  The Planck data on cosmic microwave background indicates that the
Starobinsky-type model with concave inflation potential is favored over the
convex-type chaotic inflation. Is there any reason for that? Here we argue that
if our universe began with a Euclidean wormhole, then the Starobinsky-type
inflation is probabilistically favored. It is known that for a more generic
choice of parameters than that originally assumed by Hartle and Hawking, the
Hartle-Hawking wave function is dominated by Euclidean wormholes, which can be
interpreted as the creation of two classical universes from nothing. We show
that only one end of the wormhole can be classicalized for a convex potential,
while both ends can be classicalized for a concave potential. The latter is
therefore more probable.
