Strong and Electromagnetic Mass Splittings in Heavy Mesons

The contributions to heavy meson mass differences by the strong hyperfine interaction, the light quark masses and the electromagnetic interaction are obtained from the empirical values of the $D$, $D^*$, $B$ and $B^*$ masses by means of a mass formula based on the heavy quark mass expansion. The three different types of contributions are determined with significant accuracy to next to leading order in that expansion.Comment: 12 pages, 2 figure

Analysis of Negative Parity Baryon Photoproduction Amplitudes in the 1/Nc1/N_c Expansion

We study the photoproduction helicity amplitudes of negative parity baryons in the context of the $1/N_c$ expansion of QCD. A complete analysis to next-to-leading order is carried out. The results show sub-leading effects to be within the magnitude expected from the $1/N_c$ power counting. They also show significant deviations from the quark model, in particular the need for 2-body effects.Comment: 7 pages, 5 table

Electromagnetic Mass Splittings in Heavy Mesons

The electromagnetic contribution to the isomultiplet mass splittings of heavy mesons is reanalyzed within the framework of the heavy mass expansion. It is shown that the leading term in the expansion is given to a good approximation by the elastic term. $1/m_{Q}$-corrections can only be estimated, the main source of uncertainty now being inelastic contributions. The $1/m_{Q}$-corrections to the elastic term turn out to be relatively small in both D and B pseudoscalar mesons.Comment: 16 pages, report CEBAF-TH-92-26, one figure not included (available if requested

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

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

Meson-Baryon-Baryon Vertex Function and the Ward-Takahashi Identity

Ohta proposed a solution for the well-known difficulty of satisfying the Ward-Takahashi identity for a photo-meson-baryon-baryon amplitude ($\gamma$MBB) when a dressed meson-baryon-baryon (MBB) vertex function is present. He obtained a form for the $\gamma$MBB amplitude which contained, in addition to the usual pole terms, longitudinal seagull terms which were determined entirely by the MBB vertex function. He arrived at his result by using a Lagrangian which yields the MBB vertex function at tree level. We show that such a Lagrangian can be neither hermitian nor charge conjugation invariant. We have been able to reproduce Ohta's result for the $\gamma$MBB amplitude using the Ward-Takahashi identity and no other assumption, dynamical or otherwise, and the most general form for the MBB and $\gamma$MBB vertices. However, contrary to Ohta's finding, we find that the seagull terms are not robust. The seagull terms extracted from the $\gamma$MBB vertex occur unchanged in tree graphs, such as in an exchange current amplitude. But the seagull terms which appear in a loop graph, as in the calculation of an electromagnetic form factor, are, in general, different. The whole procedure says nothing about the transverse part of the ($\gamma$MBB) vertex and its contributions to the amplitudes in question.Comment: A 20 pages Latex file and 16 Postscript figures in an uuencoded format. Use epsf.sty to include the figures into the Latex fil

R-parity violation effect on the top-quark pair production at linear colliders

We investigate in detail the effects of the R-parity lepton number violation in the minimal supersymmetric standard model (MSSM) on the top-quark pair production via both $e^--e^+$ and $\gamma-\gamma$ collision modes at the linear colliders. We find that with the present experimental constrained $\rlap/{R}$ parameters, the effect from $\rlap/{R}$ interactions on the processes $e^+e^-\to t\bar{t}$ and $e^+e^- \to \gamma\gamma \to t\bar{t}$ could be significant and may reach -30% and several percent, respectively. Our results show that the $\rlap/{R}$ effects are sensitive to the c.m.s. energy and the relevant $\rlap/{R}$ parameters. However, they are not sensitive to squark and slepton masses when $m_{\tilde{q}} \geq 400 GeV$ (or $m_{\tilde{l}} \geq 300 GeV$) and are almost independent on the $\tan\beta$Comment: Accepted by Phys.Rev.

Chiral Perturbation Theory for SU(3) Breaking in Heavy Meson Systems

The SU(3) breaking effects due to light quark masses on heavy meson masses, decay constants ($F_{D}, F_{D_{s}}$) and the form factor for semileptonic $\overline{B}\rightarrow D^{(\ast)} l\bar{\nu}_{l}$ transitions are formulated in chiral perturbation theory, using a heavy meson effective Lagrangian and expanding in inverse powers of the heavy meson mass. To leading order in this expansion, the leading chiral logarithms and the required counterterms are determined. At this level, a non-analytic correction to the mass splittings of ${\cal O}(p^3)$ appears, similar the the one found in light baryons. The correction to $F_{D_{s}}/F_{D}$ is roughly estimated to be of the order of $10\%$ and, therefore, experimentally accessible, while the correction to the form factor is likely to be substantially smaller. We explicitly check that the heavy quark symmetry is preserved by the chiral loops.Comment: 21 page

Chiral Lagrangians at finite density

The effective SU(2) chiral Lagrangian with external sources is given in the presence of non-vanishing nucleon densities by calculating the in-medium contributions of the chiral pion-nucleon Lagrangian. As a by product, a relativistic quantum field theory for Fermi many-particle systems at zero temperature is directly derived from relativistic quantum field theory with functional methods.Comment: 6 Pages, 3 figures, REVTeX. Extended version. Explicit Feynman rules are give

Excited Baryon Decay Widths in Large N_c QCD

We study excited baryon decay widths in large N_c QCD. It was suggested previously that some spin-flavor mixed-symmetric baryon states have strong couplings of O(N_c^{-1/2}) to nucleons [implying narrow widths of O(1/N_c)], as opposed to the generic expectation based on Witten's counting rules of an O(N_c^0) coupling. The calculation obtaining these narrow widths was performed in the context of a simple quark-shell model. This paper addresses the question of whether the existence of such narrow states is a general property of large N_c QCD. We show that a general large N_c QCD analysis does not predict such narrow states; rather they are a consequence of the extreme simplicity of the quark model.Comment: 9 page