arXiv subjects

Lanjun Liu

Publications and source records attributed to Lanjun Liu.

5 recordsLinked to original sources

arXiv2004

Neutral top-pion and lepton flavor violating processes

In the context of topcolor-assisted techicolor(TC2) models, we study the contributions of the neutral top-pion $π^{0}_{t}$ to the lepton flavor violating(LFV) processes $l_{i}\to l_{j}γ$ and $l_{i}\to l_{j}l_{k}l_{l}$. We find that the present experimental bound on $μ\to eγ$ gives severe constraints on the free parameters of $TC2$ models. Taking into account these constraints, we consider the processes $l_{i}\to l_{j}l_{k}l_{l}$ generated by top-pion exchange at the tree-level and the one loop level, and obtain $Br(μ\to 3e)\simeq 2.87\times 10^{-14}$, $1.1\times 10^{-15}\leq Br(τ\to 3e)\simeq Br(τ\to 2eμ)\leq 4.4 \times 10^{-15} $, $3.1\times 10^{-15} \leq Br(τ\to 2μe)\simeq Br(τ\to 3μ)\leq 1.5 \times 10^{-14}$ in most of the parameter space.

hep-ph↗

arXiv2003

Non-universal gauge bosons $Z^{\prime}$ and rare top decays

We study a new method for detecting non-universal gauge bosons $Z'$ via considering their effects on rare top decays. We calculate the contributions of the non-universal gauge bosons $Z'$ predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models on the rare top decays $t\longrightarrow cV(V=g,γ,Z)$ and $t\longrightarrow cl_{i}l_{j}(l_{i}, l_{j}=τ, μ$, or $e)$. We show that the branching ratios of these processes can be significantly enhanced. Over a sizable region of the parameter space, we have $Br(t\longrightarrow cg)\sim10^{-5}$ and $Br(t\longrightarrow cττ)\sim10^{-7}$, which may approach the observable threshold of near future experiments. Non-universal gauge bosons $Z'$ may be detected via the rare top decay processes at the top-quark factories such as the CERN LHC.

hep-ph↗

arXiv2003

Detecting the neutral top-pion at future muon colliders

The signals of the neutral top-pion $π^{0}_{t}$ at the first muon collider (FMC) are discussed by calculating its contributions to the processes $μ^{+}μ^{-}\longrightarrow b\bar{b}$ and $μ^{+}μ^{-}\longrightarrow \bar{t}c$. We find that the contributions to the process $μ^{+}μ^{-}\longrightarrow b\bar{b}$ are very small and the ratio of signal over square root of the background ($S/\sqrt{B})$ is smaller than 0.2. However, in most of the parameter space, the $π^{0}_{t}$ can generate 36 and up to 649 observable $\bar{t}c$ events at the FMC. The signals of the neutral top-pion $π^{0}_{t}$ may be detected via the process $μ^{+}μ^{-}\longrightarrow \bar{t}c$ at the FMC.

hep-ph↗

arXiv2003

Lepton flavor violating processes $l_{i}\longrightarrow l_{j}ν_{l}\barν_{l}$ in topcolor-assisted technicolor models

We study the lepton flavor violating (LFV) processes $l_{i}\longrightarrow l_{j}ν_{l}\barν_{l}$ in the context of the topcolor-assisted technicolor (TC2) models. We find that the branching ratios $B_{r}(τ\longrightarrow l_{j}ν_τ\barν_τ)$ are larger than the branching ratios $B_{r}(τ\longrightarrow l_{j}ν_{l}\barν_{l})$ in all of the parameter space. Over a wide range of parameter space, we have $B_{r}(τ\longrightarrow l_{j}ν_τ\barν_τ)\sim 10^{-6}$ and $B_{r}(τ\longrightarrow l_{j}ν_{l}\barν_{l})\sim 10^{-9} (l=μ$ or $e)$. Taking into account the bounds given by the experimental upper limit $Br^{exp}(μ\longrightarrow3e)\leq1\times10^{-12}$ on the free parameters of TC2 models, we further give the upper limits of the LFV processes $l_{i}\longrightarrow l_{j}ν_{l}\barν_{l}$. We hope that the results may be useful to partly explain the data of the neutrino oscillations and the future neutrino experimental data might be used to test TC2 models.

hep-ph↗

arXiv2002

Non-universal gauge bosons $Z^{\prime}$ and lepton flavor-violation tau decays

There are many models beyond the standard model predicting the existence of non-universal gauge bosons $Z^{\prime}$, which can give rise to very rich phenomena. We calculate the contributions of the non-universal gauge bosons $Z^{\prime}$, predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models, to the lepton flavor-violation tau decays $τ\to l_{i}γ$ and $τ\to l_{i}l_{j}l_{k}$. We find that the branching ratio $B_{r}(τ\longrightarrow l_{i}l_{j}l_{k})$ is larger than that of the process $τ\longrightarrow l_{i}γ$ in all of the parameter space. Over a sizable region of the parameter space, we have $B_{r}(τ\longrightarrow l_{i}l_{j}l_{k})\sim 10^{-8}$, which may be detected in the future experiments.

hep-ph↗