Ultraviolet Completion of the Big Bang in Quadratic Gravity
Ruolin Liu (, Waterloo, Ontario N2L 2Y5, Canada Perimeter Institute for Theoretical Physics, Department of Physics and Astronomy, Waterloo, Ontario N2L 3G1, Canada University of Waterloo, Waterloo Centre for Astrophysics, Waterloo, Ontario N2L 3G1, Canada University of Waterloo)
; Jerome Quintin (, Waterloo, Ontario N2L 2Y5, Canada Perimeter Institute for Theoretical Physics, Department of Physics, Montréal, Quebec H3A 2T8, Canada McGill University, Waterloo Centre for Astrophysics, Waterloo, Ontario N2L 3G1, Canada University of Waterloo, , Université du Québec, Montréal, Quebec H3C 1K3, Canada École de technologie supérieure, Department of Applied Mathematics, Waterloo, Ontario N2L 3G1, Canada University of Waterloo)
; Niayesh Afshordi (, Waterloo, Ontario N2L 2Y5, Canada Perimeter Institute for Theoretical Physics, Department of Physics and Astronomy, Waterloo, Ontario N2L 3G1, Canada University of Waterloo, Waterloo Centre for Astrophysics, Waterloo, Ontario N2L 3G1, Canada University of Waterloo)
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.