Flux tubes in the QCD vacuum

Abstract

The hypothesis that the QCD vacuum can be modeled as a dual superconductor is a powerful tool to describe the distribution of the color field generated by a quark-antiquark static pair and, as such, can provide useful clues for the understanding of confinement. In this work we investigate, by lattice Monte Carlo simulations of the SU (3) pure gauge theory and of (2+1)-flavor QCD with physical mass settings, some properties of the chromoelectric flux tube at zero temperature and their dependence on the physical distance between the static sources. We draw some conclusions about the validity domain of the dual superconductor picture.

QCD flux tubes across the deconfinement phase transition

“…5 nal field E l (x t ) in correspondence of temperatures 0.8T c ≤ T ≤ 1.5T c with the static quark-antiquark sources placed apart at distances 0.76 fm ≤ d ≤ 1.33 fm. The data for E l (x t ) are well fitted for all temperatures T and all distances d by using a functional form introduced long ago [29] for describing flux tubes in ordinary superconductivity and recently proposed [14][15][16] in order to describe the transverse distribution of the chromoelectric flux tube:…”

“…Indeed, Monte Carlo simulations produce samples of vacuum configurations that, in principle, contain all the relevant information on the nonperturbative sector of QCD. A wealth of numerical analyses in QCD has firmly established that the chromoelectric field between a static quark-antiquark pair distributes in tubelike structures or "flux tubes" [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. From these tubelike structures a linear potential between static color charges naturally arises, thus representing a numerical evidence of color confinement.…”

Flux tubes in Nf = 2 + 1 QCD with external magnetic fields

“…This loss of cylindircal symmetry is not particularly strong and it becomes observable only at rather large external magnetic fields (eB ∼ 1 GeV 2 ). In order to extract more information from our data for the flux tube shape at eB = 0 and at eB 0, we fitted them with the function which has been already adopted in the literature [10,11,25,26], and that has been derived to describe the magnetic field profile of an Abrikosov vortex in an ordinary superconductor away from the London limit [27]. In the context of QCD, such a function is intended to describe the shape of the color-electric flux tube within the dual superconductor interpretation of the QCD vacuum.…”

“…Hence, as well as for the determination of the Wilson Loop, it is convenient to perform some sort of smearing on the SU(3) link variables, in order to reduce the UV-fluctuations and gain a better signal-to-noise ratio. To this aim, following previous works [10], we adopted a smearing procedure with one single HYP smearing step for the temporal links [15] with coefficients α = (1, 0.5, 0.5) and N APE APE smearing steps for the spatial links [16] …”

Heavy pentaquark states and a novel color structure

“…It is well known that color flux-tube-like structures emerge by analyzing the chromo-electric fields between static quarks in lattice numerical simulations [13]. Such color flux-tube structures naturally lead to a linear confinement potential between static color charges and to a direct numeri-cal evidence of color confinement [14].…”