b -> s γand supersymmetry with large tanβ

Abstract

We discuss the constraints on the supersymmetric parameter space from the decay mode b -> s γfor large values of tanβ. We improve the theoretical prediction for the decay rate by summing very large radiative corrections to all orders in perturbation theory. This extends the validity of the perturbative calculation to the large tanβregime. This resummation of terms of order alpha_s^n tan^{n+1}βuses a recently proposed effective lagrangian for the Yukawa interaction of bottom quarks. Moreover, we identify an additional source of tanβ-enhanced terms, which are of order alpha_s tanβand involve the charged Higgs boson, and analyze their behaviour in higher orders of perturbation theory. After correcting the current expressions for this rare decay branching ratio at next-to-leading order, we obtain that, contrary to recent claims, the presently measured branching ratio of b -> s γconstrains the supersymmetric parameter space in a relevant way, even if tanβis large.

Figures (3)

• Figure 1: Comparison of the result for ${\cal BR}(b \to s \gamma)$, as obtained in this work, as a function of $\tan\beta$, with the NLO expression of cdgg, where we have replaced the appropriate signs in the next-to-leading-order corrections, as explained in the text. The charged-Higgs boson mass is $200$ GeV and the light stop mass is $250$ GeV. The values of $\mu$ and $A_t$ are indicated in the plot while $M_2$, the gluino, heavy-stop and down-squark masses are set at $800$ GeV.
• Figure 2: As in Fig. \ref{['plot1']}, but for positive $A_t=500$ GeV.
• Figure 3: Combined bound on the charged Higgs and chargino masses, for various values of the mass of the lightest stop, $m_{\tilde{t}_2}$, and $\tan^{}\!\beta$. The excluded region corresponds to light (heavy) charged Higgs (chargino) masses. We have scanned for $m_{\tilde{t}_2}<m_{\tilde{t}_1}\leq 1$ TeV, $m_{\tilde{\chi}^+_2}<m_{\tilde{\chi}^+_1}\leq 1$ TeV and $|A_t|\leq 500$ GeV, the rest of SUSY masses have been set at 1 TeV.