Phases of a polar spin-1 Bose gas in a magnetic field
  The two Bose--Einstein condensed phases of a polar spin-1 gas at nonzero magnetizations and temperatures are investigated. The Hugenholtz--Pines theorem is generalized to this system. Crossover to a quantum phase transition is also studied. Results are discussed in a mean field approximation. 
Krisztian Kis-Szabo, Peter Szepfalusy, Gergely Szirmai