773 research outputs found
Anomalous Neutrino Reactions at HERA
We study the sensitivity of HERA to new physics using the helicity suppressed
reaction , where the final neutrino can be a standard
model one or a heavy neutrino. The approach is model independent and is based
on an effective lagrangian parametrization. It is shown that HERA will put
significant bounds on the scale of new physics, though, in general, these are
more modest than previously thought. If deviations from the standard model are
observed in the above processes, future colliders such as the SSC and LHC will
be able to directly probe the physics responsible for these discrepancies}Comment: 11 Pages + 2 figures is TOPDRAWER (included at the end or available
by mail). Report UCRHEP-T113 (requires the macropackage PHYZZX). A line in
the TeX file requesting an input file has been removed, it caused problem
Aharonov-Bohm Effect and Disclinations in an Elastic Medium
In this work we investigate quasiparticles in the background of defects in
solids using the geometric theory of defects. We use the parallel transport
matrix to study the Aharonov-Bohm effect in this background. For quasiparticles
moving in this effective medium we demonstrate an effect similar to the
gravitational Aharonov- Bohm effect. We analyze this effect in an elastic
medium with one and defects.Comment: 6 pages, Revtex
Situationally-sensitive knowledge translation and relational decision making in hyperacute stroke: a qualitive study
Stroke is a leading cause of disability. Early treatment of acute ischaemic stroke with rtPA reduces the risk of longer term dependency but carries an increased risk of causing immediate bleeding complications. To understand the challenges of knowledge translation and decision making about treatment with rtPA in hyperacute stroke and hence to inform development of appropriate decision support we interviewed patients, their family and health professionals. The emergency setting and the symptomatic effects of hyper-acute stroke shaped the form, content and manner of knowledge translation to support decision making. Decision making about rtPA in hyperacute stroke presented three conundrums for patients, family and clinicians. 1) How to allow time for reflection in a severely time-limited setting. 2) How to facilitate knowledge translation regarding important treatment risks and benefits when patient and family capacity is blunted by the effects and shock of stroke. 3) How to ensure patient and family views are taken into account when the situation produces reliance on the expertise of clinicians. Strategies adopted to meet these conundrums were fourfold: face to face communication; shaping decisions; incremental provision of information; and communication tailored to the individual patient. Relational forms of interaction were understood to engender trust and allay anxiety. Shaping decisions with patients was understood as an expression of confidence by clinicians that helped alleviate anxiety and offered hope and reassurance to patients and their family experiencing the shock of the stroke event. Neutral presentations of information and treatment options promoted uncertainty and contributed to anxiety. âDrip feedingâ information created moments for reflection: clinicians literally made time. Tailoring information to the particular patient and family situation allowed clinicians to account for social and emotional contexts. The principal responses to the challenges of decision making about rtPA in hyperacute stroke were relational decision support and situationally-sensitive knowledge translation
Four-Fermi Effective Operators in Top-Quark Production and Decay
Effects of four-Fermi-type new interactions are studied in top-quark pair
production and their subsequent decays at future e^+e^- colliders.
Secondary-lepton-energy distributions are calculated for arbitrary longitudinal
beam polarizations. An optimal-observables procedure is applied for the
determination of new parameters.Comment: Polarized e^- plus unpolarized e^+ collisions were include
Statistical Mechanics of Soft Margin Classifiers
We study the typical learning properties of the recently introduced Soft
Margin Classifiers (SMCs), learning realizable and unrealizable tasks, with the
tools of Statistical Mechanics. We derive analytically the behaviour of the
learning curves in the regime of very large training sets. We obtain
exponential and power laws for the decay of the generalization error towards
the asymptotic value, depending on the task and on general characteristics of
the distribution of stabilities of the patterns to be learned. The optimal
learning curves of the SMCs, which give the minimal generalization error, are
obtained by tuning the coefficient controlling the trade-off between the error
and the regularization terms in the cost function. If the task is realizable by
the SMC, the optimal performance is better than that of a hard margin Support
Vector Machine and is very close to that of a Bayesian classifier.Comment: 26 pages, 12 figures, submitted to Physical Review
Global Study of Electron-Quark Contact Interactions
We perform a global fit of data relevant to contact interactions,
including deep inelastic scattering at high from ZEUS and H1, atomic
physics parity violation in Cesium from JILA, polarized on nuclei
scattering experiments at SLAC, Mainz and Bates, Drell-Yan production at the
Tevatron, the total hadronic cross section at LEP, and
neutrino-nucleon scattering from CCFR. With only the new HERA data, the
presence of contact interactions improves the fit compared to the Standard
Model. When other data sets are included, the size of the contact contributions
is reduced and the overall fit represents no real improvement over the Standard
Model.Comment: 26 pages (now single-spaced), Revtex, 2 eps figures, uses epsf.sty.
Some clarifications, minor corrections, 2 new references, also 3 new tables
which present 95% CL bounds on the contact interaction scales Lambd
Cumulants and the moment algebra: tools for analysing weak measurements
Recently it has been shown that cumulants significantly simplify the analysis
of multipartite weak measurements. Here we consider the mathematical structure
that underlies this, and find that it can be formulated in terms of what we
call the moment algebra. Apart from resulting in simpler proofs, the
flexibility of this structure allows generalizations of the original results to
a number of weak measurement scenarios, including one where the weakly
interacting pointers reach thermal equilibrium with the probed system.Comment: Journal reference added, minor correction
Model of the Quark Mixing Matrix
The structure of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is analyzed from
the standpoint of a composite model. A model is constructed with three families
of quarks, by taking tensor products of sufficient numbers of spin-1/2
representations and imagining the dominant terms in the mass matrix to arise
from spin-spin interactions. Generic results then obtained include the familiar
relation , and a less frequently
seen relation . The magnitudes of
and come out naturally to be of the right order. The phase in
the CKM matrix can be put in by hand, but its origin remains obscure.Comment: Presented by Mihir P. Worah at DPF 92 Meeting, Fermilab, November,
1992. 3 pages, LaTeX fil
New Solution of D=11 Supergravity on S^7 from D=4
A new static partially twisted solution of N=4, SO(4) gauged supergravity in
D=11 is obtained in this work using Cveti\^c et al embedding of four
dimensional into eleven dimensional supergravities. In four dimensions we get
two solutions: an asymptotic one corresponding to and a near horizon
fixed point solution of the form . Hence, while the former
solution has 32 supercharges the latter turns out to have only 4 conserved.
Moreover, we managed to find an exact interpolating solution, thus connecting
the above two. Aiming at a future study of duality for the theory at
hand we derived the Penrose limit of the four dimensional solutions.
Interestingly the pp-wave limit of the near horizon solution suggests itself as
being of the supernumerary supersymmetric type. In D=11 we exhibit the uplift
of the four dimensional solutions: one associated to and the
other to a foliation of , as well as their pp-wave
limits.Comment: 14 pages, LaTe
Probing Top-Quark Couplings at Polarized NLC
The energy spectrum of the lepton(s) in e^+e^- --> tt-bar --> l^{+-}
...../l^+l^-..... at next linear colliders (NLC) is studied for arbitrary
longitudinal beam polarizations as a possible test of new physics in top-quark
couplings. The most general non-standard couplings for gamma-tt-bar, Ztt-bar
and Wtb vertices are considered. Expected precision of the
non-standard-parameter determination is estimated applying the
optimal-observable procedure.Comment: Final version, To appear in Phys. Rev.
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