17,356 research outputs found
Higgs-flavon mixing and LHC phenomenology in a simplified model of broken flavor symmetry
The LHC phenomenology of a low-scale gauged flavor symmetry model with
inverted hierarchy is studied, through introduction of a simplified model of
broken flavor symmetry. A new scalar (a flavon) and a new neutral top-philic
massive gauge boson emerge with mass in the TeV range along with a new heavy
fermion associated with the standard model top quark. After checking
constraints from electroweak precision observables, we investigate the
influence of the model on Higgs boson physics, notably on its production cross
section and decay branching fractions. Limits on the flavon from
heavy Higgs boson searches at the LHC at 7 and 8 TeV are presented. The
branching fractions of the flavon are computed as a function of the flavon mass
and the Higgs-flavon mixing angle. We also explore possible discovery of the
flavon at 14 TeV, particularly via the decay
channel in the final state, and through standard model Higgs
boson pair production in the
final state. We conclude that the flavon mass range up to GeV could
probed down to quite small values of the Higgs-flavon mixing angle with 100
fb of integrated luminosity at 14 TeV.Comment: 17 pages, 14 figure
Topological Effects caused by the Fractal Substrate on the Nonequilibrium Critical Behavior of the Ising Magnet
The nonequilibrium critical dynamics of the Ising magnet on a fractal
substrate, namely the Sierpinski carpet with Hausdorff dimension =1.7925,
has been studied within the short-time regime by means of Monte Carlo
simulations. The evolution of the physical observables was followed at
criticality, after both annealing ordered spin configurations (ground state)
and quenching disordered initial configurations (high temperature state), for
three segmentation steps of the fractal. The topological effects become evident
from the emergence of a logarithmic periodic oscillation superimposed to a
power law in the decay of the magnetization and its logarithmic derivative and
also from the dependence of the critical exponents on the segmentation step.
These oscillations are discussed in the framework of the discrete scale
invariance of the substrate and carefully characterized in order to determine
the critical temperature of the second-order phase transition and the critical
exponents corresponding to the short-time regime. The exponent of the
initial increase in the magnetization was also obtained and the results suggest
that it would be almost independent of the fractal dimension of the susbstrate,
provided that is close enough to d=2.Comment: 9 figures, 3 tables, 10 page
Emergent Universe with Exotic Matter in Brane World Scenario
In this work, we have examined the emergent scenario in brane world model for
phantom and tachyonic matter. For tachyonic matter field we have obtained
emergent scenario is possible for closed, open and at model of the universe
with some restriction of potential. For normal scalar field the emergent
scenario is possible only for closed model and the result is identical with the
work of Ellis et al [2], but for phantom field the emergent scenario is
possible for closed, open and at model of the universe with some restriction of
potential
CMBR Constraint on a Modified Chaplygin Gas Model
In this paper, a modified Chaplygin gas model of unifying dark energy and
dark matter with exotic equation of state
which can also explain the recent accelerated expansion of the universe is
investigated by the means of constraining the location of the peak of the CMBR
spectrum. We find that the result of CMBR measurements does not exclude the
nonzero value of parameter , but allows it in the range .Comment: 4 pages, 3 figure
Investigating the intrinsic noise limit of Dayem bridge NanoSQUIDs
NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance ∼170 nΦ0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1–2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise
Effect on Higgs Boson Decays from Large Light-Heavy Neutrino Mixing in Seesaw Models
In seesaw models with more than one generation of light and heavy neutrinos,
nu and N, respectively, it is possible to have sizable mixing between them for
heavy-neutrino masses of order 100 GeV or less. We explore this possibility
further, taking into account current experimental constraints, and study its
effect on Higgs-boson decays in the contexts of seesaw models of types I and
III. We find that in the type-I case the Higgs decay into a pair of light and
heavy neutrinos, h -> nu N, could increase the total Higgs width in the
standard model by up to almost 30% for a relatively light Higgs-boson, which
would significantly affect Higgs searches at the LHC. The subsequent prompt
decay of N into three light fermions makes this Higgs decay effectively a
four-body decay. We further find that, in the presence of the large light-heavy
mixing, these four-body Higgs decays can have rates a few times larger than
their standard-model counterparts and therefore could provide a potentially
important window to reveal the underlying seesaw mechanism.Comment: 16 pages, 3 figures, with more discussion on experimental constraints
and references, main conclusions unchanged, to match journal versio
Algebraic Bethe Ansatz for the two species ASEP with different hopping rates
An ASEP with two species of particles and different hopping rates is
considered on a ring. Its integrability is proved and the Nested Algebraic
Bethe Ansatz is used to derive the Bethe Equations for states with arbitrary
numbers of particles of each type, generalizing the results of Derrida and
Evans. We present also formulas for the total velocity of particles of a given
type and their limit for large size of the system and finite densities of the
particles.Comment: 14 page
First mid-infrared spectrum of a faint high-z galaxy: Observations of CFRS 14.1157 with the Infrared Spectrograph on the Spitzer Space Telescope
The unprecedented sensitivity of the Infrared Spectrograph on the Spitzer
Space Telescope allows for the first time the measurement of mid-infrared
spectra from 14 to 38 microns of faint high-z galaxies. This unique capability
is demonstrated with observations of sources having 16 micron fluxes of 3.6 mJy
(CFRS 14.1157) and 0.35 mJy (CFRS 14.9025). A spectral-fitting technique is
illustrated which determines the redshift by fitting emission and absorption
features characteristic of nearby galaxies to the spectrum of an unknown
source. For CFRS 14.1157, the measured redshift is z = 1.00+/-0.20 in agreement
with the published result of z = 1.15. The spectrum is dominated by emission
from an AGN, similar to the nucleus of NGC 1068, rather than a typical
starburst with strong PAH emission like M82. Such spectra will be crucial in
characterizing the nature of newly discovered distant galaxies, which are too
faint for optical follow-up.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 5 figure
Berezinskii-Kosterlitz-Thouless-like percolation transitions in the two-dimensional XY model
We study a percolation problem on a substrate formed by two-dimensional XY
spin configurations, using Monte Carlo methods. For a given spin configuration
we construct percolation clusters by randomly choosing a direction in the
spin vector space, and then placing a percolation bond between nearest-neighbor
sites and with probability ,
where governs the percolation process. A line of percolation thresholds
is found in the low-temperature range , where
is the XY coupling strength. Analysis of the correlation function , defined as the probability that two sites separated by a distance
belong to the same percolation cluster, yields algebraic decay for , and the associated critical exponent depends on and .
Along the threshold line , the scaling dimension for is,
within numerical uncertainties, equal to . On this basis, we conjecture
that the percolation transition along the line is of the
Berezinskii-Kosterlitz-Thouless type.Comment: 23 pages, 14 figure
On the origin of multiple ordered phases in PrFe4P12
The nature of multiple electronic orders in skutterudite PrFe_4P_{12} is
discussed on the basis of a model with antiferro-quadrupole (AFQ) interaction
of \Gamma_3 symmetry. The high-field phase can be reproduced qualitatively
provided (i) ferro-type interactions are introduced between the dipoles as well
as between the octupoles of localized f-electrons, and (ii) separation is
vanishingly small between the \Gamma_1-\Gamma_4^{(1)} crystalline electric
field (CEF) levels. The high-field phase can have either the same ordering
vector q=(1,0,0) as in the low-field phase, or a different one q=0 depending on
the parameters. In the latter case, distortion of the crystal perpendicular to
the (111) axis is predicted. The corresponding anomaly in elastic constants
should also appear. The electrical resistivity is calculated with account of
scattering within the CEF quasi-quartet. It is found that the resistivity as a
function of the direction of magnetic field shows a sharp maximum around the
(111) axis at low temperatures because of the level crossing.Comment: 16 pages, 5 figure
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