209 research outputs found
Probes for 4th generation constituents of dark atoms in Higgs boson studies at the LHC
The nonbaryonic dark matter of the Universe can consist of new stable charged
species, bound in heavy neutral "atoms" by ordinary Coulomb interaction. Stable
(anti-)quarks of 4th generation, bound in stable colorless () clusters, are captured by the primordial helium, produced in
Big Bang Nucleosynthesis, thus forming neutral "atoms" of O-helium (OHe), a
specific nuclear interacting dark matter that can provide solution for the
puzzles of direct dark matter searches. However, the existence of the 4th
generation quarks and leptons should influence the production and decay rates
of Higgs boson and is ruled out by the experimental results of the Higgs boson
searches at the LHC, if the Higgs boson coupling to 4th generation fermions
with is not suppressed. Here we argue that the difference between the three
known quark-lepton families and the 4th family can naturally lead to
suppression of this coupling, relating the accelerator test for such a
composite dark matter scenario to the detailed study of the production and
modes of decay of the 125.5 GeV boson, discovered at the LHC.Comment: Prepared for the Special issue "Dark atoms and dark radiation" of
Advances in High Energy Physic
Soft elasticity in biaxial smectic and smectic-C elastomers
Ideal (monodomain) smectic- elastomers crosslinked in the smectic-
phase are simply uniaxial rubbers, provided deformations are small. From these
materials smectic- elastomers are produced by a cooling through the
smectic- to smectic- phase transition. At least in principle, biaxial
smectic elastomers could also be produced via cooling from the smectic- to a
biaxial smectic phase. These phase transitions, respectively from to and from to symmetry, spontaneously
break the rotational symmetry in the smectic planes. We study the above
transitions and the elasticity of the smectic- and biaxial phases in three
different but related models: Landau-like phenomenological models as functions
of the Cauchy--Saint-Laurent strain tensor for both the biaxial and the
smectic- phases and a detailed model, including contributions from the
elastic network, smectic layer compression, and smectic- tilt for the
smectic- phase as a function of both strain and the -director. We show
that the emergent phases exhibit soft elasticity characterized by the vanishing
of certain elastic moduli. We analyze in some detail the role of spontaneous
symmetry breaking as the origin of soft elasticity and we discuss different
manifestations of softness like the absence of restoring forces under certain
shears and extensional strains.Comment: 26 pages, 6 figure
Invisible Higgs Boson Decay into Massive Neutrinos of 4th Generation
Results from several recent experiments provide inderect evidences in the
favor of existence of a 4th generation neutrino. Such a neutrino of mass about
50 GeV is compatible with current physical and astrophysical constraints and
well motivated in the framework of superstring phenomenology. If sufficiently
stable the existence of such a neutrino leads to the drastic change of Higgs
boson physics: for a wide range of Higgs boson masses the dominant mode of
Higgs boson decay is invisible and the branching ratios for the most promising
modes of Higgs boson search are significantly reduced. The proper strategy of
Higgs boson searches in such a framework is discussed. It is shown that in the
same framework the absence of a signal in the search for invisible Higgs boson
decay at LEP means either that the mass of Higgs is greater than 113.5 GeV or
that the mass difference between the Higgs mass and doubled neutrino mass is
small.Comment: 8 pages, 2 figure
ИССЛЕДОВАНИЕ ПРОБЛЕМ БЕЗОПАСНОСТИ ИСПОЛЬЗОВАНИЯ КОРОТКИХ ССЫЛОК
В работе рассмотрены сферы применения коротких ссылок, указаны их
преимущества и недостатки. Описаны возможные уязвимости и атаки, а также
методы защиты от них. Проанализирован общий уровень безопасности использования
коротких ссылок
Aerodynamic investigations of ventilated brake discs.
The heat dissipation and performance of a ventilated brake disc strongly depends
on the aerodynamic characteristics of the flow through the rotor passages. The
aim of this investigation was to provide an improved understanding of ventilated
brake rotor flow phenomena, with a view to improving heat dissipation, as well
as providing a measurement data set for validation of computational fluid
dynamics methods. The flow fields at the exit of four different brake rotor
geometries, rotated in free air, were measured using a five-hole pressure probe
and a hot-wire anemometry system. The principal measurements were taken using
two-component hot-wire techniques and were used to determine mean and unsteady
flow characteristics at the exit of the brake rotors. Using phase-locked data
processing, it was possible to reveal the spatial and temporal flow variation
within individual rotor passages. The effects of disc geometry and rotational
speed on the mean flow, passage turbulence intensity, and mass flow were
determined. The rotor exit jet and wake flow were clearly observed as
characterized by the passage geometry as well as definite regions of high and
low turbulence. The aerodynamic flow characteristics were found to be reasonably
independent of rotational speed but highly dependent upon rotor geometry
The Effects of Fourth Generation on the double Lepton Polarization in B \rar K \ell^+ \ell^- decay
This study investigates the influence of the fourth generation quarks on the
double lepton polarizations in B \rar K \ell^+ \ell^- decay. Taking
|V_{t's}V_{t'b}|\sim \{0.01-0.03\} with phase about 100^\circ, which is
consistent with the b\to s\ell^+\ell^- rate and the B_s mixing parameter Delta
m_{B_s}$, we obtain that the double lepton(muon and tau) polarizations are
quite sensitive to the existence of fourth generation. It can serve as a good
tool to search for new physics effects, precisely, to indirect search for the
fourth generation quarks(t', b').Comment: 30 pages, 27 figure
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