arXiv subjects
Publications and source records attributed to Merab Gogberashvili.
We discuss the emergence of relativistic effects in the Machian universe with a global preferred frame and use thermodynamic considerations to clarify the origin of gravity as an entropic force and the origin of dark energy/cosmic acceleration as related to the Hawking-Unruh temperature at the universe's horizon.
We investigate the 5D massless fermionic fields within the standing wave braneworld model. We show that in the case of increasing warp factor there exist localized left spinor field zero modes on the brane, while right fermion wave functions are not normalizable.
We investigate scalar and tensor fields in the brane model solution for the 5D space-time with standing gravitational waves in the bulk and show that even in the case of increasing warp factor there exist normalizable zero modes localized on the brane.
We adopt a 'thermodynamical' formulation of Mach's principle that the rest mass of a particle in the Universe is a measure of its long-range collective interactions with all other particles inside the horizon. We consider all particles in the Universe as a 'gravitationally entangled' statistical ensemble and apply the approach of classical statistical mechanics to it. It is shown that both the Schrodinger equation and the Planck constant can be derived within this Machian model of the universe. The appearance of probabilities, complex wave functions, and quantization conditions is related to the discreetness and finiteness of the Machian ensemble.
Within the Machian model of the universe the dark energy is identified with the Machian energy of collective gravitational interactions of all particles inside the horizon. It is shown that the fine structure constant can be expressed in terms of the observed radiative, baryon and dark energy densities of the universe and the densities of various matter components are interrelated via it.
We construct simple standing wave solutions in a 5D space-time with a ghost scalar field. The nodes of these standing waves are 'islands' of 4D Minkowski space-time. For the 5D model with increasing (decreasing) warp factor there are a finite (infinite) number of nodes and thus Minkowski island-universes having different parameters, such as gravitational and cosmological constants. This feature is similar to the assumptions of the landscape models, which postulate a large number of universes with different parameters. This standing wave solution also provides a new localization mechanism - matter fields can reside only on Minkowski 'islands', where the background space-time does not oscillate.
New exact solution of the cylindrically symmetric Einstein-Maxwell equations is presented. The solution is singular on the axis of symmetry and at the radial infinity, where sources should be placed. The accepted source at the origin can be interpreted as a charged domain wall shell.
The essentials of quantum theory, the Schrödinger equation and the Planck constant, are derived using classical statistical mechanics within the non-local Machan model. The appearance of complex wave function is connected with the necessity of quantization condition when one neglects the existence of the preferred frame and assumes Galilean symmetry of the model.
We show that the coupled two-fluid gravitating system (e.g. stiff matter and 'vacuum energy') could trap nonlinear gravitational waves (e.g. Einstein-Rosen waves). The gravitational wave amplitude varies harmonically in time transferring the energy coherently to the stiff matter wave, and then the process goes to the backward direction. This process mimics the behaviour of trapped electromagnetic waves in two-level media. We have defined the limits for the frequency of this energy transfer oscillations.
We construct a plane symmetric, standing gravitational wave for a domain wall plus a massless scalar field. The scalar field can be associated with a fluid which has the properties of `stiff' matter, i.e. matter in which the speed of sound equals the speed of light. Although domain walls are observationally ruled out in the present era the solution has interesting features which might shed light on the character of exact non-linear wave solutions to Einstein's equations. Additionally this solution may act as a template for higher dimensional 'brane-world' model standing waves.
The model of a universe with a preferred frame, which nevertheless shares the main properties with traditional special and general relativity theories, is considered. We adopt Mach's interpretation of inertia and show that the energy balance equation, which includes the Machian energy of gravitational interactions with the universe, can imitate standard relativistic formulas.
The warped solution of Einstein's equations corresponding to the spherical brane in five-dimensional AdS is considered. This metric represents interiors of black holes on both sides of the brane and can provide gravitational trapping of physical fields on the shell. It is found the analytic form of the coordinate transformations from the Schwartschild to co-moving frame that exists only in five dimensions. It is shown that in the static coordinates active gravitational mass of the spherical brane, in agreement with Tolman's formula, is negative, i.e. such objects are gravitationally repulsive.
The geometrical application of split octonions is considered. The modified Fano graphic, which represents products of the basis units of split octonionic, having David's Star shape, is presented. It is shown that active and passive transformations of coordinates in octonionic '8-space' are not equivalent. The group of passive transformations that leave invariant the norm of split octonions is SO(4,4), while active rotations is done by the direct product of O(3,4)-boosts and real non-compact form of the exceptional group $G_2$. In classical limit these transformations reduce to the standard Lorentz group.
The new interpretation of Mach's principle of mass of a particle being a measure of the interactions of this particle with all other gravitating particles inside its causal spheres is introduced. It is shown that within some alternative model of gravitation that incorporates this principle, the Machian influence of the universe can reduce Planck's scale to the electro-weak scale and the large number that is needed to explain the hierarchy between the scales is the amount of gravitating particles inside the universe horizon. Our model can lead to new observable effects at cosmological distances and close to the sources of a strong gravitational field.
We examine the behavior of fermions in the presence of an internal compact 2-manifold which in one of the spherical angles exhibits a conical character with an obtuse angle. The extra manifold can be pictured as an apple-like surface i.e. a sphere with an extra "wedge" insert. Such a surface has conical singularities at north and south poles. It is shown that for this setup one can obtain, in four dimensions, three trapped massless fermion modes which differ from each other by having different values of angular momentum with respect to the internal 2-manifold. The extra angular momentum acts as the family label and these three massless modes are interpreted as the three generations of fundamental fermions.
We argue that in fat brane-world scenarios the light propagating in vacuum will, because of massive ``Kaluza-Klein'' (KK) excitations, experience a refraction. The motion of a photon inside a fat brane can be decomposed in the longitudinal and transverse directions with respect to the surface of the brane. Since the light observable propagation is related only with the longitudinal motion, the observed speed of light depends on the value of the momentum transverse fraction contributing as the massive KK excitations. This is directly connected with the energy of the particles emitting the light, and hence with the frequency of the light itself. Using recent results on the arrival times of radiation of different energies from the measurements of gamma-ray bursters with known redshifts, we establish the limit M>620 TeV on the inverse thickness of the brane, and thus on the masses of the KK excitations. This limit exceeds by at least one order of magnitude the typical energy scale currently in use to characterize brane phenomena in the realm of future colliders.
Dirac's operator and Maxwell's equations in vacuum are derived in the algebra of split octonions. The approximations are given which lead to classical Maxwell-Heaviside equations from full octonionic equations. The non-existence of magnetic monopoles in classical electrodynamics is connected with the using of associativity limit.
Relationship between the speed limit on the brane and in the bulk is discussed. We assume that the speed of light, similar to the 4-dimensional gravitational constant, is not a primary fundamental constant but depends on the gravitational potential of the brane. This opens the way to explain the hierarchy between the Plank and Higgs scales even within the simplest 5-dimensional model.