Cosmology from random multifield potentials

We consider the statistical properties of vacua and inflationary trajectories associated with a random multifield potential. Our underlying motivation is the string landscape, but our calculations apply to general potentials. Using random matrix theory, we analyse the Hessian matrices associated with the extrema of this potential. These potentials generically have a vast number of extrema. We show that if the cross-couplings (off-diagonal terms) are of the same order as the self-couplings (diagonal terms), essentially all extrema are saddles, and the number of minima is effectively zero. Avoiding this requires the same separation of scales as is needed to ensure that Newton's constant is stable against radiative corrections in a string landscape. Using the central limit theorem we find that even if the number of extrema is enormous, the typical distance between extrema is still substantial—with challenging implications for inflationary models that depend on the existence of a complicated path inside the landscape.