Hunting for ALPs with lepton flavor violation
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Springer
Received: November 26, 2019 Accepted: December 22, 2019 Published: January 27, 2020
Claudia Cornella,a,b Paride Paradisib and Olcyr Sumensarib a
Physik-Institut, Universit¨ at Z¨ urich, Building 16, Winterthurerstrasse 190, Z¨ urich CH-8057, Switzerland b Istituto Nazionale Fisica Nucleare, Sezione di Padova and Dipartamento di Fisica e Astronomia “G. Galilei”, Universit` a degli Studi di Padova, Via Francesco Marzolo, 8, Padova I-35131, Italy
E-mail: [email protected], [email protected], [email protected] Abstract: We examine the low-energy signatures of axion-like particles (ALPs) in lepton flavor violating (LFV) processes. By using a dimension-5 effective Lagrangian, we compute the most general ALP contributions to LFV decays of leptons and mesons. The provided expressions are valid for any choice of ALP mass and couplings. We explore the complementarity of different processes, identifying specific patterns to be experimentally tested. Constraints on LFV couplings are derived from existing data and prospects for forthcoming experiments are also discussed. As a by-product, we revisit the possibility of a simultaneous explanation of the observed discrepancies in the muon and electron g − 2 through ALP interactions. Keywords: Beyond Standard Model, Effective Field Theories, Heavy Quark Physics, Kaon Physics ArXiv ePrint: 1911.06279
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP01(2020)158
JHEP01(2020)158
Hunting for ALPs with lepton flavor violation
Contents 1 Introduction
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2 Effective field theory description
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4 Hadronic processes 4.1 P → `i `j and `j → `i P 4.1.1 General expressions 4.1.2 Hadronic inputs: NP 4.2 P → P 0 `i `j 4.2.1 General expressions 4.2.2 Hadronic inputs 4.3 P → V `i `j 4.3.1 General expressions 4.3.2 Hadronic inputs 4.4 Numerical results and discussion
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5 Conclusions
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A Useful formulas A.1 Loop functions A.2 `j → `i `k `k kinematic functions A.3 Form factors for `j → `i γ ∗ A.3.1 Linear contributions A.3.2 Quadratic contributions A.4 Taylor-expanded anapole form factors A.4.1 Linear contributions A.4.2 Quadratic contributions
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1
Introduction
After the long-awaited discovery of the Higgs boson at the Large Hadron Collider (LHC), no convincing evidence of heavy new physics (NP) has emerged yet. The motivation for NP at the TeV scale has thus being questioned, and alternative scenarios, with new light mediators, have received increasing attention from both experimental and theoretical com-
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3 Purely leptonic processes 3.1 `j → `i γ 3.2 `j → `i `k `k 3.3 `j → `i γγ 3.4 µ− → e− conversion in nuclei 3.5 Numerical results and discussion 3.6 On the (g − 2)e and (g − 2)µ anomalies
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munities over the past several years. A prominent example are Standard Model (SM) extensions with light pseudoscalar bosons, generically referred to as axion-like-particles (ALPs) [1–3]. ALPs might be natu
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