TY  - JOUR
A1  - Cuteri, Francesca
A1  - Philipsen, Owe
A1  - Sciarra, Alessandro
T1  - On the order of the QCD chiral phase transition for different numbers of quark flavours
T2  - Journal of high energy physics
N2  - The nature of the QCD chiral phase transition in the limit of vanishing quark masses has remained elusive for a long time, since it cannot be simulated directly on the lattice and is strongly cutoff-dependent. We report on a comprehensive ongoing study using unimproved staggered fermions with Nf ∈ [2, 8] mass-degenerate flavours on Nτ ∈ {4, 6, 8} lattices, in which we locate the chiral critical surface separating regions with first-order transitions from crossover regions in the bare parameter space of the lattice theory. Employing the fact that it terminates in a tricritical line, this surface can be extrapolated to the chiral limit using tricritical scaling with known exponents. Knowing the order of the transitions in the lattice parameter space, conclusions for approaching the continuum chiral limit in the proper order can be drawn. While a narrow first-order region cannot be ruled out, we find initial evidence consistent with a second-order chiral transition in all massless theories with Nf ≤ 6, and possibly up to the onset of the conformal window at 9 ≲ N∗f ≲ 12. A reanalysis of already published O(a)-improved Nf = 3 Wilson data on Nτ ∈ [4, 12] is also consistent with tricritical scaling, and the associated change from first to second-order on the way to the continuum chiral limit. We discuss a modified Columbia plot and a phase diagram for many-flavour QCD that reflect these possible features.
KW  - Lattice QCD
KW  - Lattice Quantum Field Theory
KW  - Phase Diagram of QCD
Y1  - 2021
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/70165
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-701651
SN  - 1029-8479
SN  - 1126-6708
VL  - 2021
IS  - 141
PB  - Springer
CY  - Berlin ; Heidelberg
ER  -