  There are several classes of homogeneous Fermi-systems which are
characterized by the topology of the energy spectrum of fermionic
quasiparticles: (1) Gapless systems with a Fermi-surface; (2) Systems with a
gap in their spectrum; (3) Gapless systems with topologically stable point
nodes (Fermi points); and (4) Gapless systems with topologically unstable lines
of nodes (Fermi lines). Superfluid 3He-A and electroweak vacuum belong to the
universality Class (3). The fermionic quasiparticles (particles) in this class
are chiral: they are left-handed or right-handed. The collective bosonic modes
of systems of Class (3) are the effective gauge and gravitational fields. The
great advantage of superfluid 3He-A is that we can perform experiments using
this condensed matter and thereby simulate many phenomena in high energy
physics, including axial anomaly, baryoproduction, and magnetogenesis. 3He-A
textures induce a nontrivial effective metrics of the space, where the free
quasiparticles move along geodesics. With 3He-A one can simulate event
horizons, Hawking radiation, rotating vacuum, etc. High-temperature
superconductors are believed to belong to Class (4). They have gapless
fermionic quasiparticles with a "relativistic" spectrum close to gap nodes,
which allows application of ideas developed for superfluid 3He-A.
