153 research outputs found
Bose-stimulated scattering off a cold atom trap
The angle and temperature dependence of the photon scattering rate for
Bose-stimulated atom recoil transitions between occupied states is compared to
diffraction and incoherent Rayleigh scattering near the Bose-Einstein
transition for an optically thin trap in the limit of large particle number, N.
Each of these processes has a range of angles and temperatures for which it
dominates over the others by a divergent factor as N->oo.Comment: 18 pages (REVTeX), no figure
Polarization and `Model Independent' Extraction of from and
We briefly discuss the predictions of the heavy quark effective theory for
the semileptonic decays of a heavy pseudoscalar to a light one, or to a light
vector meson. We point out that measurement of combinations of differential
helicity decay rates at Cleo-c and the factories can provide a model
independent means of extracting the ratio
. We briefly discuss the corrections to this prediction.Comment: 8 pages, LaTeX, 1 figur
Condensate fluctuations of a trapped, ideal Bose gas
For a non-self-interacting Bose gas with a fixed, large number of particles
confined to a trap, as the ground state occupation becomes macroscopic, the
condensate number fluctuations remain micrscopic. However, this is the only
significant aspect in which the grand canonical description differs from
canonical or microcanonical in the thermodynamic limit. General arguments and
estimates including some vanishingly small quantities are compared to explicit,
fixed-number calculations for 10^2 to 10^6 particles.Comment: 16 pages (REVTeX) plus 4 figures (ps), revision includes brief
comparison of repulsive-interaction vs. fixed-N fluctuation damping. To be
published in Phys. Rev.
Unitarity of Quantum Theory and Closed Time-Like Curves
Interacting quantum fields on spacetimes containing regions of closed
timelike curves (CTCs) are subject to a non-unitary evolution . Recently, a
prescription has been proposed, which restores unitarity of the evolution by
modifying the inner product on the final Hilbert space. We give a rigorous
description of this proposal and note an operational problem which arises when
one considers the composition of two or more non-unitary evolutions. We propose
an alternative method by which unitarity of the evolution may be regained, by
extending to a unitary evolution on a larger (possibly indefinite) inner
product space. The proposal removes the ambiguity noted by Jacobson in
assigning expectation values to observables localised in regions spacelike
separated from the CTC region. We comment on the physical significance of the
possible indefiniteness of the inner product introduced in our proposal.Comment: 13 pages, LaTeX. Final revised paper to be published in Phys Rev D.
Some changes are made to expand our discussion of Anderson's Proposal for
restoring unitarit
Space-time properties of the higher twist amplitudes
A consistent and intuitive description of the twist-4 corrections to the
hadron structure functions is presented in a QCD-improved parton model using
time-ordered perturbative theory, where the collinear singularities are
naturally eliminated. We identify the special propagators with the backward
propagators of partons in time order.Comment: 18 Pages, Latex, 8 Ps figures, To appear in Phys. Rev.
Selection rules in three-body B decay from factorization
Extending the dynamics underlying the factorization calculation of two-body
decays, we propose simple selection rules for nonresonant three-body B decays.
We predict, for instance, that in the Dalitz plot of B^0-->D^0-bar\pi^+\pi^-,
practically no events should be found in the corner of E(\pi^+) < \Lambda_{QCD}
as compared with the corner of E(\pi^-) < \Lambda_{QCD}. We also predict that
there should be very few three-body decay events with a soft meson resonance
and two energetic mesons or meson resonances. The selection rules are quite
different from the soft pion theorem, since they apply to different kinematical
regions. For B^0 -->D^0-bar\pi^+\pi^-, the latter predicts that the decay
matrix element vanishes in the zero-four-momentum limit of \pi^+ instead of
\pi^-. Since this marked difference from the soft pion theorem is directly
related to the issue of short-distance QCD dominance in the FSI of two-body B
decays, experimental test of the selection rules will shed light on strong
interaction dynamics of B decay.Comment: 12 pages in REVTEX including 3 eps figure
Multiplicative renormalizability and quark propagator
The renormalized Dyson-Schwinger equation for the quark propagator is
studied, in Landau gauge, in a novel truncation which preserves multiplicative
renormalizability. The renormalization constants are formally eliminated from
the integral equations, and the running coupling explicitly enters the kernels
of the new equations. To construct a truncation which preserves multiplicative
renormalizability, and reproduces the correct leading order perturbative
behavior, non-trivial cancellations involving the full quark-gluon vertex are
assumed in the quark self-energy loop. A model for the running coupling is
introduced, with infrared fixed point in agreement with previous
Dyson-Schwinger studies of the gauge sector, and with correct logarithmic tail.
Dynamical chiral symmetry breaking is investigated, and the generated quark
mass is of the order of the extension of the infrared plateau of the coupling,
and about three times larger than in the Abelian approximation, which violates
multiplicative renormalizability. The generated scale is of the right size for
hadronic phenomenology, without requiring an infrared enhancement of the
running coupling.Comment: 17 pages; minor corrections, comparison to lattice results added;
accepted for publication in Phys. Rev.
Momentum dependent quark mass in two-point correlators
A momentum dependent quark mass may be incorporated into a quark model in a
manner consistent with dynamically broken chiral symmetry. We use this to study
the high behavior of the vector, axialvector, scalar and pseudoscalar
two-point correlation functions. Expanding the results to order , we
show the correspondence between the dynamical quark mass and the vacuum
condensates which appear in the operator product expansion of QCD. We recover
the correct leading logarithmic dependence of the various terms in the
OPE, but we also find substantial subleading corrections which are numerically
huge in a specific case. We conclude by using the vector minus axialvector
correlator to estimate the electromagnetic mass difference.Comment: 18 pages, LaTeX, figures in accompanying uuencoded postscript file.
Published version. References adde
Two-loop corrections to the Isgur-Wise function in QCD sum rules
We complete the QCD sum rule analysis of the Isgur Wise form factor
at next-to-leading order in renormalization-group improved
perturbation theory. To this end, the exact result for the two-loop corrections
to the perturbative contribution is derived using the heavy quark effective
theory. Several techniques for the evaluation of two-loop integrals involving
two different types of heavy quark propagators are discussed in detail, among
them the methods of integration by parts and differential equations. The
order- corrections to the Isgur-Wise function turn out to be small
and well under control. At large recoil, they tend to decrease the form factor
by .Comment: 24 pages (REVTEX), 2 figures available upon request, SLAC-PUB-599
Asymptotic Freedom for Non-Relativistic Confinement
Some aspects of asymptotic freedom are discussed in the context of a simple
two-particle non-relativisitic confining potential model. In this model
asymptotic freedom follows from the similarity of the free-particle and bound
state radial wave functions at small distances and for the same angular
momentum and the same large energy. This similarity, which can be understood
using simple quantum mechanical arguments, can be used to show that the exact
response function approaches that obtained when final state interactions are
ignored. A method of calculating corrections to this limit is given and
explicit examples are given for the case of the harmonic oscillator.Comment: 16 pages, 5 figures, RevTex
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