In the Higgs sector of the minimal supersymmetric standard model, the mass of the pseudoscalar $A$ is an independent parameter together with $\tan \beta \equiv v_2{/v}_1$. If $m_A$ is small, then the process $e^{+}{e}^{-}\to h+A$ is kinematically allowed and is suppressed only if $\tan \beta$ is small, i.e., less than one. On the other hand, the mass of the charged Higgs boson is now near $M_W,$ and the decay $t\to {b+h}^{+}$ is enhanced if $\tan \beta <1\mathrm{}$. Since the former has not been observed, and the branching fraction of $t\to b+W$ cannot be too small (by comparing the experimentally derived $t\overline{t}$ cross section from the leptonic channels with the theoretical prediction), we can infer a phenomenological lower bound on $m_A$ of at least 60 GeV for all values of $\tan \beta$.

• Received 30 July 1997

DOI:https://doi.org/10.1103/PhysRevD.56.R5306