448 research outputs found
Statistical Mechanics of Broadcast Channels Using Low Density Parity Check Codes
We investigate the use of Gallager's low-density parity-check (LDPC) codes in
a broadcast channel, one of the fundamental models in network information
theory. Combining linear codes is a standard technique in practical network
communication schemes and is known to provide better performance than simple
timesharing methods when algebraic codes are used. The statistical physics
based analysis shows that the practical performance of the suggested method,
achieved by employing the belief propagation algorithm, is superior to that of
LDPC based timesharing codes while the best performance, when received
transmissions are optimally decoded, is bounded by the timesharing limit.Comment: 14 pages, 4 figure
Statistical Mechanics of Broadcast Channels Using Low Density Parity Check Codes
We investigate the use of Gallager's low-density parity-check (LDPC) codes in
a broadcast channel, one of the fundamental models in network information
theory. Combining linear codes is a standard technique in practical network
communication schemes and is known to provide better performance than simple
timesharing methods when algebraic codes are used. The statistical physics
based analysis shows that the practical performance of the suggested method,
achieved by employing the belief propagation algorithm, is superior to that of
LDPC based timesharing codes while the best performance, when received
transmissions are optimally decoded, is bounded by the timesharing limit.Comment: 14 pages, 4 figure
Analysis of common attacks in LDPCC-based public-key cryptosystems
We analyze the security and reliability of a recently proposed class of
public-key cryptosystems against attacks by unauthorized parties who have
acquired partial knowledge of one or more of the private key components and/or
of the plaintext. Phase diagrams are presented, showing critical partial
knowledge levels required for unauthorized decryptionComment: 14 pages, 6 figure
Detecting Generalized Synchronization Between Chaotic Signals: A Kernel-based Approach
A unified framework for analyzing generalized synchronization in coupled
chaotic systems from data is proposed. The key of the proposed approach is the
use of the kernel methods recently developed in the field of machine learning.
Several successful applications are presented, which show the capability of the
kernel-based approach for detecting generalized synchronization. It is also
shown that the dynamical change of the coupling coefficient between two chaotic
systems can be captured by the proposed approach.Comment: 20 pages, 15 figures. massively revised as a full paper; issues on
the choice of parameters by cross validation, tests by surrogated data, etc.
are added as well as additional examples and figure
Experimental aspects of SU(5)xU(1) supergravity
We study various aspects of supergravity as they relate to
the experimental verification or falsification of this model. We consider two
string-inspired, universal, one-parameter, no-scale soft-supersymmetry-breaking
scenarios, driven by the -terms of the moduli and dilaton fields. The model
is described in terms of the supersymmetry mass scale (\ie, the chargino mass
), , and the top-quark mass. We first determine the
combined effect on the parameter space of all presently available direct and
indirect experimental constraints, including the LEP lower bounds on sparticle
and Higgs-boson masses, the rate, the anomalous magnetic moment
of the muon, the high-precision electroweak parameters
(which imply m_t\lsim180\GeV), and the muon fluxes in underground detectors
(neutrino telescopes). For the still-allowed points in
parameter space, we re-evaluate the experimental
situation at the Tevatron, LEPII, and HERA. In the 1994 run, the Tevatron could
probe chargino masses as high as 100 GeV. At LEPII the parameter space could be
explored with probes of different resolutions: Higgs boson searches, selectron
searches, and chargino searches. Moreover, for m_t\lsim150\GeV, these
Higgs-boson searches could explore all of the allowed parameter space with
\sqrt{s}\lsim210\GeV.Comment: latex, 36 pages, 25 figures (not included). Figures are available via
anonymous ftp from hplaa02.cern.ch (/pub/lopez) as either 33 ps files
(Easpects*.ps, 8.1MB) or one uuencoded file (AllFigures.uu, 3.7MB
Uncertainties in Coupling Constant Unification
The status of coupling constant unification in the standard model and its
supersymmetric extension are discussed. Uncertainties associated with the input
coupling constants, , threshold corrections at the low and high scales,
and possible nonrenormalizable operators are parametrized and estimated. A
simple parametrization of a general supersymmetric new particle spectrum is
given. It is shown that an effective scale can be defined, but for a
realistic spectrum it may differ considerably from the typical new particle
masses. The implications of the lower (higher) values of
suggested by low-energy (-pole) experiments are discussed.Comment: LaTex, 51 pages, 6 figures (available upon request), UPR-0513
Strong disorder fixed points in the two-dimensional random-bond Ising model
The random-bond Ising model on the square lattice has several disordered
critical points, depending on the probability distribution of the bonds. There
are a finite-temperature multicritical point, called Nishimori point, and a
zero-temperature fixed point, for both a binary distribution where the coupling
constants take the values +/- J and a Gaussian disorder distribution. Inclusion
of dilution in the +/- J distribution (J=0 for some bonds) gives rise to
another zero-temperature fixed point which can be identified with percolation
in the non-frustrated case (J >= 0). We study these fixed points using
numerical (transfer matrix) methods. We determine the location, critical
exponents, and central charge of the different fixed points and study the
spin-spin correlation functions. Our main findings are the following: (1) We
confirm that the Nishimori point is universal with respect to the type of
disorder, i.e. we obtain the same central charge and critical exponents for the
+/- J and Gaussian distributions of disorder. (2) The Nishimori point, the
zero-temperature fixed point for the +/- J and Gaussian distributions of
disorder, and the percolation point in the diluted case all belong to mutually
distinct universality classes. (3) The paramagnetic phase is re-entrant below
the Nishimori point, i.e. the zero-temperature fixed points are not located
exactly below the Nishimori point, neither for the +/- J distribution, nor for
the Gaussian distribution.Comment: final version to appear in JSTAT; minor change
Probing Supergravity Models with Indirect Experimental Signatures
We explore the one-loop electroweak radiative corrections in the context of
the traditional minimal and the string-inspired
supergravity models by calculating explicitly vacuum-polarization and
vertex-correction contributions to the and
parameters. We also include in this analysis the constraint from whose inclusive branching ratio has been
actually measured very recently by CLEO. We find that by combining these three
most important indirect experimental signatures and using the most recent
experimental values for them, is excluded for
in both the minimal supergravity and the no-scale supergravity. We also find that is
excluded for any sign of in the minimal () supergravity
model.Comment: RevTeX 3.0, 16 Pages+4 figures(not included but available as a
uuencoded file from [email protected]), SNUTP-94-9
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