45,159 research outputs found
Spacecraft active thermal control technology status
Four advanced space radiator concepts that were pursued in an integrated effort to develop multi-mission-use and low cost heat rejection systems which can overcome the limitations of current radiator systems are briefly discussed and described. Also, in order to establish a firm background to compare the advanced space radiator concepts, the Orbiter active thermal control system is also briefly described
Inflation induced by Gravitino Condensation in Supergravity
We discuss the emergence of an inflationary phase in supergravity with the
super-Higgs effect due to dynamical spontaneous breaking of supersymmetry, in
which the role of the inflaton is played by the gravitino condensate. Realistic
models compatible with the Planck satellite CMB data are found in conformal
supergravity scenarios with dynamical gravitino masses that are small compared
to the Planck mass, as could be induced by a non-trivial vacuum expectation
value of the dilaton superfield of appropriate magnitude.Comment: 13 pages, Revtex, 11 pdf figures, references added on role of
gravitino torsion condensates in parallelising space-time manifolds,
hierarchy of scales involved made explicit, no effects on conclusions.
Version to appear in Physical Review
High-Energy QCD as a Topological Field Theory
We propose an identification of the conformal field theory underlying
Lipatov's spin-chain model of high-energy scattering in perturbative QCD. It is
a twisted N=2 supersymmetric topological field theory, which arises as the
limiting case of the SL(2,R)/U(1) non-linear sigma model that also plays a role
in describing the Quantum Hall effect and black holes in string theory. The
doubly-infinite set of non-trivial integrals of motion of the high-energy
spin-chain model displayed by Faddeev and Korchemsky are identified as the
Cartan subalgebra of a W_{\infty} \otimes W_{\infty} bosonic sub-symmetry
possessed by this topological theory. The renormalization group and an analysis
of instanton perturbations yield some understanding why this particular
topological spin-chain model emerges in the high-energy limit, and provide a
new estimate of the asymptotic behaviour of multi-Reggeized-gluon exchange.Comment: 24 pages LATEX, one eps figure incorporate
Hadron Spectroscopy (theory): Diquarks, Tetraquarks, Pentaquarks and no quarks
States beyond those expected in the simple constituent quark model are now
emerging. I focus on the scalar glueball and its mixing with states in the
nonet, and also on correlations in Strong QCD that may form diquarks
and seed states. Some models of the pentaquark candidate
are critically discussed.Comment: Plenary talk at ICHEP0
Quantum Decoherence in a D-Foam Background
Within the general framework of Liouville string theory, we construct a model
for quantum D-brane fluctuations in the space-time background through which
light closed-string states propagate. The model is based on monopole and vortex
defects on the world sheet, which have been discussed previously in a treatment
of 1+1-dimensional black-hole fluctuations in the space-time background, and
makes use of a T-duality transformation to relate formulations with Neumann and
Dirichlet boundary conditions. In accordance with previous general arguments,
we derive an open quantum-mechanical description of this D-brane foam which
embodies momentum and energy conservation and small mean energy fluctuations.
Quantum decoherence effects appear at a rate consistent with previous
estimates.Comment: 16 pages, Latex, two eps figures include
A supersymmetric D-brane Model of Space-Time Foam
We present a supersymmetric model of space-time foam with two stacks of eight
D8-branes with equal string tensions, separated by a single bulk dimension
containing D0-brane particles that represent quantum fluctuations in the
space-time foam. The ground state configuration with static D-branes has zero
vacuum energy. However, gravitons and other closed-string states propagating
through the bulk may interact with the D0-particles, causing them to recoil and
the vacuum energy to become non zero. This provides a possible origin of dark
energy. Recoil also distorts the background metric felt by energetic massless
string states, which travel at less than the usual (low-energy) velocity of
light. On the other hand, the propagation of chiral matter anchored on the D8
branes is not affected by such space-time foam effects.Comment: 33 pages, latex, five figure
Prospects for Discovering Supersymmetry at the LHC
Supersymmetry is one of the best-motivated candidates for physics beyond the
Standard Model that might be discovered at the LHC. There are many reasons to
expect that it may appear at the TeV scale, in particular because it provides a
natural cold dark matter candidate. The apparent discrepancy between the
experimental measurement of g_mu - 2 and the Standard model value calculated
using low-energy e+ e- data favours relatively light sparticles accessible to
the LHC. A global likelihood analysis including this, other electroweak
precision observables and B-decay observables suggests that the LHC might be
able to discover supersymmetry with 1/fb or less of integrated luminosity. The
LHC should be able to discover supersymmetry via the classic missing-energy
signature, or in alternative phenomenological scenarios. The prospects for
discovering supersymmetry at the LHC look very good.Comment: 8 pages, 11 figure
Gradient Flow in Logarithmic Conformal Field Theory
We establish conditions under which the worldsheet beta-functions of
logarithmic conformal field theories can be derived as the gradient of some
scalar function on the moduli space of running coupling constants. We derive a
renormalization group invariant version of this function and relate it to the
usual Zamolodchikov C-function expressed in terms of correlation functions of
the worldsheet energy-momentum tensor. The results are applied to the example
of D-brane recoil in string theory.Comment: 12 pages LaTeX; references updated, one added; to be published in
Physics Letters
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