852 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
Reconstruction of source location in a network of gravitational wave interferometric detectors
This paper deals with the reconstruction of the direction of a gravitational
wave source using the detection made by a network of interferometric detectors,
mainly the LIGO and Virgo detectors. We suppose that an event has been seen in
coincidence using a filter applied on the three detector data streams. Using
the arrival time (and its associated error) of the gravitational signal in each
detector, the direction of the source in the sky is computed using a chi^2
minimization technique. For reasonably large signals (SNR>4.5 in all
detectors), the mean angular error between the real location and the
reconstructed one is about 1 degree. We also investigate the effect of the
network geometry assuming the same angular response for all interferometric
detectors. It appears that the reconstruction quality is not uniform over the
sky and is degraded when the source approaches the plane defined by the three
detectors. Adding at least one other detector to the LIGO-Virgo network reduces
the blind regions and in the case of 6 detectors, a precision less than 1
degree on the source direction can be reached for 99% of the sky.Comment: Accepted in Phys. Rev.
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
Analysis of Oscillator Neural Networks for Sparsely Coded Phase Patterns
We study a simple extended model of oscillator neural networks capable of
storing sparsely coded phase patterns, in which information is encoded both in
the mean firing rate and in the timing of spikes. Applying the methods of
statistical neurodynamics to our model, we theoretically investigate the
model's associative memory capability by evaluating its maximum storage
capacities and deriving its basins of attraction. It is shown that, as in the
Hopfield model, the storage capacity diverges as the activity level decreases.
We consider various practically and theoretically important cases. For example,
it is revealed that a dynamically adjusted threshold mechanism enhances the
retrieval ability of the associative memory. It is also found that, under
suitable conditions, the network can recall patterns even in the case that
patterns with different activity levels are stored at the same time. In
addition, we examine the robustness with respect to damage of the synaptic
connections. The validity of these theoretical results is confirmed by
reasonable agreement with numerical simulations.Comment: 23 pages, 11 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
Indication of insensitivity of planetary weathering behavior and habitable zone to surface land fraction
It is likely that unambiguous habitable zone terrestrial planets of unknown
water content will soon be discovered. Water content helps determine surface
land fraction, which influences planetary weathering behavior. This is
important because the silicate weathering feedback determines the width of the
habitable zone in space and time. Here a low-order model of weathering and
climate, useful for gaining qualitative understanding, is developed to examine
climate evolution for planets of various land-ocean fractions. It is pointed
out that, if seafloor weathering does not depend directly on surface
temperature, there can be no weathering-climate feedback on a waterworld. This
would dramatically narrow the habitable zone of a waterworld. Results from our
model indicate that weathering behavior does not depend strongly on land
fraction for partially ocean-covered planets. This is powerful because it
suggests that previous habitable zone theory is robust to changes in land
fraction, as long as there is some land. Finally, a mechanism is proposed for a
waterworld to prevent complete water loss during a moist greenhouse through
rapid weathering of exposed continents. This process is named a "waterworld
self-arrest," and it implies that waterworlds can go through a moist greenhouse
stage and end up as planets like Earth with partial ocean coverage. This work
stresses the importance of surface and geologic effects, in addition to the
usual incident stellar flux, for habitability.Comment: 15 pages, 6 figures, accepted at Ap
Solutions to the cosmological constant problems
We critically review several recent approaches to solving the two
cosmological constant problems. The "old" problem is the discrepancy between
the observed value of and the large values suggested by particle
physics models. The second problem is the "time coincidence" between the epoch
of galaxy formation and the epoch of -domination t_\L. It is
conceivable that the "old" problem can be resolved by fundamental physics
alone, but we argue that in order to explain the "time coincidence" we must
account for anthropic selection effects. Our main focus here is on the
discrete- models in which can change through nucleation of
branes. We consider the cosmology of this type of models in the context of
inflation and discuss the observational constraints on the model parameters.
The issue of multiple brane nucleation raised by Feng {\it et. al.} is
discussed in some detail. We also review continuous-\L models in which the
role of the cosmological constant is played by a slowly varying potential of a
scalar field. We find that both continuous and discrete models can in principle
solve both cosmological constant problems, although the required values of the
parameters do not appear very natural. M-theory-motivated brane models, in
which the brane tension is determined by the brane coupling to the four-form
field, do not seem to be viable, except perhaps in a very tight corner of the
parameter space. Finally, we point out that the time coincidence can also be
explained in models where is fixed, but the primordial density
contrast is treated as a random variable.Comment: 30 pages, 3 figures, two notes adde
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
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
Finding Z' bosons coupled preferentially to the third family at CERN LEP and the Fermilab Tevatron
Z' bosons that couple preferentially to the third generation fermions can
arise in models with extended weak (SU(2)xSU(2)) or hypercharge (U(1)xU(1))
gauge groups. We show that existing limits on quark-lepton compositeness set by
the LEP and Tevatron experiments translate into lower bounds of order a few
hundred GeV on the masses of these Z' bosons. Resonances of this mass can be
directly produced at the Tevatron. Accordingly, we explore in detail the limits
that can be set at Run II using the process p pbar -> Z' -> tau tau -> e mu. We
also comment on the possibility of using hadronically-decaying taus to improve
the limits.Comment: LaTeX2e, 24 pages (including title page), 13 figures; version 2:
corrected typographical errors and bad figure placement; version 3: added
references and updated introduction; version 4: changes to compensate for old
latex version on arXiv server; version 5: additional references, and embedded
fonts in eps files for PRD; version 6: corrected some minor typos to address
PRD referee's comment
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