title: Inflation versus cyclic predictions for spectral tilt.
abstract: We present a nearly model-independent estimate that yields the predictions of a class of simple inflationary and ekpyrotic or cyclic models for the spectral tilt of the primordial density inhomogeneities that enables us to compare the two scenarios. Remarkably, we find that the two produce an identical result, n(s) approximately 0.95. For inflation, the same estimate predicts a ratio of tensor to scalar contributions to the low l multipoles of the microwave background anisotropy of T/S approximately 20%; the tensor contribution is negligible for ekpyrotic or cyclic models, as shown in earlier papers.
authors: ISCAP, Columbia University, New York, New York 10027, USA.
authors: Justin
authors: J
authors: Khoury
authors: Paul J
authors: PJ
authors: Steinhardt
authors: Neil
authors: N
authors: Turok