17 research outputs found
Numerical Solutions of ideal two-fluid equations very closed to the event horizon of Schwarzschild black hole
The 3+1 formalism of Thorne, Price and Macdonald has been used to derive the
linear two-fluid equations describing transverse and longitudinal waves
propagating in the two-fluid ideal collisionless plasmas surrounding a
Schwarzschild black hole. The plasma is assumed to be falling in radial
direction toward the event horizon. The relativistic two-fluid equations have
been reformulate, in analogy with the special relativistic formulation as
explained in an earlier paper, to take account of relativistic effects due to
the event horizon. Here a WKB approximation is used to derive the local
dispersion relation for these waves and solved numerically for the wave number
k.Comment: 16 pages, 15 figures. arXiv admin note: text overlap with
arXiv:0902.3766, arXiv:0807.459
Black Hole Chromosphere at the LHC
If the scale of quantum gravity is near a TeV, black holes will be copiously
produced at the LHC. In this work we study the main properties of the light
descendants of these black holes. We show that the emitted partons are closely
spaced outside the horizon, and hence they do not fragment into hadrons in
vacuum but more likely into a kind of quark-gluon plasma. Consequently, the
thermal emission occurs far from the horizon, at a temperature characteristic
of the QCD scale. We analyze the energy spectrum of the particles emerging from
the "chromosphere", and find that the hard hadronic jets are almost entirely
suppressed. They are replaced by an isotropic distribution of soft photons and
hadrons, with hundreds of particles in the GeV range. This provides a new
distinctive signature for black hole events at LHC.Comment: Incorporates changes made for the version to be published in Phys.
Rev. D. Additional details provided on the effect of the chromosphere in
cosmic ray shower
Bounds from Primordial Black Holes with a Near Critical Collapse Initial Mass Function
Recent numerical evidence suggests that a mass spectrum of primordial black
holes (PBHs) is produced as a consequence of near critical gravitational
collapse. Assuming that these holes formed from the initial density
perturbations seeded by inflation, we calculate model independent upper bounds
on the mass variance at the reheating temperature by requiring the mass density
not exceed the critical density and the photon emission not exceed current
diffuse gamma-ray measurements. We then translate these results into bounds on
the spectral index n by utilizing the COBE data to normalize the mass variance
at large scales, assuming a constant power law, then scaling this result to the
reheating temperature. We find that our bounds on n differ substantially
(\delta n > 0.05) from those calculated using initial mass functions derived
under the assumption that the black hole mass is proportional to the horizon
mass at the collapse epoch. We also find a change in the shape of the diffuse
gamma-ray spectrum which results from the Hawking radiation. Finally, we study
the impact of a nonzero cosmological constant and find that the bounds on n are
strengthened considerably if the universe is indeed vacuum-energy dominated
today.Comment: 24 pages, REVTeX, 5 figures; minor typos fixed, two refs added,
version to be published in PR
Constraints on diffuse neutrino background from primordial black holes
We calculated the energy spectra and the fluxes of electron neutrino emitted
in the process of evaporation of primordial black holes (PBHs) in the early
universe. It was assumed that PBHs are formed by a blue power-law spectrum of
primordial density fluctuations. We obtained the bounds on the spectral index
of density fluctuations assuming validity of the standard picture of
gravitational collapse and using the available data of several experiments with
atmospheric and solar neutrinos. The comparison of our results with the
previous constraints (which had been obtained using diffuse photon background
data) shows that such bounds are quite sensitive to an assumed form of the
initial PBH mass function.Comment: 18 pages,(with 7 figures
Primordial black holes in braneworld cosmologies: astrophysical constraints
In two recent papers we explored the modifications to primordial black hole
physics when one moves to the simplest braneworld model, Randall--Sundrum type
II. Both the evaporation law and the cosmological evolution of the population
can be modified, and additionally accretion of energy from the background can
be dominant over evaporation at high energies. In this paper we present a
detailed study of how this impacts upon various astrophysical constraints,
analyzing constraints from the present density, from the present high-energy
photon background radiation, from distortion of the microwave background
spectrum, and from processes affecting light element abundances both during and
after nucleosynthesis. Typically, the constraints on the formation rate of
primordial black holes weaken as compared to the standard cosmology if black
hole accretion is unimportant at high energies, but can be strengthened in the
case of efficient accretion.Comment: 17 pages RevTeX4 file with three figures incorporated; final paper in
series astro-ph/0205149 and astro-ph/0208299. Minor changes to match version
accepted by Physical Review
First-order cosmological phase transitions in the radiation dominated era
We consider first-order phase transitions of the Universe in the
radiation-dominated era. We argue that in general the velocity of interfaces is
non-relativistic due to the interaction with the plasma and the release of
latent heat. We study the general evolution of such slow phase transitions,
which comprise essentially a short reheating stage and a longer phase
equilibrium stage. We perform a completely analytical description of both
stages. Some rough approximations are needed for the first stage, due to the
non-trivial relations between the quantities that determine the variation of
temperature with time. The second stage, instead, is considerably simplified by
the fact that it develops at a constant temperature, close to the critical one.
Indeed, in this case the equations can be solved exactly, including
back-reaction on the expansion of the Universe. This treatment also applies to
phase transitions mediated by impurities. We also investigate the relations
between the different parameters that govern the characteristics of the phase
transition and its cosmological consequences, and discuss the dependence of
these parameters with the particle content of the theory.Comment: 38 pages, 3 figures; v2: Minor changes, references added; v3: several
typos correcte
Signatures of Relativistic Neutrinos in CMB Anisotropy and Matter Clustering
We present a detailed analytical study of ultra-relativistic neutrinos in
cosmological perturbation theory and of the observable signatures of
inhomogeneities in the cosmic neutrino background. We note that a modification
of perturbation variables that removes all the time derivatives of scalar
gravitational potentials from the dynamical equations simplifies their solution
notably. The used perturbations of particle number per coordinate, not proper,
volume are generally constant on superhorizon scales. In real space an
analytical analysis can be extended beyond fluids to neutrinos.
The faster cosmological expansion due to the neutrino background changes the
acoustic and damping angular scales of the cosmic microwave background (CMB).
But we find that equivalent changes can be produced by varying other standard
parameters, including the primordial helium abundance. The low-l integrated
Sachs-Wolfe effect is also not sensitive to neutrinos. However, the gravity of
neutrino perturbations suppresses the CMB acoustic peaks for the multipoles
with l>~200 while it enhances the amplitude of matter fluctuations on these
scales. In addition, the perturbations of relativistic neutrinos generate a
*unique phase shift* of the CMB acoustic oscillations that for adiabatic
initial conditions cannot be caused by any other standard physics. The origin
of the shift is traced to neutrino free-streaming velocity exceeding the sound
speed of the photon-baryon plasma. We find that from a high resolution, low
noise instrument such as CMBPOL the effective number of light neutrino species
can be determined with an accuracy of sigma(N_nu) = 0.05 to 0.09, depending on
the constraints on the helium abundance.Comment: 38 pages, 7 figures. Version accepted for publication in PR
Late-time Entropy Production from Scalar Decay and Relic Neutrino Temperature
Entropy production from scalar decay in the era of low temperatures after
neutrino decoupling will change the ratio of the relic neutrino temperature to
the CMB temperature, and, hence, the value of N_eff, the effective number of
neutrino species. Such scalar decay is relevant to reheating after thermal
inflation, proposed to dilute massive particles, like the moduli and the
gravitino, featuring in supersymmetric and string theories. The effect of such
entropy production on the relic neutrino temperature ratio is calculated in a
semi-analytic manner, and a recent lower bound on this ratio, obtained from the
WMAP satellite and 2dF galaxy data, is used to set a lower bound of ~ 1.5 x
10^-23 Gev on the scalar decay constant, corresponding to a reheating
temperature of about 3.3 Mev.Comment: 13 pages, to appear in PR
Dynamics of Two Higgs Doublet CP Violation and Baryogenesis at the Electroweak Phase Transition
We quantitatively study the charge transport mechanism of electroweak
baryogenesis in a realistic two-Higgs-doublet model, comparing the
contributions from quarks and leptons reflecting from electroweak domain walls,
and comparing the exact profile of the CP-violating phase with a commonly used
ansatz. We note that the phenomenon of spontaneous CP violation at high
temperature can occur in this model, even when there is no CP violation at zero
temperature. We include all known effects which are likely to influence the
baryon production rate, including strong sphalerons, the nontrivial dispersion
relations of the quasiparticles in the plasma, and Debye screening of gauged
charges. We confirm the claim of Joyce, Prokopec and Turok that the reflection
of tau leptons from the wall gives the dominant effect. We conclude that this
mechanism is marginally strong enough to produce the observed baryon asymmetry
of the universe.Comment: 49 pp. latex, 6 figures; section on diffusion expanded and corrected,
published versio