arXiv subjects

A. V. Kovalenko

Publications and source records attributed to A. V. Kovalenko.

16 recordsLinked to original sources

arXiv2019

Detection statistics of the RadioAstron AGN survey

The largest Key Science Program of the RadioAstron space VLBI mission is a survey of active galactic nuclei (AGN). The main goal of the survey is to measure and study the brightness of AGN cores in order to better understand the physics of their emission while taking interstellar scattering into consideration. In this paper we present detection statistics for observations on ground-space baselines of a complete sample of radio-strong AGN at the wavelengths of 18, 6, and 1.3 cm. Two-thirds of them are indeed detected by RadioAstron and are found to contain extremely compact, tens to hundreds of $μ$as structures within their cores.

astro-ph.GA↗

arXiv2017

Probing the gravitational redshift with an Earth-orbiting satellite

We present an approach to testing the gravitational redshift effect using the RadioAstron satellite. The experiment is based on a modification of the Gravity Probe A scheme of nonrelativistic Doppler compensation and benefits from the highly eccentric orbit and ultra-stable atomic hydrogen maser frequency standard of the RadioAstron satellite. Using the presented techniques we expect to reach an accuracy of the gravitational redshift test of order $10^{-5}$, a magnitude better than that of Gravity Probe A. Data processing is ongoing, our preliminary results agree with the validity of the Einstein Equivalence Principle.

gr-qc↗

arXiv2016

RadioAstron gravitational redshift experiment: status update

A test of a cornerstone of general relativity, the gravitational redshift effect, is currently being conducted with the RadioAstron spacecraft, which is on a highly eccentric orbit around Earth. Using ground radio telescopes to record the spacecraft signal, synchronized to its ultra-stable on-board H-maser, we can probe the varying flow of time on board with unprecedented accuracy. The observations performed so far, currently being analyzed, have already allowed us to measure the effect with a relative accuracy of $4\times10^{-4}$. We expect to reach $2.5\times10^{-5}$ with additional observations in 2016, an improvement of almost a magnitude over the 40-year old result of the GP-A mission.

astro-ph.IM↗

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.

hep-lat↗

arXiv2006

Peculiarities in the Spectrum of the Adjoint Scalar Kinetic Operator in Yang-Mills Theory

We study the spectrum of low-lying eigenmodes of the kinetic operator for scalar particles, in the color adjoint representation of Yang-Mills theory. The kinetic operator is the covariant Laplacian, plus a constant which serves to renormalize mass. In the pure gauge theory, our data indicates that the interval between the lowest eigenvalue and the mobility edge tends to infinity in the continuum limit. On these grounds, it is suggested that the perturbative expression for the scalar propagator may be misleading even at distance scales that are small compared to the confinement scale. We also measure the density of low-lying eigenmodes, and find a possible connection to multi-critical matrix models of order m=1.

hep-lat↗

arXiv2005

On topological properties of vacuum defects in lattice Yang-Mills theories

We study correlations between low-lying modes of the overlap Dirac operator and vacuum defects, center vortices and three-dimensional volumes, in lattice SU(2) gluodynamics. The low-lying modes are apparently sensitive to topological properties of the underlying gluon field configurations while the vacuum defects are crucial for the confinement. We find distinct positive correlation in both cases. In case of vortices the correlation is stronger.

hep-lat↗

arXiv2005

Geometry of three dimensional vacuum domains in four dimensional SU(2) gluodynamics

We review briefly recent results of lattice simulations on 3d domains in the vacuum state of SU(2) gluodynamics. The defects are defined as unification of all the negative links in central projection under condition that the total number of negative links is minimized. In the continuum limit, negative links correspond, generally speaking to singular fields. The data indicate that total volume of the defects scales in physical units. We consider also correlator of negative links. The correlator scales in physical units as well, within the error bars. A new observation reported here is a strong anisotropy of the correlator.

hep-lat↗

arXiv2004

Three dimensional vacuum domains in four dimensional SU(2) gluodynamics

Performing lattice simulations of the four dimensional SU(2)gluodynamics we find evidence for existence of three-dimensional domains whose total volume scales in physical units. Technically, the domains are defined in terms of the minimal density of negative links in Z(2) projection of gauge fields. The volume can be viewed also as the minimal volume bound by the center vortices. We argue that the three-dimensional domains are closely related to confinement.

hep-lat↗

arXiv2004

Properties of P-vortex and monopole clusters in lattice SU(2) gauge theory

We study the action and geometry of P-vortices, discriminating between the percolating and finite clusters. We also discuss the interrelation of the monopoles and P-vortices. To define P-vortices we use both the direct maximal center projection and indirect maximal center projection. We find, in particular, that the action density of the P-vortices in short clusters is substantially higher than in the percolating cluster. The surface of the percolating cluster appears random at short distances, with action density depending on the shape.

hep-lat↗

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.

hep-lat↗

arXiv2003

Self-tuning of the P-vortices

We observe that on the currently available lattices the non-Abelian action associated with the P-vortices is ultraviolet divergent. On the other hand, the total area of the vortices scales in physical units. Since both the ultraviolet and infrared scales are manifested and there is no parameter to tune, the observed phenomenon can be called self tuning.

hep-lat↗

arXiv2003

Interplay of Monopoles and P-Vortices

We show that P-Vortices in the confinement phase of SU(2) lattice gauge theory form one large percolating (infrared) cluster and a number of small (ultraviolet) clusters. We discuss the interrelation of clusters of monopoles in the maximal Abelian projection with clusters of P-vortices. To extract P-vortices we use both direct and indirect central projections and find qualitatively similar results.

hep-lat↗

arXiv2003

Fine tuned vortices in lattice SU(2) gluodynamics

We report measurements of the action associated with center vortices in SU(2) pure lattice gauge theory. In the lattice units the excess of the action on the plaquettes belonging to the vortex is approximately a constant, independent on the lattice spacing 'a'. Therefore the action of the center vortex is of order 'A/a^2', where 'A' is its area. Since the area 'A' is known to scale in the physical units, the measurements imply that the suppression due to the surface action is balanced, or fine tuned to the entropy factor which is to be an exponential of 'A/a^2'.

hep-lat↗

arXiv2002

Confining string and P-vortices in the indirect Z(2) projection of SU(2) lattice gauge theory

We study the distribution of P-vortices near the confining string in the indirect Z(2) projection of SU(2) lattice gauge theory. It occurs that the density of vortices is constant at large distances and strongly suppressed near the line connecting the test quark-antiquark pair. This means that the condensate of P-vortices is broken inside the confining string. We also find that the width of the P-vortex density distribution is proportional to the logarithm of the distance between the quark and antiquark.

hep-lat↗

arXiv2001

Monopoles and hybrids in Abelian projection of lattice QCD

We study topological defects constructed from diagonal and non-diagonal gluons in Abelian projection of zero temperature lattice QCD. We compare results obtained in the quenched and non-quenched vacuum field configurations and show that the density of hybrids is higher than the density of monopoles. The density of some hybrids is sensitive to the presence of the virtual fermions.

hep-lat↗

arXiv2000

Space-VLBI observations of OH maser OH34.26+0.15: low interstellar scattering

We report on the first space-VLBI observations of the OH34.26+0.15 maser in two main line OH transitions at 1665 and 1667 MHz. The observations involved the space radiotelescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The map of the maser region and images of individual maser spots were produced with an angular resolution of 1 milliarcsec which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature 6x10^{12} K was obtained. The maser seems to be located in the direction of low interstellar scattering, an order of magnitude lower than the scattering of a nearby extragalactic source and pulsar.

astro-ph↗