title: Designing cyclic universe models.
abstract: The phenomenological constraints on the scalar field potential in cyclic models of the Universe are presented. We show that cyclic models require a comparable degree of tuning to that needed for inflationary models. The constraints are reduced to a set of simple design rules including "fast-roll" parameters analogous to the "slow-roll" parameters in inflation.
authors.affiliation: ISCAP, Columbia University, New York, New York 10027, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Khoury
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Steinhardt
authors.forename: Neil
authors.initials: N
authors.lastname: Turok