arXiv subjects

A. F. Zakharov

Publications and source records attributed to A. F. Zakharov.

At least 19 recordsLinked to original sources

arXiv2026

SNe Ia in Standard and Conformal Cosmological Models

This article demonstrates the classical equivalence between standard and conformal cosmological models regarding the apparent luminosity of type Ia supernovae. We show that previous claims of observational discrepancies stem from differing interpretations of physical quantities when transitioning between Einstein and Jordan frames. Specifically, we establish that in the conformal picture, SNe Ia are not "standard candles" in the conventional sense because their absolute luminosity depends on redshift due to variations in local measurement units.

gr-qc↗

arXiv2026

Cosmology: 100 years after A. A. Friedmann

A. A. Friedmann (04.06.1888 -- 16.09.1925) proposed the first physical cosmological models in 1920s. Despite the fact that Friedmann's works were very famous soon after their publication, the study of dynamic models of the Universe in the USSR was actually banned in the 30s - 50s of the last century, and Soviet philosophers and propagandists wrote that models of the evolving Universe were invented by Lemaitre on the demand of the Roman Pope, because according to Soviet philosophers such the birth of the universe is very similar to the divine creation of the world described in the Bible. Thus, in the USSR, Friedman's works were in oblivion in since 1930s until 1960s.

physics.hist-ph↗

arXiv2023

Constraints on Yukawa gravity parameters from observations of bright stars

In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction $Λ$ and universal constant $δ$) with the Schwarzschild precession of the S-stars assuming that the observed values as indicated by the GRAVITY Collaboration will have a small deviation from GR prediction. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant $δ$, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction $δ$ and find that this parameter has strong influence on range of Yukawa interaction $Λ$. For that purpose we use PPN equations of motion in order to calculate the simulated orbits of S-stars in GR and Yukawa gravity. Using MCMC simulations we obtain the best-fit values and uncertainties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories.

astro-ph.GA↗

arXiv2021

Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star

After giving a short overview of previous results on constraining of Extended Gravity (EG) by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably fitted with the first post-Newtonian (pN) approximation of GR. In particular, both Keck and VLT (GRAVITY) teams declared that the gravitational redshift near its pericenter passage for the S2 star orbit corresponds to theoretical estimates found with the first pN approximation. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the GR prediction. Based on this observational fact, we evaluated parameters of the EG theories with the Schwarzschild precession of the S2 star. Using the mentioned method, we estimate the orbital precession angles for some EG models including power-law f(R), general Yukawa-like corrections, scalar-tensor gravity (STG), and non-local gravity (NLG) theories formulated in both metric and Palatini formalism. In this consideration we assume that a gravitational field is spherically symmetric, therefore, alternative theories of gravity could be described only with a few parameters. Specifically, considering the orbital precession, we estimate the range of parameters of these EG models for which the orbital precession is like in GR. We then compare these results with our previous results, which were obtained by fitting the simulated orbits of S2 star to its observed astrometric positions. In case of power-law f(R), generic Yukawa-like correction, STG and NLG theories, we were able to obtain a prograde orbital precession, like in GR. According to these results, the method is a useful tool to evaluate parameters of the gravitational potential at the GC.

gr-qc↗

arXiv2021

Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity

In this study we investigate possible applications of observed S2 orbit around Galactic Center for constraining the Yukawa gravity at scales in the range between several tens and several thousands astronomical units (AU) to obtain graviton mass constraints. In our model we suppose that bulk distribution of matter (includes stellar cluster, interstellar gas distribution and dark matter) exists near Supermassive Black Hole (SMBH) in our Galactic Center. We obtain the values of orbital precession angle for different values of mass density of matter and we require that the value of orbital precession is the same like in General Relativity (GR). From that request we determine gravity parameter $λ$ and the upper value for graviton mass. We found that in the cases where the density of extended mass is higher, the maximum allowed value for parameter $λ$ is smaller and the upper limit for graviton mass is higher. It is due to the fact that the extended mass causes the retrograde orbital precession. We believe that this study is a very efficient tool to evaluate a gravitational potential at the Galactic Center, parameter $λ$ of the Yukawa gravity model, and to constrain the graviton mass.

astro-ph.GA↗

arXiv2018

Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds

Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as $m_g < 1.2 \times 10^{-22}$ eV (Abbott et al., 2016). In the paper we analyze a potential to reduce upper bounds for graviton mass with future observational data on trajectories of bright stars near the Galactic Center. Since gravitational potentials are different for these two cases, expressions for relativistic advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume that trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity (Borka et al., 2013) and graviton mass (Zakharov et al., 2016) from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around $5 \times 10^{-23}$ eV or slightly better than current estimates obtained with LIGO observations.

gr-qc↗

arXiv2017

Radiative breaking of conformal symmetry in the Standard Model

Radiaitve mechanism of conformal symmetry breaking in a comformal-invariant version of the Standard Model is considered. The Coleman-Weinberg mechanism of dimensional transmutation in this system gives rise to finite vacuum expectation values and, consequently, masses of scalar and spinor fields. A natural bootstrap between the energy scales of the top quark and Higgs boson is suggested.

hep-ph↗

arXiv2016

Von Neumann's Quantization of General Relativity

Von Neumann's procedure is applied for quantization of General Relativity. We quantize the initial data of dynamical variables at the Planck epoch, where the Hubble parameter coincides with the Planck mass. These initial data are defined via the Fock simplex in the tangent Minkowskian space-time and the Dirac conformal interval. The Einstein cosmological principle is applied for the average of the spatial metric determinant logarithm over the spatial volume of the visible Universe. We derive the splitting of the general coordinate transformations into the diffeomorphisms (as the object of the second Nöther theorem) and the initial data transformations (as objects of the first Nöther theorem). Following von Neumann, we suppose that the vacuum state is a quantum ensemble. The vacuum state is degenerated with respect to quantum numbers of non-vacuum states with the distribution function that yields the Casimir effect in gravidynamics in analogy to the one in electrodynamics. The generation functional of the perturbation theory in gravidynamics is given as a solution of the quantum energy constraint. We discuss the region of applicability of gravidynamics and its possible predictions for explanation of the modern observational and experimental data.

gr-qc↗

arXiv2014

Spontaneous radiatively induced breaking of conformal invariance in the Standard Model

A mechanism of radiatively induced breaking of the conformal symmetry in the Standard Model is suggested. The system of one scalar (Higgs) and one fermion (top-quark) fields with Yukawa and $ϕ^4$ interactions is considered. The infrared instability of the Coleman-Weinberg effective potential for this system leads to the appearance of a finite renormalization scale and thus to breaking of the conformal symmetry. Finite condensates of both scalar and spinor fields appear. It is shown that the top quark condensate can supersede the tachyon mass of the Higgs field. The Higgs boson is treated as an elementary scalar and the standard mechanism of electroweak symmetry breaking remains unchanged. The difference from the Standard Model appears in the value of the Higgs boson self-coupling constant.

hep-ph↗

arXiv2013

Exoplanetary searches with gravitational microlensing: polarization issues

There are different methods for finding exoplanets such as radial spectral shifts, astrometrical measurements, transits, timing etc. Gravitational microlensing (including pixel-lensing) is among the most promising techniques with the potentiality of detecting Earth-like planets at distances about a few astronomical units from their host star or near the so-called snow line with a temperature in the range $0-100^0$ C on a solid surface of an exoplanet. We emphasize the importance of polarization measurements which can help to resolve degeneracies in theoretical models. In particular, the polarization angle could give additional information about the relative position of the lens with respect to the source.

astro-ph.SR↗

arXiv2013

Constraining the range of Yukawa gravity interaction from S2 star orbits

We consider possible signatures for Yukawa gravity within the Galactic Central Parsec, based on our analysis of the S2 star orbital precession around the massive compact dark object at the Galactic Centre, and on the comparisons between the simulated orbits in Yukawa gravity and two independent sets of observations. Our simulations resulted in strong constraints on the range of Yukawa interaction $Λ$ and showed that its most probable value in the case of S2 star is around 5000 - 7000 AU. At the same time, we were not able to obtain reliable constrains on the universal constant $δ$ of Yukawa gravity, because the current observations of S2 star indicated that it may be highly correlated with parameter $Λ$ in the range $(0 <δ< 1)$. For $δ> 2$ they are not correlated. However, the same universal constant which was successfully applied to clusters of galaxies and rotation curves of spiral galaxies ($δ=1/3$) also gives a satisfactory agreement with the observed orbital precession of the S2 star, and in that case the most probable value for the scale parameter is $Λ\approx 3000 \pm 1500$ AU. Also, the Yukawa gravity potential induces precession of S2 star orbit in the same direction as General Relativity for $δ> 0$ and for $δ< -1$, and in the opposite direction for $-1 <δ< 0$. The future observations with advanced facilities, such as GRAVITY or/and European Extremely Large Telescope, are needed in order to verify these claims.

astro-ph.GA↗

arXiv2013

Polarization profiles for selected microlensing events towards the galactic bulge

Gravitational microlensing, in case of relevant finite source size effects, provides an unique tool for the study of stellar atmospheres through the enhancement of a characteristic polarization signal. Here, we consider a set of highly magnified events and show that for different types of source stars (as hot, late type main sequence and cool giants) showing that the polarization strength may be of $\simeq 0.04$ percent for late type stars and up to a few percent for cool giants.

astro-ph.GA↗

arXiv2013

Condensate Mechanism of Conformal Symmetry Breaking and the Higgs Boson

A mechanism of spontaneous conformal symmetry breaking based on field condensates in the Standard Model of strong and electroweak interactions is suggested. It is shown that an existence of the top quark condensate can supersede the tachyon mass term in the Higgs potential in the standard mechanism of electroweak symmetry breaking. Considering the ratio of a field condensate to the corresponding mass power (depending on quantum statistics) for various fields as a conformal invariant, we obtain the Higgs boson mass to be about $130\pm 15$ GeV.

hep-ph↗

arXiv2013

Conformal and Affine Hamiltonian Dynamics of General Relativity

The Hamiltonian approach to the General Relativity is formulated as a joint nonlinear realization of conformal and affine symmetries by means of the Dirac scalar dilaton and the Maurer-Cartan forms. The dominance of the Casimir vacuum energy of physical fields provides a good description of the type Ia supernova luminosity distance--redshift relation. Introducing the uncertainty principle at the Planck's epoch within our model, we obtain the hierarchy of the Universe energy scales, which is supported by the observational data. We found that the invariance of the Maurer-Cartan forms with respect to the general coordinate transformation yields a single-component strong gravitational waves. The Hamiltonian dynamics of the model describes the effect of an intensive vacuum creation of gravitons and the minimal coupling scalar (Higgs) bosons in the Early Universe.

gr-qc↗

arXiv2012

Polarization in microlensing towards the Galactic bulge

Gravitational microlensing, when finite size source effects are relevant, provides an unique tool for the study of source star stellar atmospheres through an enhancement of a characteristic polarization signal. This is due to the differential magnification induced during the crossing of the source star. In this paper we consider a specific set of reported highly magnified, both single and binary exoplanetary systems, microlensing events towards the Galactic bulge and evaluate the expected polarization signal. To this purpose, we consider several polarization models which apply to different types of source stars: hot, late type main sequence and cool giants. As a result we compute the polarization signal P,which goes up to P=0.04% for late type stars and up to a few percent for cool giants, depending on the underlying physical polarization processes and atmosphere model parameters. Given a I band magnitude at maximum magnification of about 12, and a typical duration of the polarization signal up to 1 day, we conclude that the currently available technology, in particular the polarimeter in FORS2 on the VLT, potentially may allow the detection of such signals. This observational programme may take advantage of the currently available surveys plus follow up strategy already routinely used for microlensing monitoring towards the Galactic bulge (aimed at the detection of exoplanets). In particular, this allows one to predict in advance for which events and at which exact time the observing resources may be focused to make intensive polarization measurements.

astro-ph.GA↗

arXiv2012

Constraints on $R^n$ gravity from precession of orbits of S2-like stars

We study some possible observational signatures of $R^n$ gravity at Galactic scales and how these signatures could be used for constraining this type of $f(R)$ gravity. For that purpose, we performed two-body simulations in $R^n$ gravity potential and analyzed the obtained trajectories of S2-like stars around Galactic center, as well as resulting parameter space of $R^n$ gravity potential. Here, we discuss the constraints on the $R^n$ gravity which can be obtained from the observations of orbits of S2-like stars with the present and next generations of large telescopes. We make comparison between the theoretical results and observations. Our results show that the most probable value for the parameter $r_c$ in $R^n$ gravity potential in the case of S2-like stars is $\sim$100 AU, while the universal parameter $β$ is close to 0.01. Also, the $R^n$ gravity potential induces the precession of S2-like stars orbit in opposite direction with respect to General Relativity, therefore, such a behavior of orbits qualitatively is similar to a behavior of Newtonian orbits with a bulk distribution of matter (including a stellar cluster and dark matter distributions).

astro-ph.CO↗

arXiv2010

Estimating the parameters of the Sgr A* black hole

The measurement of relativistic effects around the galactic center may allow in the near future to strongly constrain the parameters of the supermassive black hole likely present at the galactic center (Sgr A*). As a by-product of these measurements it would be possible to severely constrain, in addition, also the parameters of the mass-density distributions of both the innermost star cluster and the dark matter clump around the galactic center.

astro-ph.GA↗

arXiv2010

Conformal Hamiltonian Dynamics of General Relativity

The General Relativity formulated with the aid of the spin connection coefficients is considered in the finite space geometry of similarity with the Dirac scalar dilaton. We show that the redshift evolution of the General Relativity describes the vacuum creation of the matter in the empty Universe at the electroweak epoch and the dilaton vacuum energy plays a role of the dark energy.

gr-qc↗