arXiv subjects

Merab Gogberashvili

Publications and source records attributed to Merab Gogberashvili.

At least 37 records · Page 2Linked to original sources

arXiv2020

Binary Neutron Star Mergers with Missing Electromagnetic Counterparts as Manifestations of Mirror World

We suggest that the major fraction of binary mergers, which might provide gravitational wave signal detectable by LIGO/Virgo, emerged from the hidden mirror sector. Mirror particles do not interact with an ordinary observer except gravitationally, which is the reason why no electromagnetic signals accompanying gravitational waves from mergers with components composed of mirror matter are expected. Therefore, if the dark matter budget of the universe is mostly contributed by the mirror particles, we predict that only about one binary neutron star (neutron star - black hole) merger out of ten, observable by LIGO/Virgo, in particular at favorable conditions relative to the line of sight, could be accompanied by prompt gamma ray burst and other electromagnetic signals suitable for follow up observations. It seems the list of candidate events recorded by LIGO/Virgo during third observational run supports our predictions.

astro-ph.HE↗

arXiv2019

Can Quantum Particles Cross a Horizon?

The prevalent opinion that infalling objects can freely cross a black hole horizon is based on the assumptions that the horizon region is governed by classical General Relativity and by specific singular coordinate transformations it is possible to remove divergences in the geodesic equations. However, the coordinate transformations usually used to demonstrate the geodesic completeness are of class $C^0$, while the standard causality theory requires that the metric tensor to be at least $C^1$. Introduction of $C^0$-class functions leads to the appearance of the additional delta-like sources in the Einstein equations and in the equations for quantum particles. Therefore, to explore the horizon region, in addition to the classical geodesic equations, one needs to use equation of quantum particles. Applying physical boundary conditions at the Schwarzschild and Kerr event horizons, we show existence of the exponentially decay/enhanced solutions (with the complex phases) to the Klein-Gordon equation. This means that in semi-classical approximation particles probably do not enter the black hole horizon, but are absorbed/reflected by it. Then it follows that the minimal classical size of any isolated body is its horizon radius, what potentially can solve main black hole mysteries.

gr-qc↗

arXiv2019

Hidden Conformal Symmetry of Smooth Braneworld Scenarios

In this paper we generalize our previous model (arXiv: 1705.09331), on a hidden conformal symmetry of smooth braneworld scenarios, to the case with two real scalar fields non-minimally coupled to gravity. The gauge condition reduces the action of the system to the action were gravity minimally couples to one of the scalar fields, plus a cosmological constant. We show that, depending on the internal symmetry of the scalar fields, the two possibilities, $SO(2)$ or $SO(1,1)$, emerge. In the $SO(2)$ case we get a ghost-like scalar field action, which can describe two models -- Standing Wave and Sine-Gordon smooth braneworlds. For the $SO(1,1)$ case we get the standard sign for the kinetic part of the scalar field. By breaking the $SO(1,1)$ symmetry (but keeping the conformal one) we are able to get two Randall-Sundrum models, with a non-minimal coupling and with a scalar field having hyperbolic potential. We conclude that this method can be seen as a solution-generating technique and a natural way to introduce non-trivial scalar fields that can provide smooth braneworld models.

hep-th↗

arXiv2019

Gravitational Field of a Spherical Perfect Fluid

Analyzing the spacetime for a static spherically distributed perfect fluid we show that the smooth matching of the interior and exterior metrics for a realistic source is possible only for the distances from the origin that exceeds the photon sphere radius for this object.

physics.gen-ph↗

arXiv2019

Gravitational Waves from Mirror World

In this paper we consider the properties of the 10 confirmed by the LIGO Collaboration gravitational wave signals from the black hole mergers. We want to explain non-observation of electromagnetic counterpart and higher then expected merging rates of these events, assuming the existence of their sources in the hidden mirror universe. Mirror matter, which interacts with our world only through gravity, is a candidate of dark matter and its density can exceed ordinary matter density five times. Since mirror world is considered to be colder, star formation there started earlier and mirror black holes had more time to pick up the mass and to create more binary systems within the LIGO reachable zone. In total, we estimate factor of 15 amplification of black holes merging rate in mirror world with respect to our world, which is consistent with the LIGO observations.

gr-qc↗

arXiv2019

LIGO Signals from the Mirror World

We want to explain non-observation of electromagnetic counterpart of currently confirmed ten gravitational wave signals from the black hole mergers assuming their existence in the hidden mirror universe. Mirror matter, which interacts with our world only through gravity, is a candidate of dark matter and its density can exceed ordinary matter density five times. Since mirror world is considered to be colder, star formation there started earlier and mirror black holes had more time to pick up the mass and to create more binary systems within the LIGO reachable zone. Totally we estimate a factor 10 amplification of black holes merging rate in mirror world with respect to our world, which is consistent with the LIGO observations.

gr-qc↗

arXiv2019

Geometry of the Non-Compact G(2)

Geometrical applications of the non-compact form of Cartan's exceptional Lie group G(2) is considered. This group generates specific rotations of 7-dimensional Minkowski-like space with three extra time-like coordinates and in some limiting cases imitates standard Poincare transformations. In this model space-time translations are non-commutative and are represented by the rotations towards the extra time-like coordinates. The second order Casimir element of non-compact G(2) and its expression by the Casimir operators of the Lorentz and Poincare groups are found.

physics.gen-ph↗

arXiv2018

On the singular coordinate transformations of the Schwarzschild metric

It is noted that the coordinate transformations usually used to demonstrate the continuity of geodesics at the Schwarzschild horizon are of class $C^0$, while the standard causality theory requires that the metric tensor to be at least $C^1$. Then this singular metric tensor leads to the appearance of the fictitious delta-like source in the Einstein equations, which prevents quantum particles to enter a black hole horizon.

physics.gen-ph↗

arXiv2018

Cosmological Constant from the Entropy Balance Condition

In the action formalism variations of metric tensors usually are limited by the Hubble horizon. Contrary, variations of quantum fields should be extended up to the event horizon, which is the real boundary of the spacetime. As the result the entanglement energy of quantum particles across the apparent horizon is missed in the cosmological equations written for the Hubble volume. We identify this missing boundary term with the dark energy density and express it (using the null energy assumption for the finite universe) as the critical density multiplied by the ratio of the Hubble and event horizons radii.

physics.gen-ph↗

arXiv2018

Electroweak Phase Transitions in Einstein's Static Universe

We suggest using Einstein's static universe metric for the metastable state after reheating, instead of the Friedman-Robertson-Walker spacetime. In this case strong static gravitational potential leads to the effective reduction of the Higgs vacuum expectation value, which is found to be compatible with the Standard Model first order electroweak phase transition conditions. Gravity could also increase the CP-violating effects for particles that cross the new phase bubble walls and thus is able to lead to the successful electroweak baryogenesis scenario.

gr-qc↗

arXiv2018

Supplying Dark Energy from Scalar Field Dark Matter

We consider the hypothesis that dark matter and dark energy consists of ultra-light self-interacting scalar particles. It is found that the Klein-Gordon equation with only two free parameters (mass and self-coupling) on a Schwarzschild background, at the galactic length-scales has the solution which corresponds to Bose-Einstein condensate, behaving as dark matter, while the constant solution at supra-galactic scales can explain dark energy.

astro-ph.CO↗

arXiv2018

Black Hole Information Problem and Wave Bursts

By reexamination of the boundary conditions of wave equation on a black hole horizon it is found not harmonic, but real-valued exponentially time-dependent solutions. This means that quantum particles probably do not cross the Schwarzschild horizon, but are absorbed and some are reflected by it, what potentially can solve the famous black hole information paradox. To study this strong gravitational lensing we are introducing an effective negative cosmological constant between the Schwarzschild and photon spheres. It is shown that the reflected particles can obtain their additional energy in this effective AdS space and could explain properties of some unusually strong signals, like LIGO events, gamma ray and fast radio bursts.

physics.gen-ph↗

arXiv2017

Conformal (2+4)-Braneworld

It is considered the 6D brane model where matter is trapped on the surface of a (2+4)-hyperboloid, as is suggested by the geometrical structure behind the 4D conformal group. The effective dimension of the bulk space-time for matter fields is five, with the extra space-like and time-like domains. Using the embedding theory the presence of the familiar factorizable 5D brane metrics in the both domains is shown. These metrics with exponential warp factors are able to provide with the additional reduction of the effective space-time dimensions down to four. It is demonstrated that the extra (1+1)-space is not simply connected and there is a gap in the range of the extra coordinates. This can explain stability of the model in the domain with the time-like effective fifth dimension and the appearance of the cosmological constant due to the tachyon condensation. It is found that the model exhibits orbifold symmetry and thus is free from the fermion chirality problem.

hep-th↗

arXiv2016

Size of Shell Universe in Light of Fermi GBM Transient Associated with GW150914

The possible gamma ray burst occurred in location and temporal consistence with gravitational wave event GW150914, as reported by Fermi Gamma-ray Burst Monitor (GBM), offers a new way of constraining models with extra dimensions. Using the time delay in arrival of the gamma ray transient observed by Fermi GBM relative to the gravitational waves event triggered by the LIGO detectors we investigate the size of the spherical brane-universe expanding in multi-dimensional space-time. It is shown that a joint observation of gravitational waves in association with gamma ray burst can provide a very stringent bound on the spatial curvature of the brain.

hep-ph↗

arXiv2016

Octonionic geometry and conformal transformations

We describe space-time using split octonions over the reals and use their group of automorphisms, the non-compact form of Cartan's exceptional Lie group G2, as the main geometrical group of the model. Connections of the G2-rotations of octonionic 8D space with the conformal transformations in 4D Minkowski space-time are studied. It is shown that the dimensional constant needed in these analysis naturally gives the observed value of the cosmological constant.

physics.gen-ph↗

arXiv2016

Standing Waves Braneworlds

The class of non-stationary braneworld models generated by the coupled gravitational and scalar fields is reviewed. The model represents a brane in a space-time with single time and one large (infinite) and several small (compact) space-like extra dimensions. In some particular cases the model has the solutions corresponding to the bulk gravi-scalar standing waves bounded by the brane. Pure gravitational localization mechanism of matter particles on the node of standing waves, where the brane is placed, is discussed. Cosmological applications of the model also considered.

hep-th↗

arXiv2016

Information-Probabilistic description of the Universe

We describe the universe as a single entangled ensemble of quantum particles. The total entropy of this world ensemble, which can be expressed as a sum of information, thermodynamic and entanglement components, is assumed to be always zero. This condition suggests information quantization, which we associate with the Planck's action. Then the entropy neutrality condition for the universe leads to the zero-action principle. We show that the main concepts of classical space-time and gravity naturally emerge in this picture. A generalized least action principle, which embraces the maximal entropy principles of information theory, is introduced.

physics.gen-ph↗

arXiv2016

Cosmological Constant in the Thermodynamic Models of Gravity

Within thermodynamic models of gravity, where the universe is considered as a finite ensemble of quantum particles, cosmological constant in the Einstein's equations appears as a constant of integration. Then it can be bounded using Karolyhazy uncertainty relation applied for horizon distances, as the amount of information in principle accessible to an external observer.

physics.gen-ph↗