1,218 research outputs found
Gravitational particle production in braneworld cosmology
Gravitational particle production in time variable metric of an expanding
universe is efficient only when the Hubble parameter is not too small in
comparison with the particle mass. In standard cosmology, the huge value of the
Planck mass makes the mechanism phenomenologically irrelevant. On the
other hand, in braneworld cosmology the expansion rate of the early universe
can be much faster and many weakly interacting particles can be abundantly
created. Cosmological implications are discussed.Comment: 4 pages, 1 figure, v3 with new definition of and minor text
modification
Baryogenesis from Gravitational Decay of TeV-Particles in Theories with Low Scale Gravity
In models with the fundamental gravity scale in the TeV range, early
cosmology is quite different from the standard picture, because the universe
must have arisen at a much lower temperature and the electroweak symmetry was
probably never restored. In this context, baryogenesis appears to be
problematic: if the involved physics is essentially that of the Standard Model,
``conventional'' non-conserving baryon number processes are completely
negligible at such low temperatures. In this paper we show that the observed
matter-antimatter asymmetry of the universe may be generated by gravitational
decay of TeV-mass particles: such objects can be out of equilibrium after
inflation and, if their mass is of the same order of magnitude as the true
quantum gravity scale, they can quickly decay through a black hole intermediate
state, violating global symmetries, in particular, baryon number. In this
context, we take advantage of the fact that the ``Sakharov conditions'' for
baryogenesis can be more easily satisfied with a low fundamental scale of
gravity.Comment: 18 pages, added reference
Baryogenesis, 30 Years after
A review of the basic principles of baryogenesis is given. Baryogenesis in
heavy particle decays as well as electroweak, SUSY-condensate, and spontaneous
baryogenesis are discussed. The models of abundant creation of antimatter in
the universe are briefly reviewed.Comment: 30 pages, latex twic
Difference between radiative transition rates in atoms and antiatoms
We demonstrate that CP violation results in a difference of the partial decay
rates of atoms and antiatoms. The magnitude of this difference is estimated.Comment: 5 pages, 5 figure
Massive sterile neutrinos as warm Dark Matter
We show that massive sterile neutrinos mixed with the ordinary ones may be
produced in the early universe in the right amount to be natural warm dark
matter particles. Their mass should be below 40 keV and the corresponding
mixing angles sin^2 2\theta > 10^{-11} for mixing with \nu_\mu or \nu_\tau,
while mixing with \nu_e is slightly stronger bounded with mass less than 30
keV.Comment: 13 pages, 1 figure, references and acknowledgement added; discussion
on SN bound updated, matches version in Astropart.phy
Sterile neutrinos, lepton asymmetries, primordial elements: how much of each?
We investigate quantitatively the extent to which having a primordial
leptonic asymmetry (n_nu \neq n_nubar) relaxes the bounds on light sterile
neutrinos imposed by BBN and LSS. We adopt a few assumptions that allow us to
solve the neutrino evolution equations over a broad range of mixing parameters
and asymmetries. For the general cases of sterile mixing with the electron or
muon neutrino, we identify the regions that can be reopened. For the particular
case of a LSND-like sterile neutrino, soon to be rejected or confirmed by
MiniBooNE, we find that an asymmetry of the order of 10^-4 is needed to lift
the conflicts with cosmology.Comment: 18 pages, 2 figures. v2: References and minor comments added. Matches
version published on PR
Evolution of thick domain walls in inflationary and universe
We study the evolution of thick domain walls in the different models of
cosmological inflation, in the matter-dominated and radiation-dominated
universe, or more generally in the universe with the equation of state
. We have found that the domain wall evolution crucially depends on
the time-dependent parameter , where is the
Hubble parameter and is the thickness of the wall in flat
space-time. For the physical thickness of the wall, ,
tends with time to , which is microscopically small. Otherwise, when
, the wall steadily expands and can grow up to a cosmologically
large size.Comment: 15 pages, 9 figure
Shape of the inflaton potential and the efficiency of the universe heating
It is shown that the efficiency of the universe heating by an inflaton field
depends not only on the possible presence of parametric resonance in the
production of scalar particles but also strongly depends on the character of
the inflaton approach to its mechanical equilibrium point. In particular, when
the inflaton oscillations deviate from pure harmonic ones toward a succession
of step functions, the production probability rises by several orders of
magnitude. This in turn leads to a much higher temperature of the universe
after the inflaton decay, in comparison to the harmonic case. An example of the
inflaton potential is presented which creates a proper modification of the
evolution of the inflaton toward equilibrium and does not destroy the nice
features of inflation.Comment: 14 pages, 12 figures; final version published in EPJ
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