29,271 research outputs found
Analysis of Leptogenesis in Supersymmetric Triplet Seesaw Model
We analyze leptogenesis in a supersymmetric triplet seesaw scenario that
explains the observed neutrino masses, adopting a phenomenological approach
where the decay branching ratios of the triplets and the amount of
CP--violation in its different decay channels are assumed as free parameters.
We find that the solutions of the relevant Boltzmann equations lead to a rich
phenomenology, in particular much more complex compared to the
non--supersymmetric case, mainly due to the presence of an additional Higgs
doublet. Several unexpected and counter--intuitive behaviors emerge from our
analysis: the amount of CP violation in one of the decay channels can prove to
be be irrelevant to the final lepton asymmetry, leading to successful
leptogenesis even in scenarios with a vanishing CP violation in the leptonic
sector; gauge annihilations can be the dominant effect in the determination of
the evolution of the triplet density up to very high values of its mass,
leading anyway to a sizeable final lepton asymmetry, which is also a growing
function of the wash--out parameter K=Gamma_d/H, defined as usual as the ratio
between the triplet decay amplitude Gamma_d and the Hubble constant H; on the
other hand, cancellations in the Boltzmann equations may lead to a vanishing
lepton asymmetry if in one of the decay channels both the branching ratio and
the amount of CP violation are suppressed, but not vanishing. The present
analysis suggests that in the supersymmetric triplet see-saw model successful
leptogenesis can be attained in a wide range of scenarios, provided that an
asymmetry in the decaying triplets can act as a lepton--number reservoir.Comment: 14 pages, 6 figure
Leptogenesis origin of Dirac gaugino dark matter
The Dirac nature of the gauginos (and also the Higgsinos) can be realized in
-symmetric supersymmetry models. In this class of models, the Dirac bino (or
wino) with a small mixture of the Dirac Higgsinos is a good dark matter
candidate. When the seesaw mechanism with Higgs triplet superfields is
implemented to account for the neutrino masses and mixing, the leptogenesis
driven by the heavy triplet decay is shown to produce not only the
matter-antimatter asymmetry but also the asymmetric relic density of the Dirac
gaugino dark matter. The dark matter mass turns out to be controlled by the
Yukawa couplings of the heavy Higgs triplets, and it can be naturally at the
weak scale for a mild hierarchy of the Yukawa couplings.Comment: 9 pages. Restructured for clear presentation, corrected some errors
and typos. No change in conclusio
A Supersymmetric Model with the Gauge Symmetry SU(3)_1 X SU(2)_1 X U(1)_1 X SU(3)_2 X SU(2)_2 X U(1)_2
A supersymmetric model with two copies of the Standard Model gauge groups is
constructed in the gauge mediated supersymmetry breaking scenario. The
supersymmetry breaking messengers are in a simple form. The Standard Model is
obtained after first step gauge symmetry breaking. In the case of one copy of
the gauge interactions being strong, a scenario of electroweak symmetry
breaking is discussed, and the gauginos are generally predicted to be heavier
than the sfermions.Comment: 14 pages, revtex, 1 figure, messenger contents modified, discussion
on GUTs improve
Cognitive Radio from Hell: Flipping Attack on Direct-Sequence Spread Spectrum
In this paper, we introduce a strong adversarial attack, referred to as the
flipping attack, on Direct-Sequence Spread Spectrum (DSSS) systems. In this
attack, the attacker, which is appropriately positioned between the transmitter
and the receiver, instantaneously flips the transmitted symbols in the air at
50% rate, thereby driving the channel capacity to zero. Unlike the traditional
jamming attack, this attack, when perfectly executed, cannot be detected at the
receiver using signal-to-noise-ratio measurements. However, this attack
necessitates the attacker to perfectly know the realizations of all the
channels in the model. We first introduce the consequences of the flipping
attack on narrowband frequency-flat channels, and subsequently discuss its
feasibility in wideband frequency-selective channels. From the legitimate
users' perspective, we present a method to detect this attack and also propose
heuristics to improve the error-performance under the attack. We emphasize that
future cyber-physical systems that employ DSSS should design transceivers to
detect the proposed flipping attack, and then apply appropriate
countermeasures
Vortex Structures in Model p-Wave Superconducting Sr2RuO4 -- Single 2-Dimensional Band v.s. Quasi-1-Dimensional Band
There have been an interesting debate on the primary source of chiral p-wave
superconductivity in Sr2RuO4. We present a comparative study on the vortex
structure between a single 2-dimensional (2D) band and quasi-1D band model by
using Bogoliubov-de Gennes theory. The pattern of the iso-values of the local
density of state around a vortex has a diamond shape in the quasi-1D model and
is much more isotropic in the 2D model. The spin lattice relaxation rate well
below the superconducting transition temperature is greatly enhanced in the
vortex state in the 2D model but not in the quasi-1D model. These features can
be tested by using scanning tunneling microscope and NMR to distinguish the
models for the superconductivity in Sr2RuO4.Comment: 7 pages, 6 fig
A chain theorem for internally 4-connected binary matroids
This is the post-print version of the Article - Copyright @ 2011 ElsevierLet M be a matroid. When M is 3-connected, Tutte’s Wheels-and-Whirls Theorem proves that M has a 3-connected proper minor N with |E(M) − E(N)| = 1 unless M is a wheel or a whirl. This paper establishes a corresponding result for internally 4-connected binary matroids. In particular, we prove that if M is such a matroid, then M has an internally 4-connected proper minor N with |E(M) − E(N)| at most 3 unless M or its dual is the cycle matroid of a planar or Möbius quartic ladder, or a 16-element variant of such a planar ladder.This study was partially supported by the National Security Agency
Towards a splitter theorem for internally 4-connected binary matroids
This is the post-print version of the Article - Copyright @ 2012 ElsevierWe prove that if M is a 4-connected binary matroid and N is an internally 4-connected proper minor of M with at least 7 elements, then, unless M is a certain 16-element matroid, there is an element e of E(M) such that either M\e or M/e is internally 4-connected having an N-minor. This strengthens a result of Zhou and is a first step towards obtaining a splitter theorem for internally 4-connected binary matroids.This study is partially funded by Marsden Fund of New Zealand and the National Security Agency
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