381 research outputs found
Flavour physics of the RS model with KK masses reachable at LHC
The version of the higher-dimensional Randall-Sundrum (RS) model with matter
in the bulk, which addresses the gauge hierarchy problem, has additional
attractive features. In particular, it provides an intrinsic geometrical
mechanism that can explain the origin of the large mass hierarchies among the
Standard Model fermions. Within this context, a good solution for the gauge
hierarchy problem corresponds to low masses for the Kaluza-Klein (KK)
excitations of the gauge bosons. Some scenarios have been proposed in order to
render these low masses (down to a few TeV) consistent with precision
electroweak measurements. Here, we give specific and complete realizations of
this RS version with small KK masses, down to 1 TeV, which are consistent with
the entire structure of the fermions in flavour space: (1) all the last
experimental data on quark/lepton masses and mixing angles (including massive
neutrinos of Dirac type) are reproduced, (2) flavour changing neutral current
constraints are satisfied and (3) the effective suppression scales of
non-renormalizable interactions (in the physical basis) are within the bounds
set by low energy flavour phenomenology. Our result, on the possibility of
having KK gauge boson modes as light as a few TeV, constitutes one of the first
theoretical motivations for experimental searches of direct signatures at the
LHC collider, of this interesting version of the RS model which accommodates
fermion masses.Comment: 27 pages, Latex file. References and comments adde
User evaluation of a market-based recommender system
Recommender systems have been developed for a wide variety of applications (ranging from books, to holidays, to web pages). These systems have used a number of different approaches, since no one technique is best for all users in all situations. Given this, we believe that to be effective, systems should incorporate a wide variety of such techniques and then some form of overarching framework should be put in place to coordinate them so that only the best recommendations (from whatever source) are presented to the user. To this end, in our previous work, we detailed a market-based approach in which various recommender agents competed with one another to present their recommendations to the user. We showed through theoretical analysis and empirical evaluation with simulated users that an appropriately designed marketplace should be able to provide effective coordination. Building on this, we now report on the development of this multi-agent system and its evaluation with real users. Specifically, we show that our system is capable of consistently giving high quality recommendations, that the best recommendations that could be put forward are actually put forward, and that the combination of recommenders performs better than any constituent recommende
Aggressive surgical management in localized pulmonary mycotic and nonmycotic infections for neutropenic patients with acute leukemia: Report of eighteen cases
AbstractObjective: To prevent hemoptysis and relapse during subsequent chemotherapy-induced neutropenia in patients with localized forms of invasive pulmonary aspergillosis, we adopted an aggressive surgical approach. Methods: From 1988 to 1996, 18 patients with hematologic diseases were referred with the diagnosis of localized invasive pulmonary aspergillosis. The diagnosis was based on clinical features, failure to respond to antibiotic therapy, an air crescent sign suggestive of aspergillosis on the computed tomographic scan (39%), and retrieval of fungi by bronchoalveolar lavage (44%). Results: The following procedures were done: one pneumonectomy, four bilobectomies, seven lobectomies, six wedge resections, and one lobectomy with wedge resection (one patient had two procedures). No perioperative deaths or complications occurred. The histologic examination confirmed the diagnosis of invasive pulmonary aspergillosis in 12 patients. The six other diagnoses were as follows: one case of classic aspergilloma, one case of pneumonia, and four cases of pulmonary abscess. According to univariate analysis, thoracic pain was less common in the group with noninvasive pulmonary aspergillosis (1/6) than in the group with invasive pulmonary aspergillosis (8/12) (p < 0.05). Sixteen patients required subsequent hematologic treatments. Sixty-six percent of the patients are alive with a mean follow-up of 29.1 ± 27.8 months (range 2 to 103 months), with no statistically significant difference between the invasive and the noninvasive pulmonary aspergillosis groups. Five patients died of a recurrence of their malignant disease at a mean of 17.2 ± 12.5 months (range 2 to 30 months), and one had a cerebral recurrence of Aspergillus infection during a bone marrow transplantation 3 months later. Conclusion: Aggressive surgical management radically improves the prognosis of invasive pulmonary aspergillosis, even if the surgical indications include some nonmycotic infections because of the difficulty in establishing the clinical diagnosis. (J Thorac Cardiovasc Surg 1997;115:63-9
Successful Yukawa structures in Warped Extra Dimensions
For a RS model, with SM fields in the bulk and the Higgs boson on the
TeV-brane, we suggest two specific structures for the Yukawa couplings, one
based on a permutation symmetry and the other on the Universal Strength of
Yukawa couplings hypothesis (USY). In USY, all Yukawa couplings have equal
strength and the difference in the Yukawa structure lies in some complex phase.
In both scenarios, all Yukawa couplings are of the same order of magnitude.
Thus, the main features of the fermion hierarchies are explained through the RS
geometrical mechanism, and not because some Yukawa coupling is extremely small.
We find that the RS model is particularly appropriate to incorporate the
suggested Yukawa configurations. Indeed, the RS geometrical mechanism of
fermion locations along the extra dimension, combined with the two Yukawa
scenarios, reproduces all the present experimental data on fermion masses and
mixing angles. It is quite remarkable that in the USY case, only two complex
phases of definite value +-Pi/2 are sufficient to generate the known neutrino
mass differences, while at same time, permitting large leptonic mixing in
agreement with experiment.Comment: 11 page
Constraint of B_{d,s}-bar{B}_{d,s} mixing on warped extra-dimension model
Recent CDF measurement of the Bs-Bs oscillation frequency, at the Tevatron
imposes significant constraint on various models for new physics. A warped
extra-dimension model with custodial isospin symmetry accommodates the Bd-Bd
mixing at tree level mainly through the Kaluza-Klein gluons. This is due to the
misalignment between the bulk gauge eigenstates and the localized Yukawa
eigenstates of the bulk fermions. We adopt the universal 5D Yukawa coupling
model where all Yukawa couplings are of order one. The SM fermion mass spectra
and mixings are controlled by the bulk Dirac mass parameters. With two versions
of the hadronic parameter values, we investigate the implication of the
observed BB mixings on this model. The CP-violating effects on the Bd system is
shown to provide very strong constraint: The first Kaluza-Klein mass of a gluon
has its lower bound about 3.7 TeV with 1 sigma uncertainty.Comment: published version in JHEP, CP-violating effects include
Templates for Convex Cone Problems with Applications to Sparse Signal Recovery
This paper develops a general framework for solving a variety of convex cone
problems that frequently arise in signal processing, machine learning,
statistics, and other fields. The approach works as follows: first, determine a
conic formulation of the problem; second, determine its dual; third, apply
smoothing; and fourth, solve using an optimal first-order method. A merit of
this approach is its flexibility: for example, all compressed sensing problems
can be solved via this approach. These include models with objective
functionals such as the total-variation norm, ||Wx||_1 where W is arbitrary, or
a combination thereof. In addition, the paper also introduces a number of
technical contributions such as a novel continuation scheme, a novel approach
for controlling the step size, and some new results showing that the smooth and
unsmoothed problems are sometimes formally equivalent. Combined with our
framework, these lead to novel, stable and computationally efficient
algorithms. For instance, our general implementation is competitive with
state-of-the-art methods for solving intensively studied problems such as the
LASSO. Further, numerical experiments show that one can solve the Dantzig
selector problem, for which no efficient large-scale solvers exist, in a few
hundred iterations. Finally, the paper is accompanied with a software release.
This software is not a single, monolithic solver; rather, it is a suite of
programs and routines designed to serve as building blocks for constructing
complete algorithms.Comment: The TFOCS software is available at http://tfocs.stanford.edu This
version has updated reference
Motion of a driven tracer particle in a one-dimensional symmetric lattice gas
We study the dynamics of a tracer particle subject to a constant driving
force in a one-dimensional lattice gas of hard-core particles whose
transition rates are symmetric. We show that the mean displacement of the
driven tracer grows in time, , as , rather than the linear
time dependence found for driven diffusion in the bath of non-interacting
(ghost) particles. The prefactor is determined implicitly, as the
solution of a transcendental equation, for an arbitrary magnitude of the
driving force and an arbitrary concentration of the lattice gas particles. In
limiting cases the prefactor is obtained explicitly. Analytical predictions are
seen to be in a good agreement with the results of numerical simulations.Comment: 21 pages, LaTeX, 4 Postscript fugures, to be published in Phys. Rev.
E, (01Sep, 1996
Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry
In this paper we examine the role of crystal chemistry factors in creating
conditions for formation of magnetoelectric ordering in BiFeO3. It is generally
accepted that the main reason of the ferroelectric distortion in BiFeO3 is
concerned with a stereochemical activity of the Bi lone pair. However, the lone
pair is stereochemically active in the paraelectric orthorhombic beta-phase as
well. We demonstrate that a crucial role in emerging of phase transitions of
the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order
types belongs to the change of the degree of the lone pair stereochemical
activity - its consecutive increase with the temperature decrease. Using the
structural data, we calculated the sign and strength of magnetic couplings in
BiFeO3 in the range from 945 C down to 25 C and found the couplings, which
undergo the antiferromagnetic-ferromagnetic transition with the temperature
decrease and give rise to the antiferromagnetic ordering and its delay in
regard to temperature, as compared to the ferroelectric ordering. We discuss
the reasons of emerging of the spatially modulated spin structure and its
suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table
Measurements of high-energy neutron-induced fission of (nat)Pb and (209)Bi
This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly citedThe CERN Neutron Time-Of-Flight (n_TOF) facility is well suited to measure low cross sections as those of neutron-induced fission in subactinides. The cross section ratios of (nat)Pb and (209)Bi relative to (235)U and (238)U were measured using PPAC detectors and a fragment coincidence method that allows us to identify the fission events. The present experiment provides first results for neutron-induced fission up to 1 GeV. Good agreement is found with previous experimental data below 200 MeV. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross sections is close to 1 GeV
Resonance capture cross section of 207Pb
The radiative neutron capture cross section of 207Pb has been measured at the
CERN neutron time of flight installation n_TOF using the pulse height weighting
technique in the resolved energy region. The measurement has been performed
with an optimized setup of two C6D6 scintillation detectors, which allowed us
to reduce scattered neutron backgrounds down to a negligible level. Resonance
parameters and radiative kernels have been determined for 16 resonances by
means of an R-matrix analysis in the neutron energy range from 3 keV to 320
keV. Good agreement with previous measurements was found at low neutron
energies, whereas substantial discrepancies appear beyond 45 keV. With the
present results, we obtain an s-process contribution of 77(8)% to the solar
abundance of 207Pb. This corresponds to an r-process component of 23(8)%, which
is important for deriving the U/Th ages of metal poor halo stars.Comment: 7 pages, 3 figures, to be published in Phys. Rev.
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