7 research outputs found
Observational constraints on cosmic strings: Bayesian analysis in a three dimensional parameter space
Current data exclude cosmic strings as the primary source of primordial
density fluctuations. However, in a wide class of inflationary models, strings
can form at later stages of inflation and have potentially detectable
observational signatures. We study the constraints from WMAP and SDSS data on
the fraction of primordial fluctuations sourced by local cosmic strings. The
Bayesian analysis presented in this brief report is restricted to the minimal
number of parameters. Yet it is useful for two reasons. It confirms the results
of Pogosian et al (2003) using an alternative statistical method. Secondly, it
justifies the more costly multi-parameter analysis. Already, varying only three
parameters -- the spectral index and the amplitudes of the adiabatic and string
contributions -- we find that the upper bound on the cosmic string contribution
is of order 10%. We expect that the full multi-parameter study, currently
underway, will likely loosen this bound.Comment: v3: 4 pages, 5 figures, slight modifications to match published
versio
Brane Inflation and Cosmic String Tension in Superstring Theory
In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll
condition in the D3-anti-D3-brane inflationary scenario in superstring theory
requires no more than a moderate tuning. The cosmic string tension is very
sensitive to the conformal coupling: with less fine-tuning, the cosmic string
tension (as well as the ratio of tensor to scalar perturbation mode) increases
rapidly and can easily saturate the present observational bound. In a
multi-throat brane inflationary scenario, this feature substantially improves
the chance of detecting and measuring the properties of the cosmic strings as a
window to the superstring theory and our pre-inflationary universe.Comment: Combined bounds from WMAP and SDSS Lyman alpha experiments are added
for analysis, changes are added to the tabl
Textures and Semi-Local Strings in SUSY Hybrid Inflation
Global topological defects may account for the large cold spot observed in
the Cosmic Microwave Background. We explore possibilities of constructing
models of supersymmetric F-term hybrid inflation, where the waterfall fields
are globally SU(2)-symmetric. In contrast to the case where SU(2) is gauged,
there arise Goldstone bosons and additional moduli, which are lifted only by
masses of soft-supersymmetry breaking scale. The model predicts the existence
of global textures, which can become semi-local strings if the waterfall fields
are gauged under U(1)_X. Gravitino overproduction can be avoided if reheating
proceeds via the light SU(2)-modes or right-handed sneutrinos. For values of
the inflaton- waterfall coupling >=10^-4, the symmetry breaking scale imposed
by normalisation of the power spectrum generated from inflation coincides with
the energy scale required to explain the most prominent of the cold spots. In
this case, the spectrum of density fluctuations is close to scale-invariant
which can be reconciled with measurements of the power spectrum by the
inclusion of the sub-dominant component due to the topological defects.Comment: 29 page
Magnetogenesis from Cosmic String Loops
Large-scale coherent magnetic fields are observed in galaxies and clusters,
but their ultimate origin remains a mystery. We reconsider the prospects for
primordial magnetogenesis by a cosmic string network. We show that the magnetic
flux produced by long strings has been overestimated in the past, and give
improved estimates. We also compute the fields created by the loop population,
and find that it gives the dominant contribution to the total magnetic field
strength on present-day galactic scales. We present numerical results obtained
by evolving semi-analytic models of string networks (including both one-scale
and velocity-dependent one-scale models) in a Lambda-CDM cosmology, including
the forces and torques on loops from Hubble redshifting, dynamical friction,
and gravitational wave emission. Our predictions include the magnetic field
strength as a function of correlation length, as well as the volume covered by
magnetic fields. We conclude that string networks could account for magnetic
fields on galactic scales, but only if coupled with an efficient dynamo
amplification mechanism.Comment: 10 figures; v3: small typos corrected to match published version.
MagnetiCS, the code described in paper, is available at
http://markcwyman.com/ and
http://www.damtp.cam.ac.uk/user/dhw22/code/index.htm
A Note on Noncommutative Brane Inflation
In this paper, we investigate the noncommutative KKLMMT D3/anti-D3 brane
inflation scenario in detail. Incorporation of the brane inflation scenario and
the noncommutative inflation scenario can nicely explain the large negative
running of the spectral index as indicated by WMAP three-year data and can
significantly release the fine-tuning for the parameter . Using the WMAP
three year results (blue-tilted spectral index with large negative running), we
explore the parameter space and give the constraints and predictions for the
inflationary parameters and cosmological observables in this scenario. We show
that this scenario predicts a quite large tensor/scalar ratio and what is more,
a too large cosmic string tension (assuming that the string coupling is
in its likely range from 0.1 to 1) to be compatible with the present
observational bound. A more detailed analysis reveals that this model has some
inconsistencies according to the fit to WMAP three year results.Comment: 20 pages, 5 figures; accepted for publication in JCA
Supersymmetric inflation and baryogenesis via Extra-Flat directions of the MSSM.
One interpretation of proton stability is that it implies the existence of extra-flat directions of the minimal supersymmetric standard model, in particular ucucdcec and QQQL, where the operators lifting the potential are suppressed by a mass scale Λ which is much larger than the Planck mass, . Using D-term hybrid inflation as an example, we show that such flat directions can serve as the inflaton in supersymmetric inflation models. The resulting model is a minimal version of D-term inflation which requires the smallest number of additional fields. In the case where Q-balls form from the extra-flat direction condensate after inflation, successful Affleck–Dine baryogenesis is possible if the suppression mass scale is . In this case the reheating temperature from Q-ball decay is in the range 3–100 GeV, while observable baryon isocurvature perturbations and non-thermal dark matter are possible. In the case of extra-flat directions with a large t squark component, there is no Q-ball formation and reheating is via conventional condensate decay. In this case the reheating temperature is in the range 1–100 TeV, naturally evading thermal gravitino overproduction while allowing sphaleron erasure of any large B–L asymmetry