Title: Reconciling tensor and scalar observables in G-inflation

Abstract

The simple m^2Φ2 potential as an inflationary model is coming under increasing tension with limits on the tensor-to-scalar ratio r and measurements of the scalar spectral index n_s. Cubic Galileon interactions in the context of the Horndeski action can potentially reconcile the observables. However, we show that this cannot be achieved with only a constant Galileon mass scale because the interactions turn off too slowly, leading also to gradient instabilities after inflation ends. Furthermore, allowing for a more rapid transition can reconcile the observables but moderately breaks the slow-roll approximation leading to a relatively large and negative running of the tilt αs that can be of order n_s-1. We show that the observables on CMB and large scale structure scales can be predicted accurately using the optimized slow-roll approach instead of the traditional slow-roll expansion. Upper limits on |αs| place a lower bound of r ≳ 0.005 and, conversely, a given r places a lower bound on |α_s|, both of which are potentially observable with next generation CMB and large scale structure surveys.

Authors:

Ramírez, Héctor ^[1]; Passaglia, Samuel ^[2]; Motohashi, Hayato ^[3]; Hu, Wayne ^[2]; Mena, Olga ^[4]

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+ Show Author Affiliations

1. Univ. de Valencia, Burjassot (Spain); Univ. de Valencia-CSIC, Paterna (Spain)
2. Univ. of Chicago, IL (United States)
3. Kyoto Univ. (Japan)
4. Univ. de Valencia-CSIC, Paterna (Spain)

Publication Date:

2018-04-11

Research Org.:

Univ. of Chicago, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), High Energy Physics (HEP); MINECO; European Union's Horizon; Marie Sklodowska-Curie Grant; JSPS KEKENHI Grant; National Aeronautic and Space Administration (NASA); Simon Foundation

OSTI Identifier:

1594036

Grant/Contract Number:  

FG02-13ER41958; SC0009924

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Cosmology and Astroparticle Physics

Additional Journal Information:

Journal Volume: 2018; Journal Issue: 04; Journal ID: ISSN 1475-7516

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; inflation; cosmological parameters from CMBR