2024/07/10 by Li, Hsiang-nan
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2407.07813
We continue our previous determination of the masses of the sequential fourth generation quarks in an extension of the Standard Model, and predict the mass m4 (mL) of the fourth generation neutrino ν4 (charged lepton L) by solving the dispersion relation associated with heavy fermion decays. The results m4≈ 170 GeV and mL≈ 270 GeV are extracted from the dispersive analyses of the t→ d e+ν4 and L-→ ν1 t d decay widths, respectively, where t (d, e+, ν1) denotes a top quark (down quark, positron, light neutrino). The predictions are cross-checked by examining the L-→ ν4 u d decay, u being an anti-up quark. It is shown that the fourth generation leptons with the above masses survive the current experimental bounds from Higgs boson decays into photon pairs and from the oblique parameters. We also revisit how the existence of the fourth generation leptons impacts the dispersive constraints on the neutrino masses and the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix elements. It is found that the unitarity of the 3× 3 PMNS matrix holds well up to corrections of O(mν2/mW2), mν (mW) being a light neutrino (the W boson) mass, whose mixing angles and CP phase prefer the values θ12≈ 34^∘, θ23≈ 47^∘, θ13≈ 5^∘ and δ≈ 200^∘ in the normal-ordering scenario for neutrino masses.