Finite-Size Effects for Dyonic Giant Magnons

We compute finite-size corrections to dyonic giant magnons in two ways. One is by examining the asymptotic behavior of helical strings of hep-th/0609026 as elliptic modulus k goes to unity, and the other is by applying the generalized Luscher formula for mu-term of arXiv:0708.2208 to the situation in which incoming particles are boundstates. By careful choice of poles in the su(2|2)^2-invariant S-matrix, we find agreement of the two results, which makes possible to predict the (leading) finite-size correction for dyonic giant magnons to all orders in the 't Hooft coupling.