Relaxion cosmology and the price of fine-tuning

Stefano Di Chiara, Kristjan Kannike, Luca Marzola, Antonio Racioppi, Martti Raidal, and Christian Spethmann
Phys. Rev. D 93, 103527 – Published 23 May 2016

Abstract

The relaxion scenario presents an intriguing extension of the standard model in which the particle introduced to solve to the strong CP problem, the axion, also achieves the dynamical relaxation of the Higgs boson mass term. In this work we complete this framework by proposing a scenario of inflationary cosmology that is consistent with all the observational constraints: the relaxion hybrid inflation with an asymmetric waterfall. In our scheme, the vacuum energy of the inflaton drives inflation in a natural way while the relaxion slow rolls. The constraints on the present inflationary observables are then matched through a subsequent inflationary epoch driven by the inflaton. We quantify the amount of fine-tuning of the proposed inflation scenario, concluding that the inflaton sector severely decreases the naturalness of the theory.

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  • Received 19 November 2015

DOI:https://doi.org/10.1103/PhysRevD.93.103527

© 2016 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & AstrophysicsParticles & Fields

Authors & Affiliations

Stefano Di Chiara1, Kristjan Kannike1, Luca Marzola1,2, Antonio Racioppi1, Martti Raidal1,2, and Christian Spethmann1

  • 1National Institute of Chemical Physics and Biophysics, Rävala 10, 10143 Tallinn, Estonia
  • 2Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu, Estonia

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Vol. 93, Iss. 10 — 15 May 2016

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