15 research outputs found
Effects of a Thermal Bath of Photons on Embedded String Stability
We compute the corrections of thermal photons on the effective potential for
the linear sigma model of QCD. Since we are interested in temperatures lower
than the confinement temperature, we consider the scalar fields to be out of
equilibrium. Two of the scalar field are uncharged while the other two are
charged under the U(1) gauge symmetry of electromagnetism. We find that the
induced thermal terms in the effective potential can stabilize the embedded
pion string, a string configuration which is unstable in the vacuum. Our
results are applicable in a more general context and demonstrate that embedded
string configurations arising in a wider class of field theories can be
stabilized by thermal effects. Another well-known example of an embedded string
which can be stabilized by thermal effects is the electroweak Z-string. We
discuss the general criteria for thermal stabilization of embedded defects.Comment: 6 pages, formatting changed, a few typos correcte
Lensing and CMB Anisotropies by Cosmic Strings at a Junction
The metric around straight arbitrarily-oriented cosmic strings forming a
stationary junction is obtained at the linearized level. It is shown that the
geometry is flat. The sum rules for lensing by this configuration and the
anisotropies of the CMB are obtained.Comment: 17 pages, 2 figure
Gravitational Radiation by Cosmic Strings in a Junction
The formalism for computing the gravitational power radiation from
excitations on cosmic strings forming a junction is presented and applied to
the simple case of co-planar strings at a junction when the excitations are
generated along one string leg. The effects of polarization of the excitations
and of the back-reaction of the gravitational radiation on the small scale
structure of the strings are studied.Comment: minor changes added, the published version in JCA
Unconventional Cosmology
I review two cosmological paradigms which are alternative to the current
inflationary scenario. The first alternative is the "matter bounce", a
non-singular bouncing cosmology with a matter-dominated phase of contraction.
The second is an "emergent" scenario, which can be implemented in the context
of "string gas cosmology". I will compare these scenarios with the inflationary
one and demonstrate that all three lead to an approximately scale-invariant
spectrum of cosmological perturbations.Comment: 45 pages, 10 figures; invited lectures at the 6th Aegean Summer
School "Quantum Gravity and Quantum Cosmology", Chora, Naxos, Greece, Sept.
12 - 17 2012, to be publ. in the proceedings; these lecture notes form an
updated version of arXiv:1003.1745 and arXiv:1103.227