arXiv subjects

Alexei Bazavov

Publications and source records attributed to Alexei Bazavov.

At least 55 records · Page 3Linked to original sources

arXiv2019

Color screening in (2+1)-flavor QCD

We study correlation functions of spatially separated static quark-antiquark pairs in (2+1)-flavor QCD in order to investigate onset and nature of color screening at high temperatures. We perform lattice calculations in a wide temperature range, $140 \le T \le 5814\,{\rm MeV}$, using the highly improved staggered quark action and several lattice spacings to control discretization effects. By comparing at high temperatures our lattice results to weak-coupling calculations as well as to the zero temperature result for the energy of a static quark-antiquark pair, we observe that color screening sets in at $rT \approx 0.3$. Furthermore, we also observe that in the range $0.3 \lesssim r T \lesssim 0.6$ weak-coupling calculations in the framework of suitable effective field theories provide an adequate picture of color screening.

hep-lat↗

arXiv2018

Equation of state in (2+1) flavor QCD at high temperatures

We calculate the Equation of State at high temperatures in (2+1) flavor QCD using the highly improved staggered quark (HISQ) action. We study the lattice spacing dependence of the pressure at high temperatures using lattices with temporal extent $N_τ=6,~8,~10$ and $12$ and perform continuum extrapolations. We also give a continuum estimate for the Equation of State up to temperatures $T=2\,$GeV, which are then compared with results of the weak-coupling calculations. We find reasonable agreement with the HTL calculation at the highest temperatures and a tension with the EQCD calculation of a few percent, with the lattice results in the middle between both.

hep-lat↗

arXiv2018

Universal features of the Abelian Polyakov loop in 1+1 dimension

We show that the Polyakov loop of the two-dimensional lattice Abelian Higgs model can be calculated using the tensor renormalization group approach. We check the accuracy of the results using standard Monte Carlo simulations. We show that the energy gap produced by the insertion of the Polyakov loop obeys universal finite-size scaling which persists in the time continuum limit. We briefly discuss the relevance of these results for quantum simulations.

hep-lat↗

arXiv2016

Polyakov loop correlators and cyclic Wilson loop from lattice QCD

We discuss color screening in 2+1 flavor QCD in terms of free energies of a static quark-antiquark pair. Thermal modifications of long distance correlations in quark-antiquark systems are studied in terms of static meson correlators. We calculate the Polyakov loop correlator, the color-singlet Wilson line correlator in Coulomb gauge and the cyclic Wilson loop on lattices using the HISQ/Tree action and almost physical quark mases with $N_τ= 4, 6, 8, 10, 12$. We present results in the continuum limit for temperatures up to $T \lesssim 650$ MeV and discuss the linear divergence of the cyclic Wilson loop.

hep-lat↗

arXiv2015

Effective action for the Abelian-Higgs model for a gauge-invariant implementation on optical lattices

We present a gauge-invariant effective action for the Abelian-Higgs model in 1+1 dimensions. It is constructed by integrating out the gauge field and then using the hopping parameter expansion. The latter is tested with Monte Carlo simulations for small values of the scalar self-coupling. In the opposite limit, at infinitely large self-coupling, the Higgs mode is frozen and the partition function can be written in terms of local tensors and the tensor renormalization group blocking can be applied. The numerical implementation requires truncations and the time continuum limit of the blocked transfer matrix can be obtained numerically. At zero gauge coupling and with a spin-1 truncation, the small volume energy spectrum is identical to the low energy spectrum of a two-species Bose-Hubbard model in the limit of large onsite repulsion. The procedure is extended to finite gauge coupling and we derive a spin-1 approximation of the Hamiltonian which involves terms corresponding to transitions among the two species in the Bose-Hubbard model. An optical lattice implementation involving a ladder structure is proposed.

hep-lat↗

arXiv2015

Lattice QCD at Non-Zero Temperature

This is a review of selected recent developments in finite-temperature lattice QCD. The focus is on the properties of the chiral crossover region, deconfinement and fluctuations of conserved charges, the equation of state, properties of heavy quarkonia and reconstruction of spectral functions.

hep-lat↗

arXiv2015

Gauge-invariant implementation of the Abelian Higgs model on optical lattices

We present a gauge-invariant effective action for the Abelian Higgs model (scalar electrodynamics) with a chemical potential $μ$ on a 1+1 dimensional lattice. This formulation provides an expansion in the hopping parameter $κ$ which we test with Monte Carlo simulations for a broad range of the inverse gauge coupling $β_{pl}$ and small values of the scalar self-coupling $λ$. In the opposite limit of infinitely large $λ$, the partition function can be written as a traced product of local tensors which allows us to write exact blocking formulas. Their numerical implementation requires truncations but there is no sign problem for arbitrary values of $μ$. We show that the time continuum limit of the blocked transfer matrix can be obtained numerically and, in the limit of infinite $β_{pl}$ and with a spin-1 truncation, the small volume energy spectrum is identical to the low energy spectrum of a two-species Bose-Hubbard model in the limit of large onsite repulsion. We extend this procedure for finite $β_{pl}$ and derive a spin-1 approximation of the Hamiltonian. It involves new terms corresponding to transitions among the two species in the Bose-Hubbard model. We propose an optical lattice implementation involving a ladder structure.

hep-lat↗

arXiv2015

The effective U(1)-Higgs theory at strong coupling on optical lattices?

We discuss the U(1)-Higgs model in two dimensions in the strongly coupled regime. If we neglect the plaquette interactions, we generate an effective theory where link variables are integrated out, producing 4-field operators. Plaquette interactions can be restored order by order as in recent calculations with staggered fermions. In the case of a SU(2) gauge theory with fermions, this strong coupling expansion can be related to the strong coupling expansion of Fermi-Hubbard models possibly implementable on optical lattice. We would like to provide a similar construction relating the U(1)-Higgs model to some Bose-Hubbard model. As a first step in this direction, we discuss a recent proposal to implement the O(2) model on optical lattices using a 87Rb and 41K Bose-Bose mixture of cold atoms.

hep-lat↗

arXiv2015

In-medium modifications of open and hidden strange-charm mesons from spatial correlation functions

We calculate spatial correlation functions of in-medium mesons consisting of strange--anti-strange, strange--anti-charm and charm--anti-charm quarks in (2+1)-flavor lattice QCD using the highly improved staggered quark action. A comparative study of the in-medium modifications of mesons with different flavor contents is performed. We observe significant in-medium modifications for the $ϕ$ and $D_s$ meson channels already at temperatures around the chiral crossover region. On the other hand, for the $J/ψ$ and $η_c$ meson channels in-medium modifications remain relatively small around the chiral crossover region and become significant only above 1.3 times the chiral crossover temperature.

hep-lat↗

arXiv2013

An overview of (selected) recent results in finite-temperature lattice QCD

I discuss recent results on lattice QCD calculations with the main emphasis on the thermodynamics of the crossover region, restoration of the chiral symmetry and fluctuations of conserved charges as indicator of deconfinement, that may also be used to determine the chemical freeze-out conditions in heavy-ion collision experiments.

hep-lat↗

arXiv2012

Determination of alpha_s from the QCD static energy

We compare lattice data for the short-distance part of the static energy in 2+1 flavor quantum chromodynamics (QCD) with perturbative calculations, up to next-to-next-to-next-to leading-logarithmic accuracy. We show that perturbation theory describes very well the lattice data at short distances, and exploit this fact to obtain a determination of the product of the lattice scale r_0 with the QCD scale Lambda_{MS}. With the input of the value of r_0, this provides a determination of the strong coupling alpha_s at the typical distance scale of the lattice data. We obtain alpha_s(1.5 GeV)=0.326\pm0.019, which provides a novel determination of alpha_s at low energy and with three-loop accuracy (including resummation of the leading ultrasoft logarithms). When this value is evolved to the Z-mass scale M_Z, it corresponds to alpha_s(M_Z)=0.1156^{+0.0021}_{-0.0022}.

hep-ph↗

arXiv2012

Fisher zeros and conformality in lattice models

Fisher zeros are the zeros of the partition function in the complex beta=2N_c/g^2 plane. When they pinch the real axis, finite size scaling allows one to distinguish between first and second order transition and to estimate exponents. On the other hand, a gap signals confinement and the method can be used to explore the boundary of the conformal window. We present recent numerical results for 2D O(N) sigma models, 4D U(1) and SU(2) pure gauge and SU(3) gauge theory with N_f=4 and 12 flavors. We discuss attempts to understand some of these results using analytical methods. We discuss the 2-lattice matching and qualitative aspects of the renormalization group (RG) flows in the Migdal-Kadanoff approximation, in particular how RG flows starting at large beta seem to move around regions where bulk transitions occur. We consider the effects of the boundary conditions on the nonperturbative part of the average energy and on the Fisher zeros for the 1D O(2) model.

hep-lat↗

arXiv2012

The QCD equation of state with 2+1 flavors of Highly Improved Staggered Quarks (HISQ)

One of the fundamental properties of the quark-gluon plasma (QGP), the equation of state, is a subject of extensive studies in lattice QCD and an essential requirement for the correct hydrodynamic modeling of heavy-ion collisions. Lattice QCD provides first-principle calculations for the physics in the non-perturbative regime. In this contribution, we report on recent progress by the HotQCD collaboration in studying the 2+1 flavor equation of state on lattices with the temporal extent N_tau=6, 8, 10 and 12 in Highly Improved Staggered Quarks (HISQ) discretization scheme. Comparisons with equation of state calculations with different fermion actions are also discussed.

hep-lat↗

arXiv2012

Chiral transition temperature and aspects of deconfinement in 2+1 flavor QCD with the HISQ/tree action

We present results on the chiral transition temperature Tc in 2+1 flavor QCD extrapolated to the continuum limit and the physical light quark mass. The extrapolations are based on the data from simulations on lattices with temporal extent Ntau=6, 8 and 12 with the HISQ/tree and Ntau=8 and 12 with the asqtad action. The chiral transition is analyzed in terms of universal O(N) scaling functions. After performing simultaneous asqtad and HISQ/tree continuum extrapolation the chiral transition temperature is Tc=154 +/- 9 MeV. We also discuss the deconfinement aspects of the transition in terms of the renormalized Polyakov loop, fluctuations and correlations of several conserved charges and the trace anomaly.

hep-lat↗

arXiv2011

Fisher's zeros, complex RG flows and confinement in LGT models

The zeros of the partition function in the complex beta plane (Fisher's zeros) play an important role in our understanding of phase transitions and RG flows. Recently, we argued that they act as gates or separatrices for complex RG flows. Using histogram reweighting to construct the density of states, we calculate the Fisher's zeros for pure gauge SU(2) and U(1) on L^4 lattices. For SU(2), these zeros appear to move almost horizontally when the volume increases. They stay away from the real axis which indicates a confining theory at zero temperature. We discuss the effect of an adjoint term on these results. In contrast, using recent multicanonical simulations for the U(1) model for L up to 8 we find that the zeros pinch the real axis near beta =1.0113. Preliminary results concerning U(1) at larger volumes, SU(3) with 3 light flavors and plans to delimit the boundary of the conformal window are briefly discussed.

hep-lat↗

arXiv2011

Form factors for $B$ to $Kll$ semileptonic decay from three-flavor lattice QCD

We study the $B \to Kl^+l^-$ semileptonic decay process in three-flavor lattice QCD. We analyze several ensembles generated by the MILC collaboration at different lattice spacings and sea-quark masses. We use the asqtad improved staggered action for the light quarks and the clover action with the Fermilab interpretation for the heavy $b$ quark. We present preliminary results for the vector current induced form factors for a range of kaon energies. Our analysis includes chiral and continuum extrapolations based on SU(2) staggered χPT.

hep-lat↗

arXiv2010

Taste symmetry and QCD thermodynamics with improved staggered fermions

Taste symmetry violations in staggered fermion formulations correlate strongly with the cut-off (lattice spacing) dependence in thermodynamic quantities. Better taste symmetry on the lattice can be achieved either by decreasing the lattice spacing and going to larger temporal extent in finite-temperature calculations, or by further improving the action. The highly improved staggered quark (HISQ) action offers a further degree of improvement and substantially reduces taste violations. We report on our studies of the 2+1 flavor QCD thermodynamics with the HISQ/tree action. By systematically comparing HISQ/tree, asqtad, p4 and stout calculations we quantify how the cut-off effects manifest themselves in different thermodynamic quantities, including the renormalized Polyakov loop, chiral condensate, various fluctuations and correlations of conserved charges. The implications for the equation of state and a comparison to the hadron resonance gas model are also discussed. The chiral aspects of the finite-temperature transition are discussed in the companion HotQCD contribution [1].

hep-lat↗

arXiv2010

Deconfinement and chiral transition with the highly improved staggered quark (HISQ) action

We report on investigations of the chiral and deconfinement aspects of the finite temperature transition in 2+1 flavor QCD using the Highly Improved Staggered Quark (HISQ) action on lattices with temporal extent $N_τ=6$ and $N_τ=8$. We have performed the calculations for physical values of the strange quark mass $m_s$ and the light quark masses $m_l=0.2m_s$ and $0.05m_s$. Several finite temperature observables, including the renormalized Polyakov loop, the renormalized chiral condensate and the chiral susceptibility have been calculated. We also study the fluctuations and correlations of different conserved charges as well as the trace anomaly at finite temperature. We compare our findings with previous calculations that use different improved staggered fermion formulations: asqtad, p4 and stout.

hep-lat↗