95 research outputs found
Gravitational magnetic monopoles and Majumdar-Papapetrou stars
A large amount of work has been dedicated to studying general relativity
coupled to non-Abelian Yang-Mills type theories. It has been shown that the
magnetic monopole, a solution of the Yang-Mills-Higgs equations can be coupled
to gravitation. For a low Higgs mass there are regular solutions, and for a
sufficiently massive monopole the system develops an extremal magnetic
Reissner-Nordstrom quasi-horizon. These solutions, called quasi-black holes,
although non-singular, are arbitrarily close to having a horizon. However, at
the critical value the quasi-black hole turns into a degenerate spacetime. On
the other hand, for a high Higgs mass, a sufficiently massive monopole develops
also a quasi-black hole, but it turns into an extremal true horizon, with
matter fields outside. One can also put a small Schwarzschild black hole inside
the magnetic monopole, an example of a non-Abelian black hole. Surprisingly,
Majumdar-Papapetrou systems, Abelian systems constructed from extremal dust,
also show a resembling behavior. Previously, we have reported that one can find
Majumdar-Papapetrou solutions which can be arbitrarily close of being a black
hole, displaying quasi-black hole behavior. With the aim of better
understanding the similarities between gravitational monopoles and
Majumdar-Papapetrou systems, we study a system composed of two extremal
electrically charged spherical shells (or stars, generically) in the
Einstein--Maxwell--Majumdar-Papapetrou theory. We review the gravitational
properties of the monopoles, and compare with the properties of the double
extremal electric shell system. These quasi-black holes can help in the
understanding of true black holes, and can give insight into the nature of the
entropy of black holes in the form of entanglement.Comment: 38 pages,9 Figures, minor change
The Three-Dimensional BTZ Black Hole as a Cylindrical System in Four-Dimensional General Relativity
It is shown how to transform the three dimensional BTZ black hole into a four
dimensional cylindrical black hole (i.e., black string) in general relativity.
This process is identical to the transformation of a point particle in three
dimensions into a straight cosmic string in four dimensions.Comment: Latex, 9 page
Pastagem de Tifton 85 consorciado com forrageiras de inverno.
Experimento e Avaliações em Unidades de Produção; Manejo da Pastagem e Método de Semeadura de Forrageiras de Inverno; Época e Densidade de Semeadura; Produção da Pastagem Consorciada; Espécies de Inverno para o Consórcio.bitstream/item/54182/1/CO-79.pd
Suppression of growth by multiplicative white noise in a parametric resonant system
The author studied the growth of the amplitude in a Mathieu-like equation
with multiplicative white noise. The approximate value of the exponent at the
extremum on parametric resonance regions was obtained theoretically by
introducing the width of time interval, and the exponents were calculated
numerically by solving the stochastic differential equations by a symplectic
numerical method. The Mathieu-like equation contains a parameter that
is determined by the intensity of noise and the strength of the coupling
between the variable and the noise. The value of was restricted not to
be negative without loss of generality. It was shown that the exponent
decreases with , reaches a minimum and increases after that. It was
also found that the exponent as a function of has only one minimum at
on parametric resonance regions of . This minimum
value is obtained theoretically and numerically. The existence of the minimum
at indicates the suppression of the growth by multiplicative
white noise.Comment: The title and the description in the manuscript are change
Preheating of the nonminimally coupled inflaton field
We investigate preheating of an inflaton field coupled nonminimally to
a spacetime curvature. In the case of a self-coupling inflaton potential
, the dynamics of preheating changes by the effect of
the negative . We find that the nonminimal coupling works in two ways.
First, since the initial value of inflaton field for reheating becomes
smaller with the increase of , the evolution of the inflaton quanta is
delayed for fixed . Second, the oscillation of the inflaton field is
modified and the nonadiabatic change around occurs significantly. That
makes the resonant band of the fluctuation field wider. Especially for strong
coupling regimes , the growth of the inflaton flutuation is
dominated by the resonance due to the nonminimal coupling, which leads to the
significant enhancement of low momentum modes. Although the final variance of
the inflaton fluctuation does notchange significantly compared with the
minimally coupled case, we have found that the energy transfer from the
homogeneous inflaton to created particles efficiently occurs for .Comment: 13pages, 11figure
Topological Defects and Cosmology
Many particle physics models of matter admit solutions corresponding to
stable or long-lived topological defects. In the context of standard cosmology
it is then unavoidable that such defects will form during phase transitions in
the very early Universe. Certain types of defects lead to disastrous
consequences for cosmology, others may play a useful role, as possible seeds
for the formation of structure in the Universe, or in mediating baryon number
violating processes. In all cases, topological defects lead to a fruitful
interplay between particle physics and cosmology.Comment: 17 pages, no figures; Invited lectures at WHEPP-5, IUCAA, Pune,
India, Jan. 12 - 26 199
Inflationary Reheating Classes via Spectral Methods
Inflationary reheating is almost completely controlled by the Floquet
indices, . Using spectral theory we demonstrate that the stability bands
(where ) of the Mathieu and Lam\'e equations are destroyed even in
Minkowski spacetime, leaving a fractal Cantor set or a measure zero set of
stable modes in the cases where the inflaton evolves in an almost-periodic or
stochastic manner respectively. These two types of potential model the expected
multi-field and quantum backreaction effects during reheating.Comment: 5 pages, 2 ps figures, Revtex. Version to appear in Phys. Rev. D
(Rapid Communication, July 15
The Human Nucleolar Protein FTSJ3 Associates with NIP7 and Functions in Pre-rRNA Processing
NIP7 is one of the many trans-acting factors required for eukaryotic ribosome biogenesis, which interacts with nascent pre-ribosomal particles and dissociates as they complete maturation and are exported to the cytoplasm. By using conditional knockdown, we have shown previously that yeast Nip7p is required primarily for 60S subunit synthesis while human NIP7 is involved in the biogenesis of 40S subunit. This raised the possibility that human NIP7 interacts with a different set of proteins as compared to the yeast protein. By using the yeast two-hybrid system we identified FTSJ3, a putative ortholog of yeast Spb1p, as a human NIP7-interacting protein. A functional association between NIP7 and FTSJ3 is further supported by colocalization and coimmunoprecipitation analyses. Conditional knockdown revealed that depletion of FTSJ3 affects cell proliferation and causes pre-rRNA processing defects. The major pre-rRNA processing defect involves accumulation of the 34S pre-rRNA encompassing from site A′ to site 2b. Accumulation of this pre-rRNA indicates that processing of sites A0, 1 and 2 are slower in cells depleted of FTSJ3 and implicates FTSJ3 in the pathway leading to 18S rRNA maturation as observed previously for NIP7. The results presented in this work indicate a close functional interaction between NIP7 and FTSJ3 during pre-rRNA processing and show that FTSJ3 participates in ribosome synthesis in human cells
Inflationary Reheating in Grand Unified Theories
Grand unified theories may display multiply interacting fields with strong
coupling dynamics. This poses two new problems: (1) What is the nature of
chaotic reheating after inflation, and (2) How is reheating sensitive to the
mass spectrum of these theories ? We answer these questions in two interesting
limiting cases and demonstrate an increased efficiency of reheating which
strongly enhances non-thermal topological defect formation, including monopoles
and domain walls. Nevertheless, the large fluctuations may resolve this
monopole problem via a modified Dvali-Liu-Vachaspati mechanism in which
non-thermal destabilsation of discrete symmetries occurs at reheating.Comment: 4 pages, 5 ps figures - 1 colour, Revtex. Further (colour & 3-D)
figures available from http://www.sissa.it/~bassett/reheating/ . Matched to
version to appear in Phys. Rev. let
Electrically charged compact stars and formation of charged black holes
We study the effect of electric charge in compact stars assuming that the
charge distribution is proportional to the mass density. The pressure and the
density of the matter inside the stars are large, and the gravitational field
is intense. This indicates that electric charge and a strong electric field can
also be present. The relativistic hydrostatic equilibrium equation, i.e., the
Tolman-Oppenheimer-Volkoff equation, is modified in order to include electric
charge. We perform a detailed numerical study of the effect of electric charge
using a polytropic equation of state. We conclude that in order to see any
appreciable effect on the phenomenology of the compact stars, the electric
fields have to be huge (~ 10^{21} V/m), which implies that the total charge is
Q ~ 10^{20} Coulomb. From the local effect of the forces experienced on a
single charged particle, it is expected that each individual charged particle
is quickly ejected from the star. This in turn produces a huge force imbalance,
and the gravitational force overwhelms the repulsive Coulomb and fluid pressure
forces. The star can then collapse to form a charged black hole before all the
charge leaves the system.Comment: 10 pages, 9 figures, To appear in Phys Rev.
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