A little theory of everything, with heavy neutral leptons

Abstract

Recently a new model of "Affleck-Dine inflation" was presented, that produces the baryon asymmetry from a complex inflaton carrying baryon number, while being consistent with constraints from the cosmic microwave background. We adapt this model such that the inflaton carries lepton number, and communicates the lepton asymmetry to the standard model baryons via quasi-Dirac heavy neutral leptons (HNLs) and sphalerons. One of these HNLs, with mass 4.5 GeV, can be (partially) asymmetric dark matter (DM), whose asymmetry is determined by that of the baryons. Its stability is directly related to the vanishing of the lightest neutrino mass. Neutrino masses are generated by integrating out heavy sterile neutrinos whose mass is above the inflation scale. The model provides an economical origin for all of the major ingredients missing from the standard model: inflation, baryogenesis, neutrino masses, and dark matter. The HNLs can be probed in fixed-target experiments like SHiP, possibly manifesting N -N oscillations. A light singlet scalar, needed for depleting the DM symmetric component, can be discovered in beam dump experiments and searches for rare decays, possibly explaining anomalous events recently observed by the KOTO collaboration. The DM HNL is strongly constrained by direct searches, and could have a cosmologically interesting self-interaction cross section.

Pair production of dark particles in meson decays

“…This is the case in all of our scalar portal models, especially the viable model given by Eqs. (23) and (31), as well as in the dipole portal decay. A notable exception to this is scenario (A), both in the vector portal model [Eqs.…”

“…Our paper is inspired, in part, by a recent report by the KOTO Collaboration that addressed four unexplained events after unblinding their data, at a level much larger than the SM neutrino channel, which prompts theoretical investigations of beyond-SM (BSM) physics that may lead to such a signature. In many recent studies the focus has been primarily on K L decays to a pion plus new invisible particles [16][17][18][19][20][21][22][23][24]. Other recent alternatives include new particles produced at the target that decay to γγ inside the KOTO detector [16], direct K L decay to γγ plus invisible states [25], and heavy new physics operators with flavor violation or ΔI ¼ 3=2 structure [16,[26][27][28].…”

Explaining (g−2)μ,e , the KOTO anomaly, and the MiniBooNE excess in an extended Higgs model with sterile neutrinos

“…Thus, the new physics explanation for the KOTO anomaly is required to generate three anomalous events and satisfy the GN bound. Several such solutions have been proposed in the literature [80,[130][131][132][133][134][135][136][137][138][139][140][141][142][143].…”

Three exceptions to the Grossman-Nir bound

“…Finally, the NP models of refs. [12,[14][15][16][17][18][19][20][21] do not violate the GN bound, but can allow for a large signal in KOTO since NA62 is not sensitive to X inv with a mass close to the pion mass.…”