Motion of electrons in liquid He-4

We present theoretical results on the stationary-state motion of electron bubbles in liquid (4)He both at zero and negative pressures. As the velocity increases, the moving electron bubble is squeezed along the direction of motion while it expands in the transverse directions. When the electron speed is large enough, as a consequence of this change in shape, a vortical fluid motion is induced around the bubble equator which eventually results in the formation and emission of a quantized vortex ring as a critical velocity is reached. This process occurs at zero pressure and at negative pressures down to similar to-1.2 bar. Below this value, the bubble becomes unstable and explodes as soon as the critical velocity is reached. Our results show that fast-moving electron bubbles explode in the pressure range where unidentified electron objects have been found to explode in recent cavitation experiments.