Fourth-generation Standard Model Research Articles

Updating the neutron electric dipole moment in a fourth generation standard model

A fourth generation of quarks, if it exist, may provide sufficient CP violation for the baryon asymmetry of the Universe. We estimate the neutron electric dipole moment in the presence of a fourth generation, and find it would be dominated by the strange quark chromoelectric dipole moment, assuming it does not get wiped out by a Peccei-Quinn symmetry. Both the three electroweak loop and the two-loop electroweak/one-loop gluonic contributions are considered. With m_{b'}, m_{t'} at 500 GeV or so that can be covered at the LHC, and with a Jarlskog CPV factor that is consistent with hints of New Physics in b to s transitions, the neutron EDM is found around 10^{-31}e cm, still far below the 10^{-28}e cm reach of the new experiments being planned or under construction.

Double-lepton polarization asymmetries inBs→ϕℓ+ℓ−decay in the fourth-generation standard model

In this paper, we investigate the effects of the fourth generation of quarks on the double-lepton polarization asymmetries in the ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\phi}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay. It is shown that most of these asymmetries in ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\phi}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ are quite sensitive to the fourth-generation parameters. We also compare these asymmetries with those of $B\ensuremath{\rightarrow}K{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay and show that $⟨{P}_{LT}⟩$, $⟨{P}_{TL}⟩$, $⟨{P}_{NN}⟩$, and $⟨{P}_{TT}⟩$ in ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\phi}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ decay are more sensitive to the fourth-generation parameters in comparison with those of $B\ensuremath{\rightarrow}K{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ decay. We conclude that an efficient way to establish the existence of the fourth generation of quarks could be the study of these asymmetries in the ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\phi}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay.

Unpolarized and longitudinally polarized lepton forward-backward asymmetries inB→K*l+l−decay in the fourth-generation standard model

We investigate the influence of the fourth-generation quarks on the asymmetries for unpolarized and polarized leptons in $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ decay. We obtain that for both ($\ensuremath{\mu}$, $\ensuremath{\tau}$) channels the magnitudes of the differential forward-backward (FB) asymmetries and the average forward-backward asymmetries are quite sensitive to the fourth-generation quarks' mass and mixing parameters. We also achieve that, among the double lepton polarization FB asymmetries, just longitudinally polarized leptons' FB asymmetry shows considerable discrepancy with respect to the third-generation standard model. Moreover, we find that longitudinally polarized leptons' FB asymmetry and its variation with new fourth-generation standard model parameters coincide with unpolarized FB when the lepton mass vanishes. The study of FB asymmetries can serve as a good tool to search for new-physics effects, precisely, to search for the fourth-generation quarks (${t}^{\ensuremath{'}}$, ${b}^{\ensuremath{'}}$) via its indirect manifestations in the loop diagrams.