18,564 research outputs found
Profiles of the Unitarity Triangle and CP-Violating Phases in the Standard Model and Supersymmetric Theories
We report on a comparative study of the profile of the CKM unitarity
triangle, and the resulting CP asymmetries in B decays, in the standard model
and in several variants of the minimal supersymmetric standard model (MSSM),
characterized by a single phase in the quark flavour mixing matrix. The
supersymmetric contributions to the mass differences \Delta M_d, \Delta M_s and
to the CP-violating quantity |\epsilon| are, to an excellent approximation,
equal to each other in these theories, allowing for a particularly simple way
of implementing the resulting constraints on the elements of V_{CKM} from the
present knowledge of these quantities. Incorporating the next-to-leading-order
corrections and applying the current direct and indirect constraints on the
supersymmetric parameters, we find that the predicted ranges of \sin 2 \beta in
the standard model and in MSSM models are very similar. However, precise
measurements at B-factories and hadron machines may be able to distinguish
these theories in terms of the other two CP-violating phases \alpha and \gamma.
This is illustrated for some representative values of the supersymmetric
contributions in \Delta M_d, \Delta M_s and |\epsilon|.Comment: 30 pages, 9 figures; typos corrected, minor notation change; matches
version to appear in the European Physical Journal
Positive Student Outcomes in Community Schools
Analyzes links between participation in community school supplemental programs in extended learning, family engagement, and support, and student outcomes such as English language development scores and attitudes about school. Makes policy recommendations
Electrodynamics of superconductors
An alternate set of equations to describe the electrodynamics of
superconductors at a macroscopic level is proposed. These equations resemble
equations originally proposed by the London brothers but later discarded by
them. Unlike the conventional London equations the alternate equations are
relativistically covariant, and they can be understood as arising from the
'rigidity' of the superfluid wave function in a relativistically covariant
microscopic theory. They predict that an internal 'spontaneous' electric field
exists in superconductors, and that externally applied electric fields, both
longitudinal and transverse, are screened over a London penetration length, as
magnetic fields are. The associated longitudinal dielectric function predicts a
much steeper plasmon dispersion relation than the conventional theory, and a
blue shift of the minimum plasmon frequency for small samples. It is argued
that the conventional London equations lead to difficulties that are removed in
the present theory, and that the proposed equations do not contradict any known
experimental facts. Experimental tests are discussed.Comment: Small changes following referee's and editor's comments; to be
published in Phys.Rev.
Probing New Physics via an Angular Analysis of B --> V1 V2 decays
We show that an angular analysis of B --> V1 V2 decays yields numerous tests
for new physics in the decay amplitudes. Unlike direct CP asymmetries, many of
these new-physics observables are nonzero even if the strong phase differences
vanish. For certain observables, neither time-dependent measurements nor
tagging is necessary. Should a signal for new physics be found, one can place a
lower limit on the size of the new-physics parameters, as well as on their
effect on the measurement of the phase of B0--Bbar0 mixing.Comment: 9 pages, plain latex, no figures. Title modified slightly. Paragraph
added about viability of method. Conclusions unchanged. To be published in
Europhysics Letter
New Physics Signals through CP Violation in B -> rho,pi
We describe here a method for detecting physics beyond the standard model via
CP violation in B->rho,pi decays. Using a Dalitz-plot analysis to obtain alpha,
along with an analytical extraction of the various tree (T) and penguin (P)
amplitudes, we obtain a criterion for the absence of new physics (NP). This
criterion involves the comparison of the measured |P/T| ratio with its value as
predicted by QCD factorization. We show that the detection of NP via this
method has a good efficiency when compared with the corresponding technique
using B->pi,pi decays.Comment: 8 pages, 4 figures, talk given at MRST 2004: From Quarks to
Cosmology, Concordia University, Montreal, May 200
The “Demand Side” of Transnational Bribery and Corruption: Why Leveling the Playing Field on the Supply Side Isn’t Enough
The domestic and international legal framework for combating bribery and corruption (“ABC laws”), including both private and public corrupt practices that are transnational (cross border) in character, has dramatically expanded over the last twenty years. Despite these developments, major gaps remain. This Article examines one of the largest systemic gaps: the absence of effective tools to control the demand side of transnational bribery and corruption—the corrupt solicitation of a benefit—especially when it involves a public official
Cigarette Use and Striatal Dopamine D2/3 Receptors: Possible Role in the Link between Smoking and Nicotine Dependence.
BackgroundCigarette smoking induces dopamine release in the striatum, and smoking- or nicotine-induced ventral striatal dopamine release is correlated with nicotine dependence. Smokers also exhibit lower dopamine D2/3 receptor availability in the dorsal striatum than nonsmokers. Negative correlations of striatal dopamine D2/3 receptor availability with smoking exposure and nicotine dependence, therefore, might be expected but have not been tested.MethodsTwenty smokers had positron emission tomography scans with [18F]fallypride to measure dopamine D2/3 receptor availability in ventral and dorsal regions of the striatum and provided self-report measures of recent and lifetime smoking and of nicotine dependence.ResultsAs reported before, lifetime smoking was correlated with nicotine dependence. New findings were that ventral striatal dopamine D2/3 receptor availability was negatively correlated with recent and lifetime smoking and also with nicotine dependence.ConclusionThe results suggest an effect of smoking on ventral striatal D2/3 dopamine receptors that may contribute to nicotine dependence
Race, Ethnicity and the Dynamics of Health Insurance Coverage
Using matched data from the 1996 to 2004 Current Population Survey (CPS), we examine racial patterns in annual transitions into and out of health insurance coverage. We first decompose racial differences in static health insurance coverage rates into group differences in transition rates into and out of health insurance coverage. The low rate of health insurance coverage among African-Americans is due almost entirely to higher annual rates of losing health insurance than whites. Among the uninsured, African-Americans have similar rates of gaining health insurance in the following year as whites. Estimates from the matched CPS also indicate that the lower rate of health insurance coverage among Asians is almost entirely accounted for by a relatively high rate of losing health insurance. In contrast to these findings, differences in health insurance coverage between Latinos and whites are due to group differences in both the rate of health insurance loss and gain. Using logit regression estimates, we also calculate non-linear decompositions for the racial gaps in health insurance loss and gain. We find that two main factors are responsible for differences in health insurance loss between working-age whites and minorities: job loss and education level. Higher rates of job loss account for 30 percent of the health insurance gap for African-Americans and Asians, and 16 percent of the health insurance gap for Latinos. Lower levels of education explain roughly 15 percent of the gap for African-Americans and Latinos (Asians' higher levels of education serve to close the gap). Higher rates of welfare and SSI participation among African-Americans also serve to widen the gap in health insurance loss by 8 percent.race, health insurance, insurance dynamics
All-optical reconstruction of atomic ground-state population
The population distribution within the ground-state of an atomic ensemble is
of large significance in a variety of quantum optics processes. We present a
method to reconstruct the detailed population distribution from a set of
absorption measurements with various frequencies and polarizations, by
utilizing the differences between the dipole matrix elements of the probed
transitions. The technique is experimentally implemented on a thermal rubidium
vapor, demonstrating a population-based analysis in two optical pumping
examples. The results are used to verify and calibrate an elaborated numerical
model, and the limitations of the reconstruction scheme which result from the
symmetry properties of the dipole matrix elements are discussed.Comment: 6 pages, 4 figure
Spin currents in superconductors
It is argued that experiments on rotating superconductors provide evidence
for the existence of macroscopic spin currents in superconductors in the
absence of applied external fields. Furthermore it is shown that the model of
hole superconductivity predicts the existence of such currents in all
superconductors. In addition it is pointed out that spin currents are required
within a related macroscopic (London-like) electrodynamic description of
superconductors recently proposed. The spin current arises through an intrinsic
spin Hall effect when negative charge is expelled from the interior of the
metal upon the transition to the superconducting state
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