Sprecher
Beschreibung
The violation of the conformal limit for the speed of sound, $c_s^2=1/3$, has emerged as a critical feature of dense strongly interacting matter. Astrophysical observations—including gravitational wave data from LIGO/Virgo and precise neutron star radius measurements from NICER—suggest that the equation of state must exhibit a rapid stiffening at intermediate densities. This behavior is commonly associated with a peak in the speed of sound, potentially signaling a phase transition in the dense QCD regime.
Direct lattice QCD simulations at finite baryon density are hindered by the sign problem. However, effective QCD models, as well as lattice-accessible theories such as two-color QCD and QCD at finite isospin chemical potential, provide valuable insights into the nonperturbative dynamics of dense quark matter. These approaches support the existence of a peak in $c_s^2$ offering qualitative agreement with astrophysical expectations.
We present and analyze recent numerical and analytical results obtained from effective models of QCD, emphasizing the behavior of the equation of state and its stiffening at intermediate densities. These developments provide an essential bridge between effective theoretical and phenomenological descriptions of QCD and observable signatures in astrophysics.
