  In models of Randall-Sundrum type orthopositronium (o-Ps) can disappear due
to tunnelling into additional dimension(s). The experimental signature of this
effect is the invisible decay of orthopositronium. We point out that this
process may occur at a rate within two or three orders of magnitude of the
present experimental upper limit. We discuss this in details and stress that
the existence of invisible decay of orthopositronium in vacuum could explain
the o-Ps decay rate puzzle. Thus, our result enhances the existing motivation
and justifies efforts for a more sensitive search for o-Ps->invisible decay in
a near future experiment. Possible manifestations of new physics in other rare
(exotic) decays of orthopositronium are also discussed.
