Speaker
Description
The experimental observation of the spin polarisation of the outgoing hadrons in non-central heavy ion collisions implies the existence of a strongly vortical QGP medium with finite spin density. We consider the effect of finite spin density on the QCD phase diagram using the Linear Sigma model coupled to quarks (LSMq). In our approach, we introduce the finite spin density via a quark spin potential ($\mu_s$) in the canonical formulation of the spin operator, leading to a nonlinear modification of the energy dispersion relation. Besides an expected effect on the thermal fermion loop, the spin potential also enters non-trivially in the zero-point, temperature-independent part of the fermion loop. Employing renormalization techniques [1], we observe a substantial influence of this term on the phase structure of the system at nonnegligible $\mu_s/T$. Taking both the thermal and the zero-point terms into account, we find the expectation value of the sigma condensate by minimizing the thermodynamic potential of the system. Our findings indicate that, starting from a chiral symmetry broken phase at small $T$ and $\mu_s$, the minima of the thermodynamic potential moves towards lower values of $\sigma$ with increasing $\mu_s$, indicating the restoration of chiral symmetry. This behaviour is consistent with the results from the first principle lattice simulations [2].
Keywords: Quark-Gluon-Plasma, chiral phase transition, spin potential.
References:
[1] A. Ayala, L.A. Hernandez, M. Loewe, J.C. Rojas, R. Zamora, Eur. Phys. J. A 56 (2020)71.
[2] V.V. Braguta, M.N. Chernodub, A.A. Roenko, arXiv:2503.18636
