Inflation and WMAP three year data: Features have a Future!

Abstract

The new three year WMAP data seem to confirm the presence of non-standard large scale features in the Cosmic Microwave Anisotropies power spectrum. While these features may hint at uncorrected experimental systematics, it is also possible to generate, in a cosmological way, oscillations on large angular scales by introducing a sharp step in the inflaton potential. Using current cosmological data, we derive constraints on the position, magnitude and gradient of a possible step. We show that a step in the inflaton potential, while strongly constrained by current data, is still allowed and may provide an interesting explanation to the currently measured deviations from the standard featureless spectrum. Moreover, we show that inflationary oscillations in the primordial power spectrum can significantly bias parameter estimates from standard ruler methods involving measurements of baryon oscillations.

Figures (8)

• Figure 1: Effects of a step in the potential on the power spectrum of curvature perturbations. Here we show the primordial spectrum for the two best fit points, corresponding to $b=14.81$, $c=0.0018$, $d=0.022$ (dashed line) and $b=14.34$, $c=0.00039$, $d=0.006$ (solid line).
• Figure 2: Marginalised likelihood (solid line) and projection of the likelihood distribution (dotted line) for the $b$ parameter in the case of WMAP only. Two peaks for $b$ at $b=14.3$ and $b=14.8$ are clearly visible. The one at $b=14.8$ provides a good fit to the low $\ell$ WMAP glitches. It is evident that the likelihood function is far from gaussian in this direction. The difference between the two curves is caused by a volume effect when integrating over the other parameter directions.
• Figure 3: This plot shows the temperature anisotropy angular power spectrum of the best fit step model (WMAP only, solid line) and, for reference, the best fit 6 parameter power law $\Lambda$CDM model (dashed line). The dotted line shows the effect of a feature near $b=14.8$ for WMAP data only, i.e., the "local" best fit at the lower peak in Figure \ref{['likelihoodwmaponly']}.
• Figure 4: Mean likelihood and marginalized likelihood contours in the ($b,\,c$) and $(b,\,c/d^2)$ planes at $8 \%$ and $99 \%$ c.l. for WMAP data only. The peaks comprise less than ten per cent of the total volume of the likelihood function.
• Figure 5: Likelihood contours in the $(b,\,c)$ and $(b,\,c/d^2)$ planes at $68 \%$ and $99 \%$ confidence level for CMB+SDSS.