Non-Bunch-Davies Initial State Reconciles Chaotic Models with BICEP and Planck

Abstract

The BICEP2 experiment has announced a signal for primordial gravity waves with tensor-to-scalar ratio $r=0.2_{-0.05}^{+0.07}$ [arXiv:1403.3985]. There are two ways to reconcile this result with the latest Planck experiment [arXiv:1303.5082]. One is by assuming that there is a considerable tilt of $r$, ${\mathcal{T}}_r$, with a positive sign, ${\mathcal{T}}_r=d\ln r/d\ln k\gtrsim 0.57_{-0.27}^{+0.29}$ corresponding to a blue tilt for the tensor modes of order $n_T\simeq 0.53_{-0.27}^{+0.29}$, assuming the Planck experiment best-fit value for tilt of scalar power spectrum $n_S$. The other possibility is to assume that there is a negative running in the scalar spectral index, $d{n}_S/d\ln k\simeq -0.02$ which pushes up the upper bound on $r$ from $0.11$ up to $0.26$ in the Planck analysis assuming the existence of a tensor spectrum. Simple slow-roll models fail to provide such large values for ${\mathcal{T}}_r$ or negative runnings in $n_S$ [arXiv:1403.3985]. In this note we show that a non-Bunch-Davies initial state for perturbations can provide a match between large field chaotic models (like $m^2{\varphi }^2$) with the latest Planck result [arXiv:1306.4914] and BICEP2 results by accommodating either the blue tilt of $r$ or the negative large running of $n_S$.

v1:5 pages, double column; v2: 6 pages, double column, the option of negative running of scalar spectral index and some references were added; v3: Matched the PLB version

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