ABSTRACT
Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.
ABSTRACT
The KOTO experiment recently reported four candidate events in the signal region of K_{L}âπ^{0}νν[over ¯] search, where the standard model only expects 0.10±0.02 events. If confirmed, this requires physics beyond the standard model to enhance the signal. We examine various new physics interpretations of the result including these: (1) heavy new physics boosting the standard model signal, (2) reinterpretation of "νν[over ¯]" as a new light long-lived particle, or (3) reinterpretation of the whole signal as the production of a new light long-lived particle at the fixed target. We study the above explanations in the context of a generalized new physics Grossman-Nir bound coming from the K^{+}âπ^{+}νν[over ¯] decay, bounded by data from the E949 and the NA62 experiments.
ABSTRACT
Rare kaon decays are excellent probes of light, new weakly coupled particles. If such particles X couple preferentially to muons, they can be produced in KâµνX decays. We evaluate the future sensitivity for this process at NA62 assuming X decays either invisibly or to dimuons. Our main physics target is the parameter space that resolves the (g-2)_{µ} anomaly, where X is a gauged L_{µ}-L_{τ} vector or a muonphilic scalar. The same parameter space can also accommodate dark matter freeze-out or reduce the tension between cosmological and local measurements of H_{0} if the new force decays to dark matter or neutrinos, respectively. We show that for invisible X decays, a dedicated single muon trigger analysis at NA62 could probe much of the remaining (g-2)_{µ} favored parameter space. Alternatively, if X decays to muons, NA62 can perform a dimuon resonance search in Kâ3µν events and greatly improve existing coverage for this process. Independently of its sensitivity to new particles, we find that NA62 is also sensitive to the standard model predicted rate for Kâ3µν, which has never been measured.
ABSTRACT
The chiral anomaly provides smoking-gun evidence of a new confining gauge theory. Motivated by a reported event excess in a diphoton invariant mass distribution at the LHC, we discuss a scenario that a pseudo-Nambu-Goldstone (PNG) boson of a new QCD-like theory is produced by gluon fusion and decays into a pair of the standard model gauge bosons. Despite the strong dynamics, the production cross section and the decay widths are determined by an anomaly matching condition. The excess can be explained by the PNG boson with mass of around 750 GeV. The model also predicts exotic hadrons such as a color-octet scalar and baryons. Some of them are within the reach of the LHC experiment.
ABSTRACT
The Higgs mass implies fine-tuning for minimal theories of weak-scale supersymmetry (SUSY). Nondecoupling effects can boost the Higgs mass when new states interact with the Higgs boson, but new sources of SUSY breaking that accompany such extensions threaten naturalness. We show that two singlets with a Dirac mass can increase the Higgs mass while maintaining naturalness in the presence of large SUSY breaking in the singlet sector. We explore the modified Higgs phenomenology of this scenario, which we call the "Dirac next-to-minimal supersymmetric standard model."
