Probing the Planck scale with proton decay

Abstract

We advocate the idea that proton decay may probe physics at the Planck scale instead of the GUT scale. This is possible because supersymmetric theories have dimension-5 operators that can induce proton decay at dangerous rates, even with R-parity conservation. These operators are expected to be suppressed by the same physics that explains the fermion masses and mixings. We present a thorough analysis of nucleon partial lifetimes in models with a string-inspired anomalous U (1)X family symmetry which is responsible for the fermionic mass spectrum as well as forbidding R-parity violating interactions. Protons and neutrons can decay via R-parity conserving non-renormalizable superpotential terms that are suppressed by the Planck scale and powers of the Cabibbo angle. Many of the models naturally lead to nucleon decay near present limits without any reference to grand unification.

Hybrid seesaw neutrino model in SUSY SU(5)×A4

“…On the other hand, in flavor symmetries based models there are additional nonrenormalizable couplings which involve flavon fields and can generate proton decay operators. In our model, these nonrenormalizable operators up to order to form six-dimensional operators are the most disturbing operators that lead to fast proton decay in SUSY SUð5Þ models [55,56]. These operators that are derived from the renormalizable up and down Yukawa couplings λTTH 5 and λ 0 TFH¯5 are absent in our model since they behave, respectively, as nontrivial singlets and triplet under the A 4 flavor symmetry.…”

SU(7) unification of SU(3) C × SU(4) W × U(1) B−L

“…which satisfies proton decay bounds [35]. However such requirements will lead to difficulty in giving natural Yukawa couplings.…”

Observable proton decay from Planck scale physics

“…One way Planck-scale physics might be probed is by means of proton decay [1]. There are general arguments that quantum gravity should violate global quantum numbers, such as baryon number (B) and lepton number (L).…”