1,436 research outputs found
Limits on Associated Production of Visibly and Invisibly Decaying Higgs Bosons from Z Decays
Many extensions of the standard electroweak model Higgs sector suggest that
the main Higgs decay channel is "invisible", for example, where
denotes the majoron, a weakly interacting pseudoscalar Goldstone boson
associated to the spontaneous violation of lepton number. In many of these
models the Higgs boson may also be produced in association to a massive
pseudoscalar boson (HA), in addition to the standard Bjorken mechanism (HZ). We
describe a general strategy to determine limits from LEP data on the masses and
couplings of such Higgs bosons, using the existing data on acoplanar dijet
events as well as data on four and six jet event topologies. For the sake
of illustration, we present constraints that can be obtained for the ALEPH
data.Comment: FTUV/94-36, IFIC/94-31 TIFR/TH/94--25, 12 pages + 4 figures (included
as ps files at the end
The pore structure and water absorption in Portland/slag blended hardened cement paste determined by synchrotron X-ray microtomography and neutron radiography
The pore structures of hardened Portland/slag cement pastes (>75 wt% slag content), and the initial capillary absorption of moisture through these pores, were monitored using ex situ synchrotron X-ray computerised microtomography and in situ quantitative neutron radiography. The pore structure becomes more constricted as the cement hydrates and its microstructure develops. This mechanism was effective even at a slag content as high as 90 wt% in the cementitious blend, where the lowest total porosity and a significant pore refinement were identified at extended curing ages (360 d). By combining this information with neutron radiographic imaging, and directly quantifying both depth and mass of water uptake, it was observed that 90 wt% slag cement outperformed the 75 wt% slag blend at 90 days in terms of resistance to capillary water uptake, although the higher-slag blend had not yet developed such a refined microstructure at 28 days of curing. The assumptions associated with the âsharp front modelâ for water ingress do not hold true for highly substituted slag cement pastes. Testing transport properties at 28 days may not give a true indication of the performance of these materials in service in the long term
Detailed study of BBN implications of neutrino oscillation generated neutrino asymmetries in some four neutrino models
We re-examine the evolution of neutrino asymmetries in several four neutrino
models. The first case involves the direct creation of by oscillations. In the second case, we consider the mass
hierarchy where oscillations generate a large and some of
this asymmetry is converted into by oscillations. We estimate the implications for BBN for a range of
cosmologically interesting values. The present paper improves on
previous published work by taking into account the finite repopulation rate and
the time dependence of the distortions to the neutrino momentum distributions.
The treatment of chemical decoupling is also improved.Comment: Expanded discussion on the sign of the neutrino asymmetr
The Inert Doublet Model and Inelastic Dark Matter
The annual modulation observed by DAMA/NaI and DAMA/Libra may be interpreted
in terms of elastic or inelastic scattering of dark matter particles. In this
paper we confront these two scenarios within the framework of a very simple
extension of the Standard Model, the Inert Doublet Model (IDM). In this model
the dark matter candidate is a scalar, the lightest component of an extra Higgs
doublet. We first revisit the case for the elastic scattering of a light scalar
WIMP, M_DM~10 GeV, a scenario which requires that a fraction of events in DAMA
are channelled. Second we consider the possibility of inelastic Dark Matter
(iDM). This option is technically natural in the IDM, in the sense that the
mass splitting between the lightest and next-to-lightest neutral scalars may be
protected by a Peccei-Quinn (PQ) symmetry. We show that candidates with a mass
M_DM between ~535 GeV and ~50 TeV may reproduce the DAMA data and have a cosmic
abundance in agreement with WMAP. This range may be extended to candidates as
light as ~50 GeV if we exploit the possibility that the approximate PQ symmetry
is effectively conserved and that a primordial asymmetry in the dark sector may
survive until freeze-out.Comment: 16 pages, 7 figures. v2: minor changes and discussion on the
embedding in SO(10) added. v3: matches the published version in JCA
On the quasinormal modes of the de Sitter spacetime
Modifying a method by Horowitz and Hubeny for asymptotically anti-de Sitter
black holes, we establish the classical stability of the quasinormal modes of
the de Sitter spacetime. Furthermore using a straightforward method we
calculate the de Sitter quasinormal frequencies of the gravitational
perturbations and discuss some properties of the radial functions of these
quasinormal modes.Comment: 11 pages, 4 figure
Hamiltonian Description of Composite Fermions: Magnetoexciton Dispersions
A microscopic Hamiltonian theory of the FQHE, developed by Shankar and myself
based on the fermionic Chern-Simons approach, has recently been quite
successful in calculating gaps in Fractional Quantum Hall states, and in
predicting approximate scaling relations between the gaps of different
fractions. I now apply this formalism towards computing magnetoexciton
dispersions (including spin-flip dispersions) in the , 2/5, and 3/7
gapped fractions, and find approximate agreement with numerical results. I also
analyse the evolution of these dispersions with increasing sample thickness,
modelled by a potential soft at high momenta. New results are obtained for
instabilities as a function of thickness for 2/5 and 3/7, and it is shown that
the spin-polarized 2/5 state, in contrast to the spin-polarized 1/3 state,
cannot be described as a simple quantum ferromagnet.Comment: 18 pages, 18 encapsulated ps figure
Cranked Relativistic Hartree-Bogoliubov Theory: Superdeformed Bands in the Region
Cranked Relativistic Hartree-Bogoliubov (CRHB) theory is presented as an
extension of Relativistic Mean Field theory with pairing correlations to the
rotating frame. Pairing correlations are taken into account by a finite range
two-body force of Gogny type and approximate particle number projection is
performed by Lipkin-Nogami method. This theory is applied to the description of
yrast superdeformed rotational bands observed in even-even nuclei of the mass region. Using the well established parameter sets NL1 for the
Lagrangian and D1S for the pairing force one obtains a very successful
description of data such as kinematic () and dynamic ()
moments of inertia without any adjustment of new parameters. Within the present
experimental accuracy the calculated transition quadrupole moments agree
reasonably well with the observed data.Comment: 6 pages including 4 PostScript figures, uses RevTex, revised version,
Phys.Rev. C, Rapid Communications, in pres
Reflection and Ducting of Gravity Waves Inside the Sun
Internal gravity waves excited by overshoot at the bottom of the convection
zone can be influenced by rotation and by the strong toroidal magnetic field
that is likely to be present in the solar tachocline. Using a simple Cartesian
model, we show how waves with a vertical component of propagation can be
reflected when traveling through a layer containing a horizontal magnetic field
with a strength that varies with depth. This interaction can prevent a portion
of the downward-traveling wave energy flux from reaching the deep solar
interior. If a highly reflecting magnetized layer is located some distance
below the convection zone base, a duct or wave guide can be set up, wherein
vertical propagation is restricted by successive reflections at the upper and
lower boundaries. The presence of both upward- and downward-traveling
disturbances inside the duct leads to the existence of a set of horizontally
propagating modes that have significantly enhanced amplitudes. We point out
that the helical structure of these waves makes them capable of generating an
alpha-effect, and briefly consider the possibility that propagation in a shear
of sufficient strength could lead to instability, the result of wave growth due
to over-reflection.Comment: 23 pages, 5 figures. Accepted for publication in Solar Physic
Probing R-parity violating models of neutrino mass at the Tevatron via top Squark decays
We have estimated the limiting branching ratio of the R-parity violating
(RPV) decay of the lighter top squark, \tilde t_1 \ar l^+ d ( or
and d is a down type quark of any flavor), as a function of top squark
mass(\MST) for an observable signal in the di-lepton plus di-jet channel at
the Tevatron RUN-II experiment with 2 fb luminosity. Our simulations
indicate that the lepton number violating nature of the underlying decay
dynamics can be confirmed via the reconstruction of \MST. The above decay is
interesting in the context of RPV models of neutrino mass where the RPV
couplings () driving the above decay are constrained to be
small (\lsim 10^{-3} - 10^{-4} ). If is the next lightest super
particle - a theoretically well motivated scenario - then the RPV decay can
naturally compete with the R-parity conserving (RPC) modes which also have
suppressed widths. The model independent limiting BR can delineate the
parameter space in specific supersymmetric models, where the dominating RPV
decay is observable and predict the minimum magnitude of the RPV coupling that
will be sensitive to Run-II data. We have found it to be in the same ballpark
value required by models of neutrino mass, for a wide range of \MST. A
comprehensive future strategy for linking top squark decays with models of
neutrino mass is sketched.Comment: 28 pages, 14 Figure
Background model systematics for the Fermi GeV excess
The possible gamma-ray excess in the inner Galaxy and the Galactic center
(GC) suggested by Fermi-LAT observations has triggered a large number of
studies. It has been interpreted as a variety of different phenomena such as a
signal from WIMP dark matter annihilation, gamma-ray emission from a population
of millisecond pulsars, or emission from cosmic rays injected in a sequence of
burst-like events or continuously at the GC. We present the first comprehensive
study of model systematics coming from the Galactic diffuse emission in the
inner part of our Galaxy and their impact on the inferred properties of the
excess emission at Galactic latitudes and 300 MeV to 500
GeV. We study both theoretical and empirical model systematics, which we deduce
from a large range of Galactic diffuse emission models and a principal
component analysis of residuals in numerous test regions along the Galactic
plane. We show that the hypothesis of an extended spherical excess emission
with a uniform energy spectrum is compatible with the Fermi-LAT data in our
region of interest at CL. Assuming that this excess is the extended
counterpart of the one seen in the inner few degrees of the Galaxy, we derive a
lower limit of ( CL) on its extension away from the GC. We
show that, in light of the large correlated uncertainties that affect the
subtraction of the Galactic diffuse emission in the relevant regions, the
energy spectrum of the excess is equally compatible with both a simple broken
power-law of break energy GeV, and with spectra predicted by the
self-annihilation of dark matter, implying in the case of final
states a dark matter mass of GeV.Comment: 65 pages, 28 figures, 7 table
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