[RBRC Online Seminar] The QCD chiral phase transition for different numbers of flavours

by Owe Philipsen

Thursday 14 Apr 2022, 09:30 → 11:30 US/Eastern

online

The nature of the thermal QCD transition is known to be an analytic crossover, rather than a non-analytic phase transition. However, because of the small light quark masses, it is also necessary to understand  the nature of the chiral phase transition in the massless limit, which cannot be simulated directly on the lattice. On the one hand, a possible second-order chiral transition is believed to influence the physical point via its scaling region, on the other hand the nature of the chiral transition also constrains the possibilities for the QCD phase diagram at finite baryon density.

I report recent lattice results, which resolve apparent contradictions between different lattice discretisations and suggest a final, non-perturbative answer to this longstanding open problem. Contrary to the famous Pisarski-Wilczek prediction from 1984, we find the chiral phase transition to be second order for all Nf<6, and presumably all the way to the conformal window. Implications for the finite density phase diagram are discussed.