| dc.description.abstract | In this thesis we investigate astrophysical phenomena which arise in models with compact
extra dimensions, focussing on the cosmological consequences of strings which wrap cycles
in the internal space. Embedding our strings in the Klebanov-Strassler geometry we develop
a concrete model of cosmic necklaces and investigate the formation of primordial black holes
and dark matter relics from necklace collapse. Using data from the EGRET cosmic ray experiment,
we place bounds on the parameters which de ne the warped deformed conifold,
including the value of the warp factor and the radius of the compact space. Chapter 1
provides a brief overview, while background material is included in chapter 2, and these
results are presented in chapter 3.
In chapter 4 we analyse the dynamics of wound strings with angular momentum in the
compact dimensions and determine the equation of motion for a self-oscillating loop. Finally,
in chapter 5 we suggest a eld-theoretic dual for wound-string necklaces based on a
modi cation of the standard Abelian-Higgs model. After introducing spatially-dependent
couplings for the scalar and vector elds, we propose a static, non-cylindrically symmetric
solution of the resulting eld equations which describes a \pinched" string with neighbouring
vortex and anti-vortex regions. The similarities between pinched strings and the
four-dimensional appearance of wound-string states are then examined and a correspondence
between eld theory and string theory parameters is suggested.
We nd that the topological winding number of the eld theory vortex may be expressed in
terms of parameters which de ne the winding of the dual string around the compact space.
According to this relation, the topological charge is equal to unity when the string has zero
windings, and the standard Nielsen-Olesen duality is recovered in this limit. One key result
of this work is an estimate of the Higgs boson mass (at critical coupling) in terms of the
parameters which de ne the Klebanov-Strassler geometry and which, in principle, may be
constrained by cosmological observations. | en_US |
