Tung-Mow Yan

Radiative leptonic decays of B mesons in QCD

We compute the form factors parametrizing radiative leptonic decays of heavy mesons B + → γe + ν for photon energies much larger thanQCD, where per- turbative QCD methods for exclusive processes can be combined with the heavy quark effective theory. The form factors can be reliably obtained in this region in an expansion in powers of �/Eγ. The leading term in this ex- pansion displays an additional spin symmetry manifested in the equality of form factors of vector and axial currents. The leading twist form factors can be written as the convolution of the B meson light-cone wave function with a hard scattering amplitude, which is explicitly calculated to one-loop order. The Sudakov double logarithms of the form ( αs π log 2 2E � ) n are resummed to all orders. As an application we present a method for determining the CKM ma- trix element |Vub| from a comparison of photon spectra in B and D radiative leptonic decays.

Predictions for s-wave and p-wave heavy baryons from sum rules and the constituent quark model: Strong interactions

We study the strong interactions of the L=1 orbitally excited baryons with one heavy quark in the framework of the heavy hadron chiral perturbation theory. To leading order in the heavy mass expansion, the interaction Lagrangian describing the couplings of these states among themselves and with the ground state heavy baryons contains 45 unknown couplings. We derive sum rules analogous to the Adler-Weisberger sum rule which constrain these couplings and relate them to the couplings of the s-wave heavy baryons. Using a spin-3/2 baryon as a target, we find a sum rule expressing the deviation from the quark model prediction for pion couplings to s-wave states in terms of couplings of the p-wave states. In the constituent quark model these couplings are related and can be expressed in terms of only six reduced matrix elements. Using recent CLEO data on {Sigma}{sub c}{sup {asterisk}} and {Lambda}{sub c1}{sup +} strong decays, we determine some of the unknown couplings in the chiral Lagrangian and two of the six quark model reduced matrix elements. Specific predictions are made for the decay properties of a few other L=1 charmed baryons. {copyright} {ital 1997} {ital The American Physical Society}

1/N(c) expansion for excited baryons

We derive consistency conditions which constrain the possible form of the strong couplings of the excited baryons to the pions. The consistency conditions follow from requiring the pion-excited baryon scattering amplitudes to satisfy the large-Nc Witten counting rules and are analogous to consistency conditions used by Dashen, Jenkins and Manohar and others for s-wave baryons. The consistency conditions are explicitly solved, giving the most general allowed form of the strong vertices for excited baryons in the large-Nc limit. We show that the solutions to the large-Nc consistency conditions coincide with the predictions of the nonrelativistic quark model for these states, extending the results previously obtained for the s-wave baryons. The 1/Nc corrections to these predictions are studied in the quark model with arbitrary number of colors Nc.

Corrections to chiral dynamics of heavy hadrons: 1/M correction.

In earlier publications we have analyzed the strong and radiative decays of heavy hadrons in a formalism which incorporates both heavy-quark and chiral symmetries. In particular, we have derived a heavy-hadron chiral Lagrangian whose coupling constants are related by the heavy-quark flavor-spin symmetry arising from the QCD Lagrangian with infinitely massive quarks. In this paper, we reexamine the structure of the above chiral Lagrangian by including the effects of 1/{ital m}{sub {ital Q}} corrections in the heavy-quark effective theory. The relations among the coupling constants, originally derived in the heavy-quark limit, are modified by heavy-quark symmetry-breaking interactions in QCD. Some of the implications are discussed.

Heavy-Flavor-Conserving Hadronic Weak Decays of Heavy Baryons

A bstractMore than two decades ago, we studied heavy-flavor-conserving weak decays of heavy baryons within the framework that incorporates both heavy-quark and chiral symmetries. In view of the first observation of Ξb− → Λb0π− by LHCb recently, we have reexamined these decays and presented updated predictions. The predicted rates for Ξb− → Λb0π− in the MIT bag and diquark models are consistent with experiment. The major theoretical uncertainty stems from the evaluation of baryon matrix elements. The branching fraction of Ξc → Λcπ is predicted to be of order 10−4. It is suppressed relative to ℬΞb→Λbπ

High-Energy Elastic and Inelastic Scattering in ϕ 3 Theory

\mathrm{\mathcal{B}}\left({\Xi}_b\to {\Lambda}_b\pi \right)

The Parton Model and its Applications

owing to the shorter lifetime of Ξc relative to Ξb and the destructive nonspectator W-exchange contribution. The kinematically accessible weak decays of the sextet heavy baryon ΩQ are ΩQ → ΞQπ. Due to the absence of the ℬ6−ℬ3−