3,475 research outputs found
Magnetic susceptibility and equation of state of N_f = 2+1 QCD with physical quark masses
We determine the free energy of strongly interacting matter as a function of
an applied constant and uniform magnetic field. We consider N_f = 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 explore
three different lattice spacings. For magnetic fields of the order of those
produced in non-central heavy ion collisions (eB ~ 0.1 GeV^2) 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 of the order of 10 %
for eB ~ 0.1 GeV^2.Comment: 11 pages, 10 figures, 3 tables. Final version published in Physical
Review
Magnetic Susceptibility of Strongly Interacting Matter across the Deconfinement Transition
We propose a method to determine the total magnetic susceptibility of
strongly interacting matter by lattice QCD simulations, and present first
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.Comment: 6 pages, 6 figures, 2 tables. Final version published in Physical
Review Letter
The curvature of the chiral pseudocritical line from LQCD: analytic continuation and Taylor expansion compared
We present a determination of the curvature of the chiral
pseudocritical line from lattice QCD at the physical point obtained
by adopting the Taylor expansion approach. Numerical simulations performed at
three lattice spacings lead to a continuum extrapolated curvature , a value that is in excellent agreement with continuum limit
estimates obtained via analytic continuation within the same discretization
scheme, . The agreement between the two calculations is a
solid consistency check for both methods.Comment: Quark Matter 201
Topology in full QCD at high temperature: a multicanonical approach
We investigate the topological properties of QCD with physical
quark masses, at temperatures around 500 MeV. With the aim of obtaining a
reliable sampling of topological modes in a regime where the fluctuations of
the topological charge are very rare, we adopt a multicanonical approach,
adding a bias potential to the action which enhances the probability of
suppressed topological sectors. This method permits to gain up to three orders
of magnitude in computational power in the explored temperature regime. Results
at different lattice spacings and physical spatial volumes reveal no
significant finite size effects and the presence, instead, of large finite
cut-off effects, with the topological susceptibility which decreases by 3-4
orders of magnitude while moving from fm towards the continuum
limit. The continuum extrapolation is in agreeement with previous lattice
determinations with smaller uncertainties but obtained based on ansatzes
justified by several theoretical assumptions. The parameter , related to
the fourth order coefficient in the Taylor expansion of the free energy density
, has instead a smooth continuum extrapolation which is in agreement
with the dilute instanton gas approximation (DIGA); moreover, a direct
measurement of the relative weights of the different topological sectors gives
an even stronger support to the validity of DIGA.Comment: 23 pages, 13 figure
Roberge-Weiss endpoint at the physical point of QCD
We study the phase diagram of QCD in the plane and
investigate the critical point corresponding to the onset of the Roberge-Weiss
transition, which is found for imaginary values of . We make use of
stout improved staggered fermions and of the tree level Symanzik gauge action,
and explore four different sets of lattice spacings, corresponding to , and different spatial sizes, in order to assess the universality
class of the critical point. The continuum extrapolated value of the endpoint
temperature is found to be MeV, i.e. , where is the chiral pseudocritical temperature
at zero chemical potential, while our finite size scaling analysis, performed
on and lattices, provides evidence for a critical point in
the Ising universality class.Comment: 10 pages, 14 eps figures, 2 tables, final version published in
Physical Review
Influence of magnetic fields on the color screening masses
We present some recent results obtained in the study of the color magnetic
and electric screening masses in the QCD plasma. In particular, we discuss how
the masses get modified by strong external fields which are expected to be
created in physical situations such as heavy-ion collisions.Comment: Talk presented at the 35th annual International Symposium on Lattice
Field Theory (LATTICE 2017), 18-24 June 2017, Granada, Spain. 8 Pages, 7
Figure
Gauge-invariant field-strength correlators for QCD in a magnetic background
We consider the properties of the gauge-invariant two-point correlation
functions of the gauge-field strengths for QCD in the presence of a magnetic
background field. We discuss the general structure of the correlators in this
case and provide the results of an exploratory lattice study for QCD
discretized with unimproved staggered fermions. Our analysis provides evidence
for the emergence of anisotropies in the non-perturbative part of the
correlators and for an increase of the gluon condensate as a function of the
external magnetic field.Comment: Published version. Added table with perturbative parameters values. 8
pages, 5 figure
- …