Abstract
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.
Highlights
How the light hadrons behave under the extreme conditions of nonzero temperature and/or density is a question of fundamental importance, linked to confinement and chiral symmetry
Within the uncertainty, which is dominated by the variation of m−ðTcÞ=mþð0Þ, we find that the in-medium hadron resonance gas (HRG) result agrees with the lattice data quantitatively
In this paper we determined the response of hyperons to an increase of temperature in thermal QCD, going from the hadronic phase to the quark-gluon plasma, using lattice QCD simulations
Summary
How the light hadrons behave under the extreme conditions of nonzero temperature and/or density is a question of fundamental importance, linked to confinement and chiral symmetry. There is a need to unambiguously establish if and how the masses of the light hadrons in the hadronic phase depend on the temperature, at zero and low baryon density This is a nonperturbative question in QCD, which can be addressed using either a first-principle lattice QCD computation or via effective models, suitably benchmarked against lattice QCD results. The N, Δ and Ω channels were already discussed in Ref. [17]; preliminary results in the Λ, Σ, ΣÃ, Ξ and ΞÃ channels have been presented in Ref. [24]
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