Constraining the two-Higgs-doublet-model parameter space

Abstract

We confront the two-Higgs-doublet model with a variety of experimental constraints as well as theoretical consistency conditions. The most constraining data are the $\overline{B}\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ decay rate (at low values of ${M}_{{H}^{\ifmmode\pm\else\textpm\fi{}}}$), and $\ensuremath{\Delta}\ensuremath{\rho}$ (at both low and high ${M}_{{H}^{\ifmmode\pm\else\textpm\fi{}}}$). We also take into account the $B\overline{B}$ oscillation rate and ${R}_{b}$, or the width $\ensuremath{\Gamma}(Z\ensuremath{\rightarrow}b\overline{b})$ (both of which restrict the model at low values of $\mathrm{tan}\ensuremath{\beta}$), and the ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\tau}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ decay rate, which restricts the model at high $\mathrm{tan}\ensuremath{\beta}$ and low ${M}_{{H}^{\ifmmode\pm\else\textpm\fi{}}}$. Furthermore, the LEP2 nondiscovery of a light, neutral-Higgs boson is considered, as well as the muon anomalous magnetic moment. Since perturbative unitarity excludes high values of $\mathrm{tan}\ensuremath{\beta}$, the model turns out to be very constrained. We outline the remaining allowed regions in the $\mathrm{tan}\ensuremath{\beta}$-${M}_{{H}^{\ifmmode\pm\else\textpm\fi{}}}$ plane for different values of the masses of the two lightest neutral-Higgs bosons, and describe some of their properties.