  We study theoretically the recombination within a pair of two polarons in
magnetic field subject to a strong linearly polarized ac drive. Strong drive
implies that the Zeeman frequencies of the pair-partners are much smaller than
the Rabi frequency, so that the rotating wave approximation does not apply.
What makes the recombination dynamics nontrivial, is that the partners
recombine only when they form a singlet, S. By admixing singlet to triplets,
the drive induces the triplet recombination as well. We calculate the effective
decay rate of all four spin modes. Our main finding is that, under the strong
drive, the major contribution to the decay of the modes comes from short time
intervals when the driving field passes through zero. When the recombination
time in the absence of drive is short, fast recombination from S leads to
anomalously slow recombination from the other spin states of the pair. We show
that, with strong drive, this recombination becomes even slower. The
corresponding decay rate falls off as a power law with the amplitude of the
drive.
