Low-$\ell$ CMB from String-Scale SUSY Breaking?

TL;DR

This paper explores how string-scale supersymmetry breaking models influence low-$\\ell$ CMB patterns, proposing a modified $\\Lambda$CDM model with a low-frequency cutoff that fits observational data.

Contribution

It introduces a one-parameter extension of $\\Lambda$CDM incorporating a low-frequency cutoff motivated by string-inspired inflation models and provides a likelihood analysis of its fit to CMB data.

Findings

Detected a low-frequency cutoff $\\Delta$ in the power spectrum.

Found the cutoff value at $(0.351 \\pm 0.114) \\times 10^{-3} \, \text{Mpc}^{-1}$.

The model suggests relics of an earlier deceleration epoch in the CMB.

Abstract

Models of inflation are instructive playgrounds for supersymmetry breaking in Supergravity and String Theory. In particular, combinations of branes and orientifolds that are not mutually BPS can lead to \emph{brane supersymmetry breaking}, a phenomenon where non--linear realizations are accompanied, in tachyon--free vacua, by the emergence of steep exponential potentials. When combined with milder terms, these exponentials can lead to slow--roll after a fast ascent and a turning point. This leaves behind distinctive patterns of scalar perturbations, where pre--inflationary peaks can lie well apart from an almost scale invariant profile. I review recent attempts to connect these power spectra to the low--$\ell$ CMB, and a corresponding one--parameter extension of $\Lambda$CDM with a low--frequency cut $\Delta$. A detailed likelihood analysis led to $\Delta = (0.351 \pm 0.114) \times 10^{-3} \, \mbox{Mpc}^{-1}$, at $99.4\%$ confidence level, in an extended Galactic mask with $f_{sky}=39\%$, to be compared with a nearby value at $88.5\%$ in the standard Planck 2015 mask with $f_{sky}=94\%$. In these scenarios one would be confronted, in the CMB, with relics of an epoch of deceleration that preceded the onset of slow--roll.