862 research outputs found
Hadron Electromagnetic Structure: Shedding Light on Models and their Mechanisms
Strange quark contributions to the proton magnetic moment are estimated from
a consideration of baryon magnetic moment sum rules. The environment
sensitivity of quark contributions to baryon moments is emphasized. Pion cloud
contributions to proton charge radii are examined in the framework of Chiral
Perturbation Theory. The absence of scalar-diquark clustering in the nucleon is
discussed.Comment: Lattice '93 presentation. UU-File is a single postscript file of a 3
page manuscript including figures. Ohio State U. PP #93-112
Semileptonic Decay of -Meson into and the Bjorken Sum Rule
We study the semileptonic branching fraction of -meson into higher
resonance of charmed meson by using the Bjorken sum rule and the heavy
quark effective theory(HQET). This sum rule and the current experiment of
-meson semileptonic decay into and predict that the branching
ratio into is about 1.7\%. This predicted value is larger than
the value obtained by the various theoretical hadron models based on the HQET.Comment: 10 pages, LaTex, to be published in Phys. Lett.
Nested recursions with ceiling function solutions
Consider a nested, non-homogeneous recursion R(n) defined by R(n) =
\sum_{i=1}^k R(n-s_i-\sum_{j=1}^{p_i} R(n-a_ij)) + nu, with c initial
conditions R(1) = xi_1 > 0,R(2)=xi_2 > 0, ..., R(c)=xi_c > 0, where the
parameters are integers satisfying k > 0, p_i > 0 and a_ij > 0. We develop an
algorithm to answer the following question: for an arbitrary rational number
r/q, is there any set of values for k, p_i, s_i, a_ij and nu such that the
ceiling function ceiling{rn/q} is the unique solution generated by R(n) with
appropriate initial conditions? We apply this algorithm to explore those
ceiling functions that appear as solutions to R(n). The pattern that emerges
from this empirical investigation leads us to the following general result:
every ceiling function of the form ceiling{n/q}$ is the solution of infinitely
many such recursions. Further, the empirical evidence suggests that the
converse conjecture is true: if ceiling{rn/q} is the solution generated by any
recursion R(n) of the form above, then r=1. We also use our ceiling function
methodology to derive the first known connection between the recursion R(n) and
a natural generalization of Conway's recursion.Comment: Published in Journal of Difference Equations and Applications, 2010.
11 pages, 1 tabl
Analyticity and the Isgur-Wise Function
We reconsider the recent derivation by de Rafael and Taron of bounds on the
slope of the Isgur-Wise function. We argue that one must be careful to include
cuts starting below the heavy meson pair production threshold, arising from
heavy quark-antiquark bound states, and that if such cuts are properly
accounted for then no constraints may be derived.Comment: 8 pages, uses harvmac, SLAC-PUB-5956, UCSD/PTH 92-35, CALT-68-183
Remark on Charm Quark Fragmentation to Mesons
The observed mesons have flavor quantum numbers and
spin-parity of the light degrees of freedom . In
the limit the spin of the charm quark is conserved and
the fragmentation process is characterized by the
probability for the charm quark to fragment to a meson with a given
helicity for the light degrees of freedom. We consider the calculated fragmentation functions in the limit as a qualitative model for the fragmentation
functions. We find that in this model charm quark fragmentation to
light degrees of freedom with helicities is favored over fragmentation to light
degrees of freedom with helicities .Comment: 6 pages, CALT-68-192
Form factors of heavy-light systems in point-form relativistic quantum mechanics: the Isgur-Wise function
We investigate electromagnetic and weak form factors of heavy-light mesons in
the context of point-form relativistic quantum mechanics. To this aim we treat
the physical processes from which such electroweak form factors are extracted
by means of a coupled channel approach which accounts for the dynamics of the
intermediate gauge bosons. It is shown that heavy-quark symmetry is respected
by this formulation. A simple analytical expression is obtained for the
Isgur-Wise function in the heavy-quark limit. Breaking of heavy-quark symmetry
due to realistic values of the heavy-quark mass are studied numerically.Comment: Presented at the 21st European Conference on Few-Body Problems in
Physics, Salamanca, Spain, 30 August - 3 September 201
Nonresonant Semileptonic Heavy Quark Decay
In both the large N_c limit and the valence quark model, semileptonic decays
are dominated by resonant final states. Using Bjorken's sum rule in an
"unquenched" version of the quark model, I demonstrate that in the heavy quark
limit nonresonant final states should also be produced at a significant rate.
By calculating the individual strengths of a large number of exclusive two-body
nonresonant channels, I show that the total rate for such processes is highly
fragmented. I also describe some very substantial duality-violating suppression
factors which reduce the inclusive nonresonant rate to a few percent of the
total semileptonic rate for the finite quark masses of B decay, and comment on
the importance of nonresonant decays as testing grounds for very basic ideas on
the structure, strength, and significance of the quark-antiquark sea and on
quark-hadron duality in QCD.Comment: 51 pages, 2 Postscript figure
The Baryon Isgur-Wise Function in the Large Limit
In the large limit, the and can be treated as
bound states of chiral solitons and mesons containing a heavy quark. We show
that the soliton and heavy meson are bound in an attractive harmonic oscillator
potential. The Isgur-Wise function for decay is computed in the large limit. Corrections to the
form factor which depend on can be summed exactly ( and
are the nucleon and heavy quark masses). We find that this symmetry breaking
correction at zero recoil is only .Comment: 18 pages, 0 figures, uses harvma
Chiral Perturbation Theory for and Semileptonic Transition Matrix Elements at Zero Recoil
Heavy quark symmetry predicts the value of and transition matrix elements of the current , at zero recoil (where in the rest frame of the the or
is also at rest). We use chiral perturbation theory to compute the
leading corrections to these predictions which are generated at low momentum,
below the chiral symmetry breaking scale.Comment: 10 pages, 1 figure (not included), CALT-68-1844, MIT-CTP-217
More Effective Field Theory for Nonrelativistic Scattering
An effective field theory treatment of nucleon-nucleon scattering at low
energy shows much promise and could prove a useful tool in the study of nuclear
matter at both ordinary and extreme densities. The analysis is complicated by
the existence a large length scale --- the scattering length --- which arises
due to couplings in the short distance theory being near critical values. I
show how this can be dealt with by introducing an explicit s-channel state in
the effective field theory. The procedure is worked out analytically in a toy
example. I then demonstrate that a simple effective field theory excellently
reproduces the 1S_0 np phase shift up to the pion production threshold.Comment: 15 pages, TeX ; macros: harvmac, eps
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