In superfluid 3He-B pumped magnon quasiparticles can be trapped in a
potential created by spatial variation of the magnetic field and of
the order parameter. At sufficiently large density, magnons form a
Bose-Einstein condensate which can be probed and manipulated using NMR
techniques. At temperatures below 0.2Tc the lifetime of such
condensates grows to minutes. Magnon BEC has become an important tool
to probe superfluid 3He at the lowest temperatures, including dynamics
of quantized vortices, instabilities and waves on the superfluid
interfaces and thermometry in the microkelvin regime. Our recent
observations reveal the decay of magnon condensates via interaction
with other quasiparticle types in 3He-B: First, we have found
parametric conversion of magnons to pairs of quanta of longitudinal
spin waves, which play role of "light" Higgs bosons. Second, an
additional decay channel originates from fermions bound to the surface
of the topological superfluid.