4,577 research outputs found
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
Anomaly Cancelations in Orientifolds with Quantized B Flux
We consider anomaly cancelations in Type IIB orientifolds on T^4/Z_N with
quantized NS-NS sector background B-flux. For a rank b B-flux on T^4 (b is
always even) and when N is even, the cancelation requires a 2^{b/2}
multiplicity of states in the 59-open string sector. We identify the twisted
sector R-R scalars and tensor multiplets which are involved in the
Green-Schwarz mechanism. We give more details of the construction of these
models and argue that consistency with the 2^{b/2} multiplicity of 59-sector
states requires a modification of the relation between the open string 1-loop
channel modulus and the closed string tree channel modulus in the 59-cylinder
amplitudes.Comment: Revtex 3.0, 34 pages, 2 figures, references adde
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
Phenomenology of 3-Family Grand Unified String Models
In the 3-family grand unified string models constructed so far, there is only
one adjoint (and no higher dimensional representation) Higgs field in the grand
unified gauge group. In this preliminary analysis, we address the proton-decay
problem in the 3-family E_6 and related SO(10) string models. In particular, we
analyze the doublet-triplet splitting (within certain assumptions about
non-perturbative dynamics). It appears that generically some fine-tuning is
necessary to arrange for a pair of Higgs doublets to be light, while having
color Higgs triplets superheavy. We also discuss charge-2/3 quark mass matrix
that generically also seems to require some fine-tuning to have rank 1.Comment: 12 pages, Revtex 3.0. Minor corrections mad
Studies of new media radiation induced laser
Various lasants were investigated especially, 2-iodohepafluoropropane (i-C3F7I) for the direct solar pumped lasers. Optical pumping of iodine laser was achieved using a small flashlamp. Using i-C3F7I as a laser gain medium, threshold inversion density, small signal gain, and laser performance at the elevated temperature were measured. The experimental results and analysis are presented. The iodine laser kinetics of the C3F7I and IBr system were numerically simulated. The concept of a direct solar-pumped laser amplifier using (i-C3F7I) as the laser material was evaluated and several kinetic coefficients for i-C3F7I laser system were reexamined. The results are discussed
Observing the Geometry of Warped Compactification via Cosmic Inflation
Using DBI inflation as an example, we demonstrate that the detailed geometry
of warped compactification can leave an imprint on the cosmic microwave
background (CMB). We compute CMB observables for DBI inflation in a generic
class of warped throats and find that the results (such as the sign of the tilt
of the scalar perturbations and its running) depend sensitively on the precise
shape of the warp factor. In particular, we analyze the warped deformed
conifold and find that the results can differ from those of other warped
geometries, even when these geometries approximate well the exact metric of the
warped deformed conifold.Comment: 4 pages, 3 figures. v2: References and clarifications adde
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