1,244 research outputs found
Baryon masses at second order in large- chiral perturbation theory
We consider flavor breaking in the the octet and decuplet baryon masses at
second order in large- chiral perturbation theory, where is the number
of QCD colors. We assume that , where is the number of light quark
flavors, and are the parameters controlling
flavor breaking in chiral perturbation theory. We consistently include
non-analytic contributions to the baryon masses at orders , , and . The corrections are small for
the relations that follow from symmetry alone, but the corrections to
the large- relations are large and have the wrong sign. Chiral
power-counting and large- consistency allow a 2-loop contribution at order
, and a non-trivial explicit calculation is required to show
that this contribution vanishes. At second order in the expansion, there are
eight relations that are non-trivial consequences of the expansion, all
of which are well satisfied within the experimental errors. The average
deviation at this order is 7 \MeV for the \De I = 0 mass differences and
0.35 \MeV for the \De I \ne 0 mass differences, consistent with the
expectation that the error is of order .Comment: 19 pages, 2 uuencoded ps figs, uses revte
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A Three-State Algorithm for Real Polynomials Using Quadratic Iteration
We introduce a new three-stage process for calculating the zeros of a polynomial with real coefficients. The algorithm finds either a linear or quadratic factor, working completely in real arithmetic. In the third stage the algorithm uses one of two variable-shift iterations corresponding to the linear or quadratic case. The iteration for a linear factor is a real arithmetic version of the third stage of the algorithm for complex polynomials which we studied in an earlier paper. A new variable-shift iteration is introduced in this paper which is suitable for quadratic factors. If the complex algorithm and the new real algorithm are applied to the same real polynomial, then the real algorithm is about four times as fast. We prove that the mathematical algorithm always converges and show that the rate of convergence of the third stage is faster than second order. The problem and algorithm may be recast into matrix form. The third stage is a quadratic form of shifted inverse powering and a quadratic form of generalized Rayleigh iteration. The results of extensive testing are summarized. For an ALGOL W program run on an IBM 360/67 we found that for polynomials ranging in degree from 20 to 50, the time required to calculate all zeros averaged 2n² milliseconds. An ALGOL 60 implementation of the algorithm and a program which calculates a posteriors bounds on the zeros may be found in Jenkins’ 1969 Stanford dissertation
Bosonic Operator Methods for the Quark Model
Quark model matrix elements can be computed using bosonic operators and the
holomorphic representation for the harmonic oscillator. The technique is
illustrated for normal and exotic baryons for an arbitrary number of colors.
The computations are much simpler than those using conventional quark model
wavefunctions
1/N Expansion for Exotic Baryons
The 1/N expansion for exotic baryons is developed, and applied to the masses,
meson couplings and decay widths. Masses and widths of the 27 and 35 pentaquark
states in the same tower as the Theta+ are related by spin-flavor symmetry. The
27 and 35 states can decay within the pentaquark tower, as well as to normal
baryons, and so have larger decay widths than the lightest pentaquark Theta.
The 1/N expansion also is applied to baryon exotics containing a single heavy
antiquark. The decay widths of heavy pentaquarks via pion emission, and to
normal baryons plus heavy D^(*),B^(*) mesons are studied, and relations
following from large-N spin-flavor symmetry and from heavy quark symmetry are
derived.Comment: Major additions: plots of widths and branching ratios, discussion of
strong decays of heavy pentaquarks, including consequences of heavy quark
symmetr
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
The semileptonic decays of the B_c meson
We study the semileptonic transitions B_c to \eta_c, J/\psi, D, D^*, B, B^*,
B_s, B_s^* in the framework of a relativistic constituent quark model. We use
experimental data on leptonic J/\psi decay, lattice and QCD sum rule results on
leptonic B_c decay, and on radiative \eta_c transitions to adjust the quark
model parameters. We compute all form factors of the above semileptonic
B_c-transitions and give predictions for various semileptonic B_c decay modes
including their \tau-modes when they are kinematically accessible. The
implications of heavy quark symmetry for the semileptonic decays are discussed
and are shown to be manifest in our explicit relativistic quark model
calculation. A comparison of our results with the results of other calculations
is performed.Comment: 31 pages Latex (uses epsf, revtex). Section II expanded, typos
corrected. This version will appear in Phys. Rev.
Heavy-ion irradiations of Fe and Fe–Cr model alloys Part 2: Damage evolution in thin-foils at higher doses
Charmed Strange Pentaquarks in the Large Limit
The properties of pentaquarks containing a heavy anti-quark and strange
quarks are studied in the bound state picture. In the flavor SU(3) limit, there
are many pentaquark states with the same binding energy. When the SU(3)
symmetry breaking effects are included, however, three states become
particularly stable due to a ``Gell-Mann--Okubo mechanism''. They are the and states discussed by Lipkin, and a a previously
unstudied state. These states will have and
their masses are estimated. These states, if exist, may be seen in experiments
in the near future.Comment: 12 pages in REVTeX, no figure
Large N_c, Constituent Quarks, and N, Delta Charge Radii
We show how one may define baryon constituent quarks in a rigorous manner,
given physical assumptions that hold in the large-N_c limit of QCD. This
constituent picture gives rise to an operator expansion that has been used to
study large-N_c baryon observables; here we apply it to the case of charge
radii of the N and Delta states, using minimal dynamical assumptions. For
example, one finds the relation r_p^2 - r_{Delta^+}^2 = r_n^2 - r_{Delta^0}^2
to be broken only by three-body, O(1/N_c^2) effects for any N_c.Comment: 15 pages, 1 eps figure. Version to appear in Phys. Rev.
Excited Baryons in the Large Limit
The spectrum of excited -type heavy baryons is considered in the
large limit. The universal form factors for semileptonic
decay to excited charmed baryons are calculated in the large limit. We
find that the Bjorken sum rule (for the slope of the Isgur--Wise function) and
Voloshin sum rule (for the mass of the light degrees of freedom) are saturated
by the first doublet of excited states.Comment: 9 pages, use phyzzx, CALT-68-191
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