3,454 research outputs found
Using to Probe Top Quark Couplings
Possible anomalous couplings of the top-quark to on-shell photons and gluons
are constrained by the recent results of the CLEO Collaboration on both
inclusive and exclusive radiative decays. We find that the process \bsg\
can lead to reasonable bounds on both the anomalous electric and magnetic
dipole moments of the top-quark, while essentially no limits are obtained on
the corresponding chromoelectric and chromomagnetic moments, which enter the
expression for the decay rate only through operator mixing.Comment: 10 pages plus 6 figures (available by request), LaTex,
ANL-HEP-PR-93-3
Constraints on the R-parity- and Lepton-Flavor-Violating Couplings from B0 Decats to Two Charged Leptons
We derive the upper bounds on certain products of R-parity- and
lepton-flavor-violating couplings from the decays of the neutral meson into
two charged leptons. These modes of decays can constrain the product
combinations of the couplings with one or more heavy generation indices. We
find that most of these bounds are stronger than the previous ones.Comment: Table is changed; version to appear in Phys. Rev.
Prisoner's Dilemma cellular automata revisited: evolution of cooperation under environmental pressure
We propose an extension of the evolutionary Prisoner's Dilemma cellular
automata, introduced by Nowak and May \cite{nm92}, in which the pressure of the
environment is taken into account. This is implemented by requiring that
individuals need to collect a minimum score , representing
indispensable resources (nutrients, energy, money, etc.) to prosper in this
environment. So the agents, instead of evolving just by adopting the behaviour
of the most successful neighbour (who got ), also take into account if
is above or below the threshold . If an
individual has a probability of adopting the opposite behaviour from the one
used by its most successful neighbour. This modification allows the evolution
of cooperation for payoffs for which defection was the rule (as it happens, for
example, when the sucker's payoff is much worse than the punishment for mutual
defection). We also analyse a more sophisticated version of this model in which
the selective rule is supplemented with a "win-stay, lose-shift" criterion. The
cluster structure is analyzed and, for this more complex version we found
power-law scaling for a restricted region in the parameter space.Comment: 15 pages, 8 figures; added figures and revised tex
The Assessment of Reliability Under Range Restriction: A Comparison of α, ω, and Test–Retest Reliability for Dichotomous Data
Though much research and attention has been directed at assessing the correlation coefficient under range restriction, the assessment of reliability under range restriction has been largely ignored. This article uses item response theory to simulate dichotomous item-level data to assess the robustness of KR-20 (α), ω, and test–retest under varying selection ratios. These estimators, both corrected and uncorrected for range restriction, were compared in terms of both bias and precision. Test–retest reliability was usually the best estimator of reliability across a variety of conditions. Only under indirect range restriction did KR-20 and ω performed well. All estimators suffered imprecision as a function of range restriction, above and beyond the reduction in sample size. Based on the results, a set of recommendations are proposed.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Recalculation of QCD Corrections to Decay
We give a more complete calculation of decay, including
leading log QCD corrections from to in addition to corrections
from to . We have included the full set of dimension-6 operators
and corrected numerical mistakes of anomalous dimensions in a previous
paper\cite{Cho}. Comparing with the calculations without QCD running from
to \cite{Mis}, the inclusive decay rate is found to be enhanced.
At GeV, it results in 12\% enhancement, and for GeV, 15\% is
found. The total QCD effect makes an enhanced factor of 4.2 at GeV,
and 3.2 for GeV.Comment: 16 pages, 7 figures (uuencoded ps files), Changes of description. To
appear in Phys. Rev.
Decay and Right-handed Top-bottom Charged Current
We introduce an anomalous top quark coupling (right-handed current) into
Standard Model Lagrangian. Based on this, a more complete calculation of decay including leading log QCD corrections from to
in addition to corrections from to is given. The inclusive decay
rate is found to be suppressed comparing with the case without QCD running from
to except at the time of small values of . e.g. when
, it is only of the value given before. As
goes smaller, this contribution is an enhancement like standard model case.
From the newly experiment of CLEO Collaboration, strict restrictions to
parameters of this top-bottom quark coupling are found.Comment: 20 Pages, 2 figures( ps file uuencoded)
Analysis of Charge Asymmetry in Rare Dilepton Decays
We analyze forward-backward charge asymmetry of the lepton production in rare
decays and , including
vector-resonance effects. Certain regions of phase space, in which the
asymmetry is sensitive to individual short-distance coefficients, are pointed
out. In particular, we suggest a method to test the coupling of the leptonic
axial vector current to the left-handed quark current experimentally.Comment: 27 pages, 4 figures available up to requiremen
Flavor Symmetries and The Problem of Squark Degeneracy
If supersymmetry exists at low energies, it is necessary to understand why
the squark spectrum exhibits sufficient degeneracy to suppress flavor changing
neutral currents. In this note, we point out that gauged horizontal symmetries
can yield realistic quark mass matrices, while at the same time giving just
barely enough squark degeneracy to account for neutral -meson phenomenology.
This approach suggests likely patterns for squark masses, and indicates that
there could be significant supersymmetric contributions to and
mixing and CP violation in the and systems.Comment: preprint SCIPP 93/04,SLAC-PUB-6147, 14 pages, 4 tables included; uses
macro package TABLES.TEX and phyzzx forma
Conceptual learning : the priority for higher education
The common sense notion of learning as the all-pervasive acquisition of new behaviour and knowledge, made vivid by experience, is an incomplete characterisation, because it assumes that the learning of behaviour and the learning of knowledge are indistinguishable, and that acquisition constitutes learning without reference to transfer. A psychological level of analysis is used to argue that conceptual learning should have priority in higher education
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