29 research outputs found
B-> K photon photon via intermediate eta'
We examine our previous conjecture that the eta' intermediate resonance has
the dominant role in the long distance contributions to B decay into two
photons and a strange final state hadron. We calculate the branching ratio of
the exclusive B-> K eta'-> K photon photon decay using the nonspectator
mechanism for eta' production in charmless hadronic B decays. It is shown that
the obtained branching ratio B^eta'(B-> K\gamma\gamma)~ 8.7 X 10^{-7} is more
than twice as large as the eta_c contribution to this decay mode.Comment: 6 pages, latex, no figure
Pade/renormalization-group improvement of inclusive semileptonic B decay rates
Renormalization Group (RG) and optimized Pade-approximant methods are used to
estimate the three-loop perturbative contributions to the inclusive
semileptonic b \to u and b \to c decay rates. It is noted that the \bar{MS}
scheme works favorably in the b \to u case whereas the pole mass scheme shows
better convergence in the b \to c case. Upon the inclusion of the estimated
three-loop contribution, we find the full perturbative decay rate to be
192\pi^3\Gamma(b\to u\bar\nu_\ell\ell^-)/(G_F^2| V_{ub}|^2) = 2065 \pm 290{\rm
GeV^5} and 192\pi^3\Gamma(b\to c\ell^-\bar\nu_\ell)/(G_F^2|V_{cb}|^2)= 992 \pm
198 {\rm GeV^5}, respectively. The errors are inclusive of theoretical
uncertainties and non-perturbative effects. Ultimately, these perturbative
contributions reduce the theoretical uncertainty in the extraction of the CKM
matrix elements |V_{ub}| and |V_{cb}| from their respective measured inclusive
semileptonic branching ratio(s).Comment: 3 pages, latex using espcrc2.sty. Write-up of talk given at BEACH
2002, UBC, Vancouve
Pade-Improved Estimate of Perturbative Contributions to Inclusive Semileptonic Decays
Pade-approximant methods are used to estimate the three-loop perturbative
contributions to the inclusive semileptonic decay rate. These
improved estimates of the decay rate reduce the theoretical uncertainty in the
extraction of the CKM matrix element from the measured inclusive
semileptonic branching ratio.Comment: 3 pages, latex, write-up of talk presented at DPF 200
CP violation in the decay mode
Within the framework of Standard Model, the exclusive decay mode is studied. Although the usual short distance contribution is
small compared to the similar mode, the process offers the
possibility of studying the CP violation, a feature absent in the
counterpart.Comment: 11 page latex file including 2 ps figures. Typos corrected, minor
changes. To appear in PR
Heavy Baryonic Decays of \Lambda_b \to \Lambda \eta^{(\prime)} and Nonspectator Contribution
We calculate the branching ratios of the hadronic \Lambda_b decays to \eta
and \eta^\prime in the factorization approximation where the form factors are
estimated via QCD sum rules and the pole model. Our results indicate that,
contrary to B\to K\eta^{(\prime)} decays, the branching ratios for
\Lambda_b\to\Lambda\eta and \Lambda_b\to\Lambda\eta^\prime are more or less the
same in the hadronic \Lambda_b transitions. We estimate the branching ratio of
\Lambda_b\to\Lambda\eta^{(\prime)} to be 10.80 (10.32)\times 10^{-6} in QCD sum
rules, and 2.78 (2.96)\times 10^{-6} in the pole model. We also estimate the
nonfactorizable gluon fusion contribution to \Lambda_b\to\Lambda\eta^\prime
decay by dividing this process into strong and weak vertices. Our results point
to an enhancement of more than an order of magnitude due to this mechanism.Comment: 16 pages, ReVTeX, 5 eps figure
Renormalization-Group Improvement of Effective Actions Beyond Summation of Leading Logarithms
Invariance of the effective action under changes of the renormalization scale
leads to relations between those (presumably calculated) terms
independent of at a given order of perturbation theory and those higher
order terms dependent on logarithms of . This relationship leads to
differential equations for a sequence of functions, the solutions of which give
closed form expressions for the sum of all leading logs, next to leading logs
and subsequent subleading logarithmic contributions to the effective action.
The renormalization group is thus shown to provide information about a model
beyond the scale dependence of the model's couplings and masses. This procedure
is illustrated using the model and Yang-Mills theory. In the latter
instance, it is also shown by using a modified summation procedure that the
dependence of the effective action resides solely in a multiplicative
factor of (the running coupling). This approach is also shown to
lead to a novel expansion for the running coupling in terms of the one-loop
coupling that does not require an order-by-order redefinition of the scale
factor . Finally, logarithmic contributions of the instanton
size to the effective action of an SU(2) gauge theory are summed, allowing a
determination of the asymptotic dependence on the instanton size as
goes to infinity to all orders in the SU(2) coupling constant.Comment: latex2e, 30 pages, 2 eps figures embedded in mansucript. v2 corrects
several minor errors in equation
Renormalization Group Summation and the Free Energy of Hot QCD
Using an approach developed in the context of zero-temperature QCD to
systematically sum higher order effects whose form is fixed by the
renormalization group equation, we sum to all orders the leading log (LL) and
next-to-leading log (NLL) contributions to the thermodynamic free energy in hot
QCD. While the result varies considerably less with changes in the
renormalization scale than does the purely perturbative result, a novel
ambiguity arises which reflects the strong scheme dependence of thermal
perturbation theory.Comment: 7 pages REVTEX4, 2 figures; v2: typos correcte
Large effects on \BsBs mixing by vector-like quarks
We calculate the contributions of the vector-like quark model to \BsBs
mixing, taking into account the constraints from the decay . In
this model the neutral bosons mediate flavor-changing interactions at the tree
level. However, \BsBs mixing is dominated by contributions from the box
diagrams with the top quark and the extra up-type quark. In sizable ranges of
the model parameters, the mixing parameter is much different from the
standard model prediction.Comment: 11 pages, 4 figures, To be published in Phys. Rev.
Semileptonic form factors - a model-independent approach
We demonstrate that the B->D(*) l nu form factors can be accurately predicted
given the slope parameter rho^2 of the Isgur-Wise function. Only weak
assumptions, consistent with lattice results, on the wavefunction for the light
degrees of freedom are required to establish this result. We observe that the
QCD and 1/m_Q corrections can be systematically represented by an effective
Isgur-Wise function of shifted slope. This greatly simplifies the analysis of
semileptonic B decay. We also investigate what the available semileptonic data
can tell us about lattice QCD and Heavy Quark Effective Theory. A rigorous
identity relating the form factor slope difference rho_D^2-rho_A1^2 to a
combination of form factor intercepts is found. The identity provides a means
of checking theoretically evaluated intercepts with experiment.Comment: 18 pages, Revtex, 4 postscript figures, uses epsfig.st
Observing Decays at Hadron Colliders
We examine the prospects for observing weak flavour-changing neutral current
(FCNC) decays of \B\ mesons at hadron colliders, including effects of anomalous
~vertices. Since it is very difficult to measure the inclusive rate B
\rightarrow X_s \, \lp \lm one should consider exclusive modes such as
\BKsmumu\ and \BKmumu. Even though this requires one to compute hadronic matrix
elements, we show that experimentally observable quantities (ratios of decay
rates) are not strongly parametrisation dependent. Some possibilities for
reducing the theoretical uncertainties from other experimental data are
discussed.Comment: 17 pages, uses LaTeX, epsf and uufiles. UCLA/93/TEP/2