Topological inflation with graceful exit
  We investigate a class of models of topological inflation in which a
super-Hubble-sized global monopole seeds inflation. These models are attractive
since inflation starts from rather generic initial conditions, but their not so
attractive feature is that, unless symmetry is again restored, inflation never
ends. In this work we show that, in presence of another nonminimally coupled
scalar field, that is both quadratically and quartically coupled to the Ricci
scalar, inflation naturally ends, representing an elegant solution to the
graceful exit problem of topological inflation. While the monopole core grows
during inflation, the growth stops after inflation, such that the monopole
eventually enters the Hubble radius, and shrinks to its Minkowski space size,
rendering it immaterial for the subsequent Universe's dynamics. Furthermore, we
find that our model can produce cosmological perturbations that source CMB
temperature fluctuations and seed large scale structure statistically
consistent (within one standard deviation) with all available data. In
particular, for small and (in our convention) negative nonminimal couplings,
the scalar spectral index can be as large as $n_s\simeq 0.955$, which is about
one standard deviation lower than the central value quoted by the most recent
Planck Collaboration.
