Testing moduli and flavon dynamics with neutrino oscillations
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Springer
Received: April 6, 2020 Accepted: May 29, 2020 Published: June 22, 2020
Gui-Jun Dinga,b and Ferruccio Feruglioc a
Peng Huanwu Center for Fundamental Theory, Hefei, Anhui 230026, China b Interdisciplinary Center for Theoretical Study and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China c Dipartimento di Fisica e Astronomia ‘G. Galilei’, Universit` a di Padova, INFN, Sezione di Padova, Via Marzolo 8, I-35131 Padua, Italy
E-mail: [email protected], [email protected] Abstract: We study scalar Non-Standard Neutrino Interactions (NSI) induced by moduli or flavon exchange between electrons and neutrinos. In a region with non-vanishing electron number density, they are known to determine a shift of the neutrino mass matrix. We review and extend the relevant formalism, and we update the existing limits on electron and neutrino scalar couplings. We explore the observability of scalar NSI in models of lepton masses based on flavour symmetries. We analyze models where the scalar couplings are constrained either by abelian symmetries or by modular invariance. We highlight regions of the parameter space where observable effects can occur. Keywords: Beyond Standard Model, Discrete Symmetries, Neutrino Physics ArXiv ePrint: 2003.13448
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP06(2020)134
JHEP06(2020)134
Testing moduli and flavon dynamics with neutrino oscillations
Contents 1
2 Neutrino masses and scalar interactions 2.1 Limits on electron coupling 2.2 Limits on neutrino coupling 2.3 Limits on ultralight boson masses
3 6 7 9
3 Scalar NSI from flavour symmetries
9
4 Models with abelian flavour symmetries 4.1 A toy model 4.2 A variant
12 12 15
5 Modular invariant models 5.1 Modular invariant models with flavons
18 21
6 A case study
22
7 Discussion
25
1
Introduction
In most of the frameworks aiming to a solution of the flavour puzzle, fermion masses are field-dependent quantities assuming specific values once the vacuum of the theory is selected. Yukawa couplings depends on the vacuum expectation values (VEVs) of a set of scalar fields ϕ, new dynamical degrees of freedom predicted or postulated in the underlying theory. For example, in string theory coupling constants are naturally field-dependent objects and the scalar fields ϕ can be moduli, describing shape and size of compactified extra dimensions. In a bottom-up perspective, the couplings of ϕ to the Standard Model (SM) fermions are often constrained by flavour symmetries and the observed pattern of fermion masses and mixing angles represents the effect of breaking a symmetry group acting in generation space. The scalar fields ϕ, called flavons in this context, have nontrivial transformation properties under the group, acquire non-vanishing VEVs ϕ0 and break the flavour symmetry. The observed fermion masses are shaped by the flavons VEVs ϕ0 , due to the restricted functional dependence of Yukawa couplings on ϕ. In this class of models, the new scala
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