Coloured Scalar Mediated Nucleon Decays to Invisible Fermion

Abstract

We investigate nucleon decays to light invisible fermion mediated by the coloured scalar S1 = ( 3, 1, −2/3) and compare them with the results coming from the mediation of S1 = ( 3, 1, 1/3). In the case of S1 = ( 3, 1, −2/3) up-like quarks couple to the invisible fermion, while in the case of S1 = ( 3, 1, 1/3) the down-like quarks couple to the invisible fermion. For the mass of invisible fermion smaller than the mass mp − mK , proton (neutron) can decay to K and invisible fermion and the masses of S1 and S1 are in the region ∼ 10 15 GeV. The decays of nucleons to pions and invisible fermion can occur at the tree-level, but in the case of S1 they come from dimension-9 operator and are therefore suppressed by several orders of magnitude compared to the decays into kaons. For the invisible fermion mass in the range (937.8 MeV, 938.8 MeV), decay of neutron n → χγ induced by S1 is possible at the loop level, while the proton remains stable. The branching ratio of such decay is ≤ 10 −6 , which does not explain neutron decay anomaly, but is in agreement with the Borexino experiment bound. We comment on low-energy processes with the nucleon-like mass of χ in the final state as Λ → χγ and heavy hadron decays to invisibles.

Coloured Scalars Mediated Rare Charm Meson Decays to Invisible Fermions

“…Here, we consider one χ, that can couple to both u and c quarks. These two couplings might enter in amplitudes for processes with down-like quarks at loop-level, as discussed in [20]. Obviously, due to the right-handed nature of χ, one can immediately see that in the case of S1 , the effective Lagrangian has only the contribution…”

“…Therefore, in the absence of CP violation, the robust bound on the product of the couplings can be obtained by requiring that the mixing frequency should be smaller than the world average x = 2|M 12 |/Γ = (0.43 +0.10 −0.11 )% by HFLAV [24]. The bound on this Wilson coefficient can be derived following [20,25]…”

“…The R2 leptoquark is a weak doublet and it interacts with quark doublets (3). Therefore, the appropriate couplings, ỹLR 2 sχ ỹLR * 2 bχ can be constrained from the b → sχ χ and s → dχ χ decays, as well as from observables coming from the B s − Bs , B d − Bd , K 0 − K0 oscillations as in [20]. We consider the most constraining bounds coming from decays B → K / E and from the oscillations of B s − Bs , relevant for the χ mass region (m K − m π )/2 < m χ < (m D − m π )/2.…”

Baryonic and Leptonic GeV Dark Matter

“…It was shown that Model 1B allows the neutron to have a dark decay branching fraction Br(n → χ γ) = 1%, which corresponds to m Φ ∼ O(100 TeV) for order one couplings; see [32] for a detailed review of this proposal along with its experimental signatures. It was recently argued that within the framework of Model 1A, the neutron dark decay branching fraction is constrained to be Br(n → χ γ) < 10 −6 [33].…”

Cosmological and astrophysical probes of dark baryons

“…New states with masses around a GeV that mix with the standard model (SM) baryons have been considered recently for a number of compelling reasons, such as the baryon asymmetry of the universe [1][2][3][4], models of dark matter [1,[5][6][7], mirror matter scenarios [8], the neutron lifetime anomaly [6,[9][10][11][12], the recent XENON1T excess [13], 21 cm cosmology [14], and general baryonnumber violating phenomenology [15,16]. In this paper we investigate the cosmological and astrophysical effects of a simple, minimal version: a single "dark baryon" χ that carries baryon number B = 1 and mixes with the neutron.…”