165 research outputs found
Gravitational Wave Bursts from Collisions of Primordial Black Holes in Clusters
The rate of gravitational wave bursts from the mergers of massive primordial
black holes in clusters is calculated. Such clusters of black holes can be
formed through phase transitions in the early Universe. The central black holes
in clusters can serve as the seeds of supermassive black holes in galactic
nuclei. The expected burst detection rate by the LISA gravitational wave
detector is estimated.Comment: 10 pages, 2 figure
The Formation of Primary Galactic Nuclei during Phase Transitions in the Early Universe
A new mechanism describing the formation of protogalaxies is proposed, which
is based on the second- order phase transition in the inflation stage and the
domain wall formation upon the end of inflation. The presence of closed domain
walls with the size markedly exceeding the cosmological horizon at the instant
of their formation and the wall collapse in the postinflation epoch (when the
wall size becomes comparable with the cosmological horizon), which leads to the
formation of massive black hole clusters that can serve as nuclei for the
future galaxies. The black hole mass distributions obtained do not contradict
the available experimental data. The number of black holes with M ~ 100 solar
masses () and above is comparable with the number of Galaxies in the
visible Universe. Development of the proposed approach gives ground for a
principally new scenario of the galaxy formation in the model of hot Universe.Comment: 9 page
Gravitino production by primordial black hole evaporation and constraints on the inhomogeneity of the early Universe
In supergravity models, the evaporation of light Primordial Black Holes
(PBHs) should be a source of gravitinos. By considering this process, new
stringent limits are derived on the abundance of small black holes with initial
masses less than 10^9 g. In minimal supergravity, the subsequent decay of
evaporated gravitinos into cascades of non-equilibrium particles leads to the
formation of elements whose abundance is constrained by observations. In gauge
mediated supersymmetry breaking models, their density is required not to
overclose the Universe. As a result, cosmological models with substantial
inhomogeneities on small scales are excluded.Comment: Published version. Minor changes, references adde
Non-thermal Leptogenesis and a Prediction of Inflaton Mass in a Supersymmetric SO(10) Model
The gravitino problem gives a severe constraint on the thermal leptogenesis
scenario. This problem leads us to consider some alternatives to it if we try
to keep the gravitino mass around the weak scale GeV. We
consider, in this paper, the non-thermal leptogenesis scenario in the framework
of a minimal supersymmetric SO(10) model. Even if we start with the same
minimal SO(10) model, we have different predictions for low-energy
phenomenologies dependent on the types of seesaw mechanism. This is the case
for leptogenesis: it is shown that the type-I see-saw model gives a consistent
scenario for the non-thermal leptogenesis but not for type-II. The predicted
inflaton mass needed to produce the observed baryon asymmetry of the universe
is found to be GeV for the reheating temperature
GeV.Comment: 9 pages, 2 figures; the version to appear in JCA
Mechanism for the Suppression of Intermediate-Mass Black Holes
A model for the formation of supermassive primordial black holes in galactic
nuclei with the simultaneous suppression of the formation of intermediate-mass
black holes is presented. A bimodal mass function for black holes formed
through phase transitions in a model with a "Mexican hat" potential has been
found. The classical motion of the phase of a complex scalar field during
inflation has been taken into account. Possible observational manifestations of
primordial black holes in galaxies and constraints on their number are
discussed.Comment: 12 pages, 2 figure
Leptogenesis via Collisions: Leaking Lepton Number to the Hidden Sector
We propose a lepto-baryogenesis mechanism in which the non-zero B-L of the
universe is produced in out-of-equilibrium, lepton number and CP violating
scattering processes that convert ordinary particles into particles of some
hidden sector. In particular, we consider the processes mediated by the heavy Majorana neutrinos of the seesaw
mechanism, where and are ordinary lepton and Higgs doublets and
, their hidden counterparts. Such a leptogenesis mechanism is
effective even if the reheating temperature is much smaller than the heavy
neutrino masses. In particular, it can be as low as GeV.Comment: 4 pages, revtex, 2 figures; as to appear in PRL, supplemented with an
additional remar
Phenomenology of -CDM model: a possibility of accelerating Universe with positive pressure
Among various phenomenological models, a time-dependent model is selected here to investigate the -CDM cosmology.
Using this model the expressions for the time-dependent equation of state
parameter and other physical parameters are derived. It is shown that
in model accelerated expansion of the Universe takes place at negative
energy density, but with a positive pressure. It has also been possible to
obtain the change of sign of the deceleration parameter during cosmic
evolution.Comment: 16 Latex pages, 11 figures, Considerable modifications in the text;
Accepted in IJT
Inflaton Fragmentation and Oscillon Formation in Three Dimensions
Analytical arguments suggest that a large class of scalar field potentials
permit the existence of oscillons -- pseudo-stable, non-topological solitons --
in three spatial dimensions. In this paper we numerically explore oscillon
solutions in three dimensions. We confirm the existence of these field
configurations as solutions to the Klein-Gorden equation in an expanding
background, and verify the predictions of Amin and Shirokoff for the
characteristics of individual oscillons for their model. Further, we
demonstrate that significant numbers of oscillons can be generated via
fragmentation of the inflaton condensate, consistent with the analysis of Amin.
These emergent oscillons can easily dominate the post-inflationary universe.
Finally, both analytic and numerical results suggest that oscillons are stable
on timescales longer than the post-inflationary Hubble time. Consequently, the
post-inflationary universe can contain an effective matter-dominated phase,
during which it is dominated by localized concentrations of scalar field
matter.Comment: See http://easther.physics.yale.edu/downloads.html for numerical
codes. Visualizations available at http://www.mit.edu/~mamin/oscillons.html
and http://easther.physics.yale.edu/fields.html V2 Minor fixes to reference
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