2,095 research outputs found
Optimal detection of burst events in gravitational wave interferometric observatories
We consider the problem of detecting a burst signal of unknown shape. We
introduce a statistic which generalizes the excess power statistic proposed by
Flanagan and Hughes and extended by Anderson et al. The statistic we propose is
shown to be optimal for arbitrary noise spectral characteristic, under the two
hypotheses that the noise is Gaussian, and that the prior for the signal is
uniform. The statistic derivation is based on the assumption that a signal
affects only affects N samples in the data stream, but that no other
information is a priori available, and that the value of the signal at each
sample can be arbitrary. We show that the proposed statistic can be implemented
combining standard time-series analysis tools which can be efficiently
implemented, and the resulting computational cost is still compatible with an
on-line analysis of interferometric data. We generalize this version of an
excess power statistic to the multiple detector case, also including the effect
of correlated noise. We give full details about the implementation of the
algorithm, both for the single and the multiple detector case, and we discuss
exact and approximate forms, depending on the specific characteristics of the
noise and on the assumed length of the burst event. As a example, we show what
would be the sensitivity of the network of interferometers to a delta-function
burst.Comment: 21 pages, 5 figures in 3 groups. Submitted for publication to
Phys.Rev.D. A Mathematica notebook is available at
http://www.ligo.caltech.edu/~avicere/nda/burst/Burst.nb which allows to
reproduce the numerical results of the pape
Jeans instability in the linearized Burnett regime
Jeans instability is derived for the case of a low density self-gravitating
gas beyond the Navier-Stokes equations. The Jeans instability criterium is
shown to depend on a Burnett coefficient if the formalism is taken up to fourth
order in the wave number. It is also shown that previously known viscosity
corrections to the Jeans wave-number are enhanced if the full fourth order
formalism is applied to the stability analysis.Comment: 8 pages, no figures. Submitted to Physica
Weak Chaos in a Quantum Kepler Problem
Transition from regular to chaotic dynamics in a crystal made of singular
scatterers can be reached by varying either sigma
or lambda. We map the problem to a localization problem, and find that in all
space dimensions the transition occurs at sigma=1, i.e., Coulomb potential has
marginal singularity. We study the critical line sigma=1 by means of a
renormalization group technique, and describe universality classes of this new
transition. An RG equation is written in the basis of states localized in
momentum space. The RG flow evolves the distribution of coupling parameters to
a universal stationary distribution. Analytic properties of the RG equation are
similar to that of Boltzmann kinetic equation: the RG dynamics has integrals of
motion and obeys an H-theorem. The RG results for sigma=1 are used to derive
scaling laws for transport and to calculate critical exponents.Comment: 28 pages, ReVTeX, 4 EPS figures, to appear in the I. M. Lifshitz
memorial volume of Physics Report
Optimal generalization of power filters for gravitational wave bursts, from single to multiple detectors
Searches for gravitational wave signals which do not have a precise model
describing the shape of their waveforms are often performed using power
detectors based on a quadratic form of the data. A new, optimal method of
generalizing these power detectors so that they operate coherently over a
network of interferometers is presented. Such a mode of operation is useful in
obtaining better detection efficiencies, and better estimates of the position
of the source of the gravitational wave signal. Numerical simulations based on
a realistic, computationally efficient hierarchical implementation of the
method are used to characterize its efficiency, for detection and for position
estimation. The method is shown to be more efficient at detecting signals than
an incoherent approach based on coincidences between lists of events. It is
also shown to be capable of locating the position of the source.Comment: 16 pages, 5 figure
Nuclear spin-lattice relaxation rate in the D+iD superconducting state: implications for CoO superconductor
We calculated the nuclear spin-lattice relaxation rate for the D+iD
superconducting state with impurities. We found that small amount of unitary
impurities quickly produces the residual density of states inside the gap. As a
result, the T-linear behavior in 1/T is observed at low temperatures. Our
results show that the D+iD pairing symmetry of the superconducting state of
NaCoOH O is compatible with recent Co 1/T
experiments of several groups.Comment: 5 pages, 4 figures, minor change
LISA, binary stars, and the mass of the graviton
We extend and improve earlier estimates of the ability of the proposed LISA
(Laser Interferometer Space Antenna) gravitational wave detector to place upper
bounds on the graviton mass, m_g, by comparing the arrival times of
gravitational and electromagnetic signals from binary star systems. We show
that the best possible limit on m_g obtainable this way is ~ 50 times better
than the current limit set by Solar System measurements. Among currently known,
well-understood binaries, 4U1820-30 is the best for this purpose; LISA
observations of 4U1820-30 should yield a limit ~ 3-4 times better than the
present Solar System bound. AM CVn-type binaries offer the prospect of
improving the limit by a factor of 10, if such systems can be better understood
by the time of the LISA mission. We briefly discuss the likelihood that radio
and optical searches during the next decade will yield binaries that more
closely approach the best possible case.Comment: ReVTeX 4, 6 pages, 1 figure, submitted to Phys Rev
Renormalization Group and Decoupling in Curved Space: II. The Standard Model and Beyond
We continue the study of the renormalization group and decoupling of massive
fields in curved space, started in the previous article and analyse the higher
derivative sector of the vacuum metric-dependent action of the Standard Model.
The QCD sector at low-energies is described in terms of the composite effective
fields. For fermions and scalars the massless limit shows perfect
correspondence with the conformal anomaly, but similar limit in a massive
vector case requires an extra compensating scalar. In all three cases the
decoupling goes smoothly and monotonic. A particularly interesting case is the
renormalization group flow in the theory with broken supersymmetry, where the
sign of one of the beta-functions changes on the way from the UV to IR.Comment: 27 pages, 8 figure
The use of exp(iS[x]) in the sum over histories
The use of as the generic form for a sum over histories in
configuration space is discussed critically and placed in its proper context.
The standard derivation of the sum over paths by discretizing the paths is
reviewed, and it is shown that the form is justified only
for Schrodinger-type systems which are at most second order in the momenta.
Extending this derivation to the relativistic free particle, the causal Green's
function is expressed as a sum over timelike paths, and the Feynman Green's
function is expressed both as a sum over paths which only go one way in time
and as a sum over paths which move forward and backward in time. The weighting
of the paths is shown not to be in any of these cases. The role
of the inner product and the operator ordering of the wave equation in defining
the sum over histories is discussed.Comment: 22 pages, Latex, Imperial-TP-92-93-4
Trapping of Projectiles in Fixed Scatterer Calculations
We study multiple scattering off nuclei in the closure approximation. Instead
of reducing the dynamics to one particle potential scattering, the scattering
amplitude for fixed target configurations is averaged over the target
groundstate density via stochastic integration. At low energies a strong
coupling limit is found which can not be obtained in a first order optical
potential approximation. As its physical explanation, we propose it to be
caused by trapping of the projectile. We analyse this phenomenon in mean field
and random potential approximations.
(PACS: 24.10.-i)Comment: 15 page
Multifractality of Hamiltonians with power-law transfer terms
Finite-size effects in the generalized fractal dimensions are
investigated numerically. We concentrate on a one-dimensional disordered model
with long-range random hopping amplitudes in both the strong- and the
weak-coupling regime. At the macroscopic limit, a linear dependence of on
is found in both regimes for values of q \alt 4g^{-1}, where is the
coupling constant of the model.Comment: RevTex4, 5 two-column pages, 5 .eps figures, to be published in Phys.
Rev.
- …