Leptoquarks in oblique corrections and Higgs signal strength: status and prospects
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Springer
Received: July 3, 2020 Accepted: October 1, 2020 Published: November 18, 2020
Andreas Crivellin,a,b Dario Müllera,b and Francesco Saturninoc a
Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland b Paul Scherrer Institut, Forschungsstrasse 111, CH-5232 Villigen PSI, Switzerland c Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland
E-mail: [email protected], [email protected], [email protected] Abstract: Leptoquarks (LQs) are predicted within Grand Unified Theories and are well motivated by the current flavor anomalies. In this article we investigate the impact of scalar LQs on Higgs decays and oblique corrections as complementary observables in the search for them. Taking into account all five LQ representations under the Standard Model gauge group and including the most general mixing among them, we calculate the effects in h → γγ, h → gg, h → Zγ and the Peskin-Takeuchi parameters S, T and U . We find that these observables depend on the same Lagrangian parameters, leading to interesting correlations among them. While the current experimental bounds only yield weak constraints on the model, these correlations can be used to distinguish different LQ representations at future colliders (ILC, CLIC, FCC-ee and FCC-hh), whose discovery potential we are going to discuss. Keywords: Beyond Standard Model, Higgs Physics ArXiv ePrint: 2006.10758
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP11(2020)094
JHEP11(2020)094
Leptoquarks in oblique corrections and Higgs signal strength: status and prospects
Contents 1
2 Setup and conventions
2
3 Oblique corrections
6
4 Higgs couplings to g, γ and Z
7
5 Phenomenological analysis
11
6 Conclusions
14
A Loop functions, exact results and perturbative diagonalization A.1 Loop functions A.2 Expanded matrices A.3 Exact results for the vacuum polarization functions A.4 Leading order SM amplitudes in Higgs decays
14 14 15 19 20
1
Introduction
Leptoquarks (LQs) are particles which have a specific interaction vertex, connecting a lepton with a quark. They are predicted in Grand Unified Theories [1–4] and were systematically classified in ref. [5] into ten possible representations under the Standard Model (SM) gauge group (five scalar and five vector particles). In recent years, LQs experienced a renaissance due to the emergence of the flavor anomalies. In short, hints for new physics (NP) in R(D(∗) ) [6–11], b → s`+ `− [12–17] and aµ [18] emerged, with a significance of > 3 σ [19–23], > 5σ [24–31] and > 3 σ [32], respectively. It has been shown that LQs can explain b → s`+ `− data [33–57], R(D(∗) ) [33, 34, 36–40, 42–44, 46, 47, 51–53, 55–90] and/or aµ [55, 56, 62, 71, 74, 77, 86, 91–107]. This strong motivation for LQs makes it also interesting to search for their signatures in other observables. Complementary to direct LHC searches [108–121], oblique electroweak (EW) parameters
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