Deconfinement critical point of lattice QCD with N f = 2 Wilson fermions

Sciarra

2021

J. High Energ. Phys.

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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 ≲ $$ {N}_{\mathrm{f}}^{\ast } $$ N f ∗ ≲ 12. A reanalysis of already published $$ \mathcal{O} $$ 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.

Section: Jhep11(2021)141mentioning

confidence: 76%

On the order of the QCD chiral phase transition for different numbers of quark flavours

Cuteri

Sciarra

2021

J. High Energ. Phys.

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“…Contrary to the chiral limit, this entire region can be simulated directly and a complete non-perturbative understanding should be attainable in the near future. The location of the critical line is under investigation [18][19][20][21]. While continuum extrapolations are not yet available, the presently finest lattices predict the pseudo-scalar mass evaluated on the critical point for N f " 2 to be about m c PS " 4 GeV [20].…”

Section: The Deconfinement Transitionmentioning

confidence: 99%

“…The location of the critical line is under investigation [18][19][20][21]. While continuum extrapolations are not yet available, the presently finest lattices predict the pseudo-scalar mass evaluated on the critical point for N f " 2 to be about m c PS " 4 GeV [20]. Together with the latent heat, these quantities should permit a detailed understanding of the confinement-deconfinement transition and its interplay with screening by dynamical quarks, which will be valuable for the physics interpretation of the crossover region at the physical point.…”

Section: The Deconfinement Transitionmentioning

confidence: 99%

“…This is a remarkable result telling us that up to µ B ă " 3T the dependence of thermodynamic quantities on chemical potential is rather weak and can be accurately described by a truncated leading-order Taylor series in chemical potential. (20) imag. µ, stout-smeared staggered [87] 0.0145 (25) Taylor, stout-smeared staggered [87,88] 0.016 (5) Taylor, HISQ [85] We now have the necessary information to obtain a conservative bound on the location of a possible critical point, which according to Figure 12…”

Section: The Crossover At Small Baryon Densitiesmentioning

confidence: 99%

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Lattice Constraints on the QCD Chiral Phase Transition at Finite Temperature and Baryon Density

2021

Symmetry

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The thermal restoration of chiral symmetry in QCD is known to proceed by an analytic crossover, which is widely expected to turn into a phase transition with a critical endpoint as the baryon density is increased. In the absence of a genuine solution to the sign problem of lattice QCD, simulations at zero and imaginary baryon chemical potential in a parameter space enlarged by a variable number of quark flavours and quark masses constitute a viable way to constrain the location of a possible non-analytic phase transition and its critical endpoint. In this article I review recent progress towards an understanding of the nature of the transition in the massless limit, and its critical temperature at zero density. Combined with increasingly detailed studies of the physical crossover region, current data bound a possible critical point to μB ≳ 3T.

“…A continuum extrapolation would require larger N s -values, which in turn demand higher orders for the hopping expansion to converge. Note that recent 4d QCD simulations using a hopping expanded determinant [42], as well as full QCD simulations [43] permit control over the systematics at l ¼ 0.…”

Section: Deconfinement Transition In Qcd With Heavy Quarksmentioning

confidence: 99%

Strong coupling methods in QCD thermodynamics

2021

Indian J Phys

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For a long time, strong coupling expansions have not been applied systematically in lattice QCD thermodynamics, in view of the success of numerical Monte Carlo studies. The persistent sign problem at finite baryo-chemical potential, however, has motivated investigations using these methods, either by themselves or combined with numerical evaluations, as a route to finite density physics. This article reviews the strategies, by which a number of qualitative insights have been attained, notably the emergence of the hadron resonance gas or the identification of the onset transition to baryon matter in specific regions of the QCD parameter space. For the simpler case of Yang–Mills theory, the deconfinement transition can be determined quantitatively even in the scaling region, showing possible prospects for continuum physics.