298 research outputs found
Gravitational Cherenkov Radiation from Extended Theories of Gravity
We linearize the field equations for higher order theories of gravity that
contain scalar invariants other than the Ricci scalar. We find that besides a
massless spin-2 field (the standard graviton), the theory contains also spin-0
and spin-2 massive modes with the latter being, in general, ghost modes. The
rate at which such particles would emit gravitational Cherenkov radiation is
calculated for some interesting physical cases.Comment: 6 pages, to appear in Mod. Phys. Lett. A. arXiv admin note: text
overlap with arXiv:0911.3094, arXiv:1105.619
Kaluza-Klein Dark Matter and Galactic Antiprotons
Extra dimensions offer new ways to address long-standing problems in beyond
the standard model particle physics. In some classes of extra-dimensional
models, the lightest Kaluza-Klein particle is a viable dark matter candidate.
In this work, we study indirect detection of Kaluza-Klein dark matter via its
annihilation into antiprotons. We use a sophisticated galactic cosmic ray
diffusion model whose parameters are fully constrained by an extensive set of
experimental data. We discuss how fluxes of cosmic antiprotons can be used to
exclude low Kaluza-Klein masses.Comment: 14 pages, 7 figures, 3 table
Antimatter research in Space
Two of the most compelling issues facing astrophysics and cosmology today are
to understand the nature of the dark matter that pervades the universe and to
understand the apparent absence of cosmological antimatter. For both issues,
sensitive measurements of cosmic-ray antiprotons and positrons, in a wide
energy range, are crucial. Many different mechanisms can contribute to
antiprotons and positrons production, ranging from conventional reactions up to
exotic processes like neutralino annihilation. The open problems are so
fundamental (i.e.: is the universe symmetric in matter and antimatter ?) that
experiments in this field will probably be of the greatest interest in the next
years. Here we will summarize the present situation, showing the different
hypothesis and models and the experimental measurements needed to lead to a
more established scenario.Comment: 10 pages, 7 figures, Invited talk at the 18th European Cosmic Ray
Symposium, Moscow, July 2002, submitted to Journal of Physics
Terahertz electric-field driven dynamical multiferroicity in SrTiO
The emergence of collective order in matter is among the most fundamental and
intriguing phenomena in physics. In recent years, the ultrafast dynamical
control and creation of novel ordered states of matter not accessible in
thermodynamic equilibrium is receiving much attention. Among those, the
theoretical concept of dynamical multiferroicity has been introduced to
describe the emergence of magnetization by means of a time-dependent electric
polarization in non-ferromagnetic materials. In simple terms, a large amplitude
coherent rotating motion of the ions in a crystal induces a magnetic moment
along the axis of rotation. However, the experimental verification of this
effect is still lacking. Here, we provide evidence of room temperature
magnetization in the archetypal paraelectric perovskite SrTiO due to this
mechanism. To achieve it, we resonantly drive the infrared-active soft phonon
mode with intense circularly polarized terahertz electric field, and detect a
large magneto-optical Kerr effect. A simple model, which includes two coupled
nonlinear oscillators whose forces and couplings are derived with ab-initio
calculations using self-consistent phonon theory at a finite temperature,
reproduces qualitatively our experimental observations on the temporal and
frequency domains. A quantitatively correct magnitude of the effect is obtained
when one also considers the phonon analogue of the reciprocal of the Einsten -
de Haas effect, also called the Barnett effect, where the total angular
momentum from the phonon order is transferred to the electronic one. Our
findings show a new path for designing ultrafast magnetic switches by means of
coherent control of lattice vibrations with light.Comment: Main text: 10 pages, 4 figures, methods and 8 supplemental figure
Ultrafast amplification and non-linear magneto-elastic coupling of coherent magnon modes in an antiferromagnet
We study the magnon dynamics of an antiferromagnetic NiO single crystal in a
pump-probe experiment with variable pump photon energy. Analysing the amplitude
of the energy-dependent photo-induced ultrafast spin dynamics, we detect a yet
unreported coupling between the material's characteristic THz- and a GHz-magnon
modes. We explain this unexpected coupling between two orthogonal eigenstates
of the corresponding Hamiltonian by modelling the magneto-elastic interaction
between spins in different domains. We find that such interaction, in the
non-linear regime, couples the two different magnon modes via the domain walls
and it can be optically exploited via the exciton-magnon resonance.Comment: 6 pages, 4 figure
Effects of dog-assisted therapies on cognitive mnemonic capabilities in people affected by Alzheimer's disease
Alzheimer’s disease (AD) is the most common cause of dementia in humans and, currently, a valid treatment is lacking. Our goal is to demonstrate the importance and benefits of the relationship with companion animals (considered as co-therapists), intended as a means of facilitating social relations and promoting evident wellbeing in AD patients. The study involved 30 randomly chosen patients with Alzheimer’s disease (group T) and three dogs. The group participated in a total of 24 animal-assisted interventions (AAIs) sessions over a span of 12 weeks, using the Mini-Mental State Examination (MMSE), Wellness and Cognitive Ability Questionnaire (Brief Assessment Cognition or BAC), and Alzheimer’s Disease Assessment Scale (ADAS) as assessment tests. A second group (group C), consisting of 10 people with AD, was enrolled as control group and underwent the same assessment tests but did not benefit from the presence of the dogs. Tests were carried out at time T0 (before starting sessions), T1 (end of sessions), and T2 (two months after last session). People belonging to group T achieved an overall improvement in their perceived state of wellbeing, even on a cognitive and mnemonic plane. However, two months after the end of the sessions, the test results in people suffering from AD decreased towards the baseline (T0). The study shows how such progress can be achieved through activities based on the relationship with an animal, as long as the animal is a steady presence in the life of the patient receiving the intervention. Dogs involved in other dog-assisted therapies have been found suitable also for assisting patients with AD
Deriving the mass of particles from Extended Theories of Gravity in LHC era
We derive a geometrical approach to produce the mass of particles that could
be suitably tested at LHC. Starting from a 5D unification scheme, we show that
all the known interactions could be suitably deduced as an induced symmetry
breaking of the non-unitary GL(4)-group of diffeomorphisms. The deformations
inducing such a breaking act as vector bosons that, depending on the
gravitational mass states, can assume the role of interaction bosons like
gluons, electroweak bosons or photon. The further gravitational degrees of
freedom, emerging from the reduction mechanism in 4D, eliminate the hierarchy
problem since generate a cut-off comparable with electroweak one at TeV scales.
In this "economic" scheme, gravity should induce the other interactions in a
non-perturbative way.Comment: 30 pages, 1 figur
Diffractive Interaction and Scaling Violation in pp->pi^0 Interaction and GeV Excess in Galactic Diffuse Gamma-Ray Spectrum of EGRET
We present here a new calculation of the gamma-ray spectrum from pp->pi^0 in
the Galactic ridge environment. The calculation includes the diffractive pp
interaction and incorporates the Feynman scaling violation for the first time.
Galactic diffuse gamma-rays come, predominantly, from pi^0->gamma gamma in the
sub-GeV to multi-GeV range. Hunter et al. found, however, an excess in the GeV
range ("GeV Excess") in the EGRET Galactic diffuse spectrum above the
prediction based on experimental pp->pi^0 cross-sections and the Feynman
scaling hypothesis. We show, in this work, that the diffractive process makes
the gamma-ray spectrum harder than the incident proton spectrum by ~0.05 in
power-law index, and, that the scaling violation produces 30-80% more pi^0 than
the scaling model for incident proton energies above 100GeV. Combination of the
two can explain about a half of the "GeV Excess" with the local cosmic proton
(power-law index ~2.7). The excess can be fully explained if the proton
spectral index in the Galactic ridge is a little harder (~0.2 in power-law
index) than the local spectrum. Given also in the paper is that the diffractive
process enhances e^+ over e^- and the scaling violation gives 50-100% higher
p-bar yield than without the violation, both in the multi-GeV range.Comment: 35 pages, 11 figures, to appear in Astrophysical Journa
A calorimeter coupled with a magnetic spectrometer for the detection of primary cosmic antiprotons
A tracking calorimeter made of 3200 brass streamer tubes together with 3200 pick-up strips has been built to complement a magnetic spectrometer in order to detect cosmic antiprotons in space. The characteristics of such a calorimeter, the results of a preliminary test of a prototype as well as the properties of the whole apparatus are presented. The apparatus, designed to operate on a balloon at an altitude of about 40 km, can be considered as a second generation detector, capable in principle to solve the problem of the presence of low energy (≤1 Ge V/c) antiprotons in the cosmic rays which is still open because of the disagreement between the existent experimental data
Clinical Effects of the Extract of the Seeds of the Indian Celery-Apium Graveolens-In Horses Affected by Chronic Osteoarthritis.
The extract of the seeds from Indian celery, Apium greaveolens (CSE), tested in experimental
animals (rodents), and in humans aected by chronic osteoarthritic diseases, exhibits anti-inflammatory
eects that can be compared, to some degree, to those of non-steroid anti-inflammatory drugs (NSAID).
In view of a potential use of CSE in the equine species, it was tested on horses aected by chronic
articular pathologies. The trial was performed on 20 horses divided into three dierent groups, orally
treated with 0 (controls), 7.0 or 30 g of CSE BID. Basic orthopedic examinations were conducted, vital
signs were observed, and blood samples collected. Improvement was observed at the highest dosage
tested (30 g of CSE BID), as reflected in the score values of three clinical parameters, (i) amplitude and
(ii) sensitivity to passive flexion and (iii) flexion test. Since the improvement of these parameters can
be correlated with a lower perception of the pain, the present data suggest that the CSE treatment can
have an analgesic eect in horses aected by chronic osteoarthritic diseases
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