10,604 research outputs found
Nonleptonic two-body B-decays including axial-vector mesons in the final state
We present a systematic study of exclusive charmless nonleptonic two-body B
decays including axial-vector mesons in the final state. We calculate branching
ratios of B\to PA, VA and AA decays, where A, V and P denote an axial-vector, a
vector and a pseudoscalar meson, respectively. We assume naive factorization
hypothesis and use the improved version of the nonrelativistic ISGW quark model
for form factors in B\to A transitions. We include contributions that arise
from the effective \Delta B=1 weak Hamiltonian H_{eff}. The respective
factorized amplitude of these decays are explicitly showed and their penguin
contributions are classified. We find that decays B^-to a_1^0\pi^-,\barB^0\to
a_1^{\pm}\pi^{\mp}, B^-\to a_1^-\bar K^0, \bar B^0\to a_1^+K^-, \bar B^0\to
f_1\bar K^0, B^-\to f_1K^-, B^-\to K_1^-(1400)\etap, B^-\to b_1^-\bar K^{0},
and \bar B^0\to b_1^+\pi^-(K^-) have branching ratios of the order of 10^{-5}.
We also study the dependence of branching ratios for B \to K_1P(V,A) decays
(K_1=K_1(1270),K_1(1400)) with respect to the mixing angle between K_A and K_B.Comment: 28 pages, 2 tables and one reference added, notation changed in
appendices, some numerical results and abstract correcte
Tensor mesons produced in tau lepton decays
Light tensor mesons (T = a_2, f_2 and K_2^*) can be produced in decays of tau
leptons. In this paper we compute the branching ratios of tau --> T pi nu
decays by assuming the dominance of intermediate virtual states to model the
form factors involved in the relevant hadronic matrix element. The exclusive
f_2(1270) pi^- decay mode turns out to have the largest branching ratio, of
O(10^-4) . Our results indicate that the contributions of tensor meson
intermediate states to the three-pseudoscalar channels of tau decays are rather
small.Comment: 10 pages, 1 figure. Version accepted for publication in PRD, some
typos are corrected and comments are added in section 4. Conclusions remain
unchange
Dynamics of soliton-like solutions for slowly varying, generalized gKdV equations: refraction vs. reflection
In this work we continue the description of soliton-like solutions of some
slowly varying, subcritical gKdV equations.
In this opportunity we describe, almost completely, the allowed behaviors:
either the soliton is refracted, or it is reflected by the potential, depending
on its initial energy. This last result describes a new type of soliton-like
solution for gKdV equations, also present in the NLS case.
Moreover, we prove that the solution is not pure at infinity, unlike the
standard gKdV soliton.Comment: 51 pages, submitte
Tuning surface metallicity and ferromagnetism by hydrogen adsorption at the polar ZnO(0001) surface
The adsorption of hydrogen on the polar Zn-ended ZnO(0001) surface has been
investigated by density functional {\it ab-initio} calculations. An on top
H(1x1) ordered overlayer with genuine H-Zn chemical bonds is shown to be
energetically favorable. The H covered surface is metallic and spin-polarized,
with a noticeable magnetic moment at the surface region. Lower hydrogen
coverages lead to strengthening of the H-Zn bonds, corrugation of the surface
layer and to an insulating surface. Our results explain experimental
observations of hydrogen adsorption on this surface, and not only predict a
metal-insulator transition, but primarily provide a method to reversible switch
surface magnetism by varying the hydrogen density on the surface.Comment: 4 pages, 3 figure
The Dog on the Ship: The "Canis Major Dwarf Galaxy" as an Outlying Part of the Argo Star System
Overdensities in the distribution of low latitude, 2MASS giant stars are
revealed by systematically peeling away from sky maps the bulk of the giant
stars conforming to ``isotropic'' density laws generally accounting for known
Milky Way components. This procedure, combined with a higher resolution
treatment of the sky density of both giants and dust allows us to probe to
lower Galactic latitudes than previous 2MASS giant star studies. While the
results show the swath of excess giants previously associated with the
Monoceros ring system in the second and third Galactic quadrants at distances
of 6-20 kpc, we also find a several times larger overdensity of giants in the
same distance range concentrated in the direction of the ancient constellation
Argo. Isodensity contours of the large structure suggest that it is highly
elongated and inclined by about 3 deg to the disk, although details of the
structure -- including the actual location of highest density, overall extent,
true shape -- and its origin, remain unknown because only a fraction of it lies
outside highly dust-obscured, low latitude regions. Nevertheless, our results
suggest that the 2MASS M giant overdensity previously claimed to represent the
core of a dwarf galaxy in Canis Major (l ~ 240 deg) is an artifact of a dust
extinction window opening to the overall density rise to the more significant
Argo structure centered at larger longitude (l ~ 290 +- 10 deg, b ~ -4 +- 2
deg).Comment: 4 pages, 4 figure
Langevin theory of absorbing phase transitions with a conserved magnitude
The recently proposed Langevin equation, aimed to capture the relevant
critical features of stochastic sandpiles, and other self-organizing systems is
studied numerically. This equation is similar to the Reggeon field theory,
describing generic systems with absorbing states, but it is coupled linearly to
a second conserved and static (non-diffusive) field. It has been claimed to
represent a new universality class, including different discrete models: the
Manna as well as other sandpiles, reaction-diffusion systems, etc. In order to
integrate the equation, and surpass the difficulties associated with its
singular noise, we follow a numerical technique introduced by Dickman. Our
results coincide remarkably well with those of discrete models claimed to
belong to this universality class, in one, two, and three dimensions. This
provides a strong backing for the Langevin theory of stochastic sandpiles, and
to the very existence of this new, yet meagerly understood, universality class.Comment: 4 pages, 3 eps figs, submitted to PR
Absorbing states and elastic interfaces in random media: two equivalent descriptions of self-organized criticality
We elucidate a long-standing puzzle about the non-equilibrium universality
classes describing self-organized criticality in sandpile models. We show that
depinning transitions of linear interfaces in random media and absorbing phase
transitions (with a conserved non-diffusive field) are two equivalent languages
to describe sandpile criticality. This is so despite the fact that local
roughening properties can be radically different in the two pictures, as
explained here. Experimental implications of our work as well as promising
paths for future theoretical investigations are also discussed.Comment: 4 pages. 2 Figure
The general relativistic infinite plane
Uniform fields are one of the simplest and most pedagogically useful examples
in introductory courses on electrostatics or Newtonian gravity. In general
relativity there have been several proposals as to what constitutes a uniform
field. In this article we examine two metrics that can be considered the
general relativistic version of the infinite plane with finite mass per unit
area. The first metric is the 4D version of the 5D "brane" world models which
are the starting point for many current research papers. The second case is the
cosmological domain wall metric. We examine to what extent these different
metrics match or deviate from our Newtonian intuition about the gravitational
field of an infinite plane. These solutions provide the beginning student in
general relativity both computational practice and conceptual insight into
Einstein's field equations. In addition they do this by introducing the student
to material that is at the forefront of current research.Comment: Accepted for publication in the American Journal of Physic
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