26 research outputs found
Black hole mass spectrum vs spectrum of Hawking radiation
We consider a massive selfgravitating shell as a model for collapsing body
and a null selfgravitating shell as a model for quanta of Hawking radiation. It
is show that the mass-energy spectra for the body and the radiation do not
match. The way out of this difficulty is to consider not only out-going
radiation but also the ingoing one. It means that the structure of black hole
is changing during its evaporation resulting in the Bekenstein-Mukhanov
spectrum for large masses.Comment: 11 pages, 2 figures, submitted to Phys.Rev.Let
Quasiclassical mass spectrum of the black hole model with selfgravitating dust shell
We consider a quantum mechanical black hole model introduced in {\it
Phys.Rev.}, {\bf D57}, 1118 (1998) that consists of the selfgravitating dust
shell. The Schroedinger equation for this model is a finite difference equation
with the shift of the argument along the imaginary axis. Solving this equation
in quasiclassical limit in complex domain leads to quantization conditions that
define discrete quasiclassical mass spectrum. One of the quantization
conditions is Bohr-Sommerfeld condition for the bound motion of the shell. The
other comes from the requirement that the wave function is unambiguously
defined on the Riemannian surface on which the coefficients of Schroedinger
equation are regular. The second quantization condition remains valid for the
unbound motion of the shell as well, and in the case of a collapsing null-dust
shell leads to spectrum.Comment: 35 pages, 8 figures, to appear in Phys. Rev.
Low-energy effects in brane worlds: Liennard-Wiechert potentials and Hydrogen Lamb shift
Testing extra dimensions at low-energies may lead to interesting effects. In
this work a test point charge is taken to move uniformly in the 3-dimensional
subspace of a (3+)-brane embedded in a (3++1)-space with compact and
one warped infinite spatial extra dimensions. We found that the electromagnetic
potentials of the point charge match standard Liennard-Wiechert's at large
distances but differ from them close to it. These are finite at the position of
the charge and produce finite self-energies. We also studied a localized
Hydrogen atom and take the deviation from the standard Coulomb potential as a
perturbation. This produces a Lamb shift that is compared with known
experimental data to set bounds for the parameter of the model. This work
provides details and extends results reported in a previous Letter.Comment: Manuscript (LaTeX) and 2 figure files (eps format) used by the
manuscript LaTeX fil
Colliding branes and formation of spacetime singularities in string theory
Colliding branes without symmetry and the formation of spacetime
singularities in string theory are studied. After developing the general
formulas to describe such events, we study a particular class of exact
solutions first in the 5-dimensional effective theory, and then lift it to the
10-dimensional spacetime. In general, the 5-dimensional spacetime is singular,
due to the mutual focus of the two colliding 3-branes. Non-singular cases also
exist, but with the price that both of the colliding branes violate all the
three energy conditions, weak, dominant, and strong. After lifted to 10
dimensions, we find that the spacetime remains singular, whenever it is
singular in the 5-dimensional effective theory. In the cases where no
singularities are formed after the collision, we find that the two 8-branes
necessarily violate all the energy conditions.Comment: revtex4, 13 figures. Some typos were corrected, and new refereeces
added. Final version to appear in JHE
Brane Big-Bang Brought by Bulk Bubble
We propose an alternative inflationary universe scenario in the context of
Randall-Sundrum braneworld cosmology. In this new scenario the existence of
extra-dimension(s) plays an essential role. First, the brane universe is
initially in the inflationary phase driven by the effective cosmological
constant induced by small mismatch between the vacuum energy in the
5-dimensional bulk and the brane tension. This mismatch arises since the bulk
is initially in a false vacuum. Then, the false vacuum decay occurs, nucleating
a true vacuum bubble with negative energy inside the bulk. The nucleated bubble
expands in the bulk and consequently hits the brane, bringing a hot big-bang
brane universe of the Randall-Sundrum type. Here, the termination of the
inflationary phase is due to the change of the bulk vacuum energy. The bubble
kinetic energy heats up the universe. As a simple realization, we propose a
model, in which we assume an interaction between the brane and the bubble. We
derive the constraints on the model parameters taking into account the
following requirements: solving the flatness problem, no force which prohibits
the bubble from colliding with the brane, sufficiently high reheating
temperature for the standard nucleosynthesis to work, and the recovery of
Newton's law up to 1mm. We find that a fine tuning is needed in order to
satisfy the first and the second requirements simultaneously, although, the
other constraints are satisfied in a wide range of the model parameters.Comment: 20pages, 5figures, some references added, the previous manuscript has
been largely improve
Brane matter, hidden or mirror matter, their various avatars and mixings: many faces of the same physics
Numerous papers deal with the phenomenology related to photon-hidden photon
kinetic mixing and with the effects of a mass mixing on particle-hidden
particle oscillations. In addition, recent papers underline the existence of a
geometrical mixing between branes which would allow a matter swapping between
branes. These approaches and their phenomenologies are reminiscent of each
other but rely on different physical concepts. In the present paper, we suggest
there is no rivalry between these models, which are probably many faces of the
same physics. We discuss some phenomenological consequences of a global
framework.Comment: 9 pages. Typo corrected. Published in European Physical Journal
New hadrons as ultra-high energy cosmic rays
Ultra-high energy cosmic ray (UHECR) protons produced by uniformly
distributed astrophysical sources contradict the energy spectrum measured by
both the AGASA and HiRes experiments, assuming the small scale clustering of
UHECR observed by AGASA is caused by point-like sources. In that case, the
small number of sources leads to a sharp exponential cutoff at the energy
E<10^{20} eV in the UHECR spectrum. New hadrons with mass 1.5-3 GeV can solve
this cutoff problem. For the first time we discuss the production of such
hadrons in proton collisions with infrared/optical photons in astrophysical
sources. This production mechanism, in contrast to proton-proton collisions,
requires the acceleration of protons only to energies E<10^{21} eV. The diffuse
gamma-ray and neutrino fluxes in this model obey all existing experimental
limits. We predict large UHE neutrino fluxes well above the sensitivity of the
next generation of high-energy neutrino experiments. As an example we study
hadrons containing a light bottom squark. These models can be tested by
accelerator experiments, UHECR observatories and neutrino telescopes.Comment: 17 pages, revtex style; v2: shortened, as to appear in PR
Ultra-High Energy Neutrino Fluxes and Their Constraints
Applying our recently developed propagation code we review extragalactic
neutrino fluxes above 10^{14} eV in various scenarios and how they are
constrained by current data. We specifically identify scenarios in which the
cosmogenic neutrino flux, produced by pion production of ultra high energy
cosmic rays outside their sources, is considerably higher than the
"Waxman-Bahcall bound". This is easy to achieve for sources with hard injection
spectra and luminosities that were higher in the past. Such fluxes would
significantly increase the chances to detect ultra-high energy neutrinos with
experiments currently under construction or in the proposal stage.Comment: 11 pages, 15 figures, version published in Phys.Rev.
The energy spectrum of tau leptons induced by the high energy Earth-skimming neutrinos
We present a semi-analytic calculation of the tau-lepton flux emerging from
the Earth, induced by the incident high energy neutrinos interacting inside the
Earth for . We obtain results for
the energy dependence of the tau-lepton flux coming from the Earth-skimming
neutrinos, because of the neutrino-nucleon charged-current scattering as well
as the resonant scattering. We illustrate our results for
several anticipated high energy astrophysical neutrino sources such as the
AGNs, the GRBs, and the GZK neutrino fluxes. The tau lepton fluxes resulting
from rock-skimming and ocean-skimming neutrinos are compared. Such comparisons
can render useful information for the spectral indices of incident neutrino
fluxes.Comment: 23 pages, 6 figure