3,614 research outputs found
Theory and Satellite Experiment for Critical Exponent alpha of lambda-Transition in Superfluid Helium
On the basis recent seven-loop perturbation expansion for nu^{-1} = 3/(2 -
alpha) we perform a careful reinvestigation of the critical exponent alpha
governing the power behavior |T_c-T|^{- alpha} of the specific heat of
superfluid helium near the phase transition. With the help of variational
strong-coupling theory. we find alpha = - 0.01126 +- 0.0010, in very good
agreement with the space shuttle experimental value alpha = - 0.01056 +-
0.00038.Comment: Final version to be printed in Phys. Lett. A. Author Information
under http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest
update of paper also at http://www.physik.fu-berlin.de/~kleinert/28
Distinguishing Among Strong Decay Models
Two competing models for strong hadronic decays, the and
models, are currently in use.
Attempts to rule out one or the other have been hindered by a poor
understanding of final state interactions and by ambiguities in the treatment
of relativistic effects.
In this article we study meson decays in both models, focussing on certain
amplitude ratios for which the relativistic uncertainties largely cancel out
(notably the ratios in and
), and using a Quark Born Formalism to estimate the
final state interactions.
We find that the model is strongly favoured.
In addition, we predict a amplitude ratio of for the decay
.
We also study the parameter-dependence of some individual amplitudes (as
opposed to amplitude ratios), in an attempt to identify a ``best'' version of
the model.Comment: 20 pages, uuencoded postscript file with 7 figures, MIT-CTP-2295;
CMU-HEP94-1
Parity Doubling in the Meson Spectrum
A simple argument for the restoration of parity symmetry high in the hadron
spectrum is presented. The restoration scale is estimated to be 2.5 GeV. This
in turn implies that typical quark model phenomenology such as scalar
confinement or the decay model are only useful for low lying states.
Minimal requirements for constructing more general phenomenologies are
discussed. An additional mass degeneracy between and states
is shown to occur and an isovector state is predicted at roughly 1700
MeV, in contradiction with the naive quark model. Similarly, isovector and
isoscalar states are predicted at 2000 MeV. Finally, these results
imply that Regge trajectories must become nonlinear at high spin.Comment: 5 pages, revtex, no figures, no tables. Version to appear in PL
The New Heavy Mesons: A Status Report
A survey of the experimental, phenomenological, and theoretical status of the
new heavy mesons is presented. States discussed are the , ,
, , , X(3872), X(3940), Y(3940), Z(3930), and
Y(4260). Quark models for spectra, strong decays, and hadronic interactions are
reviewed and used to interpret the new states. New results for strong decay
models, bound state decays, mesonic molecules, properties of the X(3872), and
the chiral doublet model are also presented.Comment: 62 page, 40 figs, 16 tables. v3 corrects typos, adds references.
Version to appear in Physics Report
Nucleon-Meson Coupling Constants and Form Factors in the Quark Model
We demonstrate the calculation of the coupling constants and form factors
required by effective hadron lagrangians using the quark model. These relations
follow from equating expressions for strong transition amplitudes in the two
approaches. As examples we derive the NNm nucleon-meson coupling constants and
form factors for m = pi, eta, eta', sigma, a_0, omega and rho, using harmonic
oscillator quark model meson and baryon wavefunctions and the 3P0 decay model;
this is a first step towards deriving a quark-based model of the NN force at
all separations. This technique should be useful in the application of
effective lagrangians to processes in which the lack of data precludes the
direct determination of coupling constants and form factors from experiment.Comment: 7 pages, 4 figures, 1 tabl
Hybrid Decays
The heavy quark expansion of Quantum Chromodynamics and the strong coupling
flux tube picture of nonperturbative glue are employed to develop the
phenomenology of hybrid meson decays. The decay mechanism explicitly couples
gluonic degrees of freedom to the pair produced quarks and hence does not obey
the well known, but model-dependent, selection rule which states that hybrids
do not decay to pairs of L=0 mesons. However, the nonperturbative nature of
gluonic excitations in the flux tube picture leads to a new selection rule:
light hybrids do not decay to pairs of identical mesons. New features of the
model are highlighted and partial widths are presented for several low lying
hybrid states.Comment: 13 pages, 1 table, revte
Hybrid Meson Decay Phenomenology
The phenomenology of a newly developed model of hybrid meson decay is
developed. The decay mechanism is based on the heavy quark expansion of QCD and
the strong coupling flux tube picture of nonperturbative glue. A comprehensive
list of partial decay widths of a wide variety of light, , ,
and hybrid mesons is presented. Results which appear approximately
universal are highlighted along with those which distinguish different hybrid
decay models. Finally, we examine several interesting hybrid candidates in
detail.Comment: 37 pages, 2 figures, 6 tables, Revte
The networked micro-decision context: A new lens on transformative urban governance
Recent large-scale societal disruptions, from the COVID-19 pandemic to intensifying wildfires and weather events, reveal the importance of transforming governance systems so they can address complex, transboundary, and rapidly evolving crises. Yet current knowledge of the decision-making dynamics that yield transformative governance remains scant. Studies typically focus on the aggregate outputs of government decisions, while overlooking their micro-level underpinnings. This is a key oversight because drivers of policy change, such as learning or competition, are prosecuted by people rather than organizations. We respond to this knowledge gap by introducing a new analytical lens for understanding policymaking, aimed at uncovering how characteristics of decision-makers and the structure of their relationships affect their likelihood of effectuating transformative policy responses. This perspective emphasizes the need for a more dynamic and relational view on urban governance in the context of transformation
(Re)imagining spatialities for equity in mathematics education
Contemporary discourse about the âopeningâ/âclosingâ of schools and what is âinsideâ/âoutsideâ the curriculum potentially exacerbates existing inequities in mathematics education. This paper explores how different spatial imaginaries might advance or hinder efforts to deeply and systematically pursue equity. We use critical postcolonial thought for our (re)imaginings in the South African context. We argue that viewing the school, the mathematics curriculum, and language as nouned, bounded, spatial objects highlights what needs attention and for whom, but also points to the indelible, structural nature of exclusion. We propose a notion of spatiality as experienced encountering. This recognises all people and their practices as strategic agents, and emphasises relations between people, but also between the mind, body and Earth.Online Paper Presentation is available at: https://zivahub.uct.ac.za/articles/presentation/_Re_Imagining_Spatialities_for_Equity_in_Mathematics_Education_MES11/1657859
Effects of Cannabis Use on Human Behavior, Including Cognition, Motivation, and Psychosis: A Review
With a political debate about the potential risks and benefits of cannabis use as a backdrop, the wave of legalization and liberalization initiatives continues to spread. Four states (Colorado, Washington, Oregon, and Alaska) and the District of Columbia have passed laws that legalized cannabis for recreational use by adults, and 23 others plus the District of Columbia now regulate cannabis use for medical purposes. These policy changes could trigger a broad range of unintended consequences, with profound and lasting implications for the health and social systems in our country. Cannabis use is emerging as one among many interacting factors that can affect brain development and mental function. To inform the political discourse with scientific evidence, the literature was reviewed to identify what is known and not known about the effects of cannabis use on human behavior, including cognition, motivation, and psychosis
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