Informal Pizza Seminar

Testing the k³ Component in the
Primordial Perturbation Power Spectrum

Loison Hoi

McGill

Well-known causality arguments show that events occurring at the end of inflation, associated with reheating or preheating, could contribute a blue component to the spectrum of primordial curvature perturbations, with the dependence k³. We explore the possibility that they could be observably large in current CMB, LSS, and Lyman-alpha data. We find that a k³ component with a cutoff at some maximum k can modestly improve the fits (Δ χ² = 1.4, 5.4) of the low multipoles (l ~ 10 - 50) or the second peak (l ~ 540) of the CMB angular spectrum when the three-year WMAP data are used. Moreover, the results from WMAP are consistent with the CBI, ACBAR, 2dFGRS, and SDSS data when they are included in the analysis. Including the SDSS galaxy clustering power spectrum, we find weak positive evidence for the k³ component at the level of Δ χ² = 2.4, with the caveat that the nonlinear evolution of the power spectrum may not be properly treated in the presence of the k³ distortion. To investigate the high-k regime, we use the Lyman-alpha forest data (LUQAS, Croft et al., and SDSS Lyman-alpha); here we find evidence at the level Δ χ² = 3.8. We give constraints on the ratio between the k³ component and the nearly scale-invariant component, r_σ < 1.5 over the range of wavenumbers 2.3 x 10^-3 Mpc^-1 < k < 8.2 Mpc^-1. We also discuss theoretical models which could lead to the k³ effect, including ordinary hybrid inflation, and double D-term inflation models.