2,241 research outputs found
Strings after D-term inflation: evolution and properties of chiral cosmic strings
We motivate the study of chiral cosmic strings through a scenario of
structure formation which mixes D-term inflation and strings. We then discuss
some properties of chiral cosmic strings, and results regarding their evolution
and possible cosmological consequences are presented.Comment: 4 pages, 2 figures. To appear in the proceedings of the CAPP2000
conference held at Verbier, Switzerland between july 17th and 28th, 200
Translation invariant time-dependent solutions to massive gravity
Homogeneous time-dependent solutions of massive gravity generalise the plane
wave solutions of the linearised Fierz-Pauli equations for a massive spin-two
particle, as well as the Kasner solutions of General Relativity. We show that
they also allow a clear counting of the degrees of freedom and represent a
simplified framework to work out the constraints, the equations of motion and
the initial value formulation. We work in the vielbein formulation of massive
gravity, find the phase space resulting from the constraints and show that
several disconnected sectors of solutions exist some of which are unstable. The
initial values determine the sector to which a solution belongs. Classically,
the theory is not pathological but quantum mechanically the theory may suffer
from instabilities. The latter are not due to an extra ghost-like degree of
freedom.Comment: 31 page
Translation invariant time-dependent solutions to massive gravity II
This paper is a sequel to arXiv:1310.6560 [hep-th] and is also devoted to
translation-invariant solutions of ghost-free massive gravity in its moving
frame formulation. Here we consider a mass term which is linear in the vielbein
(corresponding to a term in the 4D metric formulation) in addition to
the cosmological constant. We determine explicitly the constraints, and from
the initial value formulation show that the time-dependent solutions can have
singularities at a finite time. Although the constraints give, as in the
case, the correct number of degrees of freedom for a massive spin two
field, we show that the lapse function can change sign at a finite time causing
a singular time evolution. This is very different to the case where
time evolution is always well defined. We conclude that the mass term
can be pathological and should be treated with care.Comment: 19 pages, 1 figur
On Tachyon kinks from the DBI action
We consider solitonic solutions of the DBI tachyon effective action for a
non-BPS brane in the presence of an electric field. We find that for a constant
electric field , regular solitons compactified on a circle admit
a singular and decompactified limit corresponding to Sen's proposal provided
the tachyon potential satisfies some restrictions. On the other hand for the
critical electric field , regular and finite energy solitons are
constructed without any restriction on the potential.Comment: proceedings of the second string phenomenology conference, Durham,
30th July to 4th August 200
Gravitational wave signatures from kink proliferation on cosmic (super-) strings
Junctions on cosmic string loops give rise to the proliferation of sharp
kinks. We study the effect of this proliferation on the gravitational wave (GW)
signals emitted from string networks with junctions, assuming a scaling
solution. We calculate the rate of occurrence and the distribution in amplitude
of the GW bursts emitted at cusps and kinks in the frequency bands of LIGO and
LISA as a function of the string tension, the number of sharp kinks on loops
with junctions and the fraction of loops in the cosmological network which have
junctions. Combining our results with current observational constraints, we
find that pulsar data rule out a significant number of kinks on loops for
strings with tensions G\mu > 10^{-12}. By contrast, for smaller tensions
current observations allow for a large number of kinks on loops. If this is the
case, the incoherent superposition of small bursts emitted at kink-kink
encounters leads to an enhanced GW background that hides the strong individual
bursts from kinks and cusps.Comment: 32 pages, 13 figure
On Normal ordering and Canonical transformations in Thermal Field Theory
We look at a real scalar field in thermal equilibrium in the context of the
new normal ordering and field split defined by Evans and Steer. We show that
the field split defines a natural canonical transformation, but that this
transformation differs from others known in thermal field theory.Comment: 13 pages, LaTeX. (Revisions made to discussion and various small
errors in equations corrected
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