6 research outputs found
Reconnection of Non-Abelian Cosmic Strings
Cosmic strings in non-abelian gauge theories naturally gain a spectrum of
massless, or light, excitations arising from their embedding in color and
flavor space. This opens up the possibility that colliding strings miss each
other in the internal space, reducing the probability of reconnection. We study
the topology of the non-abelian vortex moduli space to determine the outcome of
string collision. Surprisingly we find that the probability of classical
reconnection in this system remains unity, with strings passing through each
other only for finely tuned initial conditions. We proceed to show how this
conclusion can be changed by symmetry breaking effects, or by quantum effects
associated to fermionic zero modes, and present examples where the probability
of reconnection in a U(N) gauge theory ranges from 1/N for low-energy
collisions to one at higher energies.Comment: 25 Pages, 3 Figures. v2: comment added, reference adde
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
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
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