Three exceptions to the Grossman-Nir bound
- PDF / 3,275,160 Bytes
- 39 Pages / 595.276 x 841.89 pts (A4) Page_size
- 63 Downloads / 160 Views
Springer
Received: May 13, 2020 Accepted: July 9, 2020 Published: July 30, 2020
Robert Ziegler,a Jure Zupanb and Roman Zwickyc a
Institute for Theoretical Particle Physics (TTP), Karlsruhe Institute of Technology, Engesserstrasse 7, D-76128 Karlsruhe, Germany b Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, U.S.A. c Higgs Centre for Theoretical Physics, School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, Scotland, U.K.
E-mail: [email protected], [email protected], [email protected] Abstract: We show that the Grossman-Nir (GN) bound, Br(KL → π 0 ν ν¯) ≤ 4.3 Br(K + → π + ν ν¯), can be violated in the presence of light new physics with flavor violating couplings. We construct three sample models in which the GN bound can be violated by orders of magnitude, while satisfying all other experimental bounds. In the three models the enhanced branching ratio Br(KL → π 0 + inv) is due to KL → π 0 φ1 , KL → π 0 φ1 φ1 , KL → π 0 ψ1 ψ¯1 transitions, respectively, where φ1 (ψ1 ) is a light scalar (fermion) that escapes the detector. In the three models Br(K + → π + + inv) remains very close to the SM value, while Br(KL → π 0 +inv) can saturate the present KOTO bound. Besides invisible particles in the final state (which may account for dark matter) the models require additional light mediators around the GeV-scale. Keywords: Beyond Standard Model, Kaon Physics, Chiral Lagrangians ArXiv ePrint: 2005.00451
c The Authors. Open Access, Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP07(2020)229
JHEP07(2020)229
Three exceptions to the Grossman-Nir bound
Contents 1 Introduction
1
2 The EFT analysis
4 6 7 11 12 13 15 15 16 17 19 21
4 Model 2 — scalar model leading to the three-body kaon decays 4.1 Benchmarks for Model 2 4.2 Constraints on the φ1 -couplings 4.3 φ1 as a dark matter candidate
23 24 26 26
5 Model 3 — light dark sector fermions 5.1 Benchmarks for Model 3 5.2 Constraints on the ψ1 -couplings 5.3 ψ1 as a dark matter candidate
28 29 30 31
6 Conclusions
33
¯1 decay rate A The K → πψ1 ψ
34
B Integral conventions
35
1
Introduction
In the SM, the KL → π 0 ν ν¯ and K + → π + ν ν¯ decays proceed through the same short distance operator, involving the fields of the quark level transition (s → dν ν¯). The matrix elements for the KL → π 0 ν ν¯ and K + → π + ν ν¯ transitions are thus trivially related through isospin, leading to the Grossman-Nir (GN) bound [1] Br(KL → π 0 ν ν¯) ≤ 4.3 Br(K + → π + ν ν¯).
–1–
(1.1)
JHEP07(2020)229
3 Model 1 — scalar model leading to two-body kaon decays 3.1 Estimating the transition rates using ChPT (i) ¯ 0 mixing 3.2 Constraints on gˆds from K 0 − K 3.3 Constraints from 0 / 3.4 Constraints on representative benchmarks 3.5 Constraints on the φ1 -couplings 3.5.1 Invisible pion decays 3.5.2 φ1 − π 0 mixing 3.5.3 Couplings of φ1 to photons 3.5.4 Couplings of φ1 to nucleons 3.5.5 Combined analysis of φ1 -constraints
• Model 1: KL → π 0 φ1 , where the mass of the light scalar, φ1 , can be anywhere from mφ1 .
Data Loading...
