11,127 research outputs found

### Massive scalar fields in the early Universe

We discuss the role of gravitational excitons/radions in different
cosmological scenarios. Gravitational excitons are massive moduli fields which
describe conformal excitations of the internal spaces and which, due to their
Planck-scale suppressed coupling to matter fields, are WIMPs. It is
demonstrated that, depending on the concrete scenario, observational
cosmological data set strong restrictions on the allowed masses and initial
oscillation amplitudes of these particles.Comment: 6 pages, Latex2e, talk presented at the 1st International Workshop on
Astronomy and Relativistic Astrophysics, 12-16 October, 2003, (IWARA2003),
Olinda-PE, Brazi

### Sterile neutrino dark matter in warped extra dimensions

We consider a (long-lived) sterile neutrino dark matter scenario in a five
dimensional (5D) warped extra dimension model where the fields can live in the
bulk, which is partly motivated from the absence of the absolutely stable
particles in a simple Randall-Sundrum model. The dominant production of the
sterile neutrino can come from the decay of the radion (the scalar field
representing the brane separation) around the electroweak scale. The
suppressions of the 4D parameters due to the warp factor and the small wave
function overlaps in the extra dimension help alleviate the exceeding
fine-tunings typical for a sterile neutrino dark matter scenario in a 4D setup.Comment: Typos corrected and references adde

### Pseudo-Dirac Bino Dark Matter

While the bino-dominated lightest neutralino of the minimal supersymmetric
Standard Model (MSSM) is an interesting and widely-studied candidate of the
dark matter, the p-wave suppression of its annihilation cross section requires
fine-tunings of the MSSM spectra to be consistent with WMAP observations. We
propose pseudo-Dirac bino that arises in theories with D-type
supersymmetry-breaking as an intriguing alternative candidate of dark matter.
The pseudo-Dirac nature of the bino gives a natural mechanism of enhanced
co-annihilation because these two states are degenerate in the absence of
electroweak symmetry breaking. In addition, the lightest state can be
consistent with limits of direct detection experiments because of the lack of
vector interactions, as with the case of the MSSM bino.Comment: 18 pages, 2 figures, REVTEX, to be published in PRD, made minor
changes and added comments to match the published versio

### Constraints on parameters of models with extra dimension from primordial nucleosynthesis

5D models with one 3D brane and one infinite extra dimension are studied.
Matter is confined to the brane, gravity extends to the bulk. Models with
positive and negative tension of the brane are studied. Cosmological solutions
on the brane are obtained by solving the generalized Friedmann equation. As the
input in cosmological solutions we use the present-time observational
cosmological parameters. We find constraints on dimensionless combinations of
scales of 5D models which follow from the requirement that the models reproduce
the data on production of ${}^4 He$ in primordial nucleosynthesis.Comment: 12 page

### The small mixing angle $\theta_{13}$ and the lepton asymmetry

We present the correlation of low energy CP phases, both Dirac and Majorana,
and the lepton asymmetry for the baryon asymmetry in the universe, with a
certain class of Yukawa matrices that consist of two right-handed neutrinos and
include one texture zero in themselves. For cases in which the amount of the
lepton asymmetry $Y_L$ turns out to be proportional to $\theta_{13}^2$, we
consider the relation between two types of CP phases and the relation of $Y_L$
versus the Jarlskog invariant or the amplitude of neutrinoless double beta
decay as $\theta_{13}$ varies.Comment: 17 pages, 14 figures, information for figures added, version
published in PR

### Singlino dominated LSP as CDM candidate in supersymmetric models with an extra U(1)

We consider a singlino dominated neutralino in supersymmetric models with an
extra U(1). In case both the $\mu$ term and also the $Z^\prime$ mass are
generated by the vacuum expectation value of the scalar component of the same
singlet chiral superfield, generically the lightest neutralino is not expected
to be dominated by the singlino. However, if the gaugino corresponding to the
extra U(1) is sufficiently heavy, the lightest neutralino can be dominated by
the singlino and still satisfy the constraints resulting from the $Z^\prime$
phenomenology. We assume a supersymmetry breaking scenario in which the extra
U(1) gaugino can be much heavier than other gauginos. In that framework we show
that the singlino dominated lightest neutralino may be a good candidate for
dark matter in a parameter space where various phenomenological constraints are
satisfied.Comment: 25 pages, 6 figures, title is changed, introduction is extended,
sec.2 is moved to appendix, some references are added, published versio

### Interaction of cosmic background neutrinos with matter of periodic structure

We study coherent interaction of cosmic background neutrinos(CBNs) with
matter of periodic structure. The mixing and small masses of neutrinos
discovered in neutrino oscillation experiments indicate that CBNs which have
very low energy today should be in mass states and can transform from one mass
state to another in interaction with electrons in matter. We show that in a
coherent scattering process a periodic matter structure designed to match the
scale of the mass square difference of neutrinos can enhance the conversion of
CBNs from one mass state to another. Energy of CBNs can be released in this
scattering process and momentum transfer from CBNs to electrons in target
matter can be obtained.Comment: 6 pages, 5 figures, publication versio

### Comments on Backreaction and Cosmic Acceleration

In this brief WEB note we comment on recent papers related to our paper "On
Acceleration Without Dark Energy".Comment: 5 pages WEB not

### Nonthermal Supermassive Dark Matter

We discuss several cosmological production mechanisms for nonthermal
supermassive dark matter and argue that dark matter may be elementary particles
of mass much greater than the weak scale. Searches for dark matter should not
be limited to weakly interacting particles with mass of the order of the weak
scale, but should extend into the supermassive range as well.Comment: 11 page LaTeX file. No major changes. Version accepted by PR

### Dilaton dominance in the early Universe dilutes Dark Matter relic abundances

The role of the dilaton field and its coupling to matter may result to a
dilution of Dark Matter (DM) relic densities. This is to be contrasted with
quintessence scenarios in which relic densities are augmented, due to
modification of the expansion rate, since Universe is not radiation dominated
at DM decoupling. Dilaton field, besides this, affects relic densities through
its coupling to dust which tends to decrease relic abundances. Thus two
separate mechanisms compete each other resulting, in general, to a decrease of
the relic density. This feature may be welcome and can rescue the situation if
Direct Dark Matter experiments point towards small neutralino-nucleon cross
sections, implying small neutralino annihilation rates and hence large relic
densities, at least in the popular supersymmetric scenarios. In the presence of
a diluting mechanism both experimental constraints can be met. The role of the
dilaton for this mechanism has been studied in the context of the non-critical
string theory but in this work we follow a rather general approach assuming
that the dilaton dominates only at early eras long before Big Bang
Nucleosynthesis.Comment: 11 pages, Latex, 4 figures: Comments and references added, version to
appear in Phys. Rev.

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