661 research outputs found
First upper limit analysis and results from LIGO science data: stochastic background
I describe analysis of correlations in the outputs of the three LIGO
interferometers from LIGO's first science run, held over 17 days in August and
September of 2002, and the resulting upper limit set on a stochastic background
of gravitational waves. By searching for cross-correlations between the LIGO
detectors in Livingston, LA and Hanford, WA, we are able to set a 90%
confidence level upper limit of h_{100}^2 Omega_0 < 23 +/- 4.6.Comment: 7 pages; 1 eps figures; proceeding from 2003 Edoardo Amaldi Meeting
on Gravitational Wave
Ocean Dynamics and the Inner Edge of the Habitable Zone for Tidally Locked Terrestrial Planets
Recent studies have shown that ocean dynamics can have a significant warming
effect on the permanent night sides of 1 to 1 tidally locked terrestrial
exoplanets with Earth-like atmospheres and oceans in the middle of the
habitable zone. However, the impact of ocean dynamics on the habitable zone's
boundaries (inner edge and outer edge) is still unknown and represents a major
gap in our understanding of this type of planets. Here we use a coupled
atmosphere-ocean global climate model to show that planetary heat transport
from the day to night side is dominated by the ocean at lower stellar fluxes
and by the atmosphere near the inner edge of the habitable zone. This decrease
in oceanic heat transport (OHT) at high stellar fluxes is mainly due to
weakening of surface wind stress and a decrease in surface shortwave energy
deposition. We further show that ocean dynamics have almost no effect on the
observational thermal phase curves of planets near the inner edge of the
habitable zone. For planets in the habitable zone's middle range, ocean
dynamics moves the hottest spot on the surface eastward from the substellar
point. These results suggest that future studies of the inner edge may devote
computational resources to atmosphere-only processes such as clouds and
radiation. For studies of the middle range and outer edge of the habitable
zone, however, fully coupled ocean-atmosphere modeling will be necessary. Note
that due to computational resource limitations, only one rotation period (60
Earth days) has been systematically examined in this study; future work varying
rotation period as well as other parameters such as atmospheric mass and
composition is required.Comment: 34 pages, 13 figures, and 1 tabl
The Primordial Gravitational Wave Background in String Cosmology
We find the spectrum P(w)dw of the gravitational wave background produced in
the early universe in string theory. We work in the framework of String Driven
Cosmology, whose scale factors are computed with the low-energy effective
string equations as well as selfconsistent solutions of General Relativity with
a gas of strings as source. The scale factor evolution is described by an early
string driven inflationary stage with an instantaneous transition to a
radiation dominated stage and successive matter dominated stage. This is an
expanding string cosmology always running on positive proper cosmic time. A
careful treatment of the scale factor evolution and involved transitions is
made. A full prediction on the power spectrum of gravitational waves without
any free-parameters is given. We study and show explicitly the effect of the
dilaton field, characteristic to this kind of cosmologies. We compute the
spectrum for the same evolution description with three differents approachs.
Some features of gravitational wave spectra, as peaks and asymptotic
behaviours, are found direct consequences of the dilaton involved and not only
of the scale factor evolution. A comparative analysis of different treatments,
solutions and compatibility with observational bounds or detection perspectives
is made.Comment: LaTeX, 50 pages with 2 figures. Uses epsfig and psfra
Narrow-band search of continuous gravitational-wave signals from Crab and Vela pulsars in Virgo VSR4 data
In this paper we present the results of a coherent narrow-band search for continuous gravitational-wave signals from the Crab and Vela pulsars conducted on Virgo VSR4 data. In order to take into account a possible small mismatch between the gravitational-wave frequency and two times the star rotation frequency, inferred from measurement of the electromagnetic pulse rate, a range of 0.02 Hz around two times the star rotational frequency has been searched for both the pulsars. No evidence for a signal has been found and 95% confidence level upper limits have been computed assuming both that polarization parameters are completely unknown and that they are known with some uncertainty, as derived from x-ray observations of the pulsar wind torii. For Vela the upper limits are comparable to the spin-down limit, computed assuming that all the observed spin-down is due to the emission of gravitational waves. For Crab the upper limits are about a factor of 2 below the spin-down limit, and represent a significant improvement with respect to past analysis. This is the first time the spin-down limit is significantly overcome in a narrow-band search.Fil: Quiroga, Gonzalo Damián. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Relatividad y Gravitacion; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Maglione, Cesar German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Relatividad y Gravitacion; ArgentinaFil: Reula, Oscar Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Relatividad y Gravitacion; ArgentinaFil: Aasi, J.. California Institute of Technology; Estados UnidosFil: Abbot, B. P.. California Institute of Technology; Estados UnidosFil: Abbot, R.. California Institute of Technology; Estados UnidosFil: Abbot, T.. State University of Louisiana; Estados UnidosFil: Abernathy, M. R.. California Institute of Technology; Estados UnidosFil: Acernese, F.. Universita di Salerno; Italia. Istituto Nazionale di Fisica Nucleare; ItaliaFil: Ackley, K.. University of Florida; Estados UnidosFil: Adams, C.. LIGO Livingston Observatory; Estados UnidosFil: Adams, T.. Universite de Savoie. Laboratoire d’Annecy-le-Vieux de Physique des Particules; Francia. Cardiff University; Reino UnidoFil: Adams, T.. Universite de Savoie. Laboratoire d’Annecy-le-Vieux de Physique des Particules; FranciaFil: Addesso, P.. University of Sannio at Benevento; ItaliaFil: Adhikar, R. X.. California Institute of Technology; Estados UnidosFil: Adya, V.. Max-Planck-Institut für Gravitationsphysik; AlemaniaFil: Affeldt, C.. Max-Planck-Institut für Gravitationsphysik; AlemaniaFil: Agathos, M.. Nikhef; Science Park; Países BajosFil: Agatsuma, K.. Nikhef; Science Park; Países BajosFil: Aggarwal, N.. Massachusetts Institute of Technology; Estados UnidosFil: Aguiar, O. D.. Centro de Previsao de Tempo e Estudos Climáticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Ain, A.. Inter-University Centre for Astronomy and Astrophysics; IndiaFil: Ajith, P.. Tata Institute of Fundamental Research; IndiaFil: Alemic, A.. Syracuse University; Estados UnidosFil: Allen, B.. Max-Planck-Institut für Gravitationsphysik; Alemania. University of Wisconsin; Estados UnidosFil: Allocca, A.. Università degli Studi di Siena; Italia. Istituto Nazionale di Fisica Nucleare; ItaliaFil: Amariutei, D.. University of Florida; Estados UnidosFil: Anderson, S. B.. California Institute of Technology; Estados UnidosFil: Anderson, W. G.. University of Wisconsin; Estados UnidosFil: Arai, K.. California Institute of Technology; Estados Unido
Long term study of the seismic environment at LIGO
The LIGO experiment aims to detect and study gravitational waves using ground
based laser interferometry. A critical factor to the performance of the
interferometers, and a major consideration in the design of possible future
upgrades, is isolation of the interferometer optics from seismic noise. We
present the results of a detailed program of measurements of the seismic
environment surrounding the LIGO interferometers. We describe the experimental
configuration used to collect the data, which was acquired over a 613 day
period. The measurements focused on the frequency range 0.1-10 Hz, in which the
secondary microseismic peak and noise due to human activity in the vicinity of
the detectors was found to be particularly critical to interferometer
performance. We compare the statistical distribution of the data sets from the
two interferometer sites, construct amplitude spectral densities of seismic
noise amplitude fluctuations with periods of up to 3 months, and analyze the
data for any long term trends in the amplitude of seismic noise in this
critical frequency range.Comment: To be published in Classical and Quantum Gravity. 24 pages, 15
figure
Do Quarks Obey D-Brane Dynamics?
The potential between two D0-branes at rest is calculated to be a linear.
Also the potential between two fast decaying D0-branes is found in agreement
with phenomenological heavy-quark potentials.Comment: 7 pages, no figures, LaTe
Global structure of exact cosmological solutions in the brane world
We find the explicit coordinate transformation which links two exact
cosmological solutions of the brane world which have been recently discovered.
This means that both solutions are exactly the same with each other. One of two
solutions is described by the motion of a domain wall in the well-known
5-dimensional Schwarzshild-AdS spacetime. Hence, we can easily understand the
region covered by the coordinate used by another solution.Comment: Latex, 9 pages including 5 figures; references add, accepted for
publication in Physical Review
X-ray emission during the muonic cascade in hydrogen
We report our investigations of X rays emitted during the muonic cascade in
hydrogen employing charge coupled devices as X-ray detectors. The density
dependence of the relative X-ray yields for the muonic hydrogen lines (K_alpha,
K_beta, K_gamma) has been measured at densities between 0.00115 and 0.97 of
liquid hydrogen density. In this density region collisional processes dominate
the cascade down to low energy levels. A comparison with recent calculations is
given in order to demonstrate the influence of Coulomb deexcitation.Comment: 5 pages, Tex, 4 figures, submitted to Physical Review Letter
Coherent method for detection of gravitational wave bursts
We describe a coherent network algorithm for detection and reconstruction of
gravitational wave bursts. The algorithm works for two and more arbitrarily
aligned detectors and can be used for both all-sky and triggered burst
searches. We describe the main components of the algorithm, including the
time-frequency analysis in wavelet domain, construction of the likelihood
time-frequency maps, the identification and selection of burst events.Comment: 11 pages, 3 figures, proceedings of Amaldi conference in Sydney,
Australi
Normal modes for metric fluctuations in a class of higher-dimensional backgrounds
We discuss a gauge invariant approach to the theory of cosmological
perturbations in a higher-dimensonal background. We find the normal modes which
diagonalize the perturbed action, for a scalar field minimally coupled to
gravity, in a higher-dimensional manifold M of the Bianchi-type I, under the
assumption that the translations along an isotropic spatial subsection of M are
isometries of the full, perturbed background. We show that, in the absence of
scalar field potential, the canonical variables for scalar and tensor metric
perturbations satisfy exactly the same evolution equation, and we discuss the
possible dependence of the spectrum on the number of internal dimensions.Comment: 19 pages, LATEX, an explicit example is added to discuss the possible
dependence of the perturbation spectrum on the number of internal dimensions.
To apper in Class. Quantum Gra
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