  We propose the generalized Luscher formula for multi-magnon states by which
one can compute the finite-size correction to the energy of multi giant magnons
at classical and one-loop levels. It is shown that the F-term of our formula is
consistent with the exact finite-size spectrum of the sinh-Gordon model, and
the mu-term agrees with the finite-size energy of magnon boundstate of the
asymptotic Bethe Ansatz in the su(2) sector at strong coupling. In an appendix,
we evaluate our formula at weak coupling under some approximations, and find
that the transcendental terms arise from a sum over an infinite tower of BPS
boundstates.

High Energy Physics - Theory