475 research outputs found
The Thermal Abundance of Semi-Relativistic Relics
Approximate analytical solutions of the Boltzmann equation for particles that
are either extremely relativistic or non-relativistic when they decouple from
the thermal bath are well established. However, no analytical formula for the
relic density of particles that are semi-relativistic at decoupling is yet
known. We propose a new ansatz for the thermal average of the annihilation
cross sections for such particles, and find a semi-analytical treatment for
calculating their relic densities. As examples, we consider Majorana- and
Dirac-type neutrinos. We show that such semi-relativistic relics cannot be good
cold Dark Matter candidates. However, late decays of meta-stable
semi-relativistic relics might have released a large amount of entropy, thereby
diluting the density of other, unwanted relics.Comment: 22 pages, 5 figures. Comments and references adde
Twisted Split Fermions
The observed flavor structure of the standard model arises naturally in
"split fermion" models which localize fermions at different places in an extra
dimension. It has, until now, been assumed that the bulk masses for such
fermions can be chosen to be flavor diagonal simultaneously at every point in
the extra dimension, with all the flavor violation coming from the Yukawa
couplings to the Higgs. We consider the more natural possibility in which the
bulk masses cannot be simultaneously diagonalized, that is, that they are
twisted in flavor space. We show that, in general, this does not disturb the
natural generation of hierarchies in the flavor parameters. Moreover, it is
conceivable that all the flavor mixing and CP-violation in the standard model
may come only from twisting, with the five-dimensional Yukawa couplings taken
to be universal.Comment: 15 pages, 1 figur
Punctal stenosis: definition, diagnosis, and treatment
Acquired punctal stenosis is a condition in which the external opening of the lacrimal canaliculus is narrowed or occluded. This condition is a rare cause of symptomatic epiphora, but its incidence may be higher in patients with chronic blepharitis, in those treated with various topical medications, including antihypertensive agents, and especially in patients treated with taxanes for cancer. The purpose of this review is to cover the medical literature, focusing in particular on definition, incidence, risk factors, etiology and treatment options.Uri Soiberman, Hirohiko Kakizaki, Dinesh Selva, Igal Leibovitc
Search for Higgs bosons of the Universal Extra Dimensions at the Large Hadron Collider
The Higgs sector of the Universal Extra Dimensions (UED) has a rather
involved setup. With one extra space dimension, the main ingredients to the
construct are the higher Kaluza-Klein (KK) excitations of the Standard Model
Higgs boson and the fifth components of the gauge fields which on
compactification appear as scalar degrees of freedom and can mix with the
former thus leading to physical KK-Higgs states of the scenario. In this work,
we explore in detail the phenomenology of such a Higgs sector of the UED with
the Large Hadron Collider (LHC) in focus. We work out relevant decay branching
fractions involving the KK-Higgs excitations. Possible production modes of the
KK-Higgs bosons are then discussed with an emphasis on their associated
production with the third generation KK-quarks and that under the cascade
decays of strongly interacting UED excitations which turn out to be the only
phenomenologically significant modes. It is pointed out that the collider
searches of such Higgs bosons face generic hardship due to soft end-products
which result from severe degeneracies in the masses of the involved excitations
in the minimal version of the UED (MUED). Generic implications of either
observing some or all of the KK-Higgs bosons at the LHC are discussed.Comment: 25 pages, 9 figures and 1 tabl
SU(4)_c x SU(2)_L x SU(2)_R model from 5D SUSY SU(4)_c x SU(4)_{L+R}
We investigate supersymmetric theory in 5
dimensions whose compactification on a orbifold yields N=1
supersymmetric supplemented by a
\tl{U}(1) gauge symmetry. We discuss how the problem is resolved, a
realistic Yukawa sector achieved, and a stable proton realized. Neutrino masses
and oscillations are also briefly discussed.Comment: Version to appear in Physical Review
Neutrino Democracy, Fermion Mass Hierarchies And Proton Decay From 5D SU(5)
The explanation of various observed phenomena such as large angle neutrino
oscillations, hierarchies of charged fermion masses and CKM mixings, and
apparent baryon number conservation may have a common origin. We show how this
could occur in 5D SUSY SU(5) supplemented by a flavor symmetry
and additional matter supermultiplets called 'copies'. In addition, the proton
decays into , with an estimated lifetime of order
yrs. Other decay channels include and with comparable rates. We
also expect that BRBR
Supersymmetric Froggatt-Nielsen Models with Baryon- and Lepton-Number Violation
We systematically investigate the embedding of U(1)_X Froggatt-Nielsen models
in (four-dimensional) local supersymmetry. We restrict ourselves to models with
a single flavon field. We do not impose a discrete symmetry by hand, e.g.
R-parity, baryon-parity or lepton-parity. Thus we determine the order of
magnitude of the baryon- and/or lepton violating coupling constants through the
Froggatt-Nielsen mechanism. We then scrutinize whether the predicted coupling
constants are in accord with weak or GUT scale constraints. Many models turn
out to be incompatible.Comment: Final version, references added, minor corrections; LaTeX, 46 page
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