How well constrained is the primordial power spectrum?

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I will discuss a new method of inflaton potential reconstruction that combines the flow formalism, which is a stochastic method of inflationary model generation, with an exact numerical calculation of the mode equations of quantum fluctuations. This technique allows one to explore regions of the inflationary parameter space yielding spectra that are not well parameterized as power-laws. We use this method to generate an ensemble of generalized spectral shapes that provide equally good fits to current CMB and LSS as data as do simpler power-law spectra.
Within this ensemble are spectra that exhibit a strong running on large angular scales (where cosmic variance is large) that turns off on small
scales. Such strongly running spectra are accompanied by large tensor
components that lie outside the 1 and 2 sigma limits of current WMAP3
and SDSS data. This demonstrates that the generalization of the spectral shape adversely impacts our ability to constrain key inflationary observables. The inflationary models giving rise to such spectra are characterized by an initially fast rolling inflaton, in marked contrast to the dominant paradigm of slow roll inflation.