55 research outputs found
Phenomenology of V_ub from Ratios of Inclusive B Decay Rates
We explore the theoretical feasibility of extracting V_ub from two ratios
built from B meson inclusive partial decays,
R_1 = Gamma(b-> u cbar s)/3Gamma(b -> c l nu), and
R_2 = [Gamma(b -> c X) - Gamma(b -> cbar X)]/Gamma(b -> c ubar d).
We discuss contributions to these quantities from perturbative and
nonperturbative physics, and show that they can be computed with overall
uncertainties at the level of 10%.Comment: 19 pages, 8 embedded EPS figures, uses REVTe
Observational constraints on an inflation model with a running mass
We explore a model of inflation where the inflaton mass-squared is generated
at a high scale by gravity-mediated soft supersymmetry breaking, and runs at
lower scales to the small value required for slow-roll inflation. The running
is supposed to come from the coupling of the inflaton to a non-Abelian gauge
field. In contrast with earlier work, we do not constrain the magnitude of the
supersymmetry breaking scale, and we find that the model might work even if
squark and slepton masses come from gauge-mediated supersymmetry breaking. With
the inflaton and gaugino masses in the expected range, and
in the range to (all at the high scale) the model can give
the observed cosmic microwave anisotropy, and a spectral index in the observed
range. The latter has significant variation with scale, which can confirm or
rule out the model in the forseeable future.Comment: Latex, 19 pages, 14 figures, uses epsf.st
Processing of ultrafine-size particulate metal matrix composites by advanced shear technology
Copyright @ 2009 ASM International. This paper was published in Metallurgical & Materials Transactions A 40A(3) and is made available as an electronic reprint with the permission of ASM International. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplications of any material in this paper for a fee or for commercial purposes, or modification of the content of this paper are prohibited.Lack of efficient mixing technology to achieve a uniform distribution of fine-size reinforcement within the matrix and the high cost of producing components have hindered the widespread adaptation of particulate metal matrix composites (PMMCs) for engineering applications. A new rheo-processing method, the melt-conditioning high-pressure die-cast (MC-HPDC) process, has been developed for manufacturing near-net-shape components of high integrity. The MC-HPDC process adapts the well-established high shear dispersive mixing action of a twin-screw mechanism to the task of overcoming the cohesive force of the agglomerates under a high shear rate and high intensity of turbulence. This is followed by direct shaping of the slurry into near-net-shape components using an existing cold-chamber die-casting process. The results indicate that the MC-HPDC samples have a uniform distribution of ultrafine-sized SiC particles throughout the entire sample in the as-cast condition. Compared to those produced by conventional high-pressure die casting (HPDC), MC-HPDC samples have a much improved tensile strength and ductility.EP-SR
Experimental Tests of Factorization in Charmless Non-Leptonic Two-Body B Decays
Using a theoretical framework based on the next-to-leading order QCD-improved
effective Hamiltonian and a factorization Ansatz for the hadronic matrix
elements of the four-quark operators, we reassess branching fractions in
two-body non-leptonic decays , involving the lowest lying
light pseudoscalar and vector mesons in the standard model. Using
the sensitivity of the decay rates on the effective number of colors, , as
a criterion of theoretical predictivity, we classify all the current-current
(tree) and penguin transitions in five different classes. The recently measured
charmless two-body decays and charge conjugates) are
dominated by the -stable QCD penguins (class-IV transitions) and their
estimates are consistent with data. The measured charmless and transition ,
on the other hand, belong to the penguin (class-V) and tree (class-III)
transitions. The class-V penguin transitions are in general more difficult to
predict. We propose a number of tests of the factorization framework in terms
of the ratios of branching ratios for some selected decays
involving light hadrons and , which depend only moderately on the
form factors. We also propose a set of measurements to determine the effective
coefficients of the current-current and QCD penguin operators. The potential
impact of decays on the CKM phenomenology is emphasized by
analyzing a number of decay rates in the factorization framework.Comment: 64 pages (LaTex) including 13 figures, requires epsfig.sty; submitted
to Phys. Rev.
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
Semileptonic Meson Decays in the Quark Model: An Update
We present the predictions of ISGW2, an update of the ISGW quark model for
semileptonic meson decays. The updated model incorporates a number of features
which should make it more reliable, including the constraints imposed by Heavy
Quark Symmetry, hyperfine distortions of wavefunctions, and form factors with
more realistic high recoil behaviors.Comment: All text and tables contained in the ".latex" file and all figures
(14) contained in the ".uu" file
mixing in the left-right supersymmetric model
We analyze mixing in a fully left-right supersymmetric
model. We give explicit expressions for all the chargino, gluino,
gluino-neutralino and neutralino amplitudes involved in the process. We
calculate the mass difference and CP asymmetry in
both the constrained case (where the only flavor violation comes from the
Cabibbo-Kobayashi-Maskawa matrix) and the unconstrained case (including soft
supersymmetry breaking terms). The constrained case does not contain any new
information beyond the supergravity-inspired MSSM. In the unconstrained case,
the main contribution to and the CP asymmetry is due to
either gluino diagrams, if the dominating flavor mixing arises in the down
squark sector, or chargino diagrams, if the dominant flavor mixing comes from
the up squark sector. We include numerical results and compare this analysis
with the ones performed in other models.Comment: 26 pages, 10 figure
Resistance to phosphine in Sitophilus oryzae in Australia: A national analysis of trends and frequencies over time and geographical spread
In Australia, along with many other parts of the world, fumigation with phosphine is a vital component in controlling stored grain insect pests. However, resistance is a factor that may limit the continued efficacy of this fumigant. While strong resistance to phosphine has been identified and characterised, very little information is available on the causes of its development and spread. Data obtained from a unique national resistance monitoring and management program were analysed, using Bayesian hurdle modelling, to determine which factors may be responsible. Fumigation in unsealed storages, combined with a high frequency of weak resistance, were found to be the main criteria that led to the development of strong resistance in Sitophilus oryzae. Independent development, rather than gene flow via migration, appears to be primarily responsible for the geographic incidence of strong resistance to phosphine in S. oryzae. This information can now be utilised to direct resources and education into those areas at high risk and to refine phosphine resistance management strategies
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