セミナー 2023年

seminar2023

[QCD theory Seminar] Surprises on the way toward the QCD phase diagram

  • SPEAKER Owe Philipsen, Frankfurt University
  • PLACE Online (Zoom)
A strong fermion sign problem prohibits direct lattice simulations of QCD at finite baryon density, so that knowledge of the phase diagram is limited to small chemical potentials. On the other hand, the phase diagram is severely constrained by information on the chiral limit. I discuss recent lattice results at vanishing density, which show the chiral phase transition for Nf=2-7 degenerate chiral quarks to be of second order, contrary to the expectations based on the seminal paper by Pisarski and Wilczek from 1984. Together with growing information on fluctuations, this implies phenomenologically relevant bounds on a possible critical endpoint. In another development at zero density, a dynamically emergent chiral spin symmetry was discovered in correlator multiplet stuctures in a temperature window above the chiral crossover. I discuss two additional variables, screening masses and the pion spectral functions, which also show this window and suggest its effective degrees of freedom to be hadron-like, rather than partonic.


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