Constraints on light dark matter andUbosons, fromψ,Υ,K+,

Abstract

Following searches for photinos and very light gravitinos in invisible decays of ψ and Υ, we discuss new limits on Light Dark Matter and U bosons, from ψ and Υ decays, as well as rare decays of K + and invisible decays of π • , η and η ′ ... . The new limits involving the vector couplings of the U to quarks turn out, not surprisingly, to be much less restrictive than existing ones on axial couplings, from an axionlike behavior of a light U boson, tested in ψ → γ U, Υ → γ U and K + → π + U decays (or as compared to the limit from parityviolation in atomic physics, in the presence of an axial coupling to the electron). Altogether the hypothesis of light U bosons, and light dark matter particles, remains compatible with particle physics constraints, while allowing for the appropriate annihilation cross sections required, both at freeze-out (for the relic abundance) and nowadays (if e + from LDM annihilations are at the origin of the 511 keV line from the galactic bulge).

Hidden fermion as milli-charged dark matter in StueckelbergZ′ model

“…Constraints on invisible decays of J/ψ and Υ exist (for a comprehensive review on constraints on light dark matter: see ref. [31]). A very recent update on the Υ(1S) invisible width is given in ref.…”

Rare meson decays into very light neutralinos

“…These decays in more complex, less fine-tuned models [45,46], in which the light scalars couple to new heavy fermions or a new light Uð1Þ 0 gauge boson, have been calculated in Refs. [47][48][49]. Models with extra gauged Uð1Þ symmetries also allow for light fermionic dark matter candidates [50,51], and the rare meson decays into these fermions have been calculated in Refs.…”

“…Models with extra gauged Uð1Þ symmetries also allow for light fermionic dark matter candidates [50,51], and the rare meson decays into these fermions have been calculated in Refs. [48,49]. The next-to-minimal supersymmetric standard model (NMSSM) also allows for light neutralinos, and in the NMSSM they remain a dark matter candidate [25]; the NMSSM also admits a light pseudoscalar dark matter candidate.…”

Search forη→e+e−decay with the WASA experiment

“…This numbers are at least four orders of magnitude larger then value predicted from the Standard Model calculations (BR theo ∼ 10 −9 ). The small probability of this fourthorder electromagnetic transition makes the decay sensitive to hypothetical interactions that arise from physics beyond Standard Model [2,[5][6][7] (see fig.1 right). An observation of a signal above ∼ 10 −9 level could be evidence for an unconventional process which enhances this decay rate.…”