  We report the results of a high-statistics search for H-dibaryon production
in inclusive Y(1S) and Y(2S) decays. No indication of an H-dibaryon with mass
near the M_H=2m_Lambda threshold is seen in either the H-> Lambda p pi- or
Lambda-Lambda decay channels and 90% confidence level branching-fraction upper
limits are set that are between one and two orders of magnitude below the
measured branching fractions for inclusive Y(1S) and Y(2S) decays to
antideuterons. Since Y(1,2S) decays produce flavor-SU(3)-symmetric final
states, these results put stringent constraints on H-dibaryon properties. The
results are based on analyses of 102 million Y(1S) and 158 million Y(2S) events
collected with the Belle detector at the KEKB electron-positron collider.
