The deconfinement phase transition is studied in the ensemble canonical with respect to triality. Since this ensemble implies a projection to the zero triality sector of the theory we introduce a quantity which is insensitive to $Z(N_c)$ symmetry but can reveal a critical behaviour in the theory with dynamical quarks. Further, we argue that in the canonical ensemble description of full QCD there exist domains of different $Z(N_c)$ phases which are degenerate and possess normal physical properties. This contradicts the predictions of the grand canonical ensemble. We propose a new order parameter to test the realization of the discrete $Z(N_c)$ symmetry at finite temperature and calculate it for the case of $Z(2)$ gauge fields coupled to fundamental fermions.
The string susceptibility exponents of dynamically triangulated two dimensional surfaces with sphere and torus topology were calculated using the grand-canonical Monte Carlo method. We also simulated the model coupled to d-Ising spins (d=1,2,3,5).
We consider supersymmetric domain walls of four-dimensional $mathcal{N}!=!1$ $Sp(N)$ SQCD with $F!=!N+1$ and $F!=!N+2$ flavors. First, we study numerically the differential equations defining the walls, classifying the solutions. When $F!=!N+2$, in the special case of the parity-invariant walls, the naive analysis does not provide all the expected solutions. We show that an infinitesimal deformation of the differential equations sheds some light on this issue. Second, we discuss the $3d$ $mathcal{N}!=!1$ Chern-Simons-matter theories that should describe the effective dynamics on the walls. These proposals pass various tests, including dualities and matching of the vacua of the massive $3d$ theory with the $4d$ analysis. However, for $F!=!N+2$, the semiclassical analysis of the vacua is only partially successful, suggesting that yet-to-be-understood strong coupling phenomena are into play in our $3d$ $mathcal{N}!=!1$ gauge theories.
We study the worldvolume dynamics of BPS domain walls in N=1 SQCD with N_f=N flavors, and exhibit an enhancement of supersymmetry for the reduced moduli space associated with broken flavor symmetries. We provide an explicit construction of the worldvolume superalgebra which corresponds to an N=2 Kahler sigma model in 2+1D deformed by a potential, given by the norm squared of a U(1) Killing vector, resulting from the flavor symmetries broken by unequal quark masses. This framework leads to a worldvolume description of novel two-wall junction configurations, which are 1/4-BPS objects, but nonetheless preserve two supercharges when viewed as kinks on the wall worldvolume.
Coincident D3-branes placed at a conical singularity are related to string theory on $AdS_5times X_5$, for a suitable five-dimensional Einstein manifold $X_5$. For the example of the conifold, which leads to $X_5=T^{1,1}=(SU(2)times SU(2))/U(1)$, the infrared limit of the theory on $N$ D3-branes was constructed recently. This is ${cal N}=1$ supersymmetric $SU(N)times SU(N)$ gauge theory coupled to four bifundamental chiral superfields and supplemented by a quartic superpotential which becomes marginal in the infrared. In this paper we consider D3-branes wrapped over the 3-cycles of $T^{1,1}$ and identify them with baryon-like chiral operators built out of products of $N$ chiral superfields. The supergravity calculation of the dimensions of such operators agrees with field theory. We also study the D5-brane wrapped over a 2-cycle of $T^{1,1}$, which acts as a domain wall in $AdS_5$. We argue that upon crossing it the gauge group changes to $SU(N)times SU(N+1)$. This suggests a construction of supergravity duals of ${cal N}=1$ supersymmetric $SU(N_1)times SU(N_2)$ gauge theories.
In SU(2) gluodynamics, the Debye gluon contribution W_D(A_0) to the effective action of the temporal gauge field component, A_0 = const, at high temperature is calculated in the background R^{xi} gauge. It is shown that at nonzero A_0 the standard definition k_0 = 0, |k| -> 0 corresponds to long distance correlations for the longitudinal in internal space gluons. The transversal gluons become screened by the A_0 background field. Therefore they give zero contributions and have to be excluded from the correlation corrections. The total effective action accounting for the one-loop, two-loop and correct W_D(A_0) satisfies Nielsens identity that proves gauge invariance of the A_0 condensation phenomenon.