6,588 research outputs found
Atmospheric considerations for CTA site search using global models
The Cherenkov Telescope Array (CTA) will be the next high-energy gamma-ray
observatory. Selection of the sites, one in each hemisphere, is not obvious
since several factors have to be taken into account. Among them, and probably
the most crucial, are the atmospheric conditions. Indeed, CTA will use the
atmosphere as a giant calorimeter, i.e. as part of the detector. The Southern
Hemisphere presents mainly four candidate sites: one in Namibia, one in Chile
and two in Argentina. Using atmospheric tools already validated in other air
shower experiments, the purpose of this work is to complete studies aiming to
choose the site with the best quality for the atmosphere. Three strong
requirements are checked: the cloud cover and the frequency of clear skies, the
wind speed and the backward trajectories of air masses travelling above the
sites and directly linked to the aerosol concentrations. It was found, that the
Namibian site is favoured, and one site in Argentina is clearly not suited.
Atmospheric measurements at these sites will be performed in the coming months
and will help with the selection of a CTA site.Comment: 4 pages, 4 figures, ECRS'12 - 23rd European Cosmic Ray Symposium
(July, 3-7, 2012) at Mosco
Precision Tests of Electroweak Physics
We review the current status of precision electroweak measurements and the
constraints they impose on new physics. We perform a model independent analysis
using the STU-formalism of Ref. 1, and then discuss how the Z-pole data from
LEP and SLD can be used to constrain models that are not covered within that
framework.Comment: 1 cover page + 8 pages, 8 postscript figures, LaTeX2e,
ws-p9-75x6-50.cls, Talk presented at Hadron 13, Mumbai, India, January 14-20,
199
Precessing supermassive black hole binaries and dark energy measurements with LISA
Spin induced precessional modulations of gravitational wave signals from
supermassive black hole binaries can improve the estimation of luminosity
distance to the source by space based gravitational wave missions like the
Laser Interferometer Space Antenna (LISA). We study how this impacts the ablity
of LISA to do cosmology, specifically, to measure the dark energy equation of
state (EOS) parameter . Using the CDM model of cosmology, we show
that observations of precessing binaries by LISA, combined with a redshift
measurement, can improve the determination of up to an order of magnitude
with respect to the non precessing case depending on the masses, mass ratio and
the redshift.Comment: 4 pages, 4 figures, version accepted to PR
Geodetic precession and frame dragging observed far from massive objects and close to a gyroscope
Total precession (geodetic precession and frame dragging) depends on the
velocity of each source of gravitation, which means that it depends on the
choice of the coordinate system. We consider the latter as an anomaly
specifically in the Gravity Probe B experiment, we investigated it and solved
this anomaly. Thus, we proved that if our present expression for the geodetic
precession is correct, then the frame dragging should be 25% less than its
predicted value.Comment: 11 page
Ground Beetles of Islands in the Western Basin of Lake Erie and the Adjacent Mainland (Coleoptera: Carabidae, Including Cicindelini)
We report 241 species representing 63 genera of ground beetles from the islands of the western basin of Lake Erie and selected mainland sites from a 1991-93 survey, plus specimens examined in public and private collections, and previously published sources. Most species are generally distributed; however, a restricted population of Sphaeroderus schaumii schaumii we rediscovered is no doubt imperiled. Comparison of wing morphotype frequencies of the Lake Erie island species with mainland populations from studies in Ohio and Michigan support a hypothesis that vagility is of increased import in the islands. Regression and correlation analysis show a positive relationship between species number and island area, no correlation between species number and distance from the mainland and an improved fit for a multiple regression which includes collecting effort
Testing Scalar-Tensor Gravity Using Space Gravitational-Wave Interferometers
We calculate the bounds which could be placed on scalar-tensor theories of
gravity of the Jordan, Fierz, Brans and Dicke type by measurements of
gravitational waveforms from neutron stars (NS) spiralling into massive black
holes (MBH) using LISA, the proposed space laser interferometric observatory.
Such observations may yield significantly more stringent bounds on the
Brans-Dicke coupling parameter \omega than are achievable from solar system or
binary pulsar measurements. For NS-MBH inspirals, dipole gravitational
radiation modifies the inspiral and generates an additional contribution to the
phase evolution of the emitted gravitational waveform. Bounds on \omega can
therefore be found by using the technique of matched filtering. We compute the
Fisher information matrix for a waveform accurate to second post-Newtonian
order, including the effect of dipole radiation, filtered using a currently
modeled noise curve for LISA, and determine the bounds on \omega for several
different NS-MBH canonical systems. For example, observations of a 1.4 solar
mass NS inspiralling to a 1000 solar mass MBH with a signal-to-noise ratio of
10 could yield a bound of \omega > 240,000, substantially greater than the
current experimental bound of \omega > 3000.Comment: 18 pages, 4 figures, 1 table; to be submitted to Phys. Rev.
Stability and Quasinormal Modes of Black holes in Tensor-Vector-Scalar theory: Scalar Field Perturbations
The imminent detection of gravitational waves will trigger precision tests of
gravity through observations of quasinormal ringing of black holes. While
General Relativity predicts just two polarizations of gravitational waves, the
so-called plus and cross polarizations, numerous alternative theories of
gravity predict up to six different polarizations which will potentially be
observed in current and future generations of gravitational wave detectors.
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory and its generalization fall
into one such class of theory that predict the full gamut of six polarizations
of gravitational waves. In this paper we begin the study of quasinormal modes
(QNMs) in TeVeS by studying perturbations of the scalar field in a spherically
symmetric background. We show that, at least in the case where superluminal
propagation of perturbations is not present, black holes are generically stable
to this kind of perturbation. We also make a unique prediction that, as the
limit of the various coupling parameters of the theory tend to zero, the QNM
spectrum tends to times the QNM spectrum induced by scalar
perturbations of a Schwarzschild black hole in General Relativity due to the
intrinsic presence of the background vector field. We further show that the QNM
spectrum does not vary significantly from this value for small values of the
theory's coupling parameters, however can vary by as much as a few percent for
larger, but still physically relevant parameters.Comment: Published in Physical Review
Probing Strong-Field Scalar-Tensor Gravity with Gravitational Wave Asteroseismology
We present an alternative way of tracing the existence of a scalar field
based on the analysis of the gravitational wave spectrum of a vibrating neutron
star. Scalar-tensor theories in strong-field gravity can potentially introduce
much greater differences in the parameters of a neutron star than the
uncertainties introduced by the various equations of state. The detection of
gravitational waves from neutron stars can set constraints on the existence and
the strength of scalar fields. We show that the oscillation spectrum is
dramatically affected by the presence of a scalar field, and can provide unique
confirmation of its existence.Comment: 14 pages, 7 figure
Model-independent test of gravity with a network of ground-based gravitational-wave detectors
The observation of gravitational waves with a global network of
interferometric detectors such as advanced LIGO, advanced Virgo, and KAGRA will
make it possible to probe into the nature of space-time structure. Besides
Einstein's general theory of relativity, there are several theories of
gravitation that passed experimental tests so far. The gravitational-wave
observation provides a new experimental test of alternative theories of gravity
because a gravitational wave may have at most six independent modes of
polarization, of which properties and number of modes are dependent on theories
of gravity. This paper proposes a method to reconstruct the independent modes
of polarization in time-series data of an advanced detector network. Since the
method does not rely on any specific model, it gives model-independent test of
alternative theories of gravity
A New Exponential Gravity
We propose a new exponential f(R) gravity model with f(R)=(R-\lambda
c)e^{\lambda(c/R)^n} and n>3, \lambda\geq 1, c>0 to explain late-time
acceleration of the universe. At the high curvature region, the model behaves
like the \LambdaCDM model. In the asymptotic future, it reaches a stable
de-Sitter spacetime. It is a cosmologically viable model and can evade the
local gravity constraints easily. This model share many features with other
f(R) dark energy models like Hu-Sawicki model and Exponential gravity model. In
it the dark energy equation of state is of an oscillating form and can cross
phantom divide line \omega_{de}=-1. In particular, in the parameter range 3<
n\leq 4, \lambda \sim 1, the model is most distinguishable from other models.
For instance, when n=4, \lambda=1, the dark energy equation of state will cross
-1 in the earlier future and has a stronger oscillating form than the other
models, the dark energy density in asymptotical future is smaller than the one
in the high curvature region. This new model can evade the local gravity tests
easily when n>3 and \lambda>1.Comment: 12 pages, 8 figure
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