title: Simple predictions from multifield inflationary models.
abstract: We explore whether multifield inflationary models make unambiguous predictions for fundamental cosmological observables. Focusing on N-quadratic inflation, we numerically evaluate the full perturbation equations for models with 2, 3, and O(100) fields, using several distinct methods for specifying the initial values of the background fields. All scenarios are highly predictive, with the probability distribution functions of the cosmological observables becoming more sharply peaked as N increases. For N=100 fields, 95% of our Monte Carlo samples fall in the ranges ns∈(0.9455,0.9534), α∈(-9.741,-7.047)×10-4, r∈(0.1445,0.1449), and riso∈(0.02137,3.510)×10-3 for the spectral index, running, tensor-to-scalar ratio, and isocurvature-to-adiabatic ratio, respectively. The expected amplitude of isocurvature perturbations grows with N, raising the possibility that many-field models may be sensitive to postinflationary physics and suggesting new avenues for testing these scenarios.
authors.affiliation: Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Richard
authors.initials: R
authors.lastname: Easther
authors.affiliation: Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom and Department of Theoretical Physics, University of the Basque Country UPV/EHU, 48040 Bilbao, Spain.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Frazer
authors.affiliation: Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Hiranya V
authors.initials: HV
authors.lastname: Peiris
authors.affiliation: Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Layne C
authors.initials: LC
authors.lastname: Price