Inhomogeneous preinflation across Hubble scales in full general relativity

We use the 3 + 1 formalism of numerical relativity to investigate the robustness of Starobinsky and Higgs inflation to inhomogeneous initial conditions, in the form of either a field gradient or kinetic energy density. Sub-Hubble and Hubble-sized fluctuations generically lead to inflation after an oscillatory phase between gradient and kinetic energies. Hubble-sized inhomogeneities also produce contracting regions that end up forming primordial black holes, subsequently diluted by inflation. We analyze the dynamics of the preinflation era and the generation of vector and tensor fluctuations. Our analysis further supports the robustness of inflation to any size of inhomogeneity in the field, velocity, or equation of state. At large field values, the preinflation dynamics only marginally depends on the field potential and it is expected that such behavior is universal and applies to any plateau-type inflation potential, which is favored by cosmic microwave background observations from Planck.

Automated summary

The study suggests that Starobinsky and Higgs inflation are robust in the face of inhomogeneous initial conditions. Analysis shows that Hubble-sized fluctuations can lead to the formation of primordial black holes, which are diluted by inflation. The research also indicates that at large field values, the dynamics before inflation are minimally influenced by the field potential.