56 research outputs found
Chiral bosonization as duality
We demonstrate that the technique of abelian bosonization through duality transformations can be extended to gauging anomalous symmetries. The example of a Dirac fermion theory is first illustrated. This idea is then also applied to bosonize a chiral fermion by gauging its chiral phase symmetry
Tachyonic fields in cosmology
The possibility of explanation of accelerated expansion of the Universe by
tachyonic scalar fields which homogeneously fill the world is discussed. The
dependences of potential and kinetic term on scale factor are deduced for the
case of quintessential and phantom dark energy with generalized linear
barotropic equation of state. The possibility to distinguish the tachyonic
scalar field as dark energy from other scalar field models, especially from
classical scalar field, is analyzed.Comment: 12 pages (v1,v2 in Ukrainian, v3 in English), 4 figures; accepted for
publication in Collected Physical Papers of Shevchenko Scientific Societ
Cosmology of the Tachyon in Brane Inflation
In certain implementations of the brane inflationary paradigm, the exit from
inflation occurs when the branes annihilate through tachyon condensation. We
investigate various cosmological effects produced by this tachyonic era. We
find that only a very small region of the parameter space (corresponding to
slow-roll with tiny inflaton mass) allows for the tachyon to contribute some
e-folds to inflation. In addition, non-adiabatic density perturbations are
generated at the end of inflation. When the brane is moving relativistically
this contribution can be of the same order as fluctuations produced 55 e-folds
before the end of inflation. The additional contribution is very nearly
scale-invariant and enhances the tensor/scalar ratio. Additional
non-gaussianities will also be generated, sharpening current constraints on
DBI-type models which already predict a significantly non-gaussian signal.Comment: 30 pages, 2 figures; v3, minor revision, JCAP versio
Generating Erler-Schnabl-type Solution for Tachyon Vacuum in Cubic Superstring Field Theory
We study a new set of identity-based solutions to analyze the problem of
tachyon condensation in open bosonic string field theory and cubic superstring
field theory. Even though these identity-based solutions seem to be trivial, it
turns out that after performing a suitable gauge transformation, we are left
with the known Erler-Schnabl-type solutions which correctly reproduce the value
of the D-brane tension. This result shows explicitly that how a seemingly
trivial solution can generate a non-trivial configuration which precisely
represents to the tachyon vacuum.Comment: 22 pages, references added, appendix added, 2 subsections adde
On the evolution of tachyonic perturbations at super-Hubble scales
In the slow-roll inflationary scenario, the amplitude of the curvature
perturbations approaches a constant value soon after the modes leave the Hubble
radius. However, relatively recently, it was shown that the amplitude of the
curvature perturbations induced by the canonical scalar field can grow at
super-Hubble scales if there is either a transition to fast roll inflation or
if inflation is interrupted for some period of time. In this work, we extend
the earlier analysis to the case of a non-canonical scalar field described by
the Dirac-Born-Infeld action. With the help of a specific example, we show that
the amplitude of the tachyonic perturbations can be enhanced or suppressed at
super-Hubble scales if there is a transition from slow roll to fast roll
inflation. We also illustrate as to how the growth of the entropy perturbations
during the fast roll regime proves to be responsible for the change in the
amplitude of the curvature perturbations at super-Hubble scales. Furthermore,
following the earlier analysis for the canonical scalar field, we show that the
power spectrum evaluated in the long wavelength approximation matches the exact
power spectrum obtained numerically very well. Finally, we briefly comment on
an application of this phenomenon.Comment: v1: 15 pages, 4 figures; v2: 16 pages, 5 figures, power spectrum
included, discussion in section 5 enlarged, references added; v3: 17 pages, 5
figures, enhancement AS WELL AS suppression of modes at super-Hubble scales
pointed out, title changed, discussions enlarged, references added, to appear
in JCA
Non-extremal Black Holes, Harmonic Functions, and Attractor Equations
We present a method which allows to deform extremal black hole solutions into
non-extremal solutions, for a large class of supersymmetric and
non-supersymmetric Einstein-Vector-Scalar type theories. The deformation is
shown to be largely independent of the details of the matter sector. While the
line element is dressed with an additional harmonic function, the attractor
equations for the scalars remain unmodified in suitable coordinates, and the
values of the scalar fields on the outer and inner horizon are obtained from
their fixed point values by making specific substitutions for the charges. For
a subclass of models, which includes the five-dimensional STU-model, we find
explicit solutions.Comment: 33 page
Coupled dark energy: Towards a general description of the dynamics
In dark energy models of scalar-field coupled to a barotropic perfect fluid,
the existence of cosmological scaling solutions restricts the Lagrangian of the
field \vp to p=X g(Xe^{\lambda \vp}), where X=-g^{\mu\nu} \partial_\mu \vp
\partial_\nu \vp /2, is a constant and is an arbitrary function.
We derive general evolution equations in an autonomous form for this Lagrangian
and investigate the stability of fixed points for several different dark energy
models--(i) ordinary (phantom) field, (ii) dilatonic ghost condensate, and
(iii) (phantom) tachyon. We find the existence of scalar-field dominant fixed
points (\Omega_\vp=1) with an accelerated expansion in all models
irrespective of the presence of the coupling between dark energy and dark
matter. These fixed points are always classically stable for a phantom field,
implying that the universe is eventually dominated by the energy density of a
scalar field if phantom is responsible for dark energy. When the equation of
state w_\vp for the field \vp is larger than -1, we find that scaling
solutions are stable if the scalar-field dominant solution is unstable, and
vice versa. Therefore in this case the final attractor is either a scaling
solution with constant \Omega_\vp satisfying 0<\Omega_\vp<1 or a
scalar-field dominant solution with \Omega_\vp=1.Comment: 21 pages, 5 figures; minor clarifications added, typos corrected and
references updated; final version to appear in JCA
A Quintessentially Geometric Model
We consider string inspired cosmology on a solitary -brane moving in the
background of a ring of branes located on a circle of radius . The motion of
the -brane transverse to the plane of the ring gives rise to a radion field
which can be mapped to a massive non-BPS Born-Infeld type field with a cosh
potential. For certain bounds of the brane tension we find an inflationary
phase is possible, with the string scale relatively close to the Planck scale.
The relevant perturbations and spectral indices are all well within the
expected observational bounds. The evolution of the universe eventually comes
to be dominated by dark energy, which we show is a late time attractor of the
model. However we also find that the equation of state is time dependent, and
will lead to late time Quintessence.Comment: 11 pages, 3 figures. References and comments adde
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