3,716 research outputs found
Return-Map Cryptanalysis Revisited
As a powerful cryptanalysis tool, the method of return-map attacks can be
used to extract secret messages masked by chaos in secure communication
schemes. Recently, a simple defensive mechanism was presented to enhance the
security of chaotic parameter modulation schemes against return-map attacks.
Two techniques are combined in the proposed defensive mechanism: multistep
parameter modulation and alternative driving of two different transmitter
variables. This paper re-studies the security of this proposed defensive
mechanism against return-map attacks, and points out that the security was much
over-estimated in the original publication for both ciphertext-only attack and
known/chosen-plaintext attacks. It is found that a deterministic relationship
exists between the shape of the return map and the modulated parameter, and
that such a relationship can be used to dramatically enhance return-map attacks
thereby making them quite easy to break the defensive mechanism.Comment: 11 pages, 7 figure
Three-body decays: structure, decay mechanism and fragment properties
We discuss the three-body decay mechanisms of many-body resonances. R-matrix
sequential description is compared with full Faddeev computation. The role of
the angular momentum and boson symmetries is also studied. As an illustration
we show the computed -particle energy distribution after the decay of
12C(1^+) resonance at 12.7 MeV.Comment: 4 pages, 3 figures. Proceedings of the workshop "Critical Stability
of Few-Body Quantum Systems" 200
Bayesian estimation of species divergence times using correlated quantitative characters
Discrete morphological data have been widely used to study species evolution, but the use of quantitative (or continuous) morphological characters is less common. Here, we implement a Bayesian method to estimate species divergence times using quantitative characters. Quantitative character evolution is modelled using Brownian diffusion with character correlation and character variation within populations. Through simulations, we demonstrate that ignoring the population variation (or population “noise”) and the correlation among characters leads to biased estimates of divergence times and rate, especially if the correlation and population noise are high. We apply our new method to the analysis of quantitative characters (cranium landmarks) and molecular data from carnivoran mammals. Our results show that time estimates are affected by whether the correlations and population noise are accounted for or ignored in the analysis. The estimates are also affected by the type of data analysed, with analyses of morphological characters only, molecular data only, or a combination of both; showing noticeable differences among the time estimates. Rate variation of morphological characters among the carnivoran species appears to be very high, with Bayesian model selection indicating that the independent-rates model fits the morphological data better than the autocorrelated-rates model. We suggest that using morphological continuous characters, together with molecular data, can bring a new perspective to the study of species evolution. Our new model is implemented in the MCMCtree computer program for Bayesian inference of divergence times
A Minimal Inflation Scenario
We elaborate on a minimal inflation scenario based entirely on the general
properties of supersymmetry breaking in supergravity models. We identify the
inflaton as the scalar component of the Goldstino superfield. We write
plausible candidates for the effective action describing this chiral
superfield. In particular the theory depends (apart from parameters of O(1)) on
a single free parameter: the scale of supersymmetry breaking. This can be fixed
using the amplitude of CMB cosmological perturbations and we therefore obtain
the scale of supersymmetry breaking to be 10^{12-14} GeV. The model also
incorporates explicit R-symmetry breaking in order to satisfy the slow roll
conditions. In our model the eta-problem is solved without extra fine-tuning.
We try to obtain as much information as possible in a model independent way
using general symmetry properties of the theory's effective action, this leads
to a new proposal on how to exit the inflationary phase and reheat the
Universe.Comment: matches published version (typo corrected
Kahler Anomalies in Supergravity and Flux Vacua
We review the subject of Kahler anomalies in gauged supergravity, emphasizing
that field equations are inconsistent when the Kahler potential is
non-invariant under gauge transformations or when there are elementary
Fayet-Iliopoulos couplings. Flux vacua solutions of string theory with gauged
U(1) shift symmetries appear to avoid this problem. The covariant Kahler
anomalies involve tensors which are composite functions of the scalars as well
as the gauge field strength and space-time curvature tensors. Anomaly
cancellation conditions will be discussed in a sequel to this paper.Comment: 29 pages; v2: revised presentation, section on Fayet-Iliopoulos
couplings cut, effects of gauginos on anomalies included, references adde
Electroweak precision constraints on the Lee-Wick Standard Model
We perform an analysis of the electroweak precision observables in the
Lee-Wick Standard Model. The most stringent restrictions come from the S and T
parameters that receive important tree level and one loop contributions. In
general the model predicts a large positive S and a negative T. To reproduce
the electroweak data, if all the Lee-Wick masses are of the same order, the
Lee-Wick scale is of order 5 TeV. We show that it is possible to find some
regions in the parameter space with a fermionic state as light as 2.4-3.5 TeV,
at the price of rising all the other masses to be larger than 5-8 TeV. To
obtain a light Higgs with such heavy resonances a fine-tuning of order a few
per cent, at least, is needed. We also propose a simple extension of the model
including a fourth generation of Standard Model fermions with their Lee-Wick
partners. We show that in this case it is possible to pass the electroweak
constraints with Lee-Wick fermionic masses of order 0.4-1.5 TeV and Lee-Wick
gauge masses of order 3 TeV.Comment: 24 pages, 7 figure
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Simulations of model magnetorheological fluids in squeeze flow mode
A particle-level simulation methodology is proposed to study the squeeze flow behavior of model magnetorheological (MR) fluids. The simulation algorithm takes into account Brownian motion and local field corrections to magnetic interactions of the particles. Simulation results obtained from using different initial configurations, including one single-particle-width chain per simulation box, random or lattice arrangements of preassembled single-particle-width chains as well as randomly dispersed particle suspensions, are compared with experimental data and predictions of a recently developed microscopic model. The assumption of single-particle-width chain structures in the systems has been shown to generate normal stresses larger than those found in experiments and the micromechanical model. However, much better agreement between the simulation and experimental results have been reached when using random initial configurations in the simulations
One-loop effects in a self-dual planar noncommutative theory
We study the UV properties, and derive the explicit form of the one-loop
effective action, for a noncommutative complex scalar field theory in 2+1
dimensions with a Grosse-Wulkenhaar term, at the self-dual point. We also
consider quantum effects around non-trivial minima of the classical action
which appear when the potential allows for the spontaneous breaking of the U(1)
symmetry. For those solutions, we show that the one-loop correction to the
vacuum energy is a function of a special combination of the amplitude of the
classical solution and the coupling constant.Comment: Version to appear in JHE
On Supergroups with Odd Clifford Parameters and Supersymmetry with Modified Leibniz Rule
We investigate supergroups with Grassmann parameters replaced by odd Clifford
parameters. The connection with non-anticommutative supersymmetry is discussed.
A Berezin-like calculus for odd Clifford variables is introduced. Fermionic
covariant derivatives for supergroups with odd Clifford variables are derived.
Applications to supersymmetric quantum mechanics are made. Deformations of the
original supersymmetric theories are encountered when the fermionic covariant
derivatives do not obey the graded Leibniz property. The simplest non-trivial
example is given by the N=2 SQM with a real multiplet and a cubic
potential. The action is real. Depending on the overall sign ("Euclidean" or
"Lorentzian") of the deformation, a Bender-Boettcher pseudo-hermitian
hamiltonian is encountered when solving the equation of motion of the auxiliary
field. A possible connection of our framework with the Drinfeld twist
deformation of supersymmetry is pointed out.Comment: Final version to be published in Int. J. Mod. Phys. A; 20 page
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