171 research outputs found
1/Nc Countings in Baryons
The power countings for baryon decays and configuration mixings are
determined by means of a non-relativistic quark picture. Such countings are
expected to be robust under changes in the quark masses, and therefore valid as
these become light. It is shown that excited baryons have natural widths of
. These dominant widths are due to the decays that proceed
directly to the ground state baryons, with cascade decays being suppressed to
. Configuration mixings, defined as mixings between states
belonging to different multiplets, are shown to be
sub-leading in an expansion in when they involve the ground
state baryons, while the mixings between excited states can be
.Comment: 19 pages, 1 figure An omission that changes the conclusions on
configuration mixings has been correcte
Radiative Transitions in Heavy Mesons in a Relativistic Quark Model
The radiative decays of , , and other excited heavy mesons are
analyzed in a relativistic quark model for the light degrees of freedom and in
the limit of heavy quark spin-flavor symmetry. The analysis of strong decays
carried out in the corresponding chiral quark model is used to calculate the
strong decays and determine the branching ratios of the radiative decays.
Consistency with the observed branching ratios requires the inclusion of the
heavy quark component of the electromagnetic current and the introduction of an
anomalous magnetic moment for the light quark. It is observed that not only
, but also meson transitions within a heavy quark spin multiplet are
affected by the presence of the heavy quark current.Comment: 9 pages, RevTeX. Submitted to Physical Review
Complete Analysis of Baryon Magnetic Moments in 1/N_c
We generate a complete basis of magnetic moment operators for the N_c = 3
ground-state baryons in the 1/N_c expansion, and compute and tabulate all
associated matrix elements. We then compare to previous results derived in the
literature and predict additional relations among baryon magnetic moments
holding to subleading order in 1/N_c and flavor SU(3) breaking. Finally, we
predict all unknown diagonal and transition magnetic moments to <= 0.15 mu_N
accuracy, and suggest possible experimental measurements to improve the
analysis even further.Comment: 28 pages (including 11 tables), ReVTeX. One reference and grant
acknowledgment adde
Upper bounds on all R-parity-violating \lambda\lambda'' combinations from proton stability
In an R-parity-violating supersymmetric theory, we derive upper bounds on all
the \lambda''_{ijk}\lambda_{i'j'k'}-type combinations from the consideration of
proton stability, where \lambda''_{ijk} are baryon-number-violating couplings
involving three baryonic fields and \lambda_{i'j'k'} are
lepton-number-violating couplings involving three leptonic fields.Comment: 5 pages, Latex, uses axodraw.sty; minor changes in the text. Final
versio
Thermal Pions
I discuss the absorption and dispersion of pions in hot matter. A two-loop
calculation in the framework of chiral perturbation theory is presented and its
result is compactly written in terms of the two- and three-particle forward
scattering amplitudes. At modest temperatures, MeV, the
change in the pion mass is small and its dispersion law closely resembles the
free space one. At these temperatures, all quantities of interest are given to
a good degree of accuracy by the first term in the virial expansion which is
linear in the density. (BUTP-93/16, uses espcrc1.sty from North-Holland
Publishing)Comment: 7 pp, LaTeX, uses espcrc1.sty from North-Holland Publishing,
BUTP-93/1
The Decays K_L -> l^+ l^- l'^+ l'^- Revisited
The double lepton pair decay modes of the K_L meson are analyzed including
all contributions of order p^6 in Chiral Perturbation Theory. The
experimentally established e^+ e^- e^+ e^- mode and the recently observed e^+
e^- mu^+ mu^- mode are discussed in detail.Comment: 6 pages, RevTex, one tabl
Fluctuations of particle ratios and the abundance of hadronic resonances
In this letter we will argue that the event-by-event fluctuations of the
ratio of positively over negatively charged pions provides a measurements of
the number of rho and omega mesons right after hadronization. This finding can
be utilized to put the hypothesis of chemical equilibration in relativistic
heavy ion collisions to a test.Comment: 4 pages. No figure. Uses revtex with prl, aps, and multicol style
Regularization for effective field theory with two heavy particles
A regularization for effective field theory with two propagating heavy
particles is constructed. This regularization preserves the low-energy analytic
structure, implements a low-energy power counting for the one-loop diagrams,
and preserves symmetries respected by dimensional regularization.Comment: 12 pages, 4 figures. Some typos have been corrected, a sentence has
been moved, and two formulas have been further simplifie
A relativistic chiral quark model for pseudoscalar emission from heavy mesons
The amplitudes for one-pion mediated transitions between heavy meson excited
states are obtained in the framework of the relativistic chiral quark model.
The effective coupling constants to pions and the decay widths of excited heavy
mesons with l<=2 for non-radially excited, and the l=0 radially excited mesons
are presented for both charmed and beauty mesons. We also discuss the allowed
decays of strange excited heavy mesons by emission of a K-meson.Comment: 20 pages, revte
New Physics and CP Violation in Singly Cabibbo Suppressed D Decays
We analyze various theoretical aspects of CP violation in singly Cabibbo
suppressed (SCS) D-meson decays, such as . In particular, we
explore the possibility that CP asymmetries will be measured close to the
present level of experimental sensitivity of . Such measurements
would signal new physics. We make the following points: (i) The mechanism at
work in neutral D decays could be indirect or direct CP violation (or both).
(ii) One can experimentally distinguish between these possibilities. (iii) If
the dominant CP violation is indirect, then there are clear predictions for
other modes. (iv) Tree-level direct CP violation in various known models is
constrained to be much smaller than . (v) SCS decays, unlike Cabibbo
favored or doubly Cabibbo suppressed decays, are sensitive to new contributions
from QCD penguin operators and especially from chromomagnetic dipole operators.
This point is illustrated with supersymmetric gluino-squark loops, which can
yield direct CP violating effects of .Comment: 36 pages, 5 figure
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