Ultraviolet Completion of the Big Bang in Quadratic Gravity
Ruolin Liu (Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada, Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada, Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada)
; Jerome Quintin (Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada, Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada, Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada, Department of Physics, McGill University, Montréal, Quebec H3A 2T8, Canada, École de technologie supérieure, Université du Québec, Montréal, Quebec H3C 1K3, Canada)
; Niayesh Afshordi (Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada, Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada, Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada)
We present a quantum quadratic gravity inflationary scenario that can accommodate the new cosmological constraints, which have disfavored Starobinsky inflation. The theory is asymptotically free in the ultraviolet, but 1-loop running is found to dynamically lead to slow-roll inflation toward the infrared. When a large number of matter fields contribute to the beta functions, the spectral index and the tensor-to-scalar ratio can be phenomenologically viable. We find that as inflation ends, the theory approaches its strong coupling regime and general relativity must emerge, as an effective field theory, as the universe must reheat and enter its standard radiation era. In order to avoid strong coupling, a minimum tensor-to-scalar ratio of 0.01 is predicted for this theory. Our framework offers a laboratory for connecting a concrete ultraviolet completion (quantum quadratic gravity) with inflationary dynamics, reheating, and precise cosmological observations.