arXiv subjects

Z. Berezhiani

Publications and source records attributed to Z. Berezhiani.

29 records · Page 2Linked to original sources

arXiv2005

Gravitational wave bursts induced by r-mode spin-down of hybrid stars

We show that sudden variations in the composition and structure of an hybrid star can be triggered by its rapid spin-down, induced by r-mode instabilities. The discontinuity of this process is due to the surface tension between hadronic and quark matter and in particular to the overpressure needed to nucleate new structures of quark matter in the mixed phase. The consequent mini-collapses in the star can produce highly energetic gravitational wave bursts. The possible connection between the predictions of this model and the burst signal found by EXPLORER and NAUTILUS detectors during the year 2001 is also investigated.

gr-qc↗

arXiv2003

Generation of large scale magnetic fields at recombination epoch

It is argued that large scale cosmic magnetic field could be generated in the primeval plasma slightly before hydrogen recombination. Non-zero vorticity, necessary for that, might be created by the photon diffusion in the second order in the temperature fluctuations. The resulting seed fields at galactic scale would be only 4 orders of magnitude smaller than the observed ones and with a mild galactic dynamo amplifying the seed fields by the factor $\sim 10^4$ an existence of coherent magnetic fields in galaxies may be explained.

astro-ph↗

arXiv2003

Gamma Ray Bursts from delayed collapse of neutron stars to quark matter stars

We propose a model to explain how a Gamma Rays Burst can take place days or years after a supernova explosion. Our model is based on the conversion of a pure hadronic star (neutron star) into a star made at least in part of deconfined quark matter. The conversion process can be delayed if the surface tension at the interface between hadronic and deconfined-quark-matter phases is taken into account. The nucleation time (i.e. the time to form a critical-size drop of quark matter) can be extremely long if the mass of the star is small. Via mass accretion the nucleation time can be dramaticaly reduced and the star is finally converted into the stable configuration. A huge amount of energy, of the order of 10$^{52}$--10$^{53}$ erg, is released during the conversion process and can produce a powerful Gamma Ray Burst. The delay between the supernova explosion generating the metastable neutron star and the new collapse can explain the delay proposed in GRB990705 and in GRB011211.

astro-ph↗

arXiv2002

On the Deconstruction of Time

In this note we discuss the possibility to get a time rather than space in the scenario of (de)construction of new dimension.

hep-th↗

arXiv2001

Vanishing of cosmological constant and fully localized gravity in a Brane World with extra time(s)

We construct an intersecting brane configuration in six-dimensional space with one extra space-like and one extra time-like dimensions. With a certain additional symmetry imposed on the extra space-time we have found that effective four-dimensional cosmological constant vanishes automatically, providing the static solution with gravity fully localized at the intersection region as there are no propagating massive modes of graviton. In this way, the same symmetry allows us to eliminate tachyonic states of graviton from the spectrum of the effective four-dimensional theory, thus avoiding phenomenological difficulties comming from the matter instability usually induced in theories with extra time-like dimensions.

hep-th↗

arXiv1998

$d=5$ operators in SUSY GUT: fermion masses versus proton decay

In the minimal SU(5) SUSY GUT $d =5$ operators lead to $p\to K^+ ν$ decay with the proton life time of the order of $10^{28}$ years for the natural choice of the parameters of the theory. This value is in strong contradiction with experimental bound $τ_{p\to Kν} > 10^{32}$ years. $d=5$ operators are induced by colored Higgsino exchanges and are closely (through SU(5) and super symmetry) related to another wrong prediction of SU(5) SUSY GUT: $m_d /m_s = m_e /m_μ$. We demonstrate how in the model where reasonable pattern of quark and lepton masses and CKM mixing angles are obtained proton decay can be suppressed and proton life time can be close to the present experimental bound.

hep-ph↗

arXiv1998

Field Evolution leading to hybrid inflation

In general the onset of hybrid inflation requires an extremely homogeneous field configuration at the end of Planck era. The field ϕorthogonal to the inflaton σmust be zero with high accuracy over the range exceeding the initial horizon size \sim m_{Pl}^{-1} by about two orders of magnitude. We consider a supersymmetric model that permits the decay of the oscillating field ϕinto light particles. We study the field evolution and find that the requirement of the extreme homogeneity can be relaxed. However, the field ϕmust still be smaller than the inflaton by a factor of order 1 over a region far exceeding the initial horizon size.

hep-ph↗

arXiv1997

2/3 Splitting in SUSY GUT -- Higgs as Goldstone Boson

We briefly review the GIFT (Goltstones instead of Fine Tuning) mechanism which provides a promising solution to the doublet-triplet splitting problem and some other puzzles of the supersymmetric grand unification as are the $μ$-problem, the fermion mass problem, etc. It can be naturally implemented by extending the minimal SUSY SU(5) model to the gauge SU(6) theory.

hep-ph↗

arXiv1995

Reconciling Present Neutrino Puzzles: Sterile Neutrinos as Mirror Neutrinos

We suggest that recent neutrino puzzles that are the solar and atmospheric neutrino deficits as well as the possible neutrino oscillations reported by the LSND experiment and the possibility of massive neutrinos providing the hot component of the cosmological dark matter, can all be naturally explained by assuming existence of a mirror world described by an ``electroweak'' gauge symmetry $[SU(2)\times U(1)]'$, with the breaking scale larger by about factor of 30 than the scale of the standard $SU(2)\times U(1)$ model. An interesting aspect of this model is that the sterile neutrinos arise from the hidden mirror sector of the theory and thus their lightness is more natural than in the usual neutrino mass scenarios. The needed pattern of the neutrino mass matrix in this model is obtained by assuming a conserved ZKM-type global lepton number $\bar L=L_e+L_μ-L_τ$, which is violated by Planck scale effects. One implication of our proposal is that bulk of the dark matter in the universe is a warm dark matter consisting of few KeV mass particles rather than the 100 GeV range particles of the currently popular cold dark matter scenarios.

hep-ph↗

arXiv1994

Vacuum oscillation solution to the solar neutrino problem in standard and non-standard pictures

The neutrino long wavelength (just-so) oscillation is revisited as a solution to the solar neutrino problem. We consider just-so scenario in various cases: in the framework of the solar models with relaxed prediction of the boron neutrino flux, as well as in the presence of the non-standard weak range interactions between neutrino and matter constituents. We show that the fit of the experimental data in the just-so scenario is not very good for any reasonable value of the $^8B$ neutrino flux, but it substantially improves if the non-standard $τ$-neutrino--electron interaction is included. These new interactions could also remove the conflict of the just-so picture with the shape of the SN 1987A neutrino spectrum. Special attention is devoted to the potential of the future real-time solar neutrino detectors as are Super-Kamiokande, SNO and BOREXINO, which could provide the model independent tests for the just-so scenario. In particular, these imply specific deformation of the original solar neutrino energy spectra, and time variation of the intermediate energy monochromatic neutrino ($^7Be$ and $pep$) signals.

hep-ph↗

arXiv1994

Flavour in supersymmetric Grand Unification: a democratic approach

We consider the flavour problem in a supersymmetric Grand Unified theory with gauged SU(6) group, where the Higgs doublets are understood as pseudo-Goldstone bosons of a larger $\SU(6)\otimes\SU(6)$ global symmetry of the Higgs superpotential. A key element of this work is that we never appeal to any flavour symmetry. One main interesting feature emerges: only one of the light fermions, an up-type quark, to be identified with the top, can get a Yukawa coupling at renormalizable level. This fact, together with bottom-tau Yukawa unification, also implied in our scheme, gives rise to a characteristic correlation between the top and the Higgs mass. By including a flavour-blind discrete symmetry and requiring that all higher dimensional operators be mediated by the exchange of appropriate heavy multiplets, it is possible to give an approximate description of all masses and mixing angles in term of a hierarchy of grand unified scales. A special ``texture'' arises, implying a relation between the top mass and the third generation mixing angles. Several other possible consequences of this approach are pointed out, concerning the $μ/s$ mass ratio, the Cabibbo angle and the proton decay.

hep-ph↗