### Shape of vortices for a rotating Bose Einstein condensate

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**Résumé:**

**Abstract:**

For a Bose-Einstein condensate placed in a rotating trap, we study the simplified energy of a vortex line derived in \cite{AR} in order to determine the shape of the vortex line according to the rotational velocity and the elongation of the condensate. The energy reflects the competition between the length of the vortex which needs to be minimized taking into account the anisotropy of the trap and the rotation term which pushes the vortex along the $z$ axis. We prove that if the condensate has the shape of a pancake, the vortex stays straight along the $z$ axis while in the case of a cigar, the vortex is bent. We study the local stability of the straight vortex and find an estimate for the critical angular speed at which bent vortices are nucleated. When vortices are nucleated, we prove that they must have some finite length.

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**Date:** 2002-09-30