3,147 research outputs found
Low-energy sector of 8-dimensional General Relativity: Electro-Weak model and neutrino mass
In a Kaluza-Klein space-time , we demonstrate that the
dimensional reduction of spinors provides a 4-field, whose associated SU(2)
gauge connections are geometrized. However, additional and gauge-violating
terms arise, but they are highly suppressed by a factor , which fixes
the amount of the spinor dependence on extra-coordinates. The application of
this framework to the Electro-Weak model is performed, thus giving a lower
bound for from the request of the electric charge conservation.
Moreover, we emphasize that also the Higgs sector can be reproduced, but
neutrino masses are predicted and the fine-tuning on the Higgs parameters can
be explained, too.Comment: 14 pages, 1 figure, to appear on Int. J. Mod. Phys.
The s-wave pion-nucleus optical potential
We calculate the s-wave part of the pion-nucleus optical potential using a
unitarized chiral approach that has been previously used to simultaneously
describe pionic hydrogen and deuterium data as well as low energy pi N
scattering in the vacuum. This energy dependent model allows for additional
isoscalar parts in the potential from multiple rescattering. We consider Pauli
blocking and pion polarization in an asymmetric nuclear matter environment.
Also, higher order corrections of the pi N amplitude are included. The model
can accommodate the repulsion required by phenomenological fits, though the
theoretical uncertainties are bigger than previously thought. At the same time,
we also find an enhancement of the isovector part compatible with empirical
determinations.Comment: 31 pages, 27 figure
A description of the f2(1270), rho3(1690), f4(2050), rho5(2350) and f6(2510) resonances as multi-rho(770) states
In a previous work regarding the interaction of two resonances,
the () resonance was obtained dynamically as a
two- molecule with a very strong binding energy, 135~MeV per
particle. In the present work we use the interaction in spin 2 and
isospin 0 channel to show that the resonances (),
(), () and ()
are basically molecules of increasing number of particles. We use
the fixed center approximation of the Faddeev equations to write the multi-body
interaction in terms of the two-body scattering amplitudes. We find the masses
of the states very close to the experimental values and we get an increasing
value of the binding energy per as the number of mesons is
increased.Comment: 17 pages, 6 figure
Thermodynamics of a model for RNA folding
We analyze the thermodynamic properties of a simplified model for folded RNA
molecules recently studied by G. Vernizzi, H. Orland, A. Zee (in {\it Phys.
Rev. Lett.} {\bf 94} (2005) 168103). The model consists of a chain of
one-flavor base molecules with a flexible backbone and all possible pairing
interactions equally allowed. The spatial pseudoknot structure of the model can
be efficiently studied by introducing a hermitian random matrix
model at each chain site, and associating Feynman diagrams of these models to
spatial configurations of the molecules. We obtain an exact expression for the
topological expansion of the partition function of the system. We calculate
exact and asymptotic expressions for the free energy, specific heat,
entanglement and chemical potential and study their behavior as a function of
temperature. Our results are consistent with the interpretation of as
being a measure of the concentration of in solution.Comment: 11 pages, 4 figure
Scattering of neutrinos on a polarized electron target as a test for new physics beyond the Standard Model
In this paper, we analyze the scattering of the neutrino beam on the
polarized electron target, and predict the effects of two theoretically
possible scenarios beyond the Standard Model. In both scenarios, Dirac
neutrinos are assumed to be massive.
First, we consider how the existence of CP violation phase between the
complex vector V and axial A couplings of the Left-handed neutrinos affects the
azimuthal dependence of the differential cross section. The future superbeam
and neutrino factory experiments will provide the unique opportunity for the
leptonic CP violation studies, if the large magnetized sampling calorimeters
with good event reconstruction capabilities are build.
Next, we take into account a scenario with the participation of the exotic
scalar S coupling of the Right-handed neutrinos in addition to the standard
vector V and axial A couplings of the Left-handed neutrinos. The main goal is
to show how the presence of the R-handed neutrinos, in the above process
changes the spectrum of recoil electrons in relation to the expected Standard
Model prediction, using the current limits on the non-standard couplings. The
interference terms between the standard and exotic couplings in the
differential cross section depend on the angle between the transverse
incoming neutrino polarization and the transverse electron polarization of the
target, and do not vanish in the limit of massless neutrino. The detection of
the dependence on this angle in the energy spectrum of recoil electrons would
be a signature of the presence of the R-handed neutrinos in the
neutrino-electron scattering. To make this test feasible, the polarized
artificial neutrino source needs to be identified.Comment: 11 pages, 3 eps figures, revtex, submitted to publicatio
Real time spatial cluster detection using interpoint distances among precise patient locations
BACKGROUND: Public health departments in the United States are beginning to gain timely access to health data, often as soon as one day after a visit to a health care facility. Consequently, new approaches to outbreak surveillance are being developed. When cases cluster geographically, an analysis of their spatial distribution can facilitate outbreak detection. Our method focuses on detecting perturbations in the distribution of pair-wise distances among all patients in a geographical region. Barring outbreaks, this distribution can be quite stable over time. We sought to exemplify the method by measuring its cluster detection performance, and to determine factors affecting sensitivity to spatial clustering among patients presenting to hospital emergency departments with respiratory syndromes. METHODS: The approach was to (1) define a baseline spatial distribution of home addresses for a population of patients visiting an emergency department with respiratory syndromes using historical data; (2) develop a controlled feature set simulation by inserting simulated outbreak data with varied parameters into authentic background noise, thereby creating semisynthetic data; (3) compare the observed with the expected spatial distribution; (4) establish the relative value of different alarm strategies so as to maximize sensitivity for the detection of clustering; and (5) measure factors which have an impact on sensitivity. RESULTS: Overall sensitivity to detect spatial clustering was 62%. This contrasts with an overall alarm rate of less than 5% for the same number of extra visits when the extra visits were not characterized by geographic clustering. Clusters that produced the least number of alarms were those that were small in size (10 extra visits in a week, where visits per week ranged from 120 to 472), diffusely distributed over an area with a 3 km radius, and located close to the hospital (5 km) in a region most densely populated with patients to this hospital. Near perfect alarm rates were found for clusters that varied on the opposite extremes of these parameters (40 extra visits, within a 250 meter radius, 50 km from the hospital). CONCLUSION: Measuring perturbations in the interpoint distance distribution is a sensitive method for detecting spatial clustering. When cases are clustered geographically, there is clearly power to detect clustering when the spatial distribution is represented by the M statistic, even when clusters are small in size. By varying independent parameters of simulated outbreaks, we have demonstrated empirically the limits of detection of different types of outbreaks
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
Role of heparan sulfate for attachment and entry of tick-borne encephalitis virus
AbstractAttachment of the flavivirus tick-borne encephalitis (TBE) virus to different permissive cell lines was investigated by a newly established quantitative assay using fluorescence-labeled virus. Previous work had shown that BHK-21 cell-adapted mutants of TBE virus had acquired potential heparan sulfate (HS) binding sites on the outer surface of protein E. Quantitative analysis of one of these mutants indicated that it attached to HS-expressing cell lines with a 10- to 13-fold higher affinity than wild-type TBE virus strain Neudoerfl. CHO cells deficient in HS synthesis bound less than 5% of the amount of wild-type or mutant virus that could attach to HS-containing CHO cells but were nevertheless found to be highly susceptible to infection with both viruses. Thus, even though HS is a major determinant of TBE virus attachment on HS-expressing cells, our findings suggest the existence of an alternative host cell receptor that is less abundant than HS
Probability in Orthodox Quantum Mechanics: Probability as a Postulate Versus Probability as an Emergent Phenomenon
The role of probability in quantum mechanics is reviewed, with a discussion
of the ``orthodox'' versus the statistical interpretive frameworks, and of a
number of related issues. After a brief summary of sources of unease with
quantum mechanics, a survey is given of attempts either to give a new
interpretive framework assuming quantum mechanics is exact, or to modify
quantum mechanics assuming it is a very accurate approximation to a more
fundamental theory. This survey focuses particularly on the issues of whether
probabilities in quantum mechanics are postulated or emergent.Comment: Latex; Submitted to the Proceedings of the Ischia Conference on
``Chance in Physics: Foundations and Perspectives'
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