N. Tsitverblit
Initial Friedmann universe, its spatial flatness, matter creation, 
and the cosmological term
(242K, pdf)

ABSTRACT.  In the \mbox{Friedmann} equations, an infinite initial density 
is avoided only when the universe is spatially flat. With such 
equations being then valid when the scale factor $a=0$, the universe 
must also be in the state of vacuum when $a$ is infinitesimal. Matter creation thus largely comes from nonlinearity of the \mbox{Friedmann} equations at a finite $a$. For the correspondence between such an initial vacuum and the \mbox{Friedmann} universe, therefore, a vacuum density is 
suggested to be gravitationally significant only when it could 
also have a matter phase. The effective cosmological term is 
then due to such a vacuum density.