  For a single semiconductor quantum dot embedded in a microcavity, we
theoretically and experimentally investigate phonon-assisted transitions
between excitons and the cavity mode. Within the framework of the independent
boson model we find that such transitions can be very efficient, even for
relatively large exciton-cavity detunings of several millielectron volts.
Furthermore, we predict a strong detuning asymmetry for the exciton lifetime
that vanishes for elevated lattice temperature. Our findings are corroborated
by experiment, which turns out to be in good quantitative and qualitative
agreement with theory.
