Abstract
Nonsupersymmetric minimal SU(5) with Higgs representations 24H and 5H and standard fermions in 5¯F⊕10F is well known for its failure in unification of gauge couplings and lack of predicting neutrino masses. Like standard model, it is also affected by the instability of the Higgs scalar potential. We note that extending the Higgs sector by 75H and 15H not only leads to the popular type-II seesaw ansatz for neutrino masses with a lower bound on the triplet mass MΔ>2×109 GeV, but also achieves precision unification of gauge couplings without proliferation of nonstandard light Higgs scalars or fermions near the TeV scale. Consistent with recent LUX-2016 lower bound, the model easily accommodates a singlet scalar WIMP dark matter near the TeV scale which resolves the vacuum stability issue even after inclusion of heavy triplet threshold effect. We estimate proton lifetime predictions for p→e+π0 including uncertainties due to input parameters and threshold effects due to superheavy Higgs scalars and superheavy X±4/3,Y±1/3 gauge bosons. The predicted lifetime is noted to be verifiable at Super Kamiokande and Hyper Kamiokande experiments.
Highlights
Added presence of 15퐻 and 75퐻 is noted to account for precision coupling unification with experimentally verifiable proton lifetime for p → e+π0, and type-II seesaw ansatz for neutrino masses
The limitation due to vacuum stability of the Higgs potential in SU(5) is resolved by the inclusion of a scalar singlet near the TeV scale that acts as a weakly interacting massive particle (WIMP) dark matter candidate
All the fermions and this scalar are assigned to be odd under a dark matter stabilising Z2 discrete symmetry whereas the Standard model (SM) Higgs is even
Summary
Standard model (SM) of strong and electroweak interactions has been established by numerous experimental tests, yet evidences on neutrino mass [1,2,3,4,5], the phenomena of dark matter [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25] , and baryon asymmetry of the universe (BAU) [8, 26,27,28,29] call for beyond standard model (BSM) physics. With a second triplet scalar, it is capable of predicting baryon asymmetry of the universe [57] which is one of the main motivations behind this investigation This neutrino mass generation mechanism, gauge coupling unification, dark matter, and vacuum stability are the focus of the present work. 75퐻 and 15퐻, it achieves two objectives: (i) neutrino mass and mixing generation through type-II seesaw mechanism and (ii) precision gauge coupling unification with experimentally accessible proton lifetime. This does not cure the vacuum instability problem persisting in the model as well as the need for WIMP dark matter prediction. As we will find in the subsequent sections, gauge coupling unification in the present SU(5) framework imposes the lower bound μΔ ≃ MΔ ≥ 109.23 GeV
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