Maximal axion misalignment from a minimal model
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Springer
Received: July Revised: August Accepted: September Published: October
14, 28, 19, 22,
2020 2020 2020 2020
Maximal axion misalignment from a minimal model
a
Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, ON N2L 2Y5, Canada b Instituto de F´ısica Corpuscular (CSIC-Universitat de Val`encia), C/ Catedr´ atico Jos´e Beltr´ an 2, E-46980 Paterna (Valencia), Spain
E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: The QCD axion is one of the best motivated dark matter candidates. The misalignment mechanism is well known to produce an abundance of the QCD axion consistent with dark matter for an axion decay constant of order 1012 GeV. For a smaller decay constant, the QCD axion, with Peccei-Quinn symmetry broken during inflation, makes up only a fraction of dark matter unless the axion field starts oscillating very close to the top of its potential, in a scenario called “large-misalignment”. In this scenario, QCD axion dark matter with a small axion decay constant is partially comprised of very dense structures. We present a simple dynamical model realising the large-misalignment mechanism. During inflation, the axion classically rolls down its potential approaching its minimum. After inflation, the Universe reheats to a high temperature and a modulus (real scalar field) changes the sign of its minimum dynamically, which changes the sign of the mass of a vector-like fermion charged under QCD. As a result, the minimum of the axion potential during inflation becomes the maximum of the potential after the Universe has cooled through the QCD phase transition and the axion starts oscillating. In this model, we can produce QCD axion dark matter with a decay constant as low as 6 × 109 GeV and an axion mass up to 1 meV. We also summarise the phenomenological implications of this mechanism for dark matter experiments and colliders. Keywords: Beyond Standard Model, Cosmology of Theories beyond the SM ArXiv ePrint: 2006.07379
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP10(2020)143
JHEP10(2020)143
Junwu Huang,a Amalia Madden,a Davide Raccoa and Mario Reigb
Contents 1 Introduction and summary
1
2 A toy example
7 10 11 12 14 14 15 17 19
4 Phenomenology 4.1 Model independent predictions 4.2 Model dependent constraints 4.2.1 Mixing with SM quarks and CKM unitarity 4.2.2 Collider bounds 4.2.3 Cosmological considerations
20 21 22 23 24 25
5 Discussion
25
A One-loop finite-temperature corrections
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B Phases of the explicitly broken Z2 model
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C Vacuum decay C.1 Vacuum decay rate at zero temperature in the thin-wall approximation C.2 Vacuum decay rate at finite temperature in the thin-wall approximation
31 31 32
1
Introduction and summary
The QCD axion [1–7] is one of the best motivated solutions to the strong CP problem of the Standard Model (SM).1 The strong CP problem originates from the experimental null measurement of the neutron electric dipole moment (
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