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Pushan Majumdar

Publications and source records attributed to Pushan Majumdar.

At least 37 records · Page 2Linked to original sources
arXiv2007

The condensate for two dynamical chirally improved quarks in QCD

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 distribution of k-th eigenvalues (k=1,2) in fixed topological sectors (nu=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 directly. Correcting for finite size and renormalization we obtain a mean value of -(276 (11)(16) MeV)**3 in the MS-bar scheme.

hep-lat↗
arXiv2007

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

We study the continuum limit of the string-like behaviour of flux tubes formed between static quarks and anti-quarks 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 that a modified Lennard-Jones type potential gives surprisingly good fits.

hep-lat↗
arXiv2006

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

We present here results on the fine structure of the static q\bar 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\bar 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.

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arXiv2006

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 12^3x24 lattices with spatial size up to 1.55 fm. Implementation of the Hybrid Monte-Carlo algorithm and an analysis of the results are presented.

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arXiv2006

Dirac Eigenmodes in an Environment of Dynamical Fermions

We discuss some properties of zero and near-zero modes of the Dirac operator, as observed in a recent simulation of 2-flavor QCD. The quarks have been implemented with the so-called Chirally Improved Dirac operator, which obeys the Ginsparg-Wilson relation to a good approximation. We present geometrical and statistical properties of these eigenmodes and eigenvalues.

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arXiv2005

High accuracy simulations of d=4 SU(3) qcd-string

We present here the results of our high accuracy simulations of $q\bar q$ potential in $d=4$ SU(3) Yang-Mills theory. We measure this quantity by measuring the {\it Polyakov Loop Correlators} using the {\it exponential variance reduction technique(multilevel)} of Luscher and Weisz. We further use numerical integration of the one-link integrals of SU(3) theory by adopting techniques proposed by de Forcrand and Roiesnell achieving significant speed-up in the process. Measurements were done at $β= 5.7$ on $24^3x32$ as well as $32^4$ lattices for separations between the Polyakov loops in the range $r = 2-9$ in lattice units. We analyse the results in terms of the force between $q\bar q$ pair as well as in terms of a {\em scaled second derivative} of the potential. We show that the data is accurate enough to distinguish between different string models and that it seems to favour the expression for ground state energy of a Nambu-Goto string. We conclude by discussing future plans.

hep-lat↗
arXiv2005

Implementing Hybrid Monte Carlo with stout-smeared chirally improved Dirac operators

We discuss our implementation of dynamical Ginsparg-Wilson type fermions using a stout-smeared chirally improved Dirac operator. Such operators have been studied extensively in quenched calculations within the Bern-Graz-Regensburg (BGR) collaboration. Here we discuss the development and testing of the Hybrid Monte Carlo algorithm with this Dirac operator. We study the chiral properties of this operator in a dynamical setup, comparing, e.g., the spectra of the operator for the dynamical and quenched cases. We then discuss quantitative features of the algorithm like autocorrelation and performance.

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arXiv2005

First results from dynamical chirally improved fermions

We simulate Quantum Chromodynamics in four Euclidean dimensions with two (degenerate mass) flavors of dynamical quarks. The Dirac operator is the so-called chirally improved operator that has been studied so far in quenched calculations. We now present results of an implementation with the Hybrid Monte Carlo (HMC) algorithm including stout smearing. Our results are from an 8^3x16 lattice with tadpole improved Luescher-Weisz gauge action. We present our estimate of the lattice spacing, the pi and rho meson masses and evidence for tunneling between different topological sectors.

hep-lat↗
arXiv2005

Experiences with dynamical chirally improved fermions

We simulate Quantum Chromodynamics (QCD) in four Euclidean dimensions with two (degenerate mass) flavors of dynamical quarks. The Dirac operator we use is the so-called chirally improved Dirac operator. We discuss the algorithm used for the simulation as well as the checks and some results on lattices up to size 8**4 for fermion mass parameters down to 0.1. This is the first attempt to introduce dynamical quarks with the chirally improved Dirac operator.

hep-lat↗
arXiv2004

Continuum limit of the spectrum of the hadronic string

We look at the continuum limit of the two universal predictions of the hadronic string theory namely the Luescher term and the energy difference between successive energy states in three dimensional SU(2) lattice gauge theory using Wilson loops and Polyakov loop correlators. We also compare our simulation data with the theoretical predictions in hep-th/0406205.

hep-lat↗
arXiv2004

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

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 Luescher 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.

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arXiv2003

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

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 Luescher - Weisz multi-level algorithm, we are able to go to large time separations which were not possible previously.

hep-lat↗
arXiv2003

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 Lüscher and Weisz which lets us measure the exponentially small values of large Wilson loops with sufficient accuracy.

hep-lat↗
arXiv2002

Experiences with the multi-level algorithm

Small expectation values are difficult to measure in Monte Carlo calculations as they tend to get swamped by noise. Recently an algorithm has been proposed by Luscher and Weisz which allows one to measure expectation values which previously could not be measured reliably in Monte Carlo simulations. We will test our implementation of this algorithm by looking at Polyakov loop correlators and then explore ways of applying it for measuring large Wilson loops.

hep-lat↗
arXiv2001

Susceptibilities and screening masses in two flavor QCD

We studied QCD with two flavors of dynamical staggered quarks at finite temperature, with a bare sea quark mass of about 17 MeV. We report investigations of baryon, isospin, charge and strangeness susceptibilities, as well as screening masses obtained from correlators of local and one-link separated meson operators. These were studied as functions of valence quark mass at several temperatures. Our results for susceptibilities deviate significantly from ideal gas values, and even more from the weak coupling series. We also report the first measurement of off-diagonal quark number susceptibilities below the transition temperature, Tc, where they are the main contribution to charge fluctuations. We present evidence for a close connection between the susceptibilities and the screening masses.

hep-lat↗
arXiv2001

Numerical evidence for monopoles in 3-dimensional Yang-Mills theory

Recently Anishetty, Majumdar and Sharatchandra have proposed a way of characterizing topologically non-trivial configurations for 2+1 dimensional Yang-Mills theory in a local and manifestly gauge invariant manner. In this paper paper we develop criteria to locate such objects in lattice gauge theory and find them in numerical simulations.

hep-lat↗
arXiv2000

Topologically non-trivial configurations in 3-dimensional Yang-Mills theory

Recently Anishetty, Majumdar and Sharatchandra have proposed a way of characterizing topologically non-trivial configurations for 2+1-dimensional Yang-Mills theory in a local and manifestly gauge invariant manner. Here we develop criteria to locate such objects in lattice gauge theory and find them in numerical simulations.

hep-lat↗