On the strong-coupling effects in jet bremsstrahlung in the heavy flavor decays

We address the strong-coupling regime effects in the light-like quark jets where the radiated gluons are hard but highly collinear. These may lead to additional contributions in the invariant mass (or recoil energy) spectra, on top of the Fermi motion of the initial heavy quark in decays like b->s+\gamma. It is shown that the integer moments are nevertheless free from such effects; perturbation theory corrections for the moments are driven by \alpha_s in the small coupling regime. They are modified nonperturbatively by the soft modes but not by the collinear modes.Comment: 9 pages, LaTeX, one figur

A "BPS expansion" for B and D mesons

We analyze consequences of the approximation \mu_\pi^2 -\mu_G^2 << \mu_\pi^2 (a `BPS' limit) for B and D mesons. It is shown that neglecting perturbative effects many power corrections would vanish to all orders in 1/m_Q, in particular those violating heavy flavor symmetry. Among them are corrections to B->D formfactors. A number of relations receive corrections only to the second order expanding around the BPS limit to any order in 1/m_Q, including both f_+ and f_- at zero recoil. This allows an accurate evaluation of {\cal F}_+ for B->D l\nu. Its perturbative renormalization is computed analytically in the required Wilsonian scheme, yielding the dominant 3% enhancement.Comment: 13 pages, LaTeX, two figure

Strong interaction effects in semileptonic B decays

Strong interaction effects are addressed in connection to extracting |V_{cb}|. A comprehensive approach is described not relying on a 1/m_c expansion; it allows a percent accuracy without ad hoc assumptions about higher-order effects. An alternative to the M_X^2 variable is proposed improving convergence. Intrinsic hardness of integrated observables with a cut on E_\ell is discussed; it can be responsible for the behavior of reported by BaBar. Consequences of the proximity to the `BPS' limit are considered.Comment: 5 pages (two-column), LaTeX, uses espcrc2.sty. Talk given at ICHEP-2002, July 24-31 2002, Amsterda

On Extracting Heavy Quark Parameters from Moments with Cuts

We point out that applying the photon energy cut significantly modifies the moments of energy spectrum in B->X_s+gamma decays, with a certain class of effects not accounted for in the mostly used OPE expressions. This leads to a systematic bias in the extracted values of the b quark mass and other heavy quark parameters. The apparent b quark mass increases typically by 70MeV or more, together with an even more dramatic downward shift in the kinetic expectation value. Accounting for these cut-related shifts brings different measurements into a good agreement, when the OPE-based theory employs the robust approach. These nonperturbative effects are exponential in the effective hardness severely lowered by high cuts, and do not signify a breakdown of the 1/m_b expansion itself. Similar effects in semileptonic b->c decays are briefly addressed. We stress the utility of the second moment of E_gamma once these effects are incorporated.Comment: 8 pages, LaTeX, two figure. Contributed to the Lepton-Photon Conference, 2003, FNA

A Few Aspects of Heavy Quark Expansion

Two topics in heavy quark expansion are discussed. The heavy quark potential in perturbation theory is reviewed in connection to the problem of the heavy quark mass. The nontrivial reason behind the failure of the "potential subtracted" mass in higher orders is elucidated. The heavy quark sum rules are the second subject. The physics behind the new exact sum rules is described and a simple quantum mechanical derivation is given. The question of saturation of sum rules is discussed. A comment on the nonstandard possibility which would affect analysis of BR_sl(B) vs. n_c is made.Comment: 21 pages, LaTeX, 7 eps figures. To appear in the Proceedings of the UK Phenomenology Workshop on Heavy Flavour and CP Violation, Durham, UK, 17-22 September 200

B -> D* at zero recoil revisited

We examine the B -> D* form factor at zero recoil using a continuum QCD approach rooted in the heavy quark sum rules framework. A refined evaluation of the radiative corrections as well as the most recent estimates of higher order power terms together with more careful continuum calculation are included. An upper bound on the form factor of F(1)< 0.93 is derived, based on just the positivity of inelastic contributions. A model-independent estimate of the inelastic contributions shows they are quite significant, lowering the form factor by about 6% or more. This results in an unbiased estimate F(1) \approx 0.86 with about three percent uncertainty in the central value.Comment: 9 pages, 3 figures

New Exact Heavy Quark Sum Rules

Considering nonforward scattering amplitude off the heavy quark in the Small Velocity limit two exact superconvergent sum rules are derived. The first sum rule leads to the lower bound \rho^2 > 3/4 for the slope of the Isgur-Wise function. It also provides the rationale for the fact that the vector heavy flavor mesons are heavier than the pseudoscalar ones. A spin-nonsinglet analogue \bar\Sigma of \bar\Lambda = M_B-m_b is introduced.Comment: 7 pages, LaTe