5,802 research outputs found
Synchronization in Complex Networks: a Comment on two recent PRL papers
I show that the conclusions of [Hwang, Chavez, Amann, & Boccaletti, PRL 94,
138701 (2005); Chavez, Hwang, Amann, Hentschel, & Boccaletti, PRL 94, 218701
(2005)] are closely related to those of previous publications.Comment: 2 page
Five-leg photon-neutrino interactions
In a first part, we justify the feasibility of substituting a photon leg by a
neutrino current in the Euler-Heisenberg Lagrangian to obtain an effective
Lagrangian for the process and its crossed
reactions.
We establish the link between these processes and the four-photon scattering
in both the Standard Model and the effective theory. As an application, we
compute in this effective theory the processes
and and show how to use the
results as a check. We settle the question of the
disagreement between two computations in the literature concerning the reaction
. In the second part, we present results of
the direct computation of the photon-neutrino five-leg processes in the
Standard Model, discuss possible astrophysical implications of our results, and
provide simple fits to the exact expressions.Comment: 6 pages, axodraw, ltwol2e, 5 figures, contributed paper to the 29th
International Conference on High Energy Physics (Vancouver
Inelastic photon-neutrino interactions using an effective Lagrangian
We justify the feasibility of substituting a photon leg by a neutrino current
in the Euler-Heisenberg Lagrangian to obtain an effective Lagrangian for the
process and its crossed reactions. We establish
the link between these processes and the four-photon scattering in both the
Standard Model and the effective theory. As an application, we compute the
processes and
, give their polarized cross sections, and
show how to use the results as a check. We settle
the question about the disagreement between two computations in the literature
concerning the reaction .Comment: 14 pages, RevTeX, axodraw, 3 figures, comment adde
The Lagrangian-space Effective Field Theory of Large Scale Structures
We introduce a Lagrangian-space Effective Field Theory (LEFT) formalism for
the study of cosmological large scale structures. Unlike the previous
Eulerian-space construction, it is naturally formulated as an effective field
theory of extended objects in Lagrangian space. In LEFT the resulting finite
size effects are described using a multipole expansion parameterized by a set
of time dependent coefficients and organized in powers of the ratio of the
wavenumber of interest over the non-linear scale . The
multipoles encode the effects of the short distance modes on the
long-wavelength universe and absorb UV divergences when present. There are no
IR divergences in LEFT. Some of the parameters that control the perturbative
approach are not assumed to be small and can be automatically resummed. We
present an illustrative one-loop calculation for a power law universe. We
describe the dynamics both at the level of the equations of motion and through
an action formalism.Comment: 38+13 pages. 3 figures. Minor changes. Version to appear in JCA
Tidal Disruption Flares: The Accretion Disk Phase
The evolution of an accretion disk, formed as a consequence of the disruption
of a star by a black hole, is followed by solving numerically the hydrodynamic
equations. The present investigation aims to study the dependence of resulting
light curves on dynamical and physical properties of such a transient disk
during its existence. One of main results derived from our simulations is that
black body fits of X-ray data tend to overestimate the true mean disk
temperature. The temperature derived from black body fits should be identified
with the color X-ray temperature rather than the average value derived from the
true temperature distribution along the disk. The time interval between the
beginning of the circularization of the bound debris and the beginning of the
accretion process by the black hole is determined by the viscous timescale,
which fixes also the raising part of the resulting light curve. The luminosity
peak coincides with the beginning of matter accretion by the black hole and the
late evolution of the light curve depends on the evolution of the debris
fallback rate. Peak bolometric luminosities are in the range 10^45-10^46 erg
s^-1 whereas peak luminosities in soft X-rays (0.2-2.0 keV) are typically one
order of magnitude lower. The timescale derived from our preferred models for
the flare luminosity to decay by two orders of magnitude is about 3-4 years.
Predicted soft X-ray light curves were fitted to data on galaxies in which a
variable X-ray emission, related to tidal events, was detected.Comment: 14 pages, 11 figures, Accepted for publication in Ap
Identifiability of parameters in latent structure models with many observed variables
While hidden class models of various types arise in many statistical
applications, it is often difficult to establish the identifiability of their
parameters. Focusing on models in which there is some structure of independence
of some of the observed variables conditioned on hidden ones, we demonstrate a
general approach for establishing identifiability utilizing algebraic
arguments. A theorem of J. Kruskal for a simple latent-class model with finite
state space lies at the core of our results, though we apply it to a diverse
set of models. These include mixtures of both finite and nonparametric product
distributions, hidden Markov models and random graph mixture models, and lead
to a number of new results and improvements to old ones. In the parametric
setting, this approach indicates that for such models, the classical definition
of identifiability is typically too strong. Instead generic identifiability
holds, which implies that the set of nonidentifiable parameters has measure
zero, so that parameter inference is still meaningful. In particular, this
sheds light on the properties of finite mixtures of Bernoulli products, which
have been used for decades despite being known to have nonidentifiable
parameters. In the nonparametric setting, we again obtain identifiability only
when certain restrictions are placed on the distributions that are mixed, but
we explicitly describe the conditions.Comment: Published in at http://dx.doi.org/10.1214/09-AOS689 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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