728 research outputs found

### Ultra-High Energy Cosmic Rays: The Annihilation of Super-Heavy Relics

We investigate the possibility that ultra-high energy cosmic rays (UHECRs)
originate from the annihilation of relic superheavy (SH) dark matter in the
Galactic halo. In order to fit the data on UHECRs, a cross section of
$\sim 10^{-26}\textrm{cm}^2 (M_X/10^{12} \textrm{GeV})^{3/2}$ is
required if the SH dark matter follows a Navarro--Frenk--White (NFW) density
profile. This would require extremely large-$l$ contributions to the
annihilation cross section. An interesting finding of our calculation is that
the annihilation in sub-galactic clumps of dark matter dominates over the
annihilations in the smooth dark matter halo, thus implying much smaller values
of the cross section needed to explain the observed fluxes of UHECRs.Comment: To appear in the proceedings of the TAUP conference, September 8-12,
2001 - Gran Sasso Laboratory, Ital

### Probing the stability of superheavy dark matter particles with high-energy neutrinos

Two of the most fundamental properties of the dark matter particle, the mass
and the lifetime, are only weakly constrained by the astronomical and
cosmological evidence of dark matter. We derive in this paper lower limits on
the lifetime of dark matter particles with masses in the range 10 TeV-10^15 TeV
from the non-observation of ultrahigh energy neutrinos in the AMANDA, IceCube,
Auger and ANITA experiments. For dark matter particles which produce neutrinos
in a two body or a three body decay, we find that the dark matter lifetime must
be longer than O(10^26-10^28) s for masses between 10 TeV and the Grand
Unification scale. Finally, we also calculate, for concrete particle physics
scenarios, the limits on the strength of the interactions that induce the dark
matter decay.Comment: 17 pages, 6 figures; v2: references added, discussion improved,
matches the version published at JCA

### Natural Warm Inflation

We derive the requirements that a generic axion-like field has to satisfy in
order to play the role of the inflaton field in the warm inflation scenario.
Compared to the parameter space in ordinary natural inflation models, we find
that the parameter space in our model is enlarged. In particular, we avoid the
problem of having an axion decay constant $f$ that relates to the Planck scale,
which is instead present in the ordinary natural inflation models; in fact, our
model can easily accommodate values of the axion decay constant that lie well
below the Planck scale.Comment: 19 pages, 7 figures; version accepted in JCA

### The cosmological constant and oscillating metrics

The presence of a cosmological constant, Lambda, in an action with higher
powers of the curvature can produce rapidly oscillating metrics. We develop a
perturbative approach for generating periodic solutions to the non-linear field
equations for such actions based on a small amplitude expansion. We find that
these oscillations have an amplitude proportional to \sqrt{\Lambda} and a
frequency of order the Planck mass. In a 4+1 dimensional scenario, a family of
metrics exists that are periodic in the extra dimension and are parameterized
by an effective four-dimensional cosmological constant which drives a rapid
oscillation.Comment: 15 pages, uses JHEP, no figure

### Shear and Vorticity in Inflationary Brans-Dicke Cosmology with Lambda-Term

We find a solution for exponential inflation in Brans-Dicke cosmology endowed
with a cosmological term, which includes time-varying shear and vorticity. We
find that the scalar field and the scale factor increase exponentialy while
shear, vorticity, energy density, cosmic pressure and the cosmological term
decay exponentialy for beta < 0, where beta is defined in the text.Comment: 8 pages including front one. Published by Astrophysics and Space
Scienc

### Effects of Squark Processes on the Axino CDM Abundance

We investigate the role of an effective dimension-4 axino-quark-squark
coupling in the thermal processes producing stable cold axino relics in the
early Universe. We find that, while the induced squark and quark scattering
processes are always negligible, squark decays become important in the case of
low reheat temperature and large gluino mass. The effect can tighten the bounds
on the scenario from the requirement that cold dark matter axinos do not
overclose the Universe.Comment: 20 pages, 9 figures, uses JHEP3.cl

### The Effective Potential, the Renormalisation Group and Vacuum Stability

We review the calculation of the the effective potential with particular
emphasis on cases when the tree potential or the
renormalisation-group-improved, radiatively corrected potential exhibits
non-convex behaviour. We illustrate this in a simple Yukawa model which
exhibits a novel kind of dimensional transmutation. We also review briefly
earlier work on the Standard Model. We conclude that, despite some recent
claims to the contrary, it can be possible to infer reliably that the tree
vacuum does not represent the true ground state of the theory.Comment: 23 pages; 5 figures; v2 includes minor changes in text and additional
reference

### Holomorphic selection rules, the origin of the mu term, and thermal inflation

When an abelian gauge theory with integer charges is spontaneously broken by
the expectation value of a charge Q field, there remains a Z_Q discrete
symmetry. In a supersymmetric theory, holomorphy adds additional constraints on
the operators that can appear in the effective superpotential. As a result,
operators with the same mass dimension but opposite sign charges can have very
different coupling strengths. In the present work we characterize the operator
hierarchies in the effective theory due to holomorphy, and show that there
exist simple relationships between the size of an operator and its mass
dimension and charge. Using such holomorphy-induced operator hierarchies, we
construct a simple model with a naturally small supersymmetric mu term. This
model also provides a concrete realization of late-time thermal inflation,
which has the ability to solve the gravitino and moduli problems of weak-scale
supersymmetry.Comment: 18 pages, 1 figur

### Inflation might be caused by the right

We show that the scalar field that drives inflation can have a dynamical
origin, being a strongly coupled right handed neutrino condensate. The
resulting model is phenomenologically tightly constrained, and can be
experimentally (dis)probed in the near future. The mass of the right handed
neutrino obtained this way (a crucial ingredient to obtain the right light
neutrino spectrum within the see-saw mechanism in a complete three generation
framework) is related to that of the inflaton and both completely determine the
inflation features that can be tested by current and planned experiments.Comment: 15 pages, 4 figure

### Solution Of Wheeler-De Witt Equation, Potential Well And Tunnel Effect

This paper uses the relation of the cosmic scale factor and scalar field to
solve Wheeler-DeWitt equation, gives the tunnel effect of the cosmic scale
factor a and quantum potential well of scalar field, and makes it fit with the
physics of cosmic quantum birth. By solving Wheeler-DeWitt equation we achieve
a general probability distribution of the cosmic birth, and give the analysis
of cosmic quantum birth.Comment: 12 page

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