arXiv subjects

V. G. Bornyakov

Publications and source records attributed to V. G. Bornyakov.

At least 73 records · Page 4Linked to original sources

arXiv2008

Improved Landau gauge fixing and the suppression of finite-volume effects of the lattice gluon propagator

For the gluon propagator of pure SU(2) lattice gauge theory in the Landau gauge we investigate the effect of Gribov copies and finite-volume effects. Concerning gauge fixing, we enlarge the accessible gauge orbits by adding non-periodic Z(2) gauge transformations and systematically employ the simulated annealing algorithm. Strategies to keep all Z(2) sectors under control within reasonable CPU time are discussed. We demonstrate that the finite-volume effects in the infrared regime become ameliorated. Reaching a physical volume of about (6.5 fm)^4, we find that the propagator, calculated with the indicated improvements, becomes flat in the region of smallest momenta. First signs in 4d of a final decrease towards vanishing momentum are discussed.

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arXiv2007

Finite temperature Lattice QCD with two flavors of improved Wilson fermions

We present results of finite temperature QCD from N_f=2 flavors of non-perturbatively improved Wilson fermions on lattices with N_t=8, 10 and 12. The transition temperature T_c is determined for the first time at lattice spacings as low as a = 0.08 fm, albeit at pion masses 1.3 < r_0 m_π. We furthermore compute the screening masses in various color channels at T>T_c.

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arXiv2007

The Landau gauge gluon propagator: Gribov problem and finite-size effects

The SU(2) gluon propagator in Landau gauge is studied on the lattice. Our gauge fixing procedure employs simulated annealing and Z(2)-flips. It finds higher maxima of the gauge functional compared with those obtained with the standard overrelaxation and leads to systematic deviations of the gluon propagator in the infrared region. In particular, finite-size effects for lattice sizes from (1.7 fm)^4 up to (6.5 fm)^4 become weak. The propagator shows a plateau at p \approx 300 MeV.

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arXiv2007

Study of the topological vacuum structure of SU(2) gluodynamics at T > 0 with overlap fermions and improved action

We study SU(2) gluodynamics at finite temperature near the deconfining phase transition. We create the lattice ensembles using the tadpole improved Luscher-Weisz action. The overlap Dirac operator is used to determine the following three aspects of vacuum structure: (i) The topological susceptibility is evaluated at various temperatures across the phase transition, (ii) the overlap fermion spectral density is determined and found to depend on the Polyakov loop above the phase transition and (iii) the corresponding localization properties of low lying eigenmodes are investigated.

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arXiv2007

Calorons and dyons at the thermal phase transition analyzed by overlap fermions

In a pilot study, we use the topological charge density defined by the eigenmodes of the overlap Dirac operator (with ultraviolet filtering by mode-truncation) to search for lumps of topological charge in SU(2) pure gauge theory. Augmenting this search with periodic and antiperiodic temporal boundary conditions for the overlap fermions, we demonstrate that the lumps can be classified either as calorons or as separate caloron constituents (dyons). Inside the topological charge clusters the (smeared) Polyakov loop is found to show the typical profile characteristic for calorons and dyons. This investigation, motivated by recent caloron/dyon model studies, is performed at the deconfinement phase transition for SU(2) gluodynamics on 20^3 x 6 lattices described by the tadpole improved Lüscher-Weisz action. The transition point has been carefully located. As a necessary condition for the caloron/dyon detection capability, we check that the LW action, in contrast to the Wilson action, generates lattice ensembles, for which the overlap Dirac eigenvalue spectrum smoothly behaves under smearing and under the change of the boundary conditions.

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arXiv2006

Once more on the interrelation between Abelian monopoles and P-vortices in SU(2) LGT

We study the properties of configurations from which P-vortices on one hand or Abelian monopoles on the other hand have been removed. We confirm the loss of confinement in both cases and investigate in what respect the modified ensembles differ from the confining ones from the point of view of the complementary confinement scenario.

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arXiv2005

New features of the maximal abelian projection

After fixing the Maximal Abelian gauge in SU(2) lattice gauge theory we decompose the nonabelian gauge field into the so called monopole field and the modified nonabelian field with monopoles removed. We then calculate respective static potentials and find that the potential due to the modified nonabelian field is nonconfining while, as is well known, the monopole field potential is linear. Furthermore, we show that the sum of these potentials approximates the nonabelian static potential with 5% or higher precision at all distances considered. We conclude that at large distances the monopole field potential describes the classical energy of the hadronic string while the modified nonabelian field potential describes the string fluctuations. Similar decomposition was observed to work for the adjoint static potential. A check was also made of the center projection in the direct center gauge. Two static potentials, determined by projected $Z_2$ and by modified nonabelian field without $Z_2$ component were calculated. It was found that their sum is a substantially worse approximation of the SU(2) static potential than that found in the monopole case. It is further demonstrated that similar decomposition can be made for the flux tube action/energy density.

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arXiv2005

Critical temperature in QCD with two flavors of dynamical quarks

We present results obtained in QCD with two flavors of non-perturbatively improved Wilson fermions at finite temperature on $16^3 \times 8$ and $24^3 \times 10$ lattices. We determine the transition temperature in the range of quark masses $0.6<m_π/m_ρ<0.8$ at lattice spacing a$\approx$0.1 fm and extrapolate the transition temperature to the continuum and to the chiral limits. We also discuss the order of phase transition.

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arXiv2005

Interactions of confining strings in SU(3) gluodynamics

We study the interaction energy of the confining strings in the static rectangular tetraquark system in SU(3) gluodynamics. Using a two-state approximation we calculate the energy eigenvalues and corresponding eigenvectors of string states of different geometry. The interactions are studied both for the co-aligned and for the counter-aligned parallel strings as the functions of positions of the tetraquark constituents. We formulate a simple soap-film model and show that with a good accuracy the string interaction energy corresponding to the ground state of the tetraquark system can be described by this soap-film model.

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arXiv2005

Universality check of Abelian Monopoles

We study the Abelian projected SU(2) lattice gauge theory after gauge fixing to the maximally Abelian gauge (MAG). In order to check the universality of the Abelian dominance we employ the tadpole improved tree level (TI) action. We show that the density of monopoles in the largest cluster (the IR component) is finite in the continuum limit which is approximated already at relatively large lattice spacing. The value itself is smaller than in the case of Wilson action. We present results for the ratio of the Abelian to non-Abelian string tension for both Wilson and TI actions for a number of lattice spacings in the range 0.06 fm < a < 0.35 fm. These results show that the ratio is between 0.9 and 0.95 for all considered values of lattice couplings and both actions. We compare the properties of the monopole clusters in two gauges - in MAG and in the Laplacian Abelian gauge (LAG). Whereas in MAG the infrared component of the monopole density shows a good convergence to the continuum limit, we find that in LAG it is even not clear whether a finite limit exists.

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arXiv2004

Baryonic Flux in Quenched and Two-Flavor Dynamical QCD after Abelian projection

We study the distribution of color electric flux of the three-quark system in quenched and full QCD (with N_f = 2 flavors of dynamical quarks) at zero and finite temperature. To reduce ultra-violet fluctuations, the calculations are done in the abelian projected theory fixed to the maximally abelian gauge. In the confined phase we find clear evidence for a Y--shape flux tube surrounded and formed by the solenoidal monopole current, in accordance with the dual superconductor picture of confinement. In the deconfined, high temperature phase monopoles cease to condense, and the distribution of the color electric field becomes Coulomb--like.

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arXiv2004

Finite temperature QCD with two flavors of dynamical quarks on 24^3*10 lattice

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arXiv2004

Profiles of the broken string in two-flavor QCD below and above the finite temperature transition

We study the Abelian flux tube profile of mesonic and the baryonic configurations of static quarks below and above the finite-temperature transition in $N_f=2$ full QCD. To reduce effects of ultra-violet fluctuations we measure Abelian distributions of the action density, the color-electric field and the monopole current after fixing to the maximally Abelian gauge. Changing the distance $R$ between quarks for fixed $T/T_c<1$, one can see a clear signal of string breaking for large $R$. The electric field becomes Coulomb-like and the circulating monopole current disappears. We study also the temperature dependence of the flux profile for fixed $R \approx 0.7$ fm. The disappearance of the squeezed flux is observed clearly above $T_c$. Similar behaviors are observed both in the mesonic and the baryonic systems.

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arXiv2004

Finite Temperature QCD with Two Flavors of Non-perturbatively Improved Wilson Fermions

We study QCD with two flavors of non-perturbatively improved Wilson fermions at finite temperature on the $16^3 8$ lattice. We determine the transition temperature at lattice spacings as small as $a \sim 0.12$ fm, and study string breaking below the finite temperature transition. We find that the static potential can be fitted by a two-state ansatz, including a string state and a two-meson state. We investigate the role of Abelian monopoles at finite temperature.

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arXiv2004

Abelian dominance and gluon propagators in the Maximally Abelian gauge of SU(2) lattice gauge theory

Propagators of the diagonal and the off-diagonal gluons are studied numerically in the Maximal Abelian gauge of SU(2) lattice gauge theory. It is found that in the infrared region the propagator of the diagonal gluon is strongly enhanced in comparison with the off--diagonal one. The enhancement factor is about 50 at our smallest momentum 325 MeV. We have also applied various fits to the propagator formfactors.

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arXiv2003

On the gauge dependence of the singlet and adjoint potentials

We study gauge dependence of the recently suggested definition of the singlet and adjoint potentials in SU(2) lattice gauge theory. We find that in the (time local) maximal tree axial gauge the singlet potential obtained from the gauge dependent correlator ${Tr} L(x)L^\dagger(y)$ differs from that computed in the Coulomb gauge. In the generalized Coulomb gauge we find the range of the parameter values in which the singlet potential differs from that in the Coulomb gauge.

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arXiv2003

Dynamics of Monopoles and Flux Tubes in Two-Flavor Dynamical QCD

We investigate the confining properties of the QCD vacuum with $N_f=2$ flavors of dynamical quarks, and compare the results with the properties of the quenched theory. We use non-perturbatively $\mathcal{O}(a)$ improved Wilson fermions to keep cut-off effects small. We focus on color magnetic monopoles. Among the quantities we study are the monopole density and the monopole screening length, the static potential and the profile of the color electric flux tube. We furthermore derive the low-energy effective monopole action. Marked differences between the quenched and dynamical vacuum are found.

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arXiv2003

$q\bar q$ and $2q2\bar q$ systems in terms of P-vortices

We study the action and the energy densities of the confining string in the indirect Z(2) projection of SU(2) lattice gauge theory. We find that the width of the confining string is proportional to the logarithm of the distance between the quark and antiquark. In $2q2\bar{q}$ system we observe the effect of the reconstruction of the flux tube when we change the distance between two $q\bar{q}$ pairs.

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