Vortices in rotating superfluid (3)He

In this review we first present an introduction to (3)He and to the ROTA collaboration under which most of the knowledge on vortices in superfluid (3)He has been obtained. In the physics part, we start from the exceptional properties of helium at millikelvin temperatures. The dilemma of rotating superfluids is presented. In (4)He and in (3)He-B the problem is solved by nucleating an array of singular vortex lines. Their experimental detection in (3)He by NMR is described next. The vortex cores in (3)He-B have two different structures, both of which have spontaneously broken symmetry. A spin-mass vortex has been identified as well. This object is characterized by a flow of spins around the vortex line, in addition to the usual mass current. A great variety of vortices exist in the A phase of (3)He; they are either singular or continuous, and their structure can be a line or a sheet or fill the whole liquid. Altogether seven different types of vortices have been detected in (3)He by NMR. We also describe briefly other experimental methods that have been used by ROTA scientists in studying vortices in (3)He and some important results thus obtained. Finally, we discuss the possible applications of experiments and theory of (3)He to particle physics and cosmology. In particular, we report on experiments where superfluid (3)He-B was heated locally by absorption of single neutrons. The resulting events can be used to test theoretical models of the Big Bang at the beginning of our universe.