Gauged baryon parity and nucleon stability

Abstract

We show that the Standard Model Lagrangian, including small neutrino masses, has an anomaly-free discrete Z 6 symmetry. This symmetry can emerge naturally from (I 3 R + L i + L j − 2L k ) gauge symmetry (L i is the ith lepton number) and ensure the stability of the nucleon even when the threshold of new physics Λ is low. All ∆B = 1 and ∆B = 2 (B is the baryon number) effective operators are forbidden by the Z 6 symmetry. ∆B = 3 operators are allowed, but they arise only at dimension 15. We estimate the lifetime for "triple nucleon decay" resulting from these operators and find that Λ can be as low as 10 2 GeV. We suggest a simple mechanism for realizing reasonable neutrino masses and mixings even with such a low scale for Λ.

Proton hexality in local grand unification

“…On SM fields P 6 , as defined by the charge assignments in Table 1, acts as a Z 6 symmetry which is the product of baryon triality and matter parity. Proton hexality had been discussed before in [26][27][28][29]. It forbids all dangerous dimension four and five baryon or lepton number violating couplings while phenomenologically desirable couplings are allowed.…”

Gauged discrete symmetries and proton stability

“…Next, we list the anomaly constraints, H contributes to both the fermion masses as well as to the seesaw. We note that the charge assignment is such that we have 3 generation vector-like (10) under SO 10 Z 6 . The model also eliminates the dangerous proton decay operator QQQL or operator of type m 4 =M P .…”

“…(i) the left-right symmetric model [13], (ii) the Pati-Salam model [14] and (iii) SO (10). All these models incorporate the B ÿ L gauge group, which is generally used in the discussion of the seesaw mechanism for neutrino masses [15][16][17][18][19] (for a review see e.g.…”

“…In our discussion, we follow a certain ''route of unification.'' We start with the left-right symmetric extension of the supersymmetric standard model, proceed via the Pati-Salam model to SO (10) GUTs and finally comment on how our results might be used in string compactifications. This paper is organized as follows: in Sec.…”

Search for rare processes with DAMA/LXe experiment at Gran Sasso

“…Also mechanisms for the tri-nucleon decay have been proposed in the literature; in particular, very recently in ref. [27] also tri-nucleon decay processes with ∆B = 3 have been considered. Moreover, disappearance of particles (electrons, e − , or nucleons, N ) are expected also in theories with extra dimensions [28,29,30].…”