10 research outputs found
Q-Ball Collisions in the MSSM
Collisions of non-topological solitons, Q-balls, are studied in the Minimal
Supersymmetric Standard Model in two different cases: where supersymmetry has
been broken by a gravitationally coupled hidden sector and by a gauge mediated
mechanism at a lower energy scale. Q-ball collisions are studied numerically on
a two dimensional lattice for a range of Q-ball charges. Total cross-sections
as well as cross-sections for fusion and charge exchange are calculated.Comment: 5 pages, 3 figures, to appear in the Proceedings of Strong and
Electroweak Matter (SEWM2000), Marseille, France, 14-17 June, 200
Spatial dynamics of homochiralization
The emergence and spreading of chirality on the early Earth is considered by
studying a set of reaction-diffusion equations based on a polymerization model.
It is found that effective mixing of the early oceans is necessary to reach the
present homochiral state. The possibility of introducing mass extinctions and
modifying the emergence rate of life is discussed.Comment: 8 pages, 5 figures, Int. J. Astrobiol. (in press
Fitting oscillating string gas cosmology to supernova data
In string gas cosmology, extra dimensions are stabilised by a gas of strings.
In the matter-dominated era, competition between matter pushing the extra
dimensions to expand and the string gas pulling them back can lead to
oscillations of the extra dimensions and acceleration in the visible
dimensions. We fit this model to supernova data, taking into account the Big
Bang Nucleosynthesis constraint on the energy density of the string gas. The
fit to the Union set of supernova data is acceptable, but the fit to the
ESSENCE data is poor.Comment: 17 pages, 4 figures. v2: published version. Important correction in
the calculation of distances, added reference
Non-Gaussianity from Preheating
We consider a two-field model for inflation where the second order metric
perturbations can be amplified by a parametric resonance during preheating. We
demonstrate that there can arise a considerable enhancement of non-Gaussianity
sourced by the local terms generated through the coupled perturbations. We
argue that the non-Gaussianity parameter could be as large as f_{NL} ~ 50. Our
results may provide a useful test of preheating in future CMB experiments.Comment: 4 pages ReVTeX4, discussion and references added, conclusions
unchange
Large scale structure in non-standard cosmologies
We study the growth of large scale structure in two recently proposed
non-standard cosmological models: the brane induced gravity model of Dvali,
Gabadadze and Porrati (DGP) and the Cardassian models of Freese and Lewis. A
general formalism for calculating the growth of fluctuations in models with a
non-standard Friedman equation and a normal continuity equation of energy
density is discussed. Both linear and non-linear growth are studied, together
with their observational signatures on higher order statistics and abundance of
collapsed objects. In general, models which show similar cosmic acceleration at
z ~ 1, can produce quite different normalization for large scale density
fluctuations, ie sigma_8, cluster abundance or higher order statistics, such as
the normalized skewness S_3, which is independent of the linear normalization.
For example, for a flat universe with Omega_M ~ 0.22, DGP and standard
Cardassian cosmologies predict about 2 and 3 times more clusters respectively
than the standard Lambda model at z=1.5. When normalized to CMB fluctuations
the sigma_8 amplitude turns out to be lower by a few tens of a percent. We also
find that, for a limited red-shift range, the linear growth rate can be faster
in some models (eg modified polytropic Cardassian with q>1) than in the
Einstein-deSitter universe. The value of the skewness S_3 is found to have up
to ~10 percent variations (up or down) from model to model.Comment: 18 pages, 12 figures, submitted to MNRA