7,254 research outputs found
On electroweak baryogenesis in the littlest Higgs model with T parity
We study electroweak baryogenesis within the framework of the littlest Higgs
model with T parity. This model has shown characteristics of a strong
first-order electroweak phase transition, which is conducive to baryogenesis in
the early Universe. In the T parity symmetric theory, there are two gauge
sectors, viz., the T-even and the T-odd ones. We observe that the effect of the
T-parity symmetric interactions between the T-odd and the T-even gauge bosons
on gauge-higgs energy functional is quite small, so that these two sectors can
be taken to be independent. The T-even gauge bosons behave like the Standard
Model gauge bosons, whereas the T-odd ones are instrumental in stabilizing the
Higgs mass. For the T-odd gauge bosons in the symmetric and asymmetric phases
and for the T-even gauge bosons in the asymmetric phase, we obtain, using the
formalism of Arnold and McLerran, very small values of the ratio, (Baryon
number violation rate/Universe expansion rate). We observe that this result, in
conjunction with the scenario of inverse phase transition in the present work
and the value of the ratio obtained from the lattice result of sphaleron
transition rate in the symmetric phase, can provide us with a plausible
baryogenesis scenario.Comment: 13 pages, 2 figures, published version, references modifie
Legendrian links, causality, and the Low conjecture
Let be a globally hyperbolic spacetime with Cauchy surface
diffeomorphic to an open subset of . The Legendrian Low conjecture
formulated by Nat\'ario and Tod says that two events x,y\in\ss are causally
related if and only if the Legendrian link of spheres whose points are light geodesics passing through and is
non-trivial in the contact manifold of all light geodesics in . The Low
conjecture says that for the events are causally related if and
only if is non-trivial as a topological link. We
prove the Low and the Legendrian Low conjectures. We also show that similar
statements hold for any globally hyperbolic such that a cover of
its Cauchy surface is diffeomorphic to an open domain in Comment: Version 3 - minor improvements, references added 11 pages, 1 figur
Protostellar Collapse with Various Metallicities
The thermal and chemical evolution of gravitationally collapsing protostellar
clouds is investigated, focusing attention on their dependence on metallicity.
Calculations are carried out for a range of metallicities spanning the local
interstellar value to zero. During the time when clouds are transparent to
continuous radiation, the temperatures are higher for those with lower
metallicity, reflecting lower radiative ability. However, once the clouds
become opaque, in the course of the adiabatic contraction of the transient
cores, their evolutionary trajectories in the density-temperature plane
converge to a unique curve that is determined by only physical constants. The
trajectories coincide with each other thereafter. Consequently, the size of the
stellar core at the formation is the same regardless of the gas composition of
the parent cloud.Comment: 30 pages. The Astrophysical Journal, 533, in pres
Multiple Reggeon Exchange from Summing QCD Feynman Diagrams
Multiple reggeon exchange supplies subleading logs that may be used to
restore unitarity to the Low-Nussinov Pomeron, provided it can be proven that
the sum of Feynman diagrams to all orders gives rise to such multiple regge
exchanges. This question cannot be easily tackled in the usual way except for
very low-order diagrams, on account of delicate cancellations present in the
sum which necessitate individual Feynman diagrams to be computed to subleading
orders. Moreover, it is not clear that sums of high-order Feynman diagrams with
complicated criss-crossing of lines can lead to factorization implied by the
multi-regge scenario. Both of these difficulties can be overcome by using the
recently developed nonabelian cut diagrams. We are then able to show that the
sum of -channel-ladder diagrams to all orders does lead to such multiple
reggeon exchanges.Comment: uu-encoded latex file with 11 postscript figures (20 pages
A_4 Symmetry and Lepton Masses and Mixing
Stimulated by Ma's idea which explains the tribimaximal neutrino mixing by
assuming an A_4 flavor symmetry, a lepton mass matrix model is investigated. A
Frogatt-Nielsen type model is assumed, and the flavor structures of the masses
and mixing are caused by the VEVs of SU(2)_L-singlet scalars \phi_i^u and
\phi_i^d (i=1,2,3), which are assigned to {\bf 3} and ({\bf 1}, {\bf 1}',{\bf
1}'') of A_4, respectively.Comment: 13 pages including 1 table, errors in Sec.7 correcte
Large-Scale Gravitational Instability and Star Formation in the Large Magellanic Cloud
Large-scale star formation in disk galaxies is hypothesized to be driven by
global gravitational instability. The observed gas surface density is commonly
used to compute the strength of gravitational instability, but according to
this criterion star formation often appears to occur in gravitationally stable
regions. One possible reason is that the stellar contribution to the
instability has been neglected. We have examined the gravitational instability
of the Large Magellanic Cloud (LMC) considering the gas alone, and considering
the combination of collisional gas and collisionless stars. We compare the
gravitationally unstable regions with the on-going star formation revealed by
Spitzer observations of young stellar objects. Although only 62% of the massive
young stellar object candidates are in regions where the gas alone is unstable,
some 85% lie in regions unstable due to the combination of gas and stars. The
combined stability analysis better describes where star formation occurs. In
agreement with other observations and numerical models, a small fraction of the
star formation occurs in regions with gravitational stability parameter Q > 1.
We further measure the dependence of the star formation timescale on the
strength of gravitational instability, and quantitatively compare it to the
exponential dependence expected from numerical simulations.Comment: Accepted for publication in ApJ, 10 pages, 5 figure
Revealing the electroweak properties of a new scalar resonance
One or more new heavy resonances may be discovered in experiments at the CERN
Large Hadron Collider. In order to determine if such a resonance is the
long-awaited Higgs boson, it is essential to pin down its spin, CP, and
electroweak quantum numbers. Here we describe how to determine what role a
newly-discovered neutral CP-even scalar plays in electroweak symmetry breaking,
by measuring its relative decay rates into pairs of electroweak vector bosons:
WW, ZZ, \gamma\gamma, and Z\gamma. With the data-driven assumption that
electroweak symmetry breaking respects a remnant custodial symmetry, we perform
a general analysis with operators up to dimension five. Remarkably, only three
pure cases and one nontrivial mixed case need to be disambiguated, which can
always be done if all four decay modes to electroweak vector bosons can be
observed or constrained. We exhibit interesting special cases of Higgs
look-alikes with nonstandard decay patterns, including a very suppressed
branching to WW or very enhanced branchings to \gamma\gamma and Z\gamma. Even
if two vector boson branching fractions conform to Standard Model expectations
for a Higgs doublet, measurements of the other two decay modes could unmask a
Higgs imposter.Comment: 23 pages, two figures; v2: minor revision and version to appear in
JHE
Electromyography - A Reliable Technique for Muscle Activity Assessment
In recent years, many questions have been raised on the credibility of Electromyography (EMG) as a technique to evaluate muscle activity, particularly by sports and fitness community. This questioning goes farther when it comes to surface electromyography (sEMG). This paper covers an overview of EMG, addresses some basic concepts and provide rudiment for research. Muscle activity assessment through EMG has been reviewed in terms of the type of movements. There are few limitations to EMG but these confines are addressable. The problem rather lies in the interpretation and generalization of that data. Limitations are there in every technology, precautionary measures must be taken to avoid those while using it. Reservations about EMG have been summarized along with their responses. A few techniques to analyze EMG data, and possibilities to extrapolate and interpret, are also provided. Current perspectives and practical applications of EMG and sEMG are also part of this article
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