QCD Improved b→sγb\to s\gamma Constraints on the Minimal Supergravity Model

Recent advances in the QCD corrections to $b\to s\gamma$ decay in the MSSM include i.) evaluation of the relevant operators, Wilson coefficients and anomalous dimension matrix elements for the various MSSM effective theories valid at scales beyond $Q =M_W$, ii.) calculations of most of the needed anomalous dimension matrix elements to next-to-leading order for scales m_b\alt Q , and iii.) calculations of ${\cal O}(\alpha_s)$ virtual and bremsstrahlung corrections to the $b\to s\gamma$ decay operators at scale $Q\sim m_b$. We assemble all these known results to gain an estimate of $B(b\to s\gamma )$ for the parameter space of the minimal supergravity model (mSUGRA). We find a much reduced scale dependence of our result compared to usual leading-log evaluations. Comparison with the latest CLEO results yields stringent constraints on parameter space. Much of mSUGRA parameter space is ruled out for $\mu <0$, especially for large $tan\beta$. We compare these results with other constraints from cosmology and non-standard vacua. Also, we compare with expectations for discovering mSUGRA at LEP2, the Tevatron and the CERN LHC.Comment: 14 pages REVTEX plus 7 PS figures; this version contains revised figures and text due to discovery of a bug in the program used to generate results for the previous version of this manuscrip

Mixing-induced CP Asymmetries in Radiative B Decays in and beyond the Standard Model

In the Standard Model (SM) the photon in radiative $\bar B^0$ and $\bar B_s$ decays is predominantly left-handed. Thus, mixing induced CP asymmetries in $b\to s\gamma$ and $b\to d\gamma$ are suppressed by $m_s/m_b$ and $m_d/m_b$, respectively, and are very small. In many extensions of the SM, such as the left-right symmetric model (LRSM), SU(2)xU(1) models with exotic fermions and SUSY, the amplitude of right-handed photons grows proportional to the virtual heavy fermion mass, which can lead to large asymmetries. As an example, in the LRSM, asymmetries larger than 50% are possible even when radiative decay rate measurements agree with SM predictions.Comment: 11 pages + 1 figure.p