6,908 research outputs found
Aspects of brane-antibrane inflation
I describe a dynamical mechanism for solving the fine-tuning problem of
brane-antibrane inflation. By inflating with stacks of branes and antibranes,
the branes can naturally be trapped at a metastable minimum of the potential.
As branes tunnel out of this minimum, the shape of the potential changes to
make the minimum shallower. Eventually the minimum disappears and the remaining
branes roll slowly because the potential is nearly flat. I show that even with
a small number of branes, there is a good chance of getting enough inflation.
Running of the spectral index is correlated with the tilt in such a way as to
provide a test of the model by future CMB experiments.Comment: 6 pages, 5 figures; proceedings of Theory Canada 1 conference, 2-5
June 2005, UBC, Vancouve
Leptogenesis with Left-Right domain walls
The presence of domain walls separating regions of unbroken and
is shown to provide necessary conditions for leptogenesis which
converts later to the observed Baryon aymmetry. The strength of lepton number
violation is related to the majorana neutrino mass and hence related to current
bounds on light neutrino masses. Thus the observed neutrino masses and the
Baryon asymmetry can be used to constrain the scale of Left-Right symmetry
breaking.Comment: References added, To appear in Praman
Radion Induced Spontaneous Baryogenesis
We describe a possible scenario for the baryogenesis arising when matter is
added on the branes of a Randall-Sundrum model with a radion stabilizing
potential. We show that the radion field can naturally induce spontaneous
baryogenesis when the cosmological evolution for the matter on the branes is
taken into account.Comment: LaTeX 2e, 8 pages and no figures, minor corrections to match version
to appear in MPL
Testing for Features in the Primordial Power Spectrum
Well-known causality arguments show that events occurring during or at the
end of inflation, associated with reheating or preheating, could contribute a
blue component to the spectrum of primordial curvature perturbations, with the
dependence k^3. We explore the possibility that they could be observably large
in CMB, LSS, and Lyman-alpha data. We find that a k^3 component with a cutoff
at some maximum k can modestly improve the fits (Delta chi^2=2.0, 5.4) of the
low multipoles (l ~ 10 - 50) or the second peak (l ~ 540) of the CMB angular
spectrum when the three-year WMAP data are used. Moreover, the results from
WMAP are consistent with the CBI, ACBAR, 2dFGRS, and SDSS data when they are
included in the analysis. Including the SDSS galaxy clustering power spectrum,
we find weak positive evidence for the k^3 component at the level of Delta chi'
= 2.4, with the caveat that the nonlinear evolution of the power spectrum may
not be properly treated in the presence of the k^3 distortion. To investigate
the high-k regime, we use the Lyman-alpha forest data (LUQAS, Croft et al., and
SDSS Lyman-alpha); here we find evidence at the level Delta chi^2' = 3.8.
Considering that there are two additional free parameters in the model, the
above results do not give a strong evidence for features; however, they show
that surprisingly large bumps are not ruled out. We give constraints on the
ratio between the k^3 component and the nearly scale-invariant component, r_3 <
1.5, over the range of wave numbers 0.0023/Mpc < k < 8.2/Mpc. We also discuss
theoretical models which could lead to the k^3 effect, including ordinary
hybrid inflation and double D-term inflation models. We show that the
well-motivated k^3 component is also a good representative of the generic
spikelike feature in the primordial perturbation power spectrum.Comment: 23 pages, 6 figures; added new section on theoretical motivation for
k^3 term, and discussion of double D-term hybrid inflation models; title
changed, added a new section discussing the generic spikelike features,
published in IJMP
On the origin of bimodal duration distribution of Gamma Ray Bursts
The modified version of a bullet model for gamma ray bursts is studied. The
central engine of the source produces multiple sub-jets that are contained
within a cone. The emission of photons in the source frame of a sub-jet either
takes part in an infinitesimally thin shell, or during its expansion for a
finite time. The analysis of the observed profiles of GRBs taken by BATSE leads
us to the conclusion that the latter possibility is much more favored. We also
study the statistical distribution of GRBs, in the context of their bimodality
of durations, taking into account the detector's capability of observing the
signal above a certain flux limit. The model with shells emitting for a finite
time is able to reproduce only one class of bursts, short or long, depending on
the adopted physical parameters. Therefore we suggest that the GRB bimodality
is intrinsically connected with two separate classes of sources.Comment: 12 pages, 12 figures; accepted by MNRAS. Small changes to match the
corre cted proof
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