1,749 research outputs found
Final state rescattering as a contribution to
We provide a new estimate of the long-distance component to the radiative
transition . Our mechanism involves the soft-scattering of
on-shell hadronic products of nonleptonic decay, as in the chain . We employ a phenomenological fit to scattering data
to estimate the effect. The specific intermediate states considered here modify
the decay rate at roughly the level, although
the underlying effect has the potential to be larger. Contrary to other
mechanisms of long distance physics which have been discussed in the
literature, this yields a non-negligible modification of the channel and hence will provide an uncertainty in the extraction of
. This mechanism also affects the isospin relation between the rates
for and and may generate CP
asymmetries at experimentally observable levels.Comment: 15 pages, RevTex, 3 figure
New Physics and CP Violation in Hyperon Nonleptonic Decays
The sum of the CP-violating asymmetries A(Lambda_-^0) and A(Xi_-^-) in
hyperon nonleptonic decays is presently being measured by the E871 experiment.
We evaluate contributions to the asymmetries induced by chromomagnetic-penguin
operators, whose coefficients can be enhanced in certain models of new physics.
Incorporating recent information on the strong phases in Xi->Lambda pi decay,
we show that new-physics contributions to the two asymmetries can be
comparable. We explore how the upcoming results of E871 may constrain the
coefficients of the operators. We find that its preliminary measurement is
already better than the epsilon parameter of K-Kbar mixing in bounding the
parity-conserving contributions.Comment: 12 pages, 2 figure
Asymptotic Limits and Structure of the Pion Form Factor
We use dispersive techniques to address the behavior of the pion form factor
as and . We perform the matching with the
constraints of perturbative QCD and chiral perturbation theory in the high
energy and low energy limits, leading to four sum rules. We present a version
of the dispersive input which is consistent with the data and with all
theoretical constraints. The results indicate that the asymptotic perturbative
QCD limit is approached relatively slowly, and give a model independent
determination of low energy chiral parameters.Comment: 8 pages, Latex, 2 figure
Attractive Casimir effect in an infrared modified gluon bag model
In this work, we are motivated by previous attempts to derive the vacuum
contribution to the bag energy in terms of familiar Casimir energy calculations
for spherical geometries. A simple infrared modified model is introduced which
allows studying the effects of the analytic structure as well as the geometry
in a clear manner. In this context, we show that if a class of infrared
vanishing effective gluon propagators is considered, then the renormalized
vacuum energy for a spherical bag is attractive, as required by the bag model
to adjust hadron spectroscopy.Comment: 7 pages. 1 figure. Accepted for publication in Physical Review D.
Revised version with improved analysis and presentation, references adde
Factorization Contributions and the Breaking of the Rule in Weak and Couplings
We compute the modified factorization contributions to the
and couplings and
demonstrate that these contributions naturally include terms
which are comparable ( to times) in magnitude to the
corresponding terms. As a consequence, we conclude that models
which treat vector meson exchange contributions to the weak conversion process
assuming such weak couplings to satisfy the rule are unlikely to be reliable.Comment: 13 pages, uses REVTEX Entire manuscript available as a ps file at
http://www.physics.adelaide.edu.au/theory/home.html . Also available via
anonymous ftp at ftp://adelphi.adelaide.edu.au/pub/theory/ADP-95-5.T172.ps To
appear in Physical Review
The Quantum Gravitationally Induced Stress Tensor
We derive non-perturbative relations between the expectation value of the
invariant element in a homogeneous and isotropic state and the quantum
gravitationally induced pressure and energy density. By exploiting previously
obtained bounds for the maximum possible growth of perturbative corrections to
a locally de Sitter background we show that the two loop result dominates all
higher orders. We also show that the quantum gravitational slowing of inflation
becomes non-perturbatively strong earlier than previously expected.Comment: 13 pages, LaTeX 2 epsilo
Hadronic Transitions among Quarkonium States in a Soft-Exchange-Approximation. Chiral Breaking and Spin Symmetry Breaking Processes
Although no asymptotic heavy quark spin symmetry, and even more no flavor
symmetry, are expected for systems such as quarkonium, a numerical discussion
shows that for some processes and in a preasymptotic region which may roughly
include charmonium and bottomonium, the use of the spin-symmetry may be useful
in conjunction with chiral symmetry for light hadrons (soft-exchange-
approximation regime, SEA). We continue our discussion of hadronic transitions
in the SEA-regime by studying in particular chiral breaking transitions such as
, , level splittings and transitions which break
both chiral and spin symmetry, such as , , and .Comment: LaTeX (style article) 19 pages, UGVA-DPT 12-80
Critical Evaluation of Bacteriophage to Prevent and Treat Colibacillosis in Poultry
There is a continuing need to find alternatives to antibiotics in animal and human medicine. Bacteriophages are viruses that infect and kill bacteria, with no known activity to plant and animal cells. We have conducted research to critically evaluate the efficacy of bacteriophage to both prevent and treat colibacillosis in poultry. Bacteriophages lytic to an Escherichia coli pathogenic to poultry were isolated from municipal waste water treatment plants and poultry processing plants. Two bacteriophage isolates were selected to use in studies designed to determine the efficacy of these bacteriophage to prevent and treat severe colibacillosis in poultry. Colibacillosis was induced by injecting 6 X 104 cfu of E. coli into the thoracic airsac when the birds were 1 week of age. Initial studies demonstrated that mortality was significantly reduced when the challenge culture was mixed with bacteriophage prior to challenging the birds. In subsequent studies, we have shown that an aerosol spray of bacteriophage given to the birds prior to this E. coli challenge can prevent the disease, and that an intramuscular injection of bacteriophage provides an effective treatment of this disease. We have demonstrated that bacteriophage can be used to both prevent and treat colibacillosis in poultry and may provide an effective alternative to antibiotic use in animal and human medicine
The Electromagnetic Mass Differences of Pions and Kaons
We use the Cottingham method to calculate the pion and kaon electromagnetic
mass differences with as few model dependent inputs as possible. The
constraints of chiral symmetry at low energy, QCD at high energy and
experimental data in between are used in the dispersion relation. We find
excellent agreement with experiment for the pion mass difference. The kaon mass
difference exhibits a strong violation of the lowest order prediction of
Dashen's theorem, in qualitative agreement with several other recent
calculations.Comment: 40 pages, Latex, needs axodraw. and psfig. macros, 4 figure
Dilute Nuclear Matter in Chiral Perturbation Theory
We use chiral perturbation theory to compute the effective nucleon propagator
in an expansion about low density in the chiral limit. We neglect four-nucleon
interactions and focus on pion exchange. Evaluating the nucleon self-energy on
its mass shell to leading order, we show that the effective nucleon mass
increases by a small amount. We discuss the relevance of our results to the
structure of compact stars.Comment: Manuscript rewritten, especially conclusions about mass shifts;
contact terms cannot be neglected. Computation unchange
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