21,431 research outputs found
On Distinguishing Non-Standard Interactions from Radiative Corrections in Neutrino-Electron Scattering
We present a contribution of higher order to neutrino-electron scattering
that is a charged-current counterpart of both the anomalous axial-vector
triangle and possible non-standard interaction contributions. It arises in the
standard model with massive neutrinos, and renormalizes the nondiagonal
axial-vector form-factor at low energies. We show that, due to the small size
of radiative corrections, the neutrino-electron scattering still provides a
discovery potential for some of the non-standard neutrino interactions proposed
in the literature.Comment: 9 pages, 3 figures, change in title and context of the consideration,
results of radiative corrections unchange
Gutzwiller density functional theory for correlated electron systems
We develop a new density functional theory (DFT) and formalism for correlated
electron systems by taking as reference an interacting electron system that has
a ground state wavefunction which obeys exactly the Gutzwiller approximation
for all one particle operators. The solution of the many electron problem is
mapped onto the self-consistent solution of a set of single particle
Schroedinger equations analogous to standard DFT-LDA calculations.Comment: 4 page
Higher-order components dictate higher-order dynamics in hypergraphs
The presence of the giant component is a necessary condition for the
emergence of collective behavior in complex networked systems. Unlike networks,
hypergraphs have an important native feature that components of hypergraphs
might be of higher order, which could be defined in terms of the number of
common nodes shared between hyperedges. Although the extensive higher-order
component (HOC) could be witnessed ubiquitously in real-world hypergraphs, the
role of the giant HOC in collective behavior on hypergraphs has yet to be
elucidated. In this Letter, we demonstrate that the presence of the giant HOC
fundamentally alters the outbreak patterns of higher-order contagion dynamics
on real-world hypergraphs. Most crucially, the giant HOC is required for the
higher-order contagion to invade globally from a single seed. We confirm it by
using synthetic random hypergraphs containing adjustable and analytically
calculable giant HOC.Comment: Main: 6 pages, 4 figures. Supplementary Material: 7 pages, 7 figure
A supermassive binary black hole with triple disks
Hierarchical structure formation inevitably leads to the formation of
supermassive binary black holes (BBHs) with a sub-parsec separation in galactic
nuclei. However, to date there has been no unambiguous detection of such
systems. In an effort to search for potential observational signatures of
supermassive BBHs, we performed high-resolution smoothed particle hydrodynamics
(SPH) simulations of two black holes in a binary of moderate eccentricity
surrounded by a circumbinary disk. Building on our previous work, which has
shown that gas can periodically transfer from the circumbinary disk to the
black holes when the binary is on an eccentric orbit, the current set of
simulations focuses on the formation of the individual accretion disks, their
evolution and mutual interaction, and the predicted radiative signature. The
variation in mass transfer with orbital phase from the circumbinary disk
induces periodic variations in the light curve of the two accretion disks at
ultraviolet wavelengths, but not in the optical or near-infrared. Searches for
this signal offer a promising method to detect supermassive BBHs.Comment: Accepted for publication in the Astrophysical Journal, 16 pages, 11
figures. High Resolution Version is Available at
http://www2.yukawa.kyoto-u.ac.jp/~kimitake/bbhs.htm
Particle abundance in a thermal plasma: quantum kinetics vs. Boltzmann equation
We study the abundance of a particle species in a thermalized plasma by
introducing a quantum kinetic description based on the non-equilibrium
effective action. A stochastic interpretation of quantum kinetics in terms of a
Langevin equation emerges naturally. We consider a particle species that is
stable in the vacuum and interacts with \emph{heavier} particles that
constitute a thermal bath in equilibrium and define of a fully renormalized
single particle distribution function. The distribution function thermalizes on
a time scale determined by the \emph{quasiparticle} relaxation rate. The
equilibrium distribution function depends on the full spectral density and
features off-shell contributions to the particle abundance. A model of a
bosonic field in interaction with two \emph{heavier} bosonic fields is
studied. We find substantial departures from the Bose-Einstein result both in
the high temperature and the low temperature but high momentum region. In the
latter the abundance is exponentially suppressed but larger than the
Bose-Einstein result. We obtain the Boltzmann equation in renormalized
perturbation theory and highlight the origin of the differences. We argue that
the corrections to the abundance of cold dark matter candidates are
observationally negligible and that recombination erases any possible spectral
distortions of the CMB. However we expect that the enhancement at high
temperature may be important for baryogenesis.Comment: 39 pages, 11 figures. Clarifying remarks. To appear in Physical
Review
Substrate orientation dependence of enhanced epitaxial regrowth of silicon
This work extends the study of dopant-enhanced epitaxial regrowth rate of amorphized Si from the to the and orientations of Si. Boron and phosphorus dopants are considered. The annealing temperatures are 500 and 550 °C. Phosphorus enhances the growth rates in all three orientations by a constant factor of 8.1±0.9. Boron produces a higher enhancement factor of 12.2±1.2, except in the case of . Implications of the results on various growth models are considered. The crystalline quality of regrown layers is improved in the doped samples
Assessing Regulatory Impact Analyses: The Failure of Agencies to Comply With Executive Order 12,866
None.Environment, Health and Safety, Regulatory Reform
Assessing the Quality of Regulatory Impact Analyses
This study provides the most comprehensive evaluation of the quality of recent economic analyses that agencies conduct before finalizing major regulations. We construct a new dataset that includes analyses of forty-eight major health, safety, and environmental regulations from mid-1996 to mid-1999. This dataset provides detailed information on a variety of issues, including an agency's treatment of benefits, costs, net benefits, discounting, and uncertainty. We use this dataset to assess the quality of recent economic analyses and to determine the extent to which they are consistent with President Clinton's Executive Order 12866 and the benefit-cost guidelines issued by the Office of Management and Budget (OMB). We find that economic analyses prepared by regulatory agencies typically do not provide enough information to make decisions that will maximize the efficiency or effectiveness of a rule. Agencies quantified net benefits for only 29 percent of the rules. Agencies failed to discuss alternatives in 27 percent of the rules and quantified costs and benefits of alternatives in only 31 percent of the rules. Our findings strongly suggest that agencies generally failed to comply with the executive order and adhere to the OMB guidelines. We offer specific suggestions for improving the quality of analysis and the transparency of the regulatory process, including writing clear executive summaries, making analyses available on the Internet, providing more careful consideration of alternatives to a regulation, and estimating net benefits of a regulation when data on costs and benefits are provided.
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