arXiv subjects

R. V. Gavai

Publications and source records attributed to R. V. Gavai.

At least 19 recordsLinked to original sources

arXiv2011

A faster method of computation of lattice quark number susceptibilities

We compute the quark number susceptibilities in two flavor QCD for staggered fermions by adding the chemical potential as a Lagrange multiplier for the point-split number density term. Since lesser number of quark propagators are required at any order, this method leads to faster computations. We propose a subtraction procedure to remove the inherent undesired lattice terms and check that it works well by comparing our results with the existing ones where the elimination of these terms is analytically guaranteed. We also show that the ratios of susceptibilities are robust, opening a door for better estimates of location of the QCD critical point through the computation of the tenth and twelfth order baryon number susceptibilities without significant additional computational overload.

hep-lat↗

arXiv2011

Exact chiral invariance at finite density on the lattice

We propose a lattice action for the overlap Dirac matrix with nonzero chemical potential which is shown to preserve the chiral invariance on the lattice exactly. We further demonstrate it to arise from the Domain wall by letting the chemical potential count only the physically relevant wall modes.

hep-lat↗

arXiv2010

Lattice QCD predictions for shapes of event distributions along the freezeout curve in heavy-ion collisions

We present lattice QCD results along the freezeout curve of heavy-ion collisions for the ongoing RHIC energy scan as well as the LHC heavy-ion runs planned for this year. The skew and kurtosis of the event distribution of baryon number are positive at all energies studied, We predict three ratios of non-linear susceptibilities along the freezeout curve as functions of the colliding energy, Sqrt[S_{NN}]. They have smooth behaviour except in the vicinity of a critical point; this can have multiple benefits.

hep-lat↗

arXiv2010

The QCD Phase Structure at High Baryon Density

We consider the possibility that color deconfinement and chiral symmetry restoration do not coincide in dense baryonic matter at low temperature. As a consequence, a state of massive "constituent" quarks would exist as an intermediate phase between confined nuclear matter and the plasma of deconfined massless quarks and gluons. We discuss the properties of this state and its relation to the recently proposed quarkyonic matter.

hep-ph↗

arXiv2010

Anomalies at finite density and chiral fermions

Using perturbation theory in the Euclidean (imaginary time) formalism as well as the non-perturbative Fujikawa method, we verify that the chiral anomaly equation remains unaffected in the presence of nonzero chemical potential, $μ$. We extend our considerations to fermions with exact chiral symmetry on the lattice and discuss the consequences for the recent Bloch-Wettig proposal for the Dirac operator at finite chemical potential. We propose a new simpler method of incorporating $μ$ and compare it with the Bloch-Wettig idea.

hep-lat↗

arXiv2008

Thermodynamics of free Domain Wall fermions

Studying various thermodynamic quantities for the free domain wall fermions for both finite and infinite fifth dimensional extent N_5, we find that the lattice corrections are minimum for $N_T\geq10$ for both energy density and susceptibility, for its irrelevant parameter M in the range 1.45-1.50. The correction terms are, however, quite large for small lattice sizes of $N_T\leq8$. We propose modifications of the domain wall operator, as well as the overlap operator, to reduce the finite cut-off effects to within 10% of the continuum results of the thermodynamic quantities for the currently used N_T=6-8 lattices. Incorporating chemical potential, we show that μ^2 divergences are absent for a large class of such domain wall fermion actions although the chiral symmetry is broken for $μ\neq0$.

hep-lat↗

arXiv2008

Thermodynamics of the ideal overlap quarks on the lattice

The thermodynamics of massless ideal gas of overlap quarks has been investigated both analytically and numerically for both zero and nonzero baryon chemical potential. Any μ^2-divergence is shown analytically to be absent for a class of actions with nonzero chemical potential. All such actions are shown to violate chiral invariance. While the parameter M can be shown to be irrelevant in the continuum limit, as expected, it is shown numerically that the continuum limit can be reached with relatively coarser lattices for certain ranges of M. Numerical limitations of the existing method of introduction of chemical potential are demonstrated. Finally we also show that the energy density for the massive overlap fermions has the correct continuum limit.

hep-lat↗

arXiv2008

QCD at finite chemical potential with six time slices

We investigate the Taylor expansion of the baryon number susceptibility, and hence, pressure, in a series in the baryon chemical potential (mu_B) through a lattice simulation with light dynamical staggered quarks at a finer lattice cutoff a=1/6T. We determine the QCD cross over coupling at mu_B=0. We find the radius of convergence of the series at various temeperatures, and bound the location of the QCD critical point to be T^E/T_c = 0.94 and mu_B^E/T < 1.8. We also investigate the extrapolation of various susceptibilities and linkages to finite chemical potential.

hep-lat↗

arXiv2008

Towards QCD thermodynamics using exact chiral symmetry on lattice

The thermodynamics of massless ideal gas of overlap quarks has been investigated numerically for both zero and nonzero baryon chemical potential $μ$. While the parameter M has been shown to be irrelevant in the continuum limit, it is shown numerically that the continuum limit can be reached with relatively coarser lattices for certain range of M. Numerical limitation of the existing method of introduction of chemical potential in the overlap formalism is discussed. We have also studied the energy density of free domain wall fermions in the absence of $μ$ and estimated the extent of lattice in the fifth dimension $L_5$ for which the overlap results are recovered. Interestingly, this value of $L_5$ is also minimum for the same range of M found in the overlap case.

hep-lat↗

arXiv2008

Screening correlators with chiral Fermions

We study screening correlators of quark-antiquark composites at T=2T_c, where T_c is the QCD phase transition temperature, using overlap quarks in the quenched approximation of lattice QCD. As the lattice spacing is changed from 1/4T to a=1/6T and 1/8T, we find that screening correlators change little, in contrast with the situation for other types of lattice fermions. All correlators are close to the ideal gas prediction at small separations. The long distance falloff is clearly exponential, showing that a parametrization by a single screening length is possible at distances z > 1/T. The correlator corresponding to the thermal vector is close to the ideal gas value at all distances, whereas that for the thermal scalar deviates at large distances. This is examined through the screening lengths and momentum space correlators. There is strong evidence that the screening transfer matrix does not have reflection positivity.

hep-lat↗

arXiv2008

Eigenvalues and Eigenvectors of the Staggered Dirac Operator at Finite Temperature

We examine the eigenvalues and eigenvectors of the staggered Dirac operator on thermal ensembles created in QCD with two flavours of staggered quarks. We see that across the phase transition a gap opens in the spectrum. For finite volume lattices in the low-temperature phase the eigenvectors are extended, but generic field configurations in the high temperature phase give rise to localized eigenstates. We examine measures of the stability of such localization and find that at finite volumes localization occurs through Mott's mechanism of the formation of mobility edges. However, the band gap between the localized and extended states seem to scale to zero in the limit of large volume.

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arXiv2006

The critical end point in QCD

In this talk I present the logic behind, and examine the reliability of, estimates of the critical end point (CEP) of QCD using the Taylor expansion method.

hep-lat↗

arXiv2006

Working Group Report: Heavy-Ion Physics and Quark-Gluon Plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of Quark-Gluon Plasma believed to have created in heavy-ion collisions and in early universe are reported.

hep-ph↗

arXiv2005

The critical end point of QCD

We investigate the critical end point of QCD with two flavours of light dynamical quarks at finite lattice cutoff a=1/4T using a Taylor expansion of the baryon number susceptibility. We find a strong volume dependence of the position of the critical end point. In the large volume limit we obtain T^E/T_c \~ 0.95 and mu_B^E/T^E ~ 1.1, where T_c is the cross over temperature at zero chemical potential, and T^E and mu_B^E are the temperature and the baryon chemical potential at the critical end point. The small value of mu_B^E places it in the range of observability in energy scans at the RHIC.

hep-lat↗

arXiv2005

Fluctuations, strangeness and quasi-quarks in heavy-ion collisions from lattice QCD

We report measurements of diagonal susceptibilities for the baryon number, chi_B, electrical charge, chi_Q, third component of isospin, chi_I, strangeness, chi_S, and hypercharge, chi_Y, as well as the off-diagonal chi_BQ, chi_BY, chi_BS, etc. We show that the ratios of susceptibilities in the high temperature phase are robust variables, independent of lattice spacing, and therefore give predictions for experiments. We also investigate strangeness production and flavour symmetry breaking matrix elements at finite temperature. Finally, we present evidence that in the high temperature phase of QCD the different flavour quantum numbers are excited in linkages which are exactly the same as one expects from quarks. We present some investigations of these quark-like quasi particles.

hep-lat↗

arXiv2005

Simple patterns for non-linear susceptibilities near T_c

Non-linear susceptibilities upto the eighth order have been constructed in QCD with 2 flavours of dynamical quarks. Beyond leading order, they exhibit peaks at the cross over temperature, T_c. By analyzing their behaviour in detail, we find that the dominant contributions near T_c come from a set of operators with a remarkably simple topology. Any effective theory of QCD near T_c must be able to explain these regularities.

hep-lat↗

arXiv2003

Pressure and non-linear quark number susceptibilities in QCD

We report the first measurements of sixth order non-linear quark number susceptibilities in continuum QCD. This extends our earlier computation of the continuum limit of non-linear quark number susceptibilities and the pressure in QCD for m/Tc=0.1. For T/Tc > 1.5, no phase transitions are observable for mu<30T. Systematics of off-diagonal susceptibilities are reported. The equation of state in the high temperature phase of the QCD plasma is constructed.

hep-lat↗

arXiv2001

Quenched QCD at finite temperature with overlap Fermions

We study quenched QCD just above the phase transition temperature using overlap Fermions. Exact zero modes of the overlap operator are localized. Chiral symmetry is restored, as indicated by the behavior of the chiral condensate after subtracting the effects of zero modes. The vector and pseudo-scalar screening masses are close to ideal gas values.

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