Do envelope solitons radiate?

In dispersive wave systems, when leading-order nonlinear and dispersive eff ects, are taken into account the envelope of a small-amplitude narrow-band wave pulse is known to satisfy the nonlinear Schrodinger (NLS) equation whi ch, under certain conditions, admits envelope-soliton solutions. These soli tons describe locally confined wave groups with envelopes of permanent form and find applications in various physical contexts. Here, is addressed the question of whether NLS envelope solitons survive when higher-order effect s are taken into account. Based on a kinematic argument first, it is sugges ted that oscillatory tails are inevitably emitted, and this claim is furthe r supported by numerical computations by use of a fifth-order Korteweg-deVr ies equation as a simple example. The radiation of tails is caused by a res onance mechanism that lies beyond all orders of the usual multiple-scale ex pansion leading to the NLS equation, and a procedure for calculating these tails by use of exponential asymptotics is outlined. Despite having exponen tially small amplitude in the asymptotic sense, the radiated tails can be s ignificant when pulses of relatively short duration are considered.