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arXiv · 2311.10059

Speed of sound and polytropic index in QCD matter

He Liu·Yong-Hang Yang·Chi Yuan·Min Ju·Xu-Hao Wu·Peng-Cheng Chu
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Abstract

We investigate the speed of sound and polytropic index of quantum chromodynamics (QCD) matter in the full phase diagram based on a 3-flavor Polyakov-looped Nambu-Jona-Lasinio (pNJL) model. The speed of sound and polytropic index in isothermal and adiabatic cases all have a dip structure at the low chemical potential side of the chiral phase transition boundary, and these quantities reach their global minimum values at the critical endpoint (CEP) but are not completely zero, where the values in adiabatic are lightly greater than those in isothermal. Different from the speed of sound, the polytropic index also exists a peak around the chiral phase transition boundary. Along the hypothetical chemical freeze-out lines, the speed of sound rapidly decreases near the CEP, followed by a small spinodal behavior, while the polytropic index, especially in isothermal, exhibits a more pronounced and nearly closed to zero dip structure as it approaches the CEP.

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He Liu, Yong-Hang Yang, Chi Yuan, Min Ju, Xu-Hao Wu, Peng-Cheng Chu. 2023-11-16. Speed of sound and polytropic index in QCD matter. https://doi.org/10.1103/physrevd.109.074037

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