1,720,999 research outputs found
Shape dependence and anisotropic finite-size scaling of the phase coherence of three-dimensional Bose-Einstein-condensed gases
No full textWe 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×L×La boxes, below the Bose-Einstein-condensate (BEC) transition temperature Tc. We show that the phase correlations develop peculiar anisotropic FSS for any T<Tc, in the large-L limit keeping the ratio λ≡La/L2 and the particle density fixed. This phenomenon is effectively described by the 3D spin-wave theory. Its universality is confirmed by quantum Monte Carlo simulations of the 3D Bose-Hubbard model in the BEC phase. The phase-coherence correlations of very elongated BEC systems, λ→, are characterized by the coherence length ξa∼Atρs/T, where At is the transverse area and ρs is the superfluid density
Gauge-invariant field-strength correlators for QCD in a magnetic background
Full text linkWe 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 at zero temperature. We discuss the general structure of the correlators in this case and provide the results of an exploratory lattice study for N_f = 2 QCD discretized with unimproved staggered fermions. Our analysis provides evidence for the emergence of anisotropies in the nonperturbative part of the correlators and for an increase of the gluon condensate as a function of the external magnetic field
Field-strength correlators for QCD in a magnetic background
Full text linkWe present the results of an exploratory study (by means of Monte Carlo simulations on the lattice) of the properties of the gauge-invariant two-point correlation functions of the gauge-field strengths for N_f=2 QCD at zero temperature and in the presence of a magnetic background field: the analysis provides evidence for the emergence of anisotropies in the nonperturbative part of the correlators and for an increase of the gluon condensate as a function of the external magnetic field
Magnetic field effects on the static quark potential at zero and finite temperature
Full text linkWe investigate the static QQ potential at zero and finite temperature in the presence of a constant and uniform external magnetic field B→, for several values of the lattice spacing and for different orientations with respect to B→. As a byproduct, we provide continuum limit extrapolated results for the string tension, the Coulomb coupling and the Sommer parameter at T=0 and B=0. We confirm the presence in the continuum of a B-induced anisotropy, regarding essentially the string tension, for which it is of the order of 15% at |e|B∼1 GeV2 and would suggest, if extrapolated to larger fields, a vanishing string tension along the magnetic field for GeV2. The angular dependence for GeV2 can be nicely parametrized by the first allowed term in an angular Fourier expansion, corresponding to a quadrupole deformation. Finally, for T≠0, the main effect of the magnetic field is a general suppression of the string tension, leading to a early 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 Tc as a function of B
Curvature of the chiral pseudocritical line in QCD
No full textWe determine the curvature of the pseudocritical line of strong interactions by means of numerical simulations at imaginary chemical potentials. We consider Nf=2+1 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 Nt=6 and Nt=8. 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 κ=0.013(2)(1). We also investigate the impact of a nonzero 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
Effects of a strong magnetic field on the QCD flux tube
Full text linkIn this work we investigate the effect of an external magnetic field B on the shape of flux tubes in QCD by means of lattice simulations, performed with Nf=2+1 flavors of stout improved dynamical staggered quarks with physical masses. After having discussed some difficulties in the practical definition of the flux tube at B=0, we show that these ambiguities do not affect the determination of the flux tube modifications induced by the magnetic field. Different results are obtained depending on the relative orientations of the flux tube and of the magnetic field: they confirm that the magnetic field acts as a transverse confinement catalyzer and longitudinal confinement inhibitor; moreover, the flux tube itself loses its axial symmetry when it is not directed along the magnetic background
Roberge-Weiss endpoint at the physical point of Nf=2+1 QCD
Full text linkWe study the phase diagram of Nf=2+1 QCD in the T-μB plane and investigate the critical point corresponding to the onset of the Roberge-Weiss transition, which is found for imaginary values of μB. 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 Nt=4, 6, 8, 10, 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 TRW=208(5) MeV, i.e. TRW/Tc∼1.34(7), where Tc is the chiral pseudocritical temperature at zero chemical potential, while our finite size scaling analysis, performed on Nt=4 and Nt=6 lattices, provides evidence for a critical point in the 3D Ising universality class
Anisotropy of the QQ ̄ potential in a magnetic field
Full text linkWe study how the static quark-antiquark potential for Nf = 2+1 QCD at the physical point gets modified by the presence of a constant and uniform magnetic field. We observe an anisotropy to appear in the potential: it gets steeper in the directions transverse to the magnetic field than in the longitudinal one. By comparing to the case with zero magnetic field, we show that the string tension increases (decreases) in the perpendicular (parallel) direction, while the absolute value of the Coulomb coupling and the Sommer parameter show the opposite behavior
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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