Hyperons in thermal QCD: a lattice view

Preprint number: CP3-Origins-2018-50 DNRF90
Authors: Gert Aarts (Swansea University), Chris Allton (Swansea University), Davide De Boni (Swansea University), and Benjamin Jäger (CP3-Origins & DIAS)

The hadron resonance gas (HRG) is a widely used description of matter
under extreme conditions, e.g. in the context of heavy-ion phenomenology. Commonly used implementations of the HRG employ vacuum hadron masses throughout the hadronic phase and hence do not include possible in-medium effects. Here we investigate this issue, using nonperturbative lattice simulations employing the FASTSUM anisotropic Nf = 2 + 1 ensembles. We study the fate of octet and decuplet baryons as the temperature increases, focussing in particular on the positive- and
negative-parity groundstates. While the positive-parity groundstate masses are indeed seen to be temperature independent, within the error, a strong temperature
dependence is observed in the negative-parity channels. We give a simple parametrisation of this and formulate an in-medium HRG, which is particularly effective for
hyperons. Parity doubling is seen to emerge in the deconfined phase at the level of correlators, with a noticeable effect of the heavier s quark. Channel dependence of
this transition is analysed.