65 research outputs found
Shape dependence and anisotropic finite-size scaling of the phase coherence of three-dimensional Bose-Einstein condensed gases
We investigate the equilibrium phase-coherence properties of Bose-condensed
particle systems, focusing on their shape dependence and finite-size scaling
(FSS). We consider three-dimensional (3D) homogeneous systems confined to
anisotropic L x L x L_a boxes, below the BEC transition temperature . We
show that the phase correlations develop peculiar anisotropic FSS for any
, in the large- limit keeping the ratio \lambda = L_a/L^2 fixed. This
phenomenon is effectively described by the 3D spin-wave (SW) theory. Its
universality is confirmed by quantum Monte Carlo simulations of the 3D
Bose-Hubbard model in the BEC phase. The phase-coherence properties of very
elongated BEC systems, \lambda>>1, are characterized by a coherence length
\xi_a \sim A_t \rho_s/T where A_t is the transverse area and \rho_s is the
superfluid density.Comment: 7 page
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
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
Curvature of the chiral pseudo-critical line in QCD: continuum extrapolated results
We determine the curvature of the pseudo-critical line of strong interactions
by means of numerical simulations at imaginary chemical potentials. We consider
stout improved staggered fermions with physical quark masses and the
tree level Symanzik gauge action, and explore four different sets of lattice
spacings, corresponding to , in order to extrapolate results
to the continuum limit. Our final estimate is .Comment: 11 pages, 10 figures, 4 tables. Version to appear in Physical Review
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
Curvature of the chiral pseudo-critical line in QCD
We determine the curvature of the pseudo-critical line of strong interactions
by means of numerical simulations at imaginary chemical potentials. We consider
stout improved staggered fermions with physical quark masses and the
tree level Symanzik gauge action, and explore two different sets of lattice
spacings, corresponding to temporal extensions and . Both
the renormalized chiral condensate and the renormalized chiral susceptibility
are used to locate the transition. The determinations obtained from the two
quantities are in good agreement, a preliminary continuum extrapolation yields
. We also investigate the impact of a non-zero strange
quark chemical potential and compare our results to previous determinations in
the literature, discussing the possible sources of systematic errors affecting
the various procedures.Comment: 16 pages, 12 figures, 11 tables. Published versio
Anisotropy of the quark-antiquark potential in a magnetic field
We investigate the static -potential for QCD at
the physical point in the presence of a constant and uniform external magnetic
field. The potential is found to be anisotropic and steeper in the directions
transverse to the magnetic field than in the longitudinal one. In particular,
when compared to the standard case with zero background field, the string
tension increases (decreases) in the transverse (longitudinal) direction, while
the absolute value of the Coulomb coupling and the Sommer parameter show an
opposite behavior.Comment: 6 pages, 5 figures, 1 table. Final published versio
Screening masses in strong external magnetic fields
We present results for the (color)magnetic and (color)electric screening
masses of the Quark-Gluon Plasma in the presence of an external magnetic field.
The screening masses are extracted from the correlators of Polyakov loops,
determined by lattice QCD simulations at the physical point. We explore
temperatures in the range and magnetic field intensities up to . We find that both screening masses are increasing
functions of the magnetic field and that the dependence on becomes weaker
for larger temperatures. In the case of the magnetic screening mass a slight
anisotropy is also observable.Comment: 8 pages, 2 tables, 10 eps figures; This version matches the published
on
Magnetic field effects on the static quark potential at zero and finite temperature
We investigate the static potential at zero and finite temperature
in the presence of a constant and uniform external magnetic field ,
for several values of the lattice spacing and for different orientations with
respect to . As a byproduct, we provide continuum limit extrapolated
results for the string tension, the Coulomb coupling and the Sommer parameter
at and . We confirm the presence in the continuum of a
-induced anisotropy, regarding essentially the string tension, for which it
is of the order of 15\% at and would suggest, if
extrapolated to larger fields, a vanishing string tension along the magnetic
field for GeV. The angular dependence for GeV can be nicely parametrized by the first allowed term in an angular
Fourier expansion, corresponding to a quadrupole deformation. Finally, for , the main effect of the magnetic field is a general suppression of the
string tension, leading to a precocious loss of the confining properties: this
happens even before the appearance of inverse magnetic catalysis in the chiral
condensate, supporting the idea that the influence of the magnetic field on the
confining properties is the leading effect originating the decrease of as
a function of .Comment: 13 pages, 4 tables, 14 figure
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