Can MAP and Planck map Planck physics?
L. Bergstrom, U. H. Danielsson
TL;DR
The paper tackles whether transplanckian physics during inflation can leave observable oscillations in the primordial power spectrum and the CMB. By adopting a vacuum choice fixed at a high-energy scale $\Lambda$ (not necessarily the Bunch-Davies vacuum), they derive a linear-in-$H/\Lambda$ modulation to $P(k)$, $P(k)=\left(\frac{H}{\dot{\phi}}\right)^2\left(\frac{H}{2\pi}\right)^2\left(1-\frac{H}{\Lambda}\sin\left(\frac{2\Lambda}{H}\right)\right)$, and express the modulation in slow-roll terms as $P(\varepsilon,\xi;k)=P_0(k)\left(1-\xi (k/k_n)^{-\varepsilon}\sin\left[\frac{2}{\xi}(k/k_n)^{\varepsilon}\right]\right)$ with $\xi=H/\Lambda$. For plausible parameters (e.g., $\Lambda\approx2\times10^{16}$ GeV, $H\approx7\times10^{13}$ GeV, $\varepsilon\sim0.01$) this yields about one oscillation per $\Delta\ln k$, potentially detectable by Planck at the $\mathcal{O}(10^{-3})$ level, or tightly constrained by MAP. A detection would probe transplanckian physics and high-energy/stringy effects during inflation, while null results would impose limits on the new-physics scale.
Abstract
We investigate whether a recently proposed modulation of the power spectrum of primordial density fluctuations generated through transplankian (maybe stringy) effects during inflation can be observed. We briefly review the mechanism leading to the modulation and apply it to a generic slow-roll scenario of inflation. We then investigate how these primordial modulation effects leave an imprint in the cosmic microwave background radiation. Our conclusions are that for favourable parameter values already the presently flying MAP satellite will have a chance to detect such transplanckian oscillations in the pattern of temperature fluctuations on the sky, and that the upcoming Planck satellite will either detect them or put stringent limits related to the mass scale where the new effects appear.