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Title: Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly

Abstract

Recently, the KOTO experiment at J-PARC has observed three anomalous events in the flavor-changing rare decay $$K_L → π^0ν\bar{ν}$$, which indicates that the corresponding branching ratio is almost 2 orders of magnitude larger than the Standard Model (SM) prediction. Taking this intriguing result at face value, we explore model implications of its viable explanation by a long-lived light SM-singlet scalar ($$\textit{S}$$) emission, i.e., $$K_L → π^0S$$, with $$\textit{S}$$ decaying outside the KOTO detector. We derive constraints on the parameter space of such a light scalar in the context of three simple models: (i) a real singlet scalar extension of the SM; (ii) a $$\textit{B – L}$$ extension where neutrino masses arise via type-I seesaw mechanism from $$\textit{B – L}$$ breaking; and (iii) a TeV-scale left-right symmetric model. The flavor-changing couplings needed to explain the KOTO excess in models (i) and (ii) originate from tree-level mixing of the scalar with SM Higgs field ($$\texit{h}$$), and in model (iii), from the mixing of S and h with the neutral component of the heavy bidoublet Higgs field. After taking into account the stringent constraints from high-precision searches for flavor-changing charged and neutral kaon decays at NA62, E949, KOTO and CHARM experiments, as well as the astrophysical and cosmological constraints on a light scalar, such as those from supernova energy loss, big bang nucleosynthesis and relativistic degrees of freedom, we find that the light scalar interpretation of the KOTO excess is allowed in all these models. Parts of the parameter range can be tested in future NA62 and DUNE experiments.

Authors:
; ; ORCiD logo
Publication Date:
Research Org.:
Washington Univ., St. Louis, MO (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Science Foundation (NSF)
OSTI Identifier:
1632913
Alternate Identifier(s):
OSTI ID: 1803211
Grant/Contract Number:  
SC0017987; AC02-07CH11359; PHY-1914631
Resource Type:
Published Article
Journal Name:
Physical Review D
Additional Journal Information:
Journal Name: Physical Review D Journal Volume: 101 Journal Issue: 7; Journal ID: ISSN 2470-0010
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Astronomy & Astrophysics; Physics

Citation Formats

Dev, P. S. Bhupal, Mohapatra, Rabindra N., and Zhang, Yongchao. Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly. United States: N. p., 2020. Web. doi:10.1103/PhysRevD.101.075014.
Dev, P. S. Bhupal, Mohapatra, Rabindra N., & Zhang, Yongchao. Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly. United States. https://doi.org/10.1103/PhysRevD.101.075014
Dev, P. S. Bhupal, Mohapatra, Rabindra N., and Zhang, Yongchao. Wed . "Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly". United States. https://doi.org/10.1103/PhysRevD.101.075014.
@article{osti_1632913,
title = {Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly},
author = {Dev, P. S. Bhupal and Mohapatra, Rabindra N. and Zhang, Yongchao},
abstractNote = {Recently, the KOTO experiment at J-PARC has observed three anomalous events in the flavor-changing rare decay $K_L → π^0ν\bar{ν}$, which indicates that the corresponding branching ratio is almost 2 orders of magnitude larger than the Standard Model (SM) prediction. Taking this intriguing result at face value, we explore model implications of its viable explanation by a long-lived light SM-singlet scalar ($\textit{S}$) emission, i.e., $K_L → π^0S$, with $\textit{S}$ decaying outside the KOTO detector. We derive constraints on the parameter space of such a light scalar in the context of three simple models: (i) a real singlet scalar extension of the SM; (ii) a $\textit{B – L}$ extension where neutrino masses arise via type-I seesaw mechanism from $\textit{B – L}$ breaking; and (iii) a TeV-scale left-right symmetric model. The flavor-changing couplings needed to explain the KOTO excess in models (i) and (ii) originate from tree-level mixing of the scalar with SM Higgs field ($\texit{h}$), and in model (iii), from the mixing of S and h with the neutral component of the heavy bidoublet Higgs field. After taking into account the stringent constraints from high-precision searches for flavor-changing charged and neutral kaon decays at NA62, E949, KOTO and CHARM experiments, as well as the astrophysical and cosmological constraints on a light scalar, such as those from supernova energy loss, big bang nucleosynthesis and relativistic degrees of freedom, we find that the light scalar interpretation of the KOTO excess is allowed in all these models. Parts of the parameter range can be tested in future NA62 and DUNE experiments.},
doi = {10.1103/PhysRevD.101.075014},
journal = {Physical Review D},
number = 7,
volume = 101,
place = {United States},
year = {2020},
month = {4}
}

Journal Article:
Free Publicly Available Full Text
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https://doi.org/10.1103/PhysRevD.101.075014

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