Temperature Notion in a Curved Spacetime
  Scalar radiation, represented by a massless scalar field in a Robertson-Walker metric, is taken into account. By using a weak non minimum vacuum definition, the radiation temperature as a time dependent function is obtained. When the universe evolution is nearly but non equal to $t^{1/2}$, it is possible to fit the temperature of the microwave background. A particular massive case is compared with the massless one. When the mass of the matter field is next to the Planck one and the time is going to infinite, a similar result to the Hawking radiation of the blackhole is obtained. 
Carlos E. Laciana