Abstract
In this work we analyse positive- and negative-parity channels for the nucleon (spin $1/2$ octet), $\Delta$ and $\Omega$ baryons (spin $3/2$ decuplet) using lattice QCD. In Nature, at zero temperature, chiral symmetry is spontaneously broken, causing positive- and negative-parity ground states to have different masses. However, chiral symmetry is expected to be restored (for massless quarks) around the crossover temperature, implying that the two opposite parity channels should become degenerate. Here we study what happens in a temperature range which includes both the hadronic and the quark gluon plasma (QGP) phase. By analysing the correlation and spectral functions via exponential fits and the Maximum Entropy Method respectively, we have found parity doubling for the nucleon and $\Delta$ baryon channels in the QGP phase. For the $\Omega$ baryon we see a clear signal of parity doubling at the crossover temperature, which is however not complete, due to the nonzero strange quark mass. Moreover, in-medium effects in the hadronic phase are evident for all three baryons, in particular for the negative-parity ground states. This might have implications for the hadron resonance gas model. In this work we used the FASTSUM anisotropic $N_f = 2 + 1$ ensembles.
Highlights
In Nature, at zero temperature, a considerable mass difference between the negative-parity ground state of the baryons and the positive-parity one is understood from chiral symmetry breaking
By analysing the correlation and spectral functions via exponential fits and the Maximum Entropy Method respectively, we have found parity doubling for the nucleon and ∆ baryon channels in the quark gluon plasma (QGP) phase
Since in the case of massless quarks chiral symmetry is expected to be restored above the deconfinement temperature, one would expect to see parity doubling in the QGP phase
Summary
In Nature, at zero temperature, a considerable mass difference between the negative-parity ground state of the baryons and the positive-parity one is understood from chiral symmetry breaking. In the case of the nucleon and ∆ baryon, this mass difference is far too big to be explained by the small explicit breaking of chiral symmetry due to the light u and d quarks. It is well-known that the mass difference between the opposite-parity ground states is mainly a consequence of the spontaneous breaking of chiral symmetry. Our aim here is to analyse parity doubling in the unquenched baryonic sector, in particular for the nucleon, ∆ and Ω baryons. Our previous analyses for the nucleon sector can be found in [5, 6] and, more recently, [7] for the ∆ baryon
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