Black hole formation from massive scalar field collapse in the Einstein–de Sitter universe

We study the spherically symmetric collapse of a real, minimally coupled, massive scalar field in an asymptotically Einstein–de Sitter spacetime background. By means of an eikonal approximation for the field and metric functions, we obtain a simple analytical criterion—involving the physical size and mass scales (the field's inverse Compton wavelength and the spacetime gravitational mass) of the initial matter configuration—for generic (non-time-symmetric) initial data to collapse to a black hole. This analytical condition can then be used to place constraints on the initial primordial black hole spectrum, by considering spherical density perturbations that re-entered the horizon during an early matter-dominated phase that immediately followed inflation.