Flavor changing neutral current processes in $B$ and $K$ decays in the supergravity model

Abstract

Flavor changing neutral current processes such as $b \to s \gamma$, $b \to s l^+ l^-$, $b \to s \nu \bar{\nu}$, $\epsilon_K$, $\Delta m_B$, $K^+ \to \pi^+ \nu \bar{\nu}$ and $\K_L \to \pi^0 \nu \bar{\nu}$ are calculated in the supersymmetric standard model based on supergravity. We consider two assumptions for the soft supersymmetry breaking terms. In the minimal case soft breaking terms for all scalar fields are taken to be universal at the GUT scale whereas those terms are different for the squark/slepton sector and the Higgs sector in the nonminimal case. In the calculation we have taken into account the next-to-leading order QCD correction to the $b \to s \gamma$ branching ratio, the results from the LEP II superparticles search, and the condition of the radiative electroweak symmetry breaking. We show that $\Delta m_B$ and $\epsilon_K$ can be enhanced up to 40% compared to the Standard Model values in the nonminimal case. In the same parameter region the $b \to s \nu \bar{\nu}$, $K^+ \to \pi^+ \nu \bar{\nu}$ and $\K_L \to \pi^0 \nu \bar{\nu}$ branching ratios are reduced up to 10%. The corresponding deviation in the minimal case is 20% for $\Delta m_B$ and $\epsilon_K$ and within 3% for the $b \to s \nu \bar{\nu}$, $K^+ \to \pi^+ \nu \bar{\nu}$ and $\K_L \to \pi^0 \nu \bar{\nu}$. For the $b \to s l^+ l^-$ process the significant deviation from the Standard Model is realized only when the $b \to s \gamma$ amplitude has an opposite sign to the Standard Model prediction. Significance on these results from possible future improvements of the $b \to s \gamma$ branching ratio measurement and top squark search is discussed.