Pushan Majumdar

Heavy Quark Momentum Diffusion Coefficient from Lattice QCD

The momentum diffusion coefficient for heavy quarks is studied in a deconfined gluon plasma in the static approximation by investigating a correlation function of the color electric field using Monte Carlo techniques. The diffusion coefficient is extracted from the long-distance behavior of such a correlator. For temperatures TcT≲2Tc, our nonperturbative estimate of the diffusion coefficient is found to be very different from the leading-order perturbation theory and is in the right ballpark to explain the heavy quark flow seen by the PHENIX Collaboration at the RHIC experiment.

The string spectrum from large Wilson loops

We look at energies of the low lying states of the hadronic string in three dimensional SU(2) lattice gauge theory by forming correlation matrices among different sources. We are able to go to previously inaccessible time separations. This is made possible by using a new algorithm proposed by Luscher and Weisz which lets us measure the exponentially small values of large Wilson loops with sufficient accuracy.

Static potential, force, and flux-tube profile in 4D compact U(1) lattice gauge theory with the multi-level algorithm

Abstract The long range properties of four-dimensional compact U(1) lattice gauge theory with the Wilson action in the confinement phase is studied by using the multi-level algorithm. The static potential, force and flux-tube profile between two static charges are successfully measured from the correlation function involving the Polyakov loop. The universality of the coefficient of the 1/ r correction to the static potential, known as the Luscher term, and the transversal width of the flux-tube profile as a function of its length are investigated. While the result supports the presence of the 1/ r correction, the width of the flux tube shows an almost constant behavior at a large distance.

String-like behaviour of 4d SU(3) Yang-Mills flux tubes

We present here results on the fine structure of the static q potential in d = 4 SU(3) Yang-Mills theory. The potential is obtained from Polyakov loop correlators having separations between 0.3 and 1.2 fermi. Measurements were carried out on lattices of spatial extents of about 4 and 5.4 fermi. The temporal extent was 5.4 fermi in both cases. The results are analyzed in terms of the force between a q pair as well as in terms of a scaled second derivative of the potential. The data is accurate enough to distinguish between different effective string models and it seems to favour the expression for ground state energy of a Nambu-Goto string.

The condensate for two dynamical chirally improved quarks in QCD

Abstract We compare the eigenvalue spectra of the Dirac operator from a simulation with two mass degenerate dynamical chirally improved fermions with Random Matrix Theory. Comparisons with distributions of k th eigenvalues ( k = 1 , 2 ) in fixed topological sectors ( ν = 0 , 1 ) are carried out using the Kolmogorov–Smirnov test. The eigenvalue distributions are well described by the RMT predictions. The match allows us to read off the quark condensate in the chiral limit. Correcting for finite size and renormalization we obtain a mean value of − ( 276 ( 11 ) ( 16 ) MeV ) 3 in the MS ¯ scheme.

QCD with two dynamical flavors of chirally improved quarks

Considering Ginsparg-Wilson type fermions dynamically in lattice QCD simulations is a challenging task. The hope is to be able to approach smaller pion masses and to eventually reach physical situations. The price to pay is substantially higher computational costs. Here we discuss first results of a dynamical implementation of the so-called chirally improved fermions, a Dirac operator that obeys the Ginsparg-Wilson condition approximately. The simulation is for two species of mass-degenerate quarks on 12{sup 3}x24 lattices with spatial size up to 1.55 fm. Implementation of the hybrid Monte-Carlo algorithm and an analysis of the results are presented.

Glueball masses in 4d U(1) lattice gauge theory using the multi-level algorithm

Abstract We take a new look at plaquette–plaquette correlators in 4d compact U(1) lattice gauge theory which are separated in time, both in the confined and the deconfined phases. From the behaviour of these correlators we extract glueball masses in the scalar as well as the axial-vector channels. Also in the deconfined phase, the non-zero momentum axial-vector correlator gives us information about the photon which appears as a massless particle in the spectrum. Using the Luscher–Weisz multi-level algorithm, we are able to go to large time separations which were not possible previously.

Continuum limit of string formation in 3d SU(2) LGT

Abstract We study the continuum limit of the string-like behaviour of flux tubes formed between static quarks and antiquarks in three-dimensional SU ( 2 ) lattice gauge theory. We compare our simulation data with the predictions of both effective string models as well as perturbation theory. On the string side we obtain clear evidence for convergence of data to predictions of Nambu–Goto theory. We comment on the scales at which the static potential starts departing from one-loop perturbation theory and then again being well described by effective string theories. We also estimate the leading corrections to the one-loop perturbative potential as well as the Nambu–Goto effective string. In the intermediate regions we find an empirical formula which gives surprisingly good fits. We also compare our results with earlier works.

Gauge field copies

The problem of Wu-Yang ambiguities in three dimensions is related to the problem of the existence of torsion-free driebeins for an arbitrary potential. The ambiguity is only at the level of boundary conditions. We also find that in three dimensions any smooth Yang-Mills field tensor can be uniquely written as the non-Abelian magnetic field of a smooth Yang-Mills potential.

Dual gluons and monopoles in 2+1 dimensional Yang–Mills theory

Abstract 2+1-dimensional Yang–Mills theory is reinterpreted in terms of metrics on 3-manifolds. The dual gluons are related to diffeomorphisms of the 3-manifolds. Monopoles are identified with points where the Ricci tensor has triply degenerate eigenvalues. The dual gluons have the desired interaction with these monopoles. This would give a mass for the dual gluons resulting in confinement.