Cosmological implications of the KOTO excess

Abstract

The KOTO experiment has reported an excess of K L → π 0 νν events above the Standard Model prediction, in tension with the Grossman-Nir (GN) bound. The GN bound heavily constrains new physics interpretations of an excess in this channel, but another possibility is that the observed events originate from a different process entirely: a decay of the form K L → π 0 X, where X denotes one or more new invisible species. We introduce a class of models to study this scenario with two light scalars playing the role of X, and we examine the possibility that the lighter of the two new states may also account for cosmological dark matter (DM). We show that this species can be produced thermally in the presence of additional interactions apart from those needed to account for the KOTO excess. Conversely, in the minimal version of the model, DM must be produced nonthermally. In this case, avoiding overproduction imposes constraints on the structure of the low-energy theory. Moreover, this requirement carries significant implications for the scale of reheating in the early Universe, generically preferring a low but observationally permitted reheating temperature of Oð10 MeVÞ. We discuss astrophysical and terrestrial signatures that will allow further tests of this paradigm in the coming years.

A Lesson from RττK(*)$R_{\tau \tau }^{K^{(\ast )}}$ and RννK(*)$R_{\nu \nu }^{K^{(\ast )}}$ at Belle II

“…Several beyond the standard model (BSM) scenarios have been discussed in the literature, [ 14–45 ] and it is quite challenging to formulate a scenario that would be consistent with both $$R_{D^{(\ast )}}$$ and $$R_{K^{(\ast )}}$$ and with a wealth of low energy flavor physics observables.…”

Novel multi-lepton signatures of dark sectors in light meson decays

“…Original interest in B → KXX decays [16][17][18] was driven by the minimal scalar dark matter model [19][20][21], that has since been ruled out in this mass range. Recent theoretical activity in studying dark sectors [22][23][24][25][26][27] in kaon decays was instigated by a possible excess of K L → π 0 νν signal events reported by the KOTO collaboration [28]. For instance, Ref.…”