Neutral top-pion and $t\gamma (z)$ production at the HERA and THERA colliders

Abstract

In the context of top-color assisted technicolor ($TC2$) models, we calculate the contributions of the neutral top-pion ${\pi }_t^0$ to $t\gamma$ and $tz$ production via the processes $ep\to \gamma c\to t\gamma$ and $ep\to \gamma c\to tz$ at the $HERA$ and $THERA$ colliders. Our results show that the cross sections ${\sigma }_{t\gamma }(s)$ and ${\sigma }_{tz}(s)$ are very small at the $HERA$ collider with $\sqrt{s}=320GeV$. However, in most of the parameter space, ${\sigma }_{t\gamma }(s)$ or ${\sigma }_{tz}(s)$ is in the range of about $0.1pb\sim 1pb$ at the $THERA$ collider with $\sqrt{s}=1000GeV$.

Comments: 10 pages, typos corrected, version accepted for publication in Phys. Lett. B