1,721,060 research outputs found
Curvature of the pseudocritical line in QCD: Taylor expansion matches analytic continuation
Full text linkWe determine the curvature of the pseudocritical line of Nf=2+1 QCD with physical quark masses via Taylor expansion in the quark chemical potentials. We adopt a discretization based on stout improved staggered fermions and the tree level Symanzik gauge action; the location of the pseudocritical temperature is based on chiral symmetry restoration. Simulations are performed on lattices with different temporal extent (Nt=6, 8, 10), leading to a continuum extrapolated curvature κ=0.0145(25), which is in very good agreement with the continuum extrapolation obtained via analytic continuation and the same discretization, κ=0.0135(20). This result eliminates the possible tension emerging when comparing analytic continuation with earlier results obtained via Taylor expansion
Phase diagram of QCD in a magnetic background
No full textWe provide numerical evidence that the thermal QCD crossover turns into a first order transition in the
presence of large enough magnetic background fields. The critical end point is found to be located between
eB = 4 GeV^2 [where the pseudocritical temperature is Tc = 98 MeV] and eB = 9 GeV^2 [where the
critical temperature is Tc = 63 MeV]. Results are based on the analysis of quark condensates and
number susceptibilities, determined by lattice simulations of Nf =2 + 1 QCD at the physical point,
discretized via rooted stout staggered fermions and a Symanzik tree level improved pure gauge action,
adopting two different lattice spacings, a = 0.114 and 0.086 fm, for eB = 9 GeV^2 and three, a = 0.114,
0.086, and 0.057 fm, for eB = 4 GeV^2 . We also present preliminary results regarding the confining properties of the thermal theory, suggesting that they could change drastically going across the phase transition
Magnetic properties of the strongly interacting matter
Full text linkWe study the magnetic properties of the strongly interacting matter using Lattice QCD simulations. The QCD medium shows a paramagnetic behavior in the range of temperatures 100–400MeV, with a sharp increase of the magnetic susceptibility above the deconfinement temperature. We expect a significant mag- netic contribution to the pressure of the system in non-central heavy-ion collisions
Magnetic susceptibility of strongly interacting matter across the deconfinement transition
No full textWe propose a method to determine the total magnetic susceptibility of strongly interacting matter by lattice QCD simulations and present numerical results for the theory with two light flavors, which suggest a weak magnetic activity in the confined phase and the emergence of strong paramagnetism in the deconfined, quark-gluon plasma phase
Magnetic susceptibility and equation of state of Nf=2+1 QCD with physical quark masses
No full textWe determine the free energy of strongly interacting matter as a function of an applied constant and uniform magnetic field. We consider Nf=2+1 QCD with physical quark masses, discretized on a lattice by stout improved staggered fermions and a tree-level improved Symanzik pure gauge action, and we explore three different lattice spacings. For magnetic fields of the order of those produced in noncentral heavy ion collisions (eB∼0.1 GeV2), strongly interacting matter behaves like a medium with a linear response, and is paramagnetic both above and below the deconfinement transition, with a susceptibility which steeply rises in the deconfined phase. We compute the equation of state, showing that the relative increase in the pressure due to the magnetic field gets larger around the transition and is of the order of 10% for eB∼0.1 GeV2
QCD phase diagram in a magnetic background for different values of the pion mass
Full text linkWe investigate the behavior of the pseudocritical temperature of N-f = 2 + 1 QCD as a function of a static magnetic background field for different values of the pion mass, going up to m(pi) similar or equal to 660 MeV. The study is performed by lattice QCD simulations, adopting a stout staggered discretization of the theory on lattices with N-t = 6 slices in the Euclidean temporal direction; for each value of the pion mass the temperature is changed moving along a line of constant physics. We find that the decrease of T-c as a function of B, which is observed for physical quark masses, persists in the whole explored mass range, even if the relative variation of T-c appears to be a decreasing function of m(pi), approaching zero in the quenched limit. The location of T-c is based on the renormalized quark condensate and its susceptibility; determinations based on the Polyakov loop lead to compatible results. On the contrary, inverse magnetic catalysis, i.e., the decrease of the quark condensate as a function of B in some temperature range around T-c, is not observed when the pion mass is high enough. That supports the idea that inverse magnetic catalysis might be a secondary phenomenon, while the modifications induced by the magnetic background on the gauge field distribution and on the confining properties of the medium could play a primary role in the whole range of pion masses
Higher order quark number fluctuations via imaginary chemical potentials in Nf=2+1 QCD
Full text linkWe discuss analytic continuation as a tool to extract the cumulants of the quark number fluctuations in the strongly interacting medium from lattice QCD simulations at imaginary chemical potentials. The method is applied to Nf = 2+1 QCD, discretized with stout improved staggered fermions, physical quark masses and the tree level Symanzik gauge action, exploring temperatures ranging from 135 up to 350 MeV and adopting mostly lattices with Nt = 8 sites in the temporal direction. The method is based on a global fit of various cumulants as a function of the imaginary chemical potentials. We show that it is particularly convenient to consider cumulants up to order two, and that below Tc the method can be advantageous, with respect to a direct Montecarlo sampling at μ = 0, for the determination of generalized susceptibilities of order four or higher, and especially for mixed susceptibilities, for which the gain is well above one order of magnitude. We provide cumulants up to order eight, which are then used to discuss the radius of convergence of the Taylor expansion and the possible location of the second-order critical point at real μ: no evidence for such a point is found in the explored range of T and for chemical potentials within present determinations of the pseudocritical line
Metadynamics Remedies for Topological Freezing
Full text linkIn this presentation we show that metadynamics, when used to simulate CPN−1, allows to address efficiently of freezing of topological charge, to reconstruct the free energy of the topological charge F(Q) and to compute the topological susceptibility as a function of the coupling and of the volume. We discuss possible extensions to QCD
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