# Phenomenological QCD equations of state for neutron star mergers

## TL;DR

This paper develops phenomenological QCD equations of state for neutron star mergers, focusing on thermal contributions and collective modes at high baryon density, with implications for gravitational wave observations.

## Contribution

It introduces a schematic quark model incorporating collective modes and phase shift representation to estimate thermal effects in neutron star matter.

## Key findings

- Thermal contributions depend on quark gap structure.
- High energy contributions cancel pole contributions, tempering UV behavior.
- Applicable to neutron star densities of 5-10 times nuclear saturation density.

## Abstract

Thermal QCD equations of state at high baryon density are sensitive to the phase structure and the resulting excitation modes. The leading contribution at low temperature can be either ~p_F^2 T^2 (pF: Fermi momentum, T: temperature) for phases with gapless quarks, or ~T^4 for phases with gapped quarks. In the latter the thermal pressure is dominated by collective modes. Starting with a schematic quark model developed for neutron star structure, we estimate the thermal contributions and zero point energy from the Nambu-Goldstone modes by building them upon the mean field background for the color-flavor-locked quark matter. Applying the phase shift representation for thermodynamic potentials, we include not only the bound state pairs but also resonating pairs. According to the Levinson's theorem, the high energy contributions tend to cancel the pole contributions to the thermodynamics, tempering the UV behaviors in the zero point energy. Our primary target in this talk is the domain with baryon density nB as large as ~ 5-10n_0 (n_0 = 0.16 fm^{-3}: nuclear saturation density), and the temperature T of the order ~30-100 MeV. The insights into this domain may be obtained through the future detection of gravitational waves from neutron star merging events.