Features of heavy physics in the CMB power spectrum

Abstract

The computation of the primordial power spectrum in multi-field inflation models requires us to correctly account for all relevant interactions between adiabatic and non-adiabatic modes around and after horizon crossing. One specific complication arises from derivative interactions induced by the curvilinear trajectory of the inflaton in a multi-dimensional field space. In this work we compute the power spectrum in general multi-field models and show that certain inflaton trajectories may lead to observationally significant imprints of 'heavy' physics in the primordial power spectrum if the inflaton trajectory turns, that is, traverses a bend, sufficiently fast (without interrupting slow roll), even in cases where the normal modes have masses approaching the cutoff of our theory. We emphasise that turning is defined with respect to the geodesics of the sigma model metric, irrespective of whether this is canonical or non-trivial. The imprints generically take the form of damped superimposed oscillations on the power spectrum. In the particular case of two-field models, if one of the fields is sufficiently massive compared to the scale of inflation, we are able to compute an effective low energy theory for the adiabatic mode encapsulating certain relevant operators of the full multi-field dynamics. As expected, a particular characteristic of this effective theory is a modified speed of sound for the adiabatic mode which is a functional of the background inflaton trajectory and the turns traversed during inflation. Hence in addition, we expect non-Gaussian signatures directly related to the features imprinted in the power spectrum.

Anomalous dimensions and non-gaussianity

“…Similar constraints arise in other models involving a linear mixing with the inflaton (e.g. [9][10][11][31][32][33][34]). …”

Inflation and String Theory

“…1 These fields fluctuation quantum-mechanically during inflation and therefore have to be included in the computation of the primordial perturbations. The phenomenology of these models of quasisingle-field inflation [490] has been explored in [118,207,208,239,255,265,267,[491][492][493][494][495][496][497].…”

“…As discussed in §2.1.5, a heavy mode of frequency ω can be integrated out in this way only when the adiabatic conditionω/ω 2 < 1 holds: more rapid evolution leads to excitation of the heavy modes. (Analyses of the effects of heavy fields include [493,496,505,506]. See also the discussion of resonance in §5.…”

Planck2015 results

“…On the other hand, sharp features or corners in an inflationary potential can temporarily drive the inflaton away from slow-roll; these large changes in the field and derivatives can create evenly-spaced oscillations, to be discussed in the next subsection. However, in multifield models residual oscillations after corner-turning can also lead to logspaced oscillations, just as in the resonance models (Chen 2011;Achúcarro et al 2011;Battefeld et al 2013;Chen et al 2015). A preliminary search for bispectrum resonance signals was performed in the first Planck analysis (Planck Collaboration XXIV 2014) and our purpose here is to substantially increase the frequency range and number of models investigated.…”