Curing the acausal behavior of the sound velocity in an excluded volume hadron resonance gas model

We improve the excluded volume hadron resonances gas model (EHRG) to cure the acausal behavior of the sound velocity which is typical of excluded volume models. We achieve this by including temperature (T) and density ({\mu}) dependent hadron masses in the partition function of EHRG. The temperature and density dependent masses of the constituent quarks (u,d,s) and the light mesons are obtained within Nambu-Jona-Lasinio model while for the heavy hadrons we use linear scaling rule in terms of constituent quarks. With this improvement, we observe that the velocity of sound flattens at high temperature unlike old EHRG models where the sound velocity rises very rapidly at high temperatures which is the indication of its super-luminal behavior.