2,661,933 research outputs found
Acceleration and Deceleration in Curvature Induced Phantom Model of the Late and Future Universe, Cosmic Collapse as Well as its Quantum Escape
Here, cosmology of the late and future universe is obtained from
-gravity with non-linear curvature terms and ( being the
Ricci scalar curvature). It is different from -dark enrgy models, where
non-linear curvature terms are taken as gravitational alternative of dark
energy. In the present model, neither linear nor no-linear curvature terms are
taken as dark energy. Rather, dark energy terms are induced by curvature terms
in the Friedmann equation derived from -gravitational equations. It has
advantage over - dark energy models in the sense that the present model
satisfies WMAP results and expands as during matter-dominance.
So, it does not have problems due to which -dark energy models are
criticized. Curvature-induced dark energy, obtained here, mimics phantom.
Different phases of this model, including acceleration and deceleration during
phantom phase, are investigated here.It is found that expansion of the universe
will stop at the age ( being the present
age of the universe) and after this epoch, it will contract and collapse by the
time . Further,it is shown that universe will
escape predicted collapse (obtained using classical mechanics) on making
quantum gravity corrections relevant near collapse time due to extremely high
energy density and large curvature analogous to the state of very early
universe. Interestingly, cosmological constant is also induced here, which is
very small in classical domain, but very high in quantum domain.Comment: 33 page
Semidirect Product Groups, Vacuum Alignment and Tribimaximal Neutrino Mixing
The neutrino oscillation data are in very good agreement with the
tribimaximal mixing pattern: \sin^2\theta_{23}=1/2, \sin^2\theta_{12}=1/3, and
\sin^2\theta_{13}=0. Attempts to generate this pattern based on finite family
symmetry groups typically assume that the family symmetry is broken to
different subgroups in the charged lepton and the neutrino mass matrices. This
leads to a technical problem, where the cross-couplings between the Higgs
fields responsible for the two symmetry breaking chains force their vacuum
expectation values to align, upsetting the desired breaking pattern. Here, we
present a class of models based on the semidirect product group (S_3)^4 \rtimes
A_4, where the lepton families belong to representations which are not
faithful. In effect, the Higgs sector knows about the full symmetry while the
lepton sector knows only about the A_4 factor group. This can solve the
alignment problem without altering the desired properties of the family
symmetry. Inclusion of quarks into the framework is straightforward, and leads
to small and arbitrary CKM mixing angles. Supersymmetry is not essential for
our proposal, but the model presented is easily supersymmetrized, in which case
the same family symmetry solves the SUSY flavor problem.Comment: Typos fixed, 26 pages in LaTe
The Energy Distribution in a Static Spherically Symmetric Nonsingular Black Hole Space-Time
We calculate the energy distribution in a static spherically symmetric
nonsingular black hole space-time by using the Tolman's energy-momentum
complex. All the calculations are performed in quasi-Cartesian coordinates. The
energy distribution is positive everywhere and be equal to zero at origin. We
get the same result as obtained by Y-Ching Yang by using the Einstein's and
Weinberg's prescriptions.Comment: 5 pages, no figure
Energy Associated with Schwarzschild Black Hole in a Magnetic Universe
In this paper we obtain the energy distribution associated with the Ernst
space-time (geometry describing Schwarzschild black hole in Melvin's magnetic
universe) in Einstein's prescription. The first term is the rest-mass energy of
the Schwarzschild black hole, the second term is the classical value for the
energy of the uniform magnetic field and the remaining terms in the expression
are due to the general relativistic effect. The presence of the magnetic field
is found to increase the energy of the system.Comment: RevTex, 8 pages, no figures, a few points are clarified, to appear in
Int. J. Mod. Phys. A. This paper is dedicated to Professor G. F. R. Ellis on
the occasion of his 60th birthda
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