119 research outputs found
Mirage Cosmology of U(1) Gauge Field on Unstable D3 Brane Universe
An unstable -brane universe governed by the DBI action of the tachyon
field minimally coupled to a U(1) gauge boson is examined. The cosmological
evolution of this coupled system, is further analyzed, in terms of the
expansion rate of the inflating brane, which is highly affected by the presence
of the tachyonic and gauge field charges. We show, that the minimal coupling
makes the effective brane density less divergent. However, for some sectors of
the theory the tachyon is not able to regulate it in an efficient fashion.
Also, a detailed analysis of the dependance of the effective brane density on
the scale factor of the universe is performed, which leads to various
cosmological models.Comment: ReVTeX format 20 pages; v2 1 figure added, one additional paragraph
with extra comments added, enlarged list of references, version to appear in
JHE
Cosmology of codimension-two braneworlds
We present a comprehensive study of the cosmological solutions of 6D
braneworld models with azimuthal symmetry in the extra dimensions, moduli
stabilization by flux or a bulk scalar field, and which contain at least one
3-brane that could be identified with our world. We emphasize an unusual
property of these models: their expansion rate depends on the 3-brane tension
either not at all, or in a nonstandard way, at odds with the naive expected
dimensional reduction of these systems to 4D general relativity at low
energies. Unlike other braneworld attempts to find a self-tuning solution to
the cosmological constant problem, the apparent failure of decoupling in these
models is not associated with the presence of unstabilized moduli; rather it is
due to automatic cancellation of the brane tension by the curvature induced by
the brane. This provides some corroboration for the hope that these models
provide a distinctive step toward understanding the smallness of the observed
cosmological constant. However, we point out some challenges for obtaining
realistic cosmology within this framework.Comment: 30 pages, 4 figures; generalized result for nonconventional Friedmann
equation, added referenc
The Baryon asymmetry in the Standard Model with a low cut-off
We study the generation of the baryon asymmetry in a variant of the standard
model, where the Higgs field is stabilized by a dimension-six interaction.
Analyzing the one-loop potential, we find a strong first order electroweak
phase transition for Higgs masses up to at least 170 GeV. Dimension-six
operators induce also new sources of CP violation. We compute the baryon
asymmetry in the WKB approximation. Novel source terms in the transport
equations enhance the generated baryon asymmetry. For a wide range of
parameters the model predicts a baryon asymmetry close to the observed value.Comment: 22 pages, latex, 6 figure
Electroweak Phase Transitions in left-right symmetric models
We study the finite-temperature effective potential of minimal left-right
symmetric models containing a bidoublet and two triplets in the scalar sector.
We perform a numerical analysis of the parameter space compatible with the
requirement that baryon asymmetry is not washed out by sphaleron processes
after the electroweak phase transition. We find that the spectrum of scalar
particles for these acceptable cases is consistent with present experimental
bounds.Comment: 20 pages, 5 figures (included), some comments added, typos corrected
and new references included. Final version to appear in PR
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
Finite Temperature Systems of Brane-Antibrane on a Torus
In order to study the thermodynamic properties of brane-antibrane systems in
the toroidal background, we compute the finite temperature effective potential
of tachyon T in this system on the basis of boundary string field theory. We
first consider the case that all the radii of the target space torus are about
the string scale. If the Dp-antiDp pair is extended in all the non-compact
directions, the sign of the coefficient of |T|^2 term of the potential changes
slightly below the Hagedorn temperature. This means that a phase transition
occurs near the Hagedorn temperature. On the other hand, if the Dp-antiDp pair
is not extended in all the non-compact directions, the coefficient is kept
negative, and thus a phase transition does not occur. Secondly, we consider the
case that some of the radii of the target space torus are much larger than the
string scale and investigate the behavior of the potential for each value of
the radii and the total energy. If the Dp-antiDp pair is extended in all the
non-compact directions, a phase transition occurs for large enough total
energy.Comment: 23 pages, 3 figures, minor errors corrected, version to appear in
JHE
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