In this contribution we review some recent results about the emergence of 2D integrable systems in 3D Lattice Gauge Theories near the deconfinement transition. We focus on some concrete examples involving the flux tube thickness, the ratio of k-string tensions and Polyakov loops correlators in various models.
In presence of a static pair of sources, the spectrum of low-lying states of any confining gauge theory in D space-time dimensions is described, at large source separations, by an effective string theory. Recently two important advances improved our
understanding of this effective theory. First, it was realized that the form of the effective action is strongly constrained by the requirement of the Lorentz invariance of the gauge theory, which is spontaneously broken by the formation of a long confining flux tube in the vacuum. This constraint is strong enough to fix uniquely the first few subleading terms of the action. Second, it has been realized that the first of these allowed terms - a quartic polynomial in the field derivatives - is exactly the composite field $Tbar{T}$, built with the chiral components, $T$ and $bar{T}$, of the energy-momentum tensor of the 2d QFT describing the infrared limit of the effective string. This irrelevant perturbation is quantum integrable and yields, through the thermodynamic Bethe Ansatz (TBA), the energy levels of the string which exactly coincide with the Nambu-Goto spectrum. In this talk we first review the general implications of these two results and then, as a test of the power of these methods, use them to construct the first few boundary corrections to the effective string action.
We study the underlying topology of gauge fields in 2+1 flavor QCD with domain wall fermions on lattices of size $32^3times 8$, at and immediately above the chiral crossover transition. Using valence overlap fermions with exact index theorem, we focu
s on its zero modes for different choices of periodicity phases along the temporal direction. Our studies show that the zero modes are due to fractionally charged topological objects, the instanton-dyons. We further provide qualitative study of the interactions between those and compare with the available semi-classical results, finding remarkably accurate agreement in all cases.
We present possible indications for flavor separation during the QCD crossover transition based on continuum extrapolated lattice QCD calculations of higher order susceptibilities. We base our findings on flavor specific quantities in the light and s
trange quark sector. We propose a possible experimental verification of our prediction, based on the measurement of higher order moments of identified particle multiplicities. Since all our calculations are performed at zero baryochemical potential, these results are of particular relevance for the heavy ion program at the LHC.
Analyzing correlation functions of charmonia at finite temperature ($T$) on $32^3times(32-96)$ anisotropic lattices by the maximum entropy method (MEM), we find that $J/psi$ and $eta_c$ survive as distinct resonances in the plasma even up to $T simeq
1.6 T_c$ and that they eventually dissociate between $1.6 T_c$ and $1.9 T_c$ ($T_c$ is the critical temperature of deconfinement). This suggests that the deconfined plasma is non-perturbative enough to hold heavy-quark bound states. The importance of having sufficient number of temporal data points in the MEM analysis is also emphasized.
In the framework of a holographic QCD approach we study an influence of matters on the deconfinement temperature, $T_c$. We first consider quark flavor number ($N_f$) dependence of $T_c$. We observe that $T_c$ decreases with $N_f$, which is consisten
t with a lattice QCD result. We also delve into how the quark number density $rho_q$ affects the value of $T_c$. We find that $T_c$ drops with increasing $rho_q$. In both cases, we confirm that the contributions from quarks are suppressed by $1/N_c$, as it should be, compared to the ones from a gravitational action (pure Yang-Mills).