Alleviating the tension at low through axion monodromy

P. Daniel Meerburg
Phys. Rev. D 90, 063529 – Published 30 September 2014

Abstract

There exists some tension on large scales between the Planck data and the ΛCDM concordance model of the Universe, which has been amplified by the recently claimed discovery of nonzero tensor-to-scalar ratio r. At the same time, the current best-fit value of r suggests large field inflation Δϕinf>Mp, which requires a UV complete description of inflation. A very promising working example that predicts large tensor modes and can be UV completed is axion monodromy inflation. This realization of inflation naturally produces oscillating features, as consequence of a broken shift symmetry. We analyze a combination of Planck, ACT, SPT, WMAP low polarization, and BICEP2 data and show a long wavelength feature from a periodic potential can alleviate the tension at low multipoles with an improvement Δχ22.54 per degree of freedom, depending on the level of foreground subtraction. As with an introduction of running, one expects that any scale dependence should lead to a worsened fit at high multipoles. We show that the logarithmic nature of the axion feature in combination with a tilt ns1 allows the fit to be identical to a no-feature model at the 2% level on scales 1003500 and quite remarkably actually slightly improves the fit at scales >2000. We also consider possible unremoved dust foregrounds and show that including these hardly changes the best-fit parameters. Corrected for potential foregrounds and fixing the frequency to the best fit value, we find an amplitude of the feature δns=0.0950.05+0.03, a spectral index ns=1.00.04+0.03, the overall amplitude log1010As=3.06±0.04, and a phase ϕ=0.851.6+0.9. These parameters suggest an axion decay constant of f/MpO(.01). We discuss how Planck measurements of the temperature-Emode polarization (TE) and Emode polarization-Emode polarization (EE) spectra can further constrain axion monodromy inflation with such a large feature. A measurement of the large scale structure power spectrum is even more promising, as the effect is much bigger since the tensor modes do not affect the large scales. At the same time, a feature could also lead to a lower σ8, lifting the tension between cosmic microwave background and Sunyaev-Zel’dovich (SZ) constraints on σ8.

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  • Received 18 June 2014

DOI:https://doi.org/10.1103/PhysRevD.90.063529

© 2014 American Physical Society

Authors & Affiliations

P. Daniel Meerburg*

  • Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08540, USA

  • *meerburg@princeton.edu

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Issue

Vol. 90, Iss. 6 — 15 September 2014

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