Probing the power spectrum bend with recent cosmic microwave background data

We constrain the spectrum of primordial curvature perturbations P(k) by using the new data on the cosmic microwave background from the Boomerang and MAXIMA experiments. Our study is based on slow-roll inflationary models, and we consider the possibility of a running spectral index. Specifically, we expand the power spectrum P(k) to second order in ln k, thus allowing the power spectrum to bend in k-space. We show that allowing the power spectrum to bend erases the ability of the present data to measure the tensor to scalar perturbation ratio. Moreover, if the primordial baryon density Omega (b)h(2) is as low as found from big bang nucleo synthesis, the data favor a negative bending of the power spectrum, corresponding to a bump-like feature in the power spectrum around a scale of k = 0.004 Mp c(-1). (C) 2001 Elsevier Science B.V. All rights reserved.