2,959 research outputs found
Gravitational Waves from Abelian Gauge Fields and Cosmic Strings at Preheating
Primordial gravitational waves provide a very important stochastic background
that could be detected soon with interferometric gravitational wave antennas or
indirectly via the induced patterns in the polarization anisotropies of the
cosmic microwave background. The detection of these waves will open a new
window into the early Universe, and therefore it is important to characterize
in detail all possible sources of primordial gravitational waves. In this paper
we develop theoretical and numerical methods to study the production of
gravitational waves from out-of-equilibrium gauge fields at preheating. We then
consider models of preheating after hybrid inflation, where the symmetry
breaking field is charged under a local U(1) symmetry. We analyze in detail the
dynamics of the system in both momentum and configuration space, and show that
gauge fields leave specific imprints in the resulting gravitational wave
spectra, mainly through the appearence of new peaks at characteristic
frequencies that are related to the mass scales in the problem. We also show
how these new features in the spectra correlate with string-like spatial
configurations in both the Higgs and gauge fields that arise due to the
appearance of topological winding numbers of the Higgs around Nielsen-Olesen
strings. We study in detail the time evolution of the spectrum of gauge fields
and gravitational waves as these strings evolve and decay before entering a
turbulent regime where the gravitational wave energy density saturates.Comment: This paper is dedicated to the memory of Lev Kofman. Added references
and comments in Sec. III.B. Version accepted in PR
Evidence for strong extragalactic magnetic fields from Fermi observations of TeV blazars
Magnetic fields in galaxies are produced via the amplification of seed
magnetic fields of unknown nature. The seed fields, which might exist in their
initial form in the intergalactic medium, were never detected. We report a
lower bound ~gauss on the strength of intergalactic
magnetic fields, which stems from the nonobservation of GeV gamma-ray emission
from electromagnetic cascade initiated by tera-electron volt gamma-ray in
intergalactic medium. The bound improves as if magnetic
field correlation length, , is much smaller than a megaparsec. This
lower bound constrains models for the origin of cosmic magnetic fields.Comment: 14 pages, 3 figure
A Gravitational Wave Background from Reheating after Hybrid Inflation
The reheating of the universe after hybrid inflation proceeds through the
nucleation and subsequent collision of large concentrations of energy density
in the form of bubble-like structures moving at relativistic speeds. This
generates a significant fraction of energy in the form of a stochastic
background of gravitational waves, whose time evolution is determined by the
successive stages of reheating: First, tachyonic preheating makes the amplitude
of gravity waves grow exponentially fast. Second, bubble collisions add a new
burst of gravitational radiation. Third, turbulent motions finally sets the end
of gravitational waves production. From then on, these waves propagate
unimpeded to us. We find that the fraction of energy density today in these
primordial gravitational waves could be significant for GUT-scale models of
inflation, although well beyond the frequency range sensitivity of
gravitational wave observatories like LIGO, LISA or BBO. However, low-scale
models could still produce a detectable signal at frequencies accessible to BBO
or DECIGO. For comparison, we have also computed the analogous gravitational
wave background from some chaotic inflation models and obtained results similar
to those found by other groups. The discovery of such a background would open a
new observational window into the very early universe, where the details of the
process of reheating, i.e. the Big Bang, could be explored. Moreover, it could
also serve in the future as a new experimental tool for testing the
Inflationary Paradigm.Comment: 22 pages, 18 figures, uses revtex
Strictly Anomaly Mediated Supersymmetry Breaking
We consider an MSSM extension with anomaly mediation as the source of
supersymmetry-breaking, and a U(1) symmetry which solves the tachyonic slepton
problem, and introduces both the see-saw mechanism for neutrino masses, and the
Higgs mu-term. We compare its spectra with those from so-called minimal anomaly
mediated supersymmetry breaking. We find a Standard Model-like Higgs of mass
125 GeV with a gravitino mass of 140 TeV and tan(beta)=16. However, the muon
anomalous magnetic moment is 3 sigma away from the experimental value.
The model naturally produces a period of hybrid inflation, which can exit to
a false vacuum characterised by large Higgs vevs, reaching the true ground
state after a period of thermal inflation. The scalar spectral index is reduced
to approximately 0.975, and the correct abundance of neutralino dark matter can
be produced by decays of thermally-produced gravitinos, provided the gravitino
mass (and hence the Higgs mass) is high. Naturally light cosmic strings are
produced, satisfying bounds from the Cosmic Microwave Background. The
complementary pulsar timing and cosmic ray bounds require that strings decay
primarily via loops into gravitational waves. Unless the loops are extremely
small, the next generation pulsar timing array will rule out or detect the
string-derived gravitational radiation background in this model.Comment: 38 pages, 1 figure. Discussion of 125GeV Higgs possibility, and of
U(1) decoupling limi
The impact of dementia in the prison setting: A systematic review
© The Author(s) 2018. Older prisoners are the fastest growing group in the prison population, with an accelerated aging process they are at a high risk of developing dementia. However, no systematic review has explored the impact of dementia in the prison setting. The objectives of this review were to identify the prevalence of dementia in the prison setting and how prison, health and social care providers assess, diagnose, treat, support and care for prisoners with dementia. A systematic search of the literature from the following databases was undertaken: CINHAL, PubMed, BNI, PsychINFO, and MEDLINE. Search strategies were tailored for each database and included recognised Medical Subject Headings. Hand searching of prominent journals in correctional services and dementia, as well as reference lists of included papers was completed. Open Grey website was searched to identify relevant government, local council and charity publications regarding dementia in the prison setting. The appropriate Critical Appraisal Skills Programmes Checklist for all included studies was completed. Following the application of inclusion and exclusion criteria, 10 studies were included in the review. Due to the nature of the data extracted, a meta-synthesis was not possible; therefore, a thematic synthesis was completed. Three themes emerged: prevalence of dementia in the prison population, identification of older prisoner’s needs, and knowledge of correctional officers and legal professionals. The prevalence and incidence of dementia in prison populations remain largely unknown. There is a need for national policies and local strategies that support a multi-disciplinary approach to early detection, screening and diagnosis of cognitive impairment and dementia across prison settings. Alongside the development of structured prison environments, non-pharmacological interventions, continued assessment of prisoners with a dynamic care plan, and training for health, social and prison staff and prisoners
Performances of multi-gap timing RPCs for relativistic ions in the range Z=1-6
We present the performance of Multi-gap timing RPCs under irradiation by
fully stripped relativistic ions (gamma*beta=2.7, Z=1-6). A time resolution of
80 ps at high efficiency has been obtained by just using standard `off the
shelf' 4-gap timing RPCs from the new HADES ToF wall. The resolution worsened
to 100 ps for ~ 1 kHz/cm2 proton flux and for ~ 100 Hz/cm2 Carbon flux. The
chambers were operated at a standard field of E=100 kV/cm and showed a high
stability during the experiment, supporting the fact that RPCs are a convenient
choice when accommodating a very broad range of ionizing particles is needed.
The data provides insight in the region of very highly ionizing particles (up
to x 36 mips) and can be used to constrain the existing avalanche and
Space-Charge models far from the usual `mip valley'. The implications of these
results for the general case of detection based on secondary processes (n,
gamma) resulting in highly ionizing particles with characteristic energy
distributions will be discussed, together with the nature of the time-charge
correlation curve.Comment: 31 pages, 19 figures, submitted to JINS
On the Transverse-Traceless Projection in Lattice Simulations of Gravitational Wave Production
It has recently been pointed out that the usual procedure employed in order
to obtain the transverse-traceless (TT) part of metric perturbations in lattice
simulations was inconsistent with the fact that those fields live in the
lattice and not in the continuum. It was claimed that this could lead to a
larger amplitude and a wrong shape for the gravitational wave (GW) spectra
obtained in numerical simulations of (p)reheating. In order to address this
issue, we have defined a consistent prescription in the lattice for extracting
the TT part of the metric perturbations. We demonstrate explicitly that the GW
spectra obtained with the old continuum-based TT projection only differ
marginally in amplitude and shape with respect to the new lattice-based ones.
We conclude that one can therefore trust the predictions appearing in the
literature on the spectra of GW produced during (p)reheating and similar
scenarios simulated on a lattice.Comment: 22 pages, 8 figures, Submitted to JCA
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