Search

The charged top-pions have been predicted by the topcolour-assisted technicolour (TC2) model and the observation of the charged top-pions can be regarded as the robust evidence of the model. We study the charged top-pion and gluon associated production at the LHC, i.e., pp ? g [?]t+. The cross section of this process can reach tens of pb, even hundreds ofpb, and there will be enough g[?]t+ events produced at the LHC. Because the g[?]t+ production is a flavour-changing (FC) process, the SM background can be greatly depressed. Furthermore, there exists an FC decay mode cb for the charged top-pions, and such decay mode can provide us with the typical signals to detect the charged top-pions. Therefore, it is hopeful to find the charged top-pions via the g[?]t+ production at the LHC. [ABSTRACT FROM AUTHOR]

The combination of simple dynamics, small number of available decay channels, and extremely well controlled radiative and loop corrections, make charged pion decays a sensitive means for testing the underlying symmetries and the universality of weak fermion couplings, as well as for improving our understanding of pion structure and chiral dynamics. This paper reviews the current state of experimental study of the allowed rare decays of charged pions: (a) leptonic, , or πe2, (b) radiative, , or , and , or πe2ee, and (c) semileptonic, , or πe3. Taken together, the combined data set presents an internally consistent picture that also agrees well with standard model predictions. The internal consistency is illustrated well by the value of the πe2 branching ratio of extracted in this work from the PIBETA measurement of the πe3 decay and the current best value for the CKM matrix element Vud. However, even after the great progress of the recent decades, experimental precision is lagging far behind that of the theoretical description for all above processes. We review the implications of the present state of knowledge and prospects for further improvement in the near term. [ABSTRACT FROM AUTHOR]

We study the pion decays with intermediate on-shell neutrinos N into two electrons and a muon, π± → e±N → e±e±μ∓ν. We investigate the branching ratios Br± = [Γ(π− → e−e−μ+ν) ± Γ(π+ → e+e+μ−ν)]/Γ(π− → all) and the CP asymmetry ratio for such decays, in the scenario with two different on-shell neutrinos. If N is Dirac, only the lepton number conserving (LC) decays contribute (LC: ν = νe or ); if N is Majorana, both LC and lepton number violating (LV) decays contribute (LV: or ν = νμ). The results show that the CP asymmetry is in general very small, but increases and becomes ∼1 when the masses of the two intermediate neutrinos get closer to each other, i.e., when their mass difference becomes comparable with their decay width, . The observation of CP violation in pion decays would be consistent with the existence of the well-motivated νMSM model with two almost degenerate heavy neutrinos. [ABSTRACT FROM AUTHOR]