45 research outputs found
Stochastic background of gravitational waves
A continuous stochastic background of gravitational waves (GWs) for burst
sources is produced if the mean time interval between the occurrence of bursts
is smaller than the average time duration of a single burst at the emission,
i.e., the so called duty cycle must be greater than one. To evaluate the
background of GWs produced by an ensemble of sources, during their formation,
for example, one needs to know the average energy flux emitted during the
formation of a single object and the formation rate of such objects as well. In
many cases the energy flux emitted during an event of production of GWs is not
known in detail, only characteristic values for the dimensionless amplitude and
frequencies are known. Here we present a shortcut to calculate stochastic
backgrounds of GWs produced from cosmological sources. For this approach it is
not necessary to know in detail the energy flux emitted at each frequency.
Knowing the characteristic values for the ``lumped'' dimensionless amplitude
and frequency we show that it is possible to calculate the stochastic
background of GWs produced by an ensemble of sources.Comment: 6 pages, 4 eps figures, (Revtex) Latex. Physical Review D (in press
Surface Gap Soliton Ground States for the Nonlinear Schr\"{o}dinger Equation
We consider the nonlinear Schr\"{o}dinger equation , with and and with periodic in each coordinate direction. This problem
describes the interface of two periodic media, e.g. photonic crystals. We study
the existence of ground state solutions (surface gap soliton ground
states) for . Using a concentration compactness
argument, we provide an abstract criterion for the existence based on ground
state energies of each periodic problem (with and ) as well as a more practical
criterion based on ground states themselves. Examples of interfaces satisfying
these criteria are provided. In 1D it is shown that, surprisingly, the criteria
can be reduced to conditions on the linear Bloch waves of the operators
and .Comment: definition of ground and bound states added, assumption (H2) weakened
(sign changing nonlinearity is now allowed); 33 pages, 4 figure
Resonant and nonresonant D+ -> K- pi+ l+ nu(l) semileptonic decays
We analyse the semileptonic decay D+ -> K- pi+ l+ nu(l) using an effective
Lagrangian developed previously to describe the decays D -> P l nu(l) and D ->
V l nu(l). Light vector mesons are included in the model which combines the
heavy quark effective Lagrangian and chiral perturbation theory approach. The
nonresonant and resonant contributions are compared. With no new parameters the
model correctly reproduces the measured ratio Gamma(nres)/Gamma(nres + res). We
also present useful nonresonant decay distributions. Finally, a similar model,
but with a modified current which satisfies the soft pion theorems at the
expense of introducing another parameter, is analyzed and the results of the
models are compared.Comment: 17 pages, 3 Postscript figures, standard Latex, extended revision,
title, abstract and text (especially Sec. IV) changed, results unchange
Light-flavor sea-quark distributions in the nucleon in the SU(3) chiral quark soliton model (I) -- phenomenological predictions --
Theoretical predictions are given for the light-flavor sea-quark
distributions including the strange quark ones on the basis of the flavor SU(3)
version of the chiral quark soliton model. Careful account is taken here of the
SU(3) symmetry breaking effects due to the mass difference between the strange
and nonstrange quarks. This effective mass difference between the
strange and nonstrange quarks is the only one parameter necessary for the
flavor SU(3) generalization of the model. A particular emphasis of study is put
on the {\it light-flavor sea-quark asymmetry} as exemplified by the observables
as well as on the {\it particle-antiparticle asymmetry} of
the strange quark distributions represented by etc. As for the unpolarized
sea-quark distributions, the predictions of the model seem qualitatively
consistent with the available phenomenological information provided by the NMC
data for , the E866 data for , the CCFR data and Barone et al.'s fit for etc. The
model is shown to give several unique predictions also for the spin-dependent
sea-quark distribution, such that and , although the verification
of these predictions must await more elaborate experimental investigations in
the near future.Comment: 36 pages, 20 EPS figures. The revised version accepted for
publication in Phys. Rev. D. The title has been changed, and the body of the
paper has been divided into two pieces, i.e.. the present one which discusses
the main phenomenological predictions of the model and the other one which
describes the detailed formulation of the flavor SU(3) chiral quark soliton
model to predict light-flavor quark and antiquark distribution functions in
the nucleo
Substructures in lens galaxies: PG1115+080 and B1555+375, two fold configurations
We study the anomalous flux ratio which is observed in some four-image lens
systems, where the source lies close to a fold caustic. In this case two of the
images are close to the critical curve and their flux ratio should be equal to
unity, instead in several cases the observed value differs significantly. The
most plausible solution is to invoke the presence of substructures, as for
instance predicted by the Cold Dark Matter scenario, located near the two
images. In particular, we analyze the two fold lens systems PG1115+080 and
B1555+375, for which there are not yet satisfactory models which explain the
observed anomalous flux ratios. We add to a smooth lens model, which reproduces
well the positions of the images but not the anomalous fluxes, one or two
substructures described as singular isothermal spheres. For PG1115+080 we
consider a smooth model with the influence of the group of galaxies described
by a SIS and a substructure with mass as well as a
smooth model with an external shear and one substructure with mass . For B1555+375 either a strong external shear or two substructures
with mass reproduce the data quite well.Comment: 26 pages, updated bibliography, Accepted for publication in
Astrophysics & Space Scienc
Cosmological distance indicators
We review three distance measurement techniques beyond the local universe:
(1) gravitational lens time delays, (2) baryon acoustic oscillation (BAO), and
(3) HI intensity mapping. We describe the principles and theory behind each
method, the ingredients needed for measuring such distances, the current
observational results, and future prospects. Time delays from strongly lensed
quasars currently provide constraints on with < 4% uncertainty, and with
1% within reach from ongoing surveys and efforts. Recent exciting discoveries
of strongly lensed supernovae hold great promise for time-delay cosmography.
BAO features have been detected in redshift surveys up to z <~ 0.8 with
galaxies and z ~ 2 with Ly- forest, providing precise distance
measurements and with < 2% uncertainty in flat CDM. Future BAO
surveys will probe the distance scale with percent-level precision. HI
intensity mapping has great potential to map BAO distances at z ~ 0.8 and
beyond with precisions of a few percent. The next years ahead will be exciting
as various cosmological probes reach 1% uncertainty in determining , to
assess the current tension in measurements that could indicate new
physics.Comment: Review article accepted for publication in Space Science Reviews
(Springer), 45 pages, 10 figures. Chapter of a special collection resulting
from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in
the Space Ag
Microlensing as a probe of the Galactic structure; 20 years of microlensing optical depth studies
Microlensing is now a very popular observational astronomical technique. The
investigations accessible through this effect range from the dark matter
problem to the search for extra-solar planets. In this review, the techniques
to search for microlensing effects and to determine optical depths through the
monitoring of large samples of stars will be described. The consequences of the
published results on the knowledge of the Milky-Way structure and its dark
matter component will be discussed. The difficulties and limitations of the
ongoing programs and the perspectives of the microlensing optical depth
technique as a probe of the Galaxy structure will also be detailed.Comment: Accepted for publication in General Relativity and Gravitation.
General Relativity and Gravitation in press (2010) 0
Mathematics of Gravitational Lensing: Multiple Imaging and Magnification
The mathematical theory of gravitational lensing has revealed many generic
and global properties. Beginning with multiple imaging, we review
Morse-theoretic image counting formulas and lower bound results, and
complex-algebraic upper bounds in the case of single and multiple lens planes.
We discuss recent advances in the mathematics of stochastic lensing, discussing
a general formula for the global expected number of minimum lensed images as
well as asymptotic formulas for the probability densities of the microlensing
random time delay functions, random lensing maps, and random shear, and an
asymptotic expression for the global expected number of micro-minima. Multiple
imaging in optical geometry and a spacetime setting are treated. We review
global magnification relation results for model-dependent scenarios and cover
recent developments on universal local magnification relations for higher order
caustics.Comment: 25 pages, 4 figures. Invited review submitted for special issue of
General Relativity and Gravitatio
Survey of Gravitationally Lensed Objects in HSC Imaging (SuGOHI): VII. Discovery and confirmation of three strongly lensed quasars
Large scale structure and cosmolog
Searching for doubly charged Higgs bosons in M\"{o}ller scattering by resonance effects at linear collider
We discuss the parity-violating left-right asymmetries (LRAs) in M\"{o}ller
scattering at the International Linear Collider (ILC) induced by doubly charged
Higgs bosons in models with triplet and singlet scalar bosons, which
couple to the left- and right-handed charged leptons, respectively. These
bosons are important in the scenarios for the generation of the neutrino mass.
We demonstrate that the contributions to the LRAs from the triplet and singlet
bosons are opposite to each other. In particular, we show that the doubly
charged Higgs boson from the singlet scalar can be tested at the ILC by using
the resonance effect.Comment: 12 pages, 5 figures; version published in Eur.Phys.J.C60:119-124,200