Four-Loop Anomalous Dimensions for Radiative Flavour-Changing Decays

We evaluate the complete four-loop anomalous dimension matrix that is necessary for determining the effective flavour-changing neutral current couplings qbar-q'-gamma and qbar-q'-g at the next-to-next-to-leading order in QCD. The resulting O(alpha_s^2(mu_b)) correction to the B -> X_s gamma branching ratio amounts to around -2.9% for mu_b = 5 GeV, and -4.4% for mu_b = 2.5 GeVComment: 19 page

QCD challenges in radiative B decays

Radiative decays of the B meson are known to provide important constraints on the MSSM and many other realistic new physics models in the sub-TeV range. The inclusive branching ratio BR(B -> Xs gamma) being the key observable is currently measured to about 7% accuracy. Reaching a better precision on the theory side is a challenge both for the perturbative QCD calculations and for analyses of non-perturbative hadronic effects. The current situation is briefly summarized here.Comment: Overview talk presented at the International Workshop on QCD, Theory and Experiment "QCD@Work'', Martina Franca, Italy, June 20th-23rd, 201

Theory of radiative B decays

Theory of charmless radiative B decays is reviewed. Existence of uncontrolled non-perturbative effects in the inclusive rate at O(alpha_s) is reminded.Comment: Talk at the 3rd International Conference on B Physics and CP Violation, Taipei, December 3-7, 1999. 10 pages, including figures, uses graphic

Weak Radiative Decays of the B Meson and Bounds on MH±M_{H^\pm} in the Two-Higgs-Doublet Model

In a recent publication [6], the Belle collaboration updated their analysis of the inclusive weak radiative B-meson decay, including the full dataset of (772 +_ 11) x 10^6 BBbar pairs. Their result for the branching ratio is now below the Standard Model prediction [7,8], though it remains consistent with it. However, bounds on the charged Higgs boson mass in the Two-Higgs-Doublet Model get affected in a significant manner. In the so-called Model-II, the 95% C.L. lower bound on $M_{H^\pm}$ is now in the 570-800 GeV range, depending quite sensitively on the method applied for its determination. Our present note is devoted to presenting and discussing the updated bounds, as well as to clarifying several ambiguities that one might encounter in evaluating them. One of such ambiguities stems from the photon energy cutoff choice, which deserves re-consideration in view of the improved experimental accuracy.Comment: 15 pages, 4 figure

On The Dimensional Methods in Rare b Decays

Since several years there exists a question whether the dimensional reduction and the usual dimensional regularization give different results for the QCD-improved $b \rightarrow s \gamma$ and $b \rightarrow s$ $gluon$ decay rates. Here it is demonstrated explicitly that this is not the case: As long as physically meaningful quantities are considered, the results obtained with help of both techniques agree.Comment: 14 pages (including 1 page figures