119 research outputs found
Comments on matter collineations of plane symmetric, cylindrically symmetric and spherically symmetric spacetimes
Comments are made on some recently published papers on matter collineations
of plane symmetric, cylindrically symmetric and spherically symmetric
spacetimes
Primordial Black Holes in Phantom Cosmology
We investigate the effects of accretion of phantom energy onto primordial
black holes. Since Hawking radiation and phantom energy accretion contribute to
a {\it decrease} of the mass of the black hole, the primordial black hole that
would be expected to decay now due to the Hawking process would decay {\it
earlier} due to the inclusion of the phantom energy. Equivalently, to have the
primordial black hole decay now it would have to be more massive initially. We
find that the effect of the phantom energy is substantial and the black holes
decaying now would be {\it much} more massive -- over 10 orders of magnitude!
This effect will be relevant for determining the time of production and hence
the number of evaporating black holes expected in a universe accelerating due
to phantom energy.Comment: 17 pages, 10 figures, accepted for publication in Gen. Relativ.
Gravi
Higgs dark energy in inert doublet model
Scalar fields are among the possible candidates for dark energy. This paper
is devoted to the scalar fields from the inert doublet model, where instead of
one as in the standard model, two SU(2) Higgs doublets are used. The component
fields of one SU(2) doublet () act in an identical way to the standard
model Higgs while the component fields of the second SU(2) doublet ()
are taken to be the dark energy candidate (which is done by assuming that the
phase transition in the field has not yet occurred). It is found that one can
arrange for late time acceleration (dark energy) by using an SU(2) Higgs
doublet in the inert Higgs doublet model, whose vacuum expectation value is
zero, in the quintessential regime.Comment: 6 pages, 4 figure
Geometric Linearization of Ordinary Differential Equations
The linearizability of differential equations was first considered by Lie for
scalar second order semi-linear ordinary differential equations. Since then
there has been considerable work done on the algebraic classification of
linearizable equations and even on systems of equations. However, little has
been done in the way of providing explicit criteria to determine their
linearizability. Using the connection between isometries and symmetries of the
system of geodesic equations criteria were established for second order
quadratically and cubically semi-linear equations and for systems of equations.
The connection was proved for maximally symmetric spaces and a conjecture was
put forward for other cases. Here the criteria are briefly reviewed and the
conjecture is proved.Comment: This is a contribution to the Proc. of the Seventh International
Conference ''Symmetry in Nonlinear Mathematical Physics'' (June 24-30, 2007,
Kyiv, Ukraine), published in SIGMA (Symmetry, Integrability and Geometry:
Methods and Applications) at http://www.emis.de/journals/SIGMA
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