On the effect of a variable vacuum energy density upon the spectrum of the cosmological microwave background radiation

According to contempory ideas, the cosmological term Λ admitted by the Einstein equations represents the energy density of the vacuum. Kirzhnits and Linde have pointed out that if the gauge theories with broken symmetry are applicable to the Universe, then this cosmological term is not a constant. Rather, it must vary with temperature, and this causes a violation of the first law of thermodynamics, in its usual form: the vacuum assumes a dynamical role, and interacts with the observable matter, via the gravitational field. One consequence of this interaction is that the spectrum of equilibrium radiation which is decoupled from other matter cannot maintain an initially Planckian shape as the Universe evolves. The magnitude of this effect is determined by the relative size of the cosmological term and how it depends upon temperature, estimates of which have been made by Canuto and Lee, to first approximation, in three different models. Using these estimates, it is found, at least for one of these models, that it is possible to reproduce the distortion to the cosmological microwave background radiation observed by Woody and Richards, if it is assumed that variation of the cosmological term is accompanied by non-conservation of photon number. During the radiation-dominated phase of the Universe, a time-dependence of photon number is equivalent to a time-dependence of the gravitational constant G, whose value at the epoch of helium production would be approximately twice its value today. Such a change is not inconsistent with the theory of helium synthesis and its relation to observations. (author)