130 research outputs found
Black hole shadow of a rotating polytropic black hole by the Newman--Janis algorithm without complexification
In this work, starting from a spherically symmetric polytropic black hole, a
rotating solution is obtained by following the Newman--Janis algorithm without
complexification. Besides studying the horizon, the static conditions and
causality issues of the rotating solution, we obtain and discuss the shape of
its shadow. Some other physical features as the Hawking temperature and
emission rate of the rotating polytropic black hole solution are also
discussed.Comment: 9 pages, 2 figures, some references adde
Gravitino dark matter in brane-world cosmology
The gravitino dark matter hypothesis in the brane cosmology is studied. The
theoretical framework is the CMSSM for particle physics and RS II brane model
for gravity. It is found that the gravitino can play the role of dark matter in
the universe and we determine what the gravitino mass should be for different
values of the five-dimensional Planck mass. An upper bound is obtained for the
latter.Comment: Improved version with minor corrections, to appear in JCA
Holographic techniques for recording ultrafast events
In this paper we report on a holographic method used to record fast events in the nanosecond time scale. Several frames of the expansion of shock waves in air and in a polymer sample are recorded holographically in a single shot experiment, using a pulse train generated with a single pulse from a Q-switched Nd:YAG laser. The time resolution is limited by the laser pulse width, which is 5.9 ns. The different frames are recorded on the holographic material using angle multiplexing. Two cavities are used to generate the signal and reference pulses at different angles. We also present a method in which the recording material is replaced by a CCD camera. In this method the holograms are recorded directly on the CCD and digitally reconstructed. The holograms are recorded on a single frame of the CCD camera and then digitally separated and reconstructed
Cosmic strings and Natural Inflation
In the present work we discuss cosmic strings in natural inflation. Our
analysis is based entirely on the CMB quadrupole temperature anisotropy and on
the existing upper bound on the cosmic string tension. Our results show that
the allowed range for both parameters of the inflationary model is very
different from the range obtained recently if cosmic strings are formed at the
same time with inflation, while if strings are formed after inflation we find
that the parameters of the inflationary model are similar to the ones obtained
recently.Comment: 12 pages, 0 tables, 4 figures, accepted for publication in JHE
D-term inflation in D-brane cosmology
We consider hybrid inflation in the braneworld scenario. In particular, we
consider inflation in global supersymmetry with the D-terms in the scalar
potential for the inflaton field to be the dominant ones (D-term inflation). We
find that D-term dominated inflation can naturally accomodate all requirements
of the successful hybrid inflationary model also in the framework of D-brane
cosmology with global supersymmetry. The reheating temperature after inflation
can be high enough () for successful thermal leptogenesis.Comment: 11 pages, 2 figures, one reference adde
Holographic recording of fast events on a CCD camera
We report on holographic recording of nanosecond events on a conventional CCD camera. Three frames of an air-discharge event, with resolution of 5.9 ns and frame interval of 12 ns, are recorded in a single CCD frame. Each individual frame is reconstructed by digital filtering of the CCD frame, since successively recorded holograms are centered at different carrier frequencies in the spatial frequency domain. (C) 2002 Optical Society of America
Constraining non-minimally coupled tachyon fields by Noether symmetry
A model for a spatially flat homogeneous and isotropic Universe whose
gravitational sources are a pressureless matter field and a tachyon field
non-minimally coupled to the gravitational field is analyzed. Noether symmetry
is used to find the expressions for the potential density and for the coupling
function, and it is shown that both must be exponential functions of the
tachyon field. Two cosmological solutions are investigated: (i) for the early
Universe whose only source of the gravitational field is a non-minimally
coupled tachyon field which behaves as an inflaton and leads to an exponential
accelerated expansion and (ii) for the late Universe whose gravitational
sources are a pressureless matter field and a non-minimally coupled tachyon
field which plays the role of dark energy and is the responsible of the
decelerated-accelerated transition period.Comment: 11 pages, 5 figures. Version accepted for publication in Classical
and Quantum Gravit
Bound states between dark matter particles and emission of gravitational radiation
Bound states of two weakly interactive massive particles are studied. It is
assumed that the WIMPonium is formed due to the gravitational interaction,
since the weak interaction can sometimes be repulsive. The lifetimes of the
spontaneous emission of gravitational radiation and of the WIMPs annihilation
into a pair of gravitons are computed, and are shown to be many orders of
magnitude larger than the age of the universe.Comment: Accepted for publication in GER
Dark matter in supersymmetric models with axino LSP in Randall-Sundrum II brane model
The axino dark matter hypothesis in RSII brane model is studied. Within the
framework of CMSSM we assume that the lightest neutralino or stau is the NLSP,
and that the axino production has a single contribution from the NLSP decay. It
is found that the axino can play the role of dark matter in the universe and we
determine what the axino mass should be for different values of the
five-dimensional Planck mass. An upper bound is obtained for the latterComment: 12 pages,3 figures, accepted in JHE
Dark Sector from Interacting Canonical and Non-Canonical Scalar Fields
In this work it is investigated general models with interactions between two
canonical scalar fields and between one non-canonical (tachyon-type) and one
canonical scalar field. The potentials and couplings to the gravity are
selected through the Noether symmetry approach. These general models are
employed to describe interactions between dark energy and dark matter, with the
fields being constrained by the astronomical data. The cosmological solutions
of some cases are compared with the observed evolution of the late Universe.Comment: 20 pages, 13 figures, correction of misprints in eqs. (4), (5), (43),
(44
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