Constraint on the amplitude of isothermal perturbations imposed by an isotropy of the cosmic microwave background radiation
The evolution of initially isothermal perturbations produced in a radiation-dominated universe is investigated until the time of recombination. The ratio of the amplitude of baryon irregularities to that of radiation generated in the course of the evolution of the universe is determined. Combining it with the observed upper bound on the anisotropy of the cosmic background radiation, the authors obtain a severe constraint on the amplitude of initially isothermal fluctuations at the time of recombination. This constraint poses a serious difficulty for the theory of galaxy formation based on isothermal perturbations.