Small-amplitude fully localised solitary waves for the full-dispersion Kadomtsev-Petviashvili equation

The KP-I equation arises as a weakly nonlinear model equation for gravity-capillary waves with strong surface tension (Bond number ). This equation admits-as an explicit solution-a 'fully localised' or 'lump' solitary wave which decays to zero in all spatial directions. Recently there has been interest in the full-dispersion KP-I equation where is the Fourier multiplier with symbol which is obtained by retaining the exact dispersion relation from the water-wave problem. In this paper we show that the FDKP-I equation also has a fully localised solitary-wave solution. The existence theory is variational and perturbative in nature. A variational principle for fully localised solitary waves is reduced to a locally equivalent variational principle featuring a perturbation of the variational functional associated with fully localised solitary-wave solutions of the KP-I equation. A nontrivial critical point of the reduced functional is found by minimising it over its natural constraint set.