9,232 research outputs found
B -> X_u l nu decay distributions to order alpha_s
An analytic result for the O(alpha_s corrections to the triple differential B
-> X_u l nu decay rate is presented, to leading order in the heavy-quark
expansion. This is relevant for computing partially integrated decay
distributions with arbitrary cuts on kinematic variables. Several double and
single differential distributions are derived, most of which generalize known
results. In particular, an analytic result for the O(alpha_s) corrections to
the hadronic invariant mass spectrum is presented. The effects of Fermi motion,
which are important for the description of decay spectra close to infrared
sensitive regions, are included. The behaviour of perturbation theory in the
region of time-like momenta is also investigatedComment: 24 pages, 11 figures, 1 typo in eq.(5.4) corrected; version published
in JHEP06(1999)01
Radiative meson decays and - mixing: a QCD sum rule analysis
The radiative transitions and are analysed using QCD sum-rules. The results we obtain for and are in very good agreement with
existing experimental data. The related issue of mixing is
discussed and we give predictions for the and decay
constants in the framework of a mixing scheme in the quark-flavour basis.Comment: Latex, 15 pages, 3figures. Some typos correcte
Multistability of a Josephson parametric amplifier coupled to a mechanical resonator
We study the dynamics of Josephson Parametric Amplifier (JPA) coupled to a
mechanical oscillator, as realised with a dc Superconducting Quantum
Interference Device (SQUID) with an embedded movable arm. We analyse this
system in the regime when the frequency of the mechanical oscillator is
comparable in magnitude with the plasma oscillation of the SQUID. When the
nano-mechanical resonator is driven, it strongly affects the dynamics of the
JPA. We show that this coupling can considerably modify the dynamics of JPA and
induce its multistability rather than common bistability. This analysis is
relevant if one considers a JPA for detection of mechanical motion.Comment: 8 pages, 5 figures, accepted for publication in Phys. Rev.
Shot noise in charge and magnetization currents of a quantum ring
The shot noise in a quantum ring, connected to leads, is studied in the
presence of electron interactions in the sequential tunneling regime. Two
qualitatively different noise correlations with distinctly different behaviors
are identified and studied in a large range of parameters. Noise in the total
current is due to the discreteness of the electron charge and can become
super-Poissonian as result of electron interaction. The noise in the
magnetization current is comparatively insensitive to the interaction but can
be greatly enhanced if population inversion of the angular states is assumed.
The characteristic time scales are studied by a Monte-Carlo simulation.Comment: 5 pages, 5 color figure
Measuring von Neumann entanglement entropies without wave functions
We present a method to measure the von Neumann entanglement entropy of ground
states of quantum many-body systems which does not require access to the system
wave function. The technique is based on a direct thermodynamic study of
entanglement Hamiltonians, whose functional form is available from field
theoretical insights. The method is applicable to classical simulations such as
quantum Monte Carlo methods, and to experiments that allow for thermodynamic
measurements such as the density of states, accessible via quantum quenches. We
benchmark our technique on critical quantum spin chains, and apply it to
several two-dimensional quantum magnets, where we are able to unambiguously
determine the onset of area law in the entanglement entropy, the number of
Goldstone bosons, and to check a recent conjecture on geometric entanglement
contribution at critical points described by strongly coupled field theories
The Relationship Between Banking Market Competition and Risk-taking: Do Size and Capitalization Matter?
This paper aims to study the effect of banking competition on Latin American banks' risk-taking and whether capitalization and size changes this relationship. We conclude that: (1) competition affects risk in a non-linear manner: high/low (average) competition are related to more (less) stability; (2) bank's size explains the advantage from competition, while capitalization is only positive for larger banks in this case; (3) capital ratio explains the advantage from lower competition. These results are of uttermost importance for bank regulation, especially due to the recent turmoil in worldwide financial markets.
Profit, Cost and Scale Efficiency for Latin American Banks: Concentration-Performance Relationship
Using a sample of 495 Latin American banks over the period 2001-2008, this paper investigates how bank concentration influences cost and profit efficiency. We calculate scale efficiency to assess whether these banks are close to their optimal size. We find that banks are more inefficient in profits than in costs; concentration impairs cost efficiency; larger banks have higher performance, but this advantage decreases in concentrated markets; private and foreign banks are the most efficient; most banks are operating under increasing returns of scale, which contributes to the discussion on Basel III.
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