10 research outputs found
Brane Inflation
We present a novel inflationary scenario in theories with low scale (TeV)
quantum gravity, in which the standard model particles are localized on the
branes whereas gravity propagates in the bulk of large extra dimensions. This
inflationary scenario is natural in the brane world picture. In the lowest
energy state, a number of branes sit on top of each other (or at an orientifold
plane), so the vacuum energy cancels out. In the cosmological setting, some of
the branes "start out" relatively displaced in the extra dimensions and the
resulting vacuum energy triggers the exponential growth of the 3 non-compact
dimensions. The number of e-foldings can be very large due to the very weak
brane-brane interaction at large distances. In the effective four-dimensional
field theory, the brane motion is described by a slowly rolling scalar field
with an extremely flat plateau potential. When branes approach each other to a
critical distance, the potential becomes steep and inflation ends rapidly. Then
the branes "collide" and oscillate about the equilibrium point, releasing
energy mostly into radiation on the branes.Comment: 15 pages, Late
Collider Signatures from the Brane World
We discuss some collider signatures of the brane world. In addition to the
usual bulk (closed string) fields and brane (open string) fields in the Type I
string picture, there are closed string fields, namely, twisted modes, which
are not confined on the branes but nonetheless are localized in the extra
compactified dimensions. While the coupling of the Standard Model (brane)
fields with a bulk mode (such as the graviton) is suppressed by powers of the
Planck mass, their coupling to a twisted mode is suppressed only by powers of
the string scale M_s, which can be as low as a few TeV. This means these
localized twisted fields can have important observable effects in the TeV
range, including resonances in dijet invariant mass distributions in \bar p p,
pp \to jets + X. Given the current lower bound on the fundamental
higher-dimensional Planck scale, the experimental effects of these twisted
fields may turn out to be larger than the effects of virtual and real KK
gravity modes. The collider signatures of anomalous U(1) gauge symmetries as
well as other phenomenological implications of the brane world are also
discussed.Comment: Published version (paper shortened to satisfy the requirements of
Phys. Lett. B; see version 1 for original-length paper
Brane World Models With Bulk Scalar Fields
We examine several different types of five dimensional stationary spacetimes
with bulk scalar fields and parallel 3-branes. We study different methods for
avoiding the appearance of spacetime singularities in the bulk for models with
and without cosmological expansion. For non-expanding models, we demonstrate
that in general the Randall-Sundrum warp factor is recovered in the asymptotic
bulk region, although elsewhere the warping may be steeper than exponential. We
show that nonsingular expanding models can be constructed as long as the
gradient of the bulk scalar field vanishes at zeros of the warp factor, which
are then analogous to the particle horizons found in expanding models with a
pure AdS bulk. Since the branes in these models are stabilized by bulk scalar
fields, we expect there to be no linearly unstable radion modes. As an
application, we find a specific class of expanding, stationary solutions with
no singularities in the bulk in which the four dimensional cosmological
constant and mass hierarchy are naturally very small.Comment: 16 page
Particle Horizon and Warped Phenomenology
Giant resonances of gravity Kaluza-Klein modes (with tensor couplings) in
high energy collisions are expected in the Randall-Sundrum orbifold model that
incorporates a plausible solution to the hierarchy problem. When the model is
extended to incorporate an exponentially small 4-D cosmological constant, the
KK spectrum becomes continuous, even in the compactified case. This is due to
the presence of a particle horizon, which provides a way to evade Weinberg's
argument of the need of fine-tuning to get a very small cosmological constant.Comment: 10 pages, 1 figure, REVTE
Probe Brane Dynamics and the Cosmological Constant
Recently a brane world perspective on the cosmological constant and the
hierarchy problems was presented. Here, we elaborate on some aspects of that
particular scenario and discuss the stability of the stationary brane solution
and the dynamics of a probe brane. Even though the brane is unstable under a
small perturbation from its stationary position, such instability is harmless
when the 4-D cosmological constant is very small, as is the case of our
universe. One may also introduce radion stabilizing potentials in a more
realistic scenario.Comment: 13 pages, 1 figure, REVTE
Closer towards inflation in string theory
In brane inflation, the relative brane position in the bulk of a brane world
is the inflaton. For branes moving in a compact manifold, the approximate
translational (or shift) symmetry is necessary to suppress the inflaton mass,
which then allows a slow-roll phase for enough inflation. Following recent
works, we discuss how inflation may be achieved in superstring theory. Imposing
the shift symmetry, we obtain the condition on the superpotential needed for
inflation and suggest how this condition may be naturally satisfied.Comment: 12 pages, 1 figure. Two references and few comments adde
Inter-Brane Potential and the Decay of a non-BPS-D-brane to Closed Strings
We calculate the potential for Dp-\Dbar p pair and show that the coincident
Dp-\Dbar p system has tachyonic modes, with of them due to
radiative corrections. We propose that the decay width of an unstable
non-BPS--brane to closed strings is given by the imaginary part of the
one-loop contribution to the effective potential of the open string tachyon
mode.Comment: 16 Pages, 3 Figure
Construction of the K=8 Fractional Superconformal Algebras
We construct the K=8 fractional superconformal algebras. There are two such
extended Virasoro algebras, one of which was constructed earlier, involving a
fractional spin (equivalently, conformal dimension) 6/5 current. The new
algebra involves two additional fractional spin currents with spin 13/5. Both
algebras are non-local and satisfy non-abelian braiding relations. The
construction of the algebras uses the isomorphism between the Z_8 parafermion
theory and the tensor product of two tricritical Ising models. For the special
value of the central charge c=52/55, corresponding to the eighth member of the
unitary minimal series, the 13/5 currents of the new algebra decouple, while
two spin 23/5 currents (level-2 current algebra descendants of the 13/5
currents) emerge. In addition, it is shown that the K=8 algebra involving the
spin 13/5 currents at central charge c=12/5 is the appropriate algebra for the
construction of the K=8 (four-dimensional) fractional superstring.Comment: 53 pages (or 82/2 = 41 pages in reduced format
The Production, Spectrum and Evolution of Cosmic Strings in Brane Inflation
Brane inflation in superstring theory predicts that cosmic strings (but not
domain walls or monopoles) are produced towards the end of the inflationary
epoch. Here, we discuss the production, the spectrum and the evolution of such
cosmic strings, properties that differentiate them from those coming from an
abelian Higgs model. As D-branes in extra dimensions, some type of cosmic
strings will dissolve rapidly in spacetime, while the stable ones appear with a
spectrum of cosmic string tensions. Moreover, the presence of the extra
dimensions reduces the interaction rate of the cosmic strings in some
scenarios, resulting in an order of magnitude enhancement of the number/energy
density of the cosmic string network when compared to the field theory case.Comment: 7 pages, revtex
Brane Interaction as the Origin of Inflation
We reanalyze brane inflation with brane-brane interactions at an angle, which
include the special case of brane-anti-brane interaction. If nature is
described by a stringy realization of the brane world scenario today (with
arbitrary compactification), and if some additional branes were present in the
early universe, we find that an inflationary epoch is generically quite
natural, ending with a big bang when the last branes collide. In an interesting
brane inflationary scenario suggested by generic string model-building, we use
the density perturbation observed in the cosmic microwave background and the
coupling unification to find that the string scale is comparable to the GUT
scale.Comment: 28 pages, 8 figures, 2 tables, JHEP forma