Baryonic Response of Dense Holographic QCD

TL;DR

This paper investigates the baryonic response functions in dense holographic QCD models, revealing different phases' properties, including insulator, diffusive conductor, and visco-elastic modes, with implications for understanding dense hadronic matter.

Contribution

It provides a detailed analysis of baryonic response functions in dense holographic QCD models across different phases, highlighting novel transport phenomena and spectral features.

Findings

Confined phase is an uncompressible baryonic insulator with a gapped spectrum.

Deconfined phase exhibits diffusive baryonic conduction with restored chiral symmetry.

At zero temperature, a baryonic visco-elastic mode with a specific sound speed is identified.

Abstract

The response function of a homogeneous and dense hadronic system to a time-dependent (baryon) vector potential is discussed for holographic dense QCD (D4/D8 embedding) both in the confined and deconfined phases. Confined holographic QCD is an uncompressible and static baryonic insulator at large N_c and large \lambda, with a gapped vector spectrum and a massless pion. Deconfined holographic QCD is a diffusive conductor with restored chiral symmetry and a gapped transverse baryonic current. Similarly, dense D3/D7 is diffusive for any non-zero temperature at large N_c and large \lambda. At zero temperature dense D3/D7 exhibits a baryonic longitudinal visco-elastic mode with a first sound speed \lambda/\sqrt{3} and a small width due to a shear viscosity to baryon ratio \eta/n_B=\hbar/4. This mode is turned diffusive by arbitrarily small temperatures, a hallmark of holography.