Abstract
We present a semi-analytic exploration of some low-[Formula: see text] angular power spectra inspired by “brane supersymmetry breaking (BSB)”. This mechanism splits Bose and Fermi excitations in string theory, leaving behind an exponential potential that is just too steep for the inflaton to emerge from the initial singularity while descending it. As a result, the scalar generically bounces against the exponential wall, which typically introduces an infrared depression and a pre-inflationary peak in the power spectrum of scalar perturbations. We elaborate on a possible link between this phenomenon and the low-[Formula: see text] CMB. For the first 32 multipoles, combining the hard exponential with a milder one leading to [Formula: see text] and with a small Gaussian bump, we have attained a reduction of [Formula: see text] to about 46% of the standard ΛCDM setting, with both WMAP9 and PLANCK 2013 data. This result corresponds to a [Formula: see text] of about 0.45, to be compared with a ΛCDM value of about 0.85. The preferred choices combine naturally quadrupole depression, a first peak around [Formula: see text] and a wide minimum around [Formula: see text]. We have also gathered some evidence that similar spectra emerge if the hard exponential is combined with more realistic models of inflation. A problem of the preferred examples is their slow convergence to an almost scale-invariant profile.
Highlights
String Theory is an enticing framework for High–Energy Physics beyond the Standard Model, whose foundations remain somewhat mysterious
The main thrust of this work was to take seriously some low–l anomalies of the CMB angular power spectrum, under the spell of some clues provided by String Theory
A notable class of string vacua with “brane supersymmetry breaking”, where supersymmetry is broken at the scale of string excitations, involves an exponential potential that is just too steep for a scalar field to emerge from the initial singularity while descending it
Summary
String Theory (for reviews see [1]-[5]) is an enticing framework for High–Energy Physics beyond the Standard Model, whose foundations remain somewhat mysterious. Can toy combine a models are bounce and an inflationary phase with relatively simple 1 and were studied in spectral index ns detail in [30, 31] These the resulting power spectra of scalar perturbations with pre–inflationary peaks are qualitatively similar to those obtained if the mild exponential in eq (1.3) is replaced with a more realistic Starobinsky potential. The resulting potentials of eq (1.4) are an interesting theoretical laboratory since, depending on the choice of φ0, the resulting power spectra can recover the feature described in [60, 61], their generalizations described in [28, 30, 31] or new types of double peaks All these effects arise from regions that are close the exponential wall, right before the scalar attains slow–roll, so that the available options appear somehow exhausted in this fashion. We shall leave aside all technical details about the computation, since they were clearly spelled out in [30, 31]
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