Precision constraints on extra fermion generations

The Speed of Light Predicts the Number of Lepton Families

Vacuum fluctuations of charged particles appear in the vacuum as particle–antiparticle pairs so that quantum numbers such as charge, baryon number, and lepton number are conserved. To minimize the violation of conservation of energy and conserve angular momentum, the pair appears in the most tightly bound state that has zero angular momentum. The permittivity ϵ0 of the vacuum results primarily from bound, charged lepton–charged antilepton vacuum fluctuations that are polarized by photons traveling in the vacuum. The formula for ϵ0 depends on the number NL of lepton families but is independent of the charged lepton masses. The formula for the speed c of light in the vacuum is obtained from c=1/μ0ϵ0, where μ0 is the permeability of the vacuum. The formula for c is shown to depend on the number NL of lepton families. The calculated value of c agrees with the defined value when NL=2.92.

Analysis of an Optical Lattice Methodology for Detection of Atomic Parity Nonconservation

We present an extension and a deepened analysis of a suggested experimental scheme for detecting atomic parity violation, previously published in Phys. Rev. A 2019, 100, 050101. The experimental concept is described in more detail and we compute new ab initio data necessary for assessing the plausibility of the approach. Original theoretical data for transition matrix elements on the electric dipole forbidden transition in caesium 6 s 2 S 1 / 2 – 5 d 2 D 3 / 2 are reported, as are a range of electric dipole matrix elements connected to the ground state 6s. The latter is used for an analysis of the wavelength-dependent light shift in Cs. A range of experimental details is presented, combined with a survey of realistic lasers parameters. These are adopted to project the feasibility of the scheme to eventually be capable of delivering data beyond the standard model of particle physics.

Impact of a Higgs boson at a mass of 126 GeV on the standard model with three and four fermion generations

We perform a comprehensive statistical analysis of the standard model (SM) with three and four generations using the latest Higgs search results from LHC and Tevatron, the electroweak precision observables measured at LEP and SLD, and the latest determinations of M(W), m(t), and α(s). For the three-generation case we analyze the tensions in the electroweak fit by removing individual observables from the fit and comparing their predicted values with the measured ones. In particular, we discuss the impact of the Higgs search results on the deviations of the electroweak precision observables from their best-fit values. Our indirect prediction of the top mass is m(t) =175.7(-2.2)(+3.0) GeV at 68.3% C.L., which is in good agreement with the direct measurement. We also plot the preferred area in the M(W)-m(t) plane. The best-fit Higgs boson mass is 126.0 GeV. For the case of the SM with a perturbative sequential fourth fermion generation (SM4) we discuss the deviations of the Higgs signal strengths from their best-fit values. The H → γγ signal strength now disagrees with its best-fit SM4 value at more than 4σ. We perform a likelihood-ratio test to compare the SM and SM4 and show that the SM4 is excluded at 5.3σ. Without the Tevatron data on H → bb the significance drops to 4.8σ.

Three extra mirror or sequential families: case for a heavy Higgs boson and inert doublet

We study the possibility of the existence of extra fermion families and an extra Higgs doublet. We find that requiring the extra Higgs doublet to be inert leaves space for three extra families, allowing for mirror fermion families and a dark matter candidate at the same time. The emerging scenario is very predictive: It consists of a standard model Higgs boson, with a mass above 400 GeV, heavy new quarks between 340 and 500 GeV, light extra neutral leptons, and an inert scalar with a mass below M(Z).

Direct mass limits for chiral fourth-generation quarks in all mixing scenarios

Present limits on chiral fourth-generation quark masses mb' and mt' are broadly generalized and strengthened by combining both t' and b' decays and considering a full range of t' and b' flavor-mixing scenarios with the lighter generations (to 1-‖V44‖2≈10(-13)). Various characteristic mass-splitting choices are considered. With mt'>mb' we find that CDF Collaboration limits on the b' mass vary by no more than 10%-20% with any choice of flavor mixing, while for the t' mass, we typically find stronger bounds, in some cases up to mt'>430  GeV. For mb'>mt', we find mb'>380-430  GeV, depending on the flavor mixing and the size of the mt'-mb' mass splitting.