Séminaire de Physique ThéoriqueVortex lines in fluids - from string theory
Sebastian Garcia-Saenz (Institut d’Astrophysique de Paris)
Thursday 23 November 2017 14:00 - Tours - Salle 1180 (Bât E2)
Thin vortices in fluids and superfluids admit an effective field theory (EFT) description in which they can be treated as one-dimensional extended objects, or strings. In this theory, vortex lines can interact among each other as well as with the “bulk” fluid by the exchange of phonons, whose dynamics can be described by a simple scalar effective theory. The coupling between vortices and sound is however more complicated, as it requires switching to a magnetic-type dual formulation in which the phonon field is encoded by a gauge two-form. After a review of the theory and its applications, I will discuss recent work where we show that the EFT can be recast into the simpler scalar field language, in a description that is valid for closed string configurations and for bulk modes of wavelength much longer than the typical string size. This is essentially a systematic expansion of the original EFT in which the string is regarded as a point-like source with degrees of freedom given by the string’s multipole moments. As an illustration we compute the sound emitted by an oscillating vortex ring, a calculation that in our field theory language reduces to a simple Feynman diagram to leading order.