421 research outputs found
A connection between inclusive semileptonic decays of bound and free heavy quarks
A relativistic constituent quark model, formulated on the light-front, is
used to derive a new parton approximation for the inclusive semileptonic decay
width of the B-meson. A simple connection between the decay rate of a free
heavy-quark and the one of a heavy-quark bound in a meson or in a baryon is
established. The main features of the new approach are the treatment of the
b-quark as an on-mass-shell particle and the inclusion of the effects arising
from the b-quark transverse motion in the B-meson. In a way conceptually
similar to the deep-inelastic scattering case, the B-meson inclusive width is
expressed as the integral of the free b-quark partial width multiplied by a
bound-state factor related to the b-quark distribution function in the B-meson.
The non-perturbative meson structure is described through various quark-model
wave functions, constructed via the Hamiltonian light-front formalism using as
input both relativized and non-relativistic potential models. A link between
spectroscopic quark models and the B-meson decay physics is obtained in this
way. Our predictions for the B -> X_c l nu_l and B -> X_u l nu_l decays are
used to extract the CKM parameters |V_cb| and |V_ub| from available inclusive
data. After averaging over the various quark models adopted and including
leading-order perturbative QCD corrections, we obtain |V_cb| = (43.0 +/-
0.7_exp +/- 1.8_th) 10^-3 and |V_ub| = (3.83 +/- 0.48_exp +/- 0.14_th) 10^-3,
implying |V_ub / V_cb| = 0.089 +/- 0.011_exp +/- 0.005_th, in nice agreement
with existing predictions.Comment: revised version with pQCD corrections included, to appear in Physical
Review
Linear Field Dependence of the Normal-State In-Plane Magnetoresistance of Sr2RuO4
The transverse and longitudinal in-plane magnetoresistances in the normal
state of superconducting Sr2RuO4 single crystals have been measured. At low
temperatures, both of them were found to be positive with a linear
magnetic-field dependence above a threshold field, a result not expected from
electronic band theory. We argue that such behavior is a manifestation of a
novel coherent state characterized by a spin pseudo gap in the quasi-particle
excitation spectrum in Sr2RuO4.Comment: 4 pages + 5 figure
Neutron EDM from Electric and Chromoelectric Dipole Moments of Quarks
Using QCD sum rules, we calculate the electric dipole moment of the neutron
d_n induced by all CP violating operators up to dimension five. We find that
the chromoelectric dipole moments of quarks \tilde d_i, including that of the
strange quark, provide significant contributions comparable in magnitude to
those induced by the quark electric dipole moments d_i. When the theta term is
removed via the Peccei-Quinn symmetry, the strange quark contribution is also
suppressed and d_n =(1\pm 0.5)[1.1e(\tilde d_d + 0.5\tilde
d_u)+1.4(d_d-0.25d_u)].Comment: 4 pages, revtex, v2: missing overall factor of two reinstate
Nonperturbative QCD Contributions to the Semileptonic Decay Width of the B Meson
Nonperturbative QCD contributions to the inclusive semileptonic decay of the
B meson consist of the dynamic and kinematic components. We calculate the decay
width in an approach based on the light-cone expansion and the heavy quark
effective theory, which is able to include both components of nonperturbative
QCD contributions. The kinematic component results in the phase-space extension
and is shown to be quantitatively crucial, which could increase the decay width
significantly. We find that the semileptonic decay width is enhanced by
long-distance strong interactions by +(9\pm 6)%. This analysis is used to
determine the CKM matrix element |V_{cb}| with a controlled theoretical error.
Implications of the phase-space effects for the nonleptonic decay widths of b
hadrons are briefly discussed. The experimental evidence for the phase-space
effects is pointed out.Comment: 16 pages, Latex, 3 eps figures included, published version
(discussion extended, references updated, the main result unchanged
Improved Determination of the Mass of the Light Hybrid Meson From QCD Sum Rules
We calculate the next-to-leading order (NLO) -corrections to the
contributions of the condensates and in the
current-current correlator of the hybrid current
g\barq(x)\gamma_{\nu}iF_{\mu\nu}^aT^aq(x) using the external field method in
Feynman gauge. After incorporating these NLO contributions into the Laplace
sum-rules, the mass of the = light hybrid meson is recalculated
using the QCD sum rule approach. We find that the sum rules exhibit enhanced
stability when the NLO -corrections are included in the sum rule
analysis, resulting in a light hybrid meson mass of approximately 1.6
GeV.Comment: revtex4, 10 pages, 7 eps figures embedded in manuscrip
Anisotropic superconductivity mediated by phonons in layered compounds with weak screening effect
Anisotropic pairing interactions mediated by phonons are examined in layer
systems. It is shown that the screening effects become weaker when the layer
spacing increases. Then the anisotropic components of the pairing interactions
increase with the screening length since the momentum dependence changes. As a
result, various types of anisotropic superconductivity occur depending on the
parameter region. For example, p-wave superconductivity occurs when the
short-range part of Coulomb repulsion is strong and the layer spacing is large.
Two kinds of inter-layer pairing may occur when the layer spacing is not too
large. Although the phonon contribution to the d-wave pairing interaction is
weaker than the p-wave interaction, it increases with the layer spacing.
Relevance of the present results to organic superconductors, high-T_c cuprates,
and Sr_2RuO_4 is discussed.Comment: 8 pages, 5 figures, (Latex, revtex.sty, epsf.sty
Strong Couplings of Heavy Mesons to A Light Vector Meson in QCD
We make a detailed analysis of the and
strong couplings and
using QCD light cone sum rules(LCSR). The
existing some negligence is pointed out in the previous LCSR calculation on
) and an updated estimate is presented. Our
findings can be used to understand the behavior of the
semileptonic form factors at large momentum transitions.Comment: 15 pages, latex, 2 figures, version appearing in PRD, typos correcte
Josephson current in s-wave superconductor / Sr_2RuO_4 junctions
The Josephson current between an s-wave and a spin-triplet superconductor
SrRuO (SRO) is studied theoretically. In spin-singlet / spin-triplet
superconductor junctions, there is no Josephson current proportional to in the absence of the spin-flip scattering near junction interfaces,
where is a phase-difference across junctions. Thus a dominant term of
the Josephson current is proportional to . The spin-orbit
scattering at the interfaces gives rise to the Josephson current proportional
to , which is a direct consequence of the chiral paring symmetry in
SRO
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
Spectroscopic study of impurities and associated defects in nanodiamonds from Efremovka (CV3) and Orgueil (CI) meteorites
The results of spectroscopic and structural studies of phase composition and
of defects in nanodiamonds from Efremovka (CV3) and Orgueil (CI) chondrites
indicate that nitrogen atomic environment in meteoritic nanodiamonds (MND) is
similar to that observed in synthetic counterparts produced by detonation and
by the Chemical Vapour Deposition (CVD)-process. Most of the nitrogen in MND
appears to be confined to lattice imperfections, such as crystallite/twin
boundaries and other extended defects, while the concentration of nitrogen in
the MND lattice is low. It is suggested that the N-rich sub-population of MND
grains may have been formed with high growth rates in environments rich in
accessible N (i.e., N in atomic form or as weakly bonded compounds). For the
first time the silicon-vacancy complex (the "silicon" defect) is observed in
MND by photoluminescence spectroscopy.Comment: 33 pages, 5 figures, submitted to Geochimica et Cosmochimica Act
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