21,792 research outputs found
Asymmetric binary covering codes
An asymmetric binary covering code of length n and radius R is a subset C of
the n-cube Q_n such that every vector x in Q_n can be obtained from some vector
c in C by changing at most R 1's of c to 0's, where R is as small as possible.
K^+(n,R) is defined as the smallest size of such a code. We show K^+(n,R) is of
order 2^n/n^R for constant R, using an asymmetric sphere-covering bound and
probabilistic methods. We show K^+(n,n-R')=R'+1 for constant coradius R' iff
n>=R'(R'+1)/2. These two results are extended to near-constant R and R',
respectively. Various bounds on K^+ are given in terms of the total number of
0's or 1's in a minimal code. The dimension of a minimal asymmetric linear
binary code ([n,R]^+ code) is determined to be min(0,n-R). We conclude by
discussing open problems and techniques to compute explicit values for K^+,
giving a table of best known bounds.Comment: 16 page
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
M Theory from World-Sheet Defects in Liouville String
We have argued previously that black holes may be represented in a D-brane
approach by monopole and vortex defects in a sine-Gordon field theory model of
Liouville dynamics on the world sheet. Supersymmetrizing this sine-Gordon
system, we find critical behaviour in 11 dimensions, due to defect condensation
that is the world-sheet analogue of D-brane condensation around an extra
space-time dimension in M theory. This supersymmetric description of Liouville
dynamics has a natural embedding within a 12-dimensional framework suggestive
of F theory.Comment: 17 pages LATEX, 1 epsf figure include
Effects of Higher-Order Threshold Corrections in High-E_T Jet Production
Results for higher-order threshold enhancements in high-E_T jet production in
hadron-hadron collisions are presented. Expressions are given for the
next-to-next-to-leading order (NNLO) threshold corrections to the single-jet
inclusive cross section at next-to-leading logarithmic (NLL) accuracy. The
corrections are found to be small for the specific choice of E_T/2 for the
factorization and renormalization scales, and the corrected cross section shows
a substantial reduction of the scale dependence. A comparison to experimental
results from the Tevatron is presented.Comment: 24 pages LaTeX, 5 figure
Time-Dependent Vacuum Energy Induced by D-Particle Recoil
We consider cosmology in the framework of a `material reference system' of D
particles, including the effects of quantum recoil induced by closed-string
probe particles. We find a time-dependent contribution to the cosmological
vacuum energy, which relaxes to zero as for large times . If
this energy density is dominant, the Universe expands with a scale factor . We show that this possibility is compatible with recent
observational constraints from high-redshift supernovae, and may also respect
other phenomenological bounds on time variation in the vacuum energy imposed by
early cosmology.Comment: 14 pages LATEX, no figure
Statistics of Entropy Production in Linearized Stochastic System
We consider a wide class of linear stochastic problems driven off the
equilibrium by a multiplicative asymmetric force. The force brakes detailed
balance, maintained otherwise, thus producing entropy. The large deviation
function of the entropy production in the system is calculated explicitly. The
general result is illustrated using an example of a polymer immersed in a
gradient flow and subject to thermal fluctuations.Comment: 4 pages, 1 figur
Brany Liouville Inflation
We present a specific model for cosmological inflation driven by the
Liouville field in a non-critical supersymmetric string framework, in which the
departure from criticality is due to open strings stretched between the two
moving Type-II 5-branes. We use WMAP and other data on fluctuations in the
cosmic microwave background to fix parameters of the model, such as the
relative separation and velocity of the 5-branes, respecting also the
constraints imposed by data on light propagation from distant gamma-ray
bursters. The model also suggests a small, relaxing component in the present
vacuum energy that may accommodate the breaking of supersymmetry.Comment: 23 pages LATEX, two eps figures incorporated; version accepted for
publication in NJ
Passive Evolution: Are the Faint Blue Galaxy Counts Produced by a Population of Eternally Young Galaxies?
A constant age population of blue galaxies, postulated in the model of
Gronwall & Koo (1995), seems to provide an attractive explanation of the excess
of very blue galaxies in the deep galaxy counts. Such a population may be
generated by a set of galaxies with cycling star formation rates, or at the
other extreme, be maintained by the continual formation of new galaxies which
fade after they reach the age specified in the Gronwall and Koo model. For both
of these hypotheses, we have calculated the luminosity functions including the
respective selection criteria, the redshift distributions, and the number
counts in the B_J and K bands. We find a substantial excess in the number of
galaxies at low redshift (0 < z < 0.05) over that observed in the CFH redshift
survey (Lilly et al. 1995) and at the faint end of the Las Campanas luminosity
function (Lin et al. 1996). Passive or mild evolution fails to account for the
deep galaxy counts because of the implications for low redshift determinations
of the I-selected redshift distribution and the r-selected luminosity function
in samples where the faded counterparts of the star-forming galaxies would be
detectable.Comment: 11 pages, LaTeX type (aaspp4.sty), 3 Postscript figures, submitted to
ApJ Letter
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