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P. Bialas

Publications and source records attributed to P. Bialas.

At least 37 records · Page 2Linked to original sources
arXiv2004

A Gauge Theory of Wilson Lines as a Dimensionally Reduced Model of QCD_3

We analyze a two dimensional SU(3) gauge model of Wilson lines as a dimensionally reduced model of high temperature QCD_3. In contrast to perturbative dimensional reduction it has an explicit global Z(3) symmetry in the action. The phase diagram of the model is studied in the space of two free parameters used to describe the self interaction of the Wilson lines. In addition to the confinement-deconfinement transition, the model also exhibits a new Z(3)-breaking phase. These findings are obtained by numerical simulations, and supported by a perturbative calculation to one loop. A screening mass from Polyakov loop correlations is calculated numerically. It matches the known QCD_3 mass in a domain of parameters belonging to the normal deconfined phase.

hep-lat↗
arXiv2004

Ensemble of causal trees

We discuss the geometry of trees endowed with a causal structure using the conventional framework of equilibrium statistical mechanics. We show how this ensemble is related to popular growing network models. In particular we demonstrate that on a class of afine attachment kernels the two models are identical but they can differ substantially for other choice of weights. We show that causal trees exhibit condensation even for asymptotically linear kernels. We derive general formulae describing the degree distribution, the ancestor-descendant correlation and the probability a randomly chosen node lives at a given geodesic distance from the root. It is shown that the Hausdorff dimension d_H of the causal networks is generically infinite.

cond-mat.stat-mech↗
arXiv2004

Dimensional reduction in QCD: Lessons from lower dimensions

In this contribution we present the results of a series of investigations of dimensional reduction, applied to SU(3) gauge theory in 2 + 1 dimensions. We review earlier results, present a new reduced model with Z(3) symmetry, and discuss the results of numerical simulations of this model.

hep-lat↗
arXiv2003

Tree Networks with Causal Structure

Geometry of networks endowed with a causal structure is discussed using the conventional framework of equilibrium statistical mechanics. The popular growing network models appear as particular causal models. We focus on a class of tree graphs, an analytically solvable case. General formulae are derived, describing the degree distribution, the ancestor-descendant correlation and the probability a randomly chosen node lives at a given geodesic distance from the root. It is shown that the Hausdorff dimension $d_H$ of the causal networks is generically infinite, in contrast to the maximally random trees, where it is generically finite.

cond-mat.stat-mech↗
arXiv2001

Towards the lattice study of M-theory (II)

We present new results of the quenched simulations of the reduced D=4 supersymmetric Yang - Mills quantum mechanics for larger gauge groups SU(N), 2<N<9. The model, studied at finite temperature, reveals existence of the two distinct regions which may be precursors of a black hole and the elementary D0 branes phases of M-theory conjectured in the literature. Present results for higher groups confirm the picture found already for N=2. Similar behaviour is observed in the preliminary simulations for the D=6 and D=10 models.

hep-lat↗
arXiv2001

Lattice study of the simplified model of M-theory for larger gauge groups

Lattice discretization of the supersymmetric Yang-Mills quantum mechanics is dis cussed. First results of the quenched Monte Carlo simulations, for D=4 and with higher g auge groups (3 <= N <= 8), are presented. We confirm an earlier (N=2) evidence tha t the system reveals different behaviours at low and high temperatures separated by a narrow transiti on region. These two regimes may correspond to a black hole and elementary excitations phases conjectured in the M-theory. Dependence of the "transition temperature" on N is consistent with 't Hooft scaling and shows a smooth saturation of lattice results towards the large N limit. Is not yet resolved if the observed change between the two regimes corresponds to a genuine phase transition or to a gentle crossover . A new, noncompact formulation of the lattice model is also proposed and its advantages are briefly discussed.

hep-lat↗
arXiv2001

Lattice study of the simplified model of M-theory

Lattice discretization of the supersymmetric Yang-Mills quantum mechanics is reviewed and results of the Monte Carlo simulations of the simplified model are presented. The D=4, N=2, quenched system, studied at finite temperature, reveals existence of the two distinct regions which may correspond to a black hole and the elementary 0-branes phases of the M-theory conjectured in the literature. New results for higher gauge groups N < 9 lead to the similar picture, however the nature of the transition between the two phases and its precise scaling with N is yet unresolved.

hep-lat↗
arXiv2001

QCD with Adjoint Scalars in 2D: Properties in the Colourless Scalar Sector

We present a numerical study of an SU(3) gauged 2D model for adjoint scalar fields, defined by dimensional reduction of pure gauge QCD in (2+1)D at high temperature. In the symmetric phase of its global Z_2 symmetry, two colourless boundstates, even and odd under Z_2, are identified. Their respective contributions (poles) in correlation functions of local composite operators A_n of degree n=2p and 2p+1 in the scalar fields (p=1,2) fulfill factorization. The contributions of two particle states (cuts) are detected. Their size agrees with estimates based on a meanfield-like decomposition of the p=2 operators into polynomials in p=1 operators. No sizable signal in any A_n correlation can be attributed to 1/n times a Debye screening length associated with n elementary fields. These results are quantitatively consistent with the picture of scalar ``matter'' fields confined within colourless boundstates whose residual ``strong'' interactions are very weak.

hep-lat↗
arXiv2000

Large N limit of the IKKT matrix model

Using the dynamical triangulation approach we perform a numerical study of a supersymmetric random surface model that corresponds to the large N limit of the four-dimensional version of the IKKT matrix model. We show that the addition of fermionic degrees of freedom suppresses the spiky world-sheet configurations that are responsible for the pathological behaviour of the purely bosonic model. We observe that the distribution of the gyration radius has a power-like tail p(R) ~ R^{-2.4}. We check numerically that when the number of fermionic degrees of freedom is not susy-balanced, p(R) grows with $R$ and the model is not well-defined. Numerical sampling of the configurations in the tail of the distribution shows that the bosonic degrees of freedom collapse to a one-dimensional tube with small transverse fluctuations. Assuming that the vertex positions can fluctuate independently within the tube, we give a theoretical argument which essentially explains the behaviour of p(R) in the different cases, in particular predicting p(R) ~ R^{-3} in the supersymmetric case. Extending the argument to six and ten dimensions, we predict p(R) ~ R^{-7} and p(R) ~ R^{-15}, respectively.

hep-lat↗
arXiv2000

High Temperature 3D QCD: Dimensional Reduction at Work

We investigate the three-dimensional SU(3) gauge theory at finite temperature in the framework of dimensional reduction. The large scale properties of this theory are expected to be conceptually more complicated than in four dimensions. The dimensionally reduced action is computed in closed analytical form. The resulting effective two-dimensional theory is studied numerically both in the electric and magnetic sector. We find that dimensional reduction works excellently down to temperatures of 1.5 times the deconfinement phase transition temperature and even on rather short length scales. We obtain strong evidence that for ${\rm QCD}_3$, even at high temperature the colour averaged potential is represented by the exchange of a single state, at variance with the usual Debye screening picture involving a pair of electric gluons.

hep-lat↗
arXiv1999

Finite size scaling of the balls in boxes model

We discuss the finite size behaviour in the canonical ensemble of the balls in boxes model. We compare theoretical predictions and numerical results for the finite size scaling of cumulants of the energy distribution in the canonical ensemble and perform a detailed analysis of the first and third order phase transitions which appear for different parameter values in the model.

hep-lat↗
arXiv1999

Connected Correlators in Random Geometries

We analyze correlation functions in a toy model of a random geometry interacting with matter. We show that in general the connected correlator will contain a long-range scaling part which is in some sense a remnant of the disconnected part. This result supports the previously conjectured general form of correlation functions. We discuss the interplay between matter and geometry and the role of the symmetry in the matter sector.

hep-lat↗
arXiv1999

The Weak-Coupling Limit of 3D Simplicial Quantum Gravity

We investigate the weak-coupling limit, kappa going to infinity, of 3D simplicial gravity using Monte Carlo simulations and a Strong Coupling Expansion. With a suitable modification of the measure we observe a transition from a branched polymer to a crinkled phase. However, the intrinsic geometry of the latter appears similar to that of non-generic branched polymer, probable excluding the existence of a sensible continuum limit in this phase.

hep-lat↗
arXiv1998

The Weak-Coupling Limit of Simplicial Quantum Gravity

In the weak-coupling limit, kappa_0 going to infinity, the partition function of simplicial quantum gravity is dominated by an ensemble of triangulations with the ratio N_0/N_D close to the upper kinematic limit. For a combinatorial triangulation of the D--sphere this limit is 1/D. Defining an ensemble of maximal triangulations, i.e. triangulations that have the maximal possible number of vertices for a given volume, we investigate the properties of this ensemble in three dimensions using both Monte Carlo simulations and a strong-coupling expansion of the partition function, both for pure simplicial gravity and a with a suitable modified measure. For the latter we observe a continuous phase transition to a crinkled phase and we investigate the fractal properties of this phase.

hep-lat↗
arXiv1998

Connected Correlators in Quantum Gravity

We discuss the concept of connected, reparameterization invariant matter correlators in quantum gravity. We analyze the effect of discretization in two solvable cases: branched polymers and two-dimensional simplicial gravity. In both cases the naively defined connected correlators for a fixed volume display an anomalous behavior, which could be interpreted as a long-range order. We suggest that this is in fact only a highly non-trivial finite-size effect and propose an improved definition of the connected correlator, which reduces the effect. Using this definition we illustrate the appearance of a long-range spin order in the Ising model on a two-dimensional random lattice in an external magnetic field $H$, when $H \to 0$ and $β=β_C$.

hep-lat↗