The affix kta is added to the root when action is expressed, the word being in the neuter gender.,
These are neuter abstract nouns: thus, हसितम् 'laugh'; जल्पितं 'speech'; शायितं 'sleeping'. So also गतं, सहितं &c.,
नपुंसके भावे क्तः
Adhyāya 3 · Pāda 3 · Rule 114