the massive Thirring / sine-Gordon model. Using the exact Bethe ansatz solution, the derived bounds are compared directly with the exact zero-temperature EoS across a wide range of couplings and densities. The constraints remain quantitatively useful throughout, becoming exact in the low-density limit and constraining the EoS within a factor of two at high density.