Giant magnon solution and dispersion relation in string theory in AdS3×S3×T4 with mixed flux

We address the question of the exact form of the dispersion relation for light-cone string excitations in string theory in AdS3×S3×T4 with mixed R–R and NS–NS 3-form fluxes. The analogy with string theory in AdS5×S5 suggests that in addition to the data provided by the perturbative near-BMN expansion and symmetry algebra considerations there is another source of information for the dispersion relation – the semiclassical giant magnon solution. In earlier work in arXiv:1303.1037 and arXiv:1304.4099 we found that the symmetry algebra constraints, which are consistent with a perturbative expansion, do not completely determine the form of the dispersion relation. The aim of the present paper is to fix the dispersion relation by constructing a generalisation of the known dyonic giant magnon soliton on S3 to the presence of a non-zero NS–NS flux described by a WZ term in the string action (with coefficient q ). We find that the angular momentum of this soliton gets shifted by a term linear in world-sheet momentum p. We also discuss the symmetry algebra of the string light-cone S-matrix and show that the exact dispersion relation, which should have the correct perturbative BMN and semiclassical giant magnon limits, should also contain such a linear momentum term. The simplicity of the resulting bound-state picture provides a strong argument in favour of this dispersion relation