1,536 research outputs found
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
Theta dependence of the deconfinement temperature in Yang-Mills theories
We determine the theta dependence of the deconfinement temperature of SU(3)
pure gauge theory, finding that it decreases in presence of a topological theta
term. We do that by performing lattice simulations at imaginary theta, then
exploiting analytic continuation. We also give an estimate of such dependence
in the limit of a large number of colors N, and compare it with our numerical
results.Comment: 5 pages, 4 figures, 1 table. Discussion and references added. Final
version published in Phys. Rev. Let
Phase diagram of Yang-Mills theories in the presence of a theta term
We study the phase diagram of non-Abelian pure gauge theories in the presence
of a topological theta term. The dependence of the deconfinement temperature on
theta is determined on the lattice both by analytic continuation and by
reweighting, obtaining consistent results. The general structure of the diagram
is discussed on the basis of large-N considerations and of the possible
analogies and dualities existing with the phase diagram of QCD in presence of
an imaginary baryon chemical potential.Comment: 14 pages, 3 tables, 13 figures. Final version published in Physical
Review
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
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
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
Susceptibility of the QCD vacuum to CP-odd electromagnetic background fields
We investigate two flavor QCD in presence of CP-odd electromagnetic
background fields and determine, by means of lattice QCD simulations, the
induced effective theta term to the first order in the scalar product of E and
B. We employ a rooted staggered discretization and study lattice spacings down
to 0.1 fm and Goldstone pion masses around 480 MeV. In order to deal with a
positive measure, we consider purely imaginary electric fields and real
magnetic fields, then exploiting analytic continuation. Our results are
relevant to a description of the effective pseudoscalar QED-QCD interactions.Comment: 5 pages, 4 figures, 1 table. New data and references added. Matches
the published versio
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
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
- …