1,902 research outputs found
Pairing and persistent currents - the role of the far levels
We calculate the orbital magnetic response to Aharonov Bohm flux of
disordered metallic rings with attractive pairing interaction. We consider the
reduced BCS model, and obtain the result as an expansion of its exact solution
to first order in the interaction. We emphasize the connection between the
large magnetic response and the finite occupation of high energy levels in the
many-body ground state of the ring.Comment: 10 pages, contribution to MS+S200
Translation \u3cem\u3eal Mercato del Pesce\u3c/em\u3e: The Importance of Human Input for Machine Translation
This thesis investigates translation of Italian idioms and metaphors into English, and the difficulties encountered by Machine Translation in this process. I use a framework of foreign concepts to explain many of the difficulties, as well as interviews with native Italian and English speakers to provide further context for the cultural knowledge encoded in figurative language. I conclude that in Machine Translation a consistent human input interface as well as a continuous training in language corpora is crucial to improve the accuracy of translated metaphors and idioms, using Italian to English translation as a case study
Low energy scattering with a nontrivial pion
An earlier calculation in a generalized linear sigma model showed that the
well-known current algebra formula for low energy pion pion scattering held
even though the massless Nambu Goldstone pion contained a small admixture of a
two-quark two-antiquark field. Here we turn on the pion mass and note that the
current algebra formula no longer holds exactly. We discuss this small
deviation and also study the effects of an SU(3) symmetric quark mass type term
on the masses and mixings of the eight SU(3) multiplets in the model. We
calculate the s wave scattering lengths, including the beyond current algebra
theorem corrections due to the scalar mesons, and observe that the model can
fit the data well. In the process, we uncover the way in which linear sigma
models give controlled corrections (due to the presence of scalar mesons) to
the current algebra scattering formula. Such a feature is commonly thought to
exist only in the non-linear sigma model approach.Comment: 15 pages, 8 figure
Marked hydrophobicity of the NH2-terminal extra piece of immunoglobulin light-chain precursors: possible physiological functions of the extra piece.
Role of Light Vector Mesons in the Heavy Particle Chiral Lagrangian
We give the general framework for adding "light" vector particles to the
heavy hadron effective chiral Lagrangian. This has strong motivations both from
the phenomenological and aesthetic standpoints. An application to the already
observed D \rightarrow \overbar{K^*} weak transition amplitude is discussed.Comment: 19 pages, LaTeX documen
A Supersymmetric Solution to the Solar and Atmospheric Neutrino Problems
The simplest unified extension of the Minimal Supersymmetric Standard Model
with bi-linear R--Parity violation provides a predictive scheme for neutrino
masses which can account for the observed atmospheric and solar neutrino
anomalies in terms of bi-maximal neutrino mixing. The maximality of the
atmospheric mixing angle arises dynamically, by minimizing the scalar
potential, while the solar neutrino problem can be accounted for either by
large or by small mixing oscillations. One neutrino picks up mass by mixing
with neutralinos, while the degeneracy and masslessness of the other two is
lifted only by loop corrections. Despite the smallness of neutrino masses
R-parity violation is observable at present and future high-energy colliders,
providing an unambiguous cross-check of the model.Comment: 5 pages, final version published in Phys. Rev. D61, 2000, 071703(R
Generalized Bounds on Majoron-neutrino couplings
We discuss limits on neutrino-Majoron couplings both from laboratory
experiments as well as from astrophysics. They apply to the simplest class of
Majoron models which covers a variety of possibilities where neutrinos acquire
mass either via a seesaw-type scheme or via radiative corrections. By adopting
a general framework including CP phases we generalize bounds obtained
previously. The combination of complementary bounds enables us to obtain a
highly non-trivial exclusion region in the parameter space. We find that the
future double beta project GENIUS, together with constraints based on supernova
energy release arguments, could restrict neutrino-Majoron couplings down to the
10^{-7} level.Comment: 17 pages, LateX, 7 figures, version to be published in Phys. Rev.
CP-violating Majorana phases, lepton-conserving processes and final state interactions
The CP-violating phases associated with Majorana neutrinos can give rise to
CP-violating effects even in processes that conserve total Lepton number, such
as \mu -> eee+, \mu + e -> e + e and others. After explaining the reasons that
make this happen, we consider the calculation of the rates for the process of
the form \ell_a + \ell_b -> \ell_a + \ell_c, and its conjugate \bar\ell_a +
\bar\ell_b -> \bar\ell_a + \bar\ell_c, where \ell_a, \ell_b and \ell_c denote
charged leptons of different flavors. In the context of the Standard Model with
Majorana neutrinos, we show that the difference in the rates depends on such
phases. Our calculations illustrate in detail the mechanics that operate behind
the scene, and set the stage for carrying out the analogous, more complicated
(as we explain), calculations for other processes such as \mu -> eee+ and its
conjugate.Comment: Latex, axodraw, 24 page
Generalization of the Bound State Model
In the bound state approach the heavy baryons are constructed by binding,
with any orbital angular momentum, the heavy meson multiplet to the nucleon
considered as a soliton in an effective meson theory. We point out that this
picture misses an entire family of states, labeled by a different angular
momentum quantum number, which are expected to exist according to the geometry
of the three-body constituent quark model (for N_C=3). To solve this problem we
propose that the bound state model be generalized to include orbitally excited
heavy mesons bound to the nucleon. In this approach the missing angular
momentum is ``locked-up'' in the excited heavy mesons. In the simplest
dynamical realization of the picture we give conditions on a set of coupling
constants for the binding of the missing heavy baryons of arbitrary spin. The
simplifications made include working in the large M limit, neglecting nucleon
recoil corrections, neglecting mass differences among different heavy spin
multiplets and also neglecting the effects of light vector mesons.Comment: 35 pages (ReVTeX), 2 PostScript Figure
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