131 research outputs found
Enhanced Nonperturbative Effects in Z Decays to Hadrons
We use soft collinear effective field theory (SCET) to study nonperturbative
strong interaction effects in Z decays to hadronic final states that are
enhanced in corners of phase space. These occur, for example, in the jet energy
distribution for two jet events near E_J=M_Z/2, the thrust distribution near
unity and the jet invariant mass distribution near zero. The extent to which
such nonperturbative effects for different observables are related is
discussed.Comment: 17 pages. Paper reorganized, and more discussion and results include
B-->pi and B-->K transitions in standard and quenched chiral perturbation theory
We study the effects of chiral logs on the heavy-->light pseudoscalar meson
transition form factors by using standard and quenched chiral perturbation
theory combined with the static heavy quark limit. The resulting expressions
are used to indicate the size of uncertainties due to the use of the quenched
approximation in the current lattice studies. They may also be used to assess
the size of systematic uncertainties induced by missing chiral log terms in
extrapolating toward the physical pion mass. We also provide the coefficient
multiplying the quenched chiral log, which may be useful if the quenched
lattice studies are performed with very light mesons.Comment: 33 pages, 8 PostScript figures, version to appear in PR
Next--to--Leading Order Corrections to Meson Masses in the Heavy Quark Effective Theory
We use the QCD sum rule approach to calculate the splitting between vector
and pseudoscalar mesons containing one light and one heavy quark, and the
kinetic energy of the heavy quark. Our result for the splitting induced by the
chromomagnetic interaction agrees to the experimental data on charm and beauty
mesons. For the matrix element of the kinetic energy operator, we obtain the
value .Comment: 33 ps., PS figures included, requires REVTEX.3 and psfig,
TUM-T31-42/93/R (additional contribution to kinetic energy taken into
account, marginal changes in the results
Tests of the random phase approximation for transition strengths
We investigate the reliability of transition strengths computed in the
random-phase approximation (RPA), comparing with exact results from
diagonalization in full shell-model spaces. The RPA and
shell-model results are in reasonable agreement for most transitions; however
some very low-lying collective transitions, such as isoscalar quadrupole, are
in serious disagreement. We suggest the failure lies with incomplete
restoration of broken symmetries in the RPA. Furthermore we prove, analytically
and numerically, that standard statements regarding the energy-weighted sum
rule in the RPA do not hold if an exact symmetry is broken.Comment: 11 pages, 7 figures; Appendix added with new proof regarding
violation of energy-weighted sum rul
Nonfactorizable contributions in B decays to charmonium: the case of
Nonleptonic to charmonium decays generally show deviations from the
factorization predictions. For example, the mode has
been experimentally observed with sizeable branching fraction while its
factorized amplitude vanishes. We investigate the role of rescattering effects
mediated by intermediate charmed meson production in this class of decay modes,
and consider with the meson.
Using an effective lagrangian describing interactions of pairs of heavy-light
mesons with a quarkonium state, we relate this mode to the
analogous mode with in the final state. We find large enough to be measured at the factories, so that this decay
mode could be used to study the poorly known .Comment: RevTex, 16 pages, 2 eps figure
A Heavy-Light Chiral Quark Model
We present a new chiral quark model for mesons involving a heavy and a light
(anti-) quark. The model relates various combinations of a quark - meson
coupling constant and loop integrals to physical quantities. Then, some
quantities may be predicted and some used as input. The extension from other
similar models is that the present model includes the lowest order gluon
condensate of the order (300 MeV)^4 determined by the mass splitting of the 0^-
and the 1^- heavy meson states. Within the model, we find a reasonable
description of parameters such as the decay constants f_B and f_D, the
Isgur-Wise function and the axial vector coupling g_A in chiral perturbation
theory for light and heavy mesons.Comment: 31 pages, 13 figures, RevTex4.
Dichromatic state sum models for four-manifolds from pivotal functors
A family of invariants of smooth, oriented four-dimensional manifolds is defined via handle decompositions and the Kirby calculus of framed link diagrams. The invariants are parametrised by a pivotal functor from a spherical fusion category into a ribbon fusion category.
A state sum formula for the invariant is constructed via the chain-mail procedure, so a large class of topological state sum models can be expressed as link invariants. Most prominently, the Crane-Yetter state sum over an arbitrary ribbon fusion category is recovered, including the nonmodular case. It is shown that the Crane-Yetter invariant for nonmodular categories is stronger than signature and Euler invariant.
A special case is the four-dimensional untwisted Dijkgraaf-Witten model. Derivations of state space dimensions of TQFTs arising from the state sum model agree with recent calculations of ground state degeneracies in Walker-Wang models.
Relations to different approaches to quantum gravity such as Cartan geometry and teleparallel gravity are also discussed
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
Being, Becoming and the Undivided Universe: A Dialogue between Relational Blockworld and the Implicate Order Concerning the Unification of Relativity and Quantum Theory
In this paper two different approaches to unification will be compared,
Relational Blockworld (RBW) and Hiley's implicate order. Both approaches are
monistic in that they attempt to derive matter and spacetime geometry 'at once'
in an interdependent and background independent fashion from something
underneath both quantum theory and relativity. Hiley's monism resides in the
implicate order via Clifford algebras and is based on process as fundamental
while RBW's monism resides in spacetimematter via path integrals over graphs
whereby space, time and matter are co-constructed per a global constraint
equation. RBW's monism therefore resides in being (relational blockworld) while
that of Hiley's resides in becoming (elementary processes). Regarding the
derivation of quantum theory and relativity, the promises and pitfalls of both
approaches will be elaborated. Finally, special attention will be paid as to
how Hiley's process account might avoid the blockworld implications of
relativity and the frozen time problem of canonical quantum gravity.Comment: 33 pages, 7 figures. Revised to include modified Regge calculus
results. Accepted for publication in Foundations of Physics. arXiv admin
note: substantial text overlap with arXiv:1106.333
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