Natural axion model from flavour
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Springer
Received: June 1, Revised: August 6, Accepted: August 19, Published: September 21,
2020 2020 2020 2020
Salvador Centelles Chuli´ a,a Christian D¨ oring,b Werner Rodejohannb and Ulises J. Salda˜ na-Salazarb a
AHEP Group, Institut de F´ısica Corpuscular — C.S.I.C./Universitat de Val`encia, Parc Cient´ıfic de Paterna, C/ Catedr´ atico Jos´e Beltr´ an, 2 E-46980 Paterna (Valencia), Spain b Max-Planck-Institut f¨ ur Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg, Germany
E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: We explore a common symmetrical origin for two long standing problems in particle physics: the strong CP and the fermion mass hierarchy problems. The PecceiQuinn mechanism solves the former one with an anomalous global U(1)PQ symmetry. Here we investigate how this U(1)PQ could at the same time explain the fermion mass hierarchy. We work in the context of a four-Higgs-doublet model which explains all quark and charged fermion masses with natural, i.e. order 1, Yukawa couplings. Moreover, the axion of the model constitutes a viable dark matter candidate and neutrino masses are incorporated via the standard type-I seesaw mechanism. A simple extension of the model allows for Dirac neutrinos. Keywords: Anomalies in Field and String Theories, Beyond Standard Model, Global Symmetries, Higgs Physics ArXiv ePrint: 2005.13541
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP09(2020)137
JHEP09(2020)137
Natural axion model from flavour
Contents 1 Introduction
1
2 A4 2.1 2.2 2.3
3 3 4 7
Higgs doublet model with order one Yukawa couplings General structure of the model Fermion sector Scalar sector
10
4 Conclusions
16
A Benchmark scenario
17
B Dirac neutrinos from PQ symmetry
21
1
Introduction
Though having been very successful, the standard model of particle physics (SM) lacks the explanation for a number of experimental observations that strongly point towards, amongst other things, the existence of dark matter (DM) and a non-zero neutrino mass. Furthermore the SM poses so called fine-tuning problems in which symmetry-allowed parameters have to be assigned very small numbers in order to fit the experimental results. One of such problems is the strong CP problem. The non-trivial topological structure ˜ µν in the QCD of the QCD vacuum leads to a CP-violating total derivative term θ Gµν G Lagrangian with the gluon field strength tensor Gµν , its dual, and the CP violating angle θ. Naturally1 one expects such parameters to be of O(1). Measurements of the neutron electric dipole moment, however, limit the angle from above to be |θ| < 10−10 , thus hinting to some new physics that explains such smallness. Among other proposals, the introduction of a light pseudo-scalar field [3, 4], called axion [5] is the most popular solution to the problem. Hereby θ is promoted from being a parameter to a dynamical real pseudo-scalar field, coming along with a QCD anomalous global U(1)PQ
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