What is kriyacitta according to various Buddhist schools? And to whom does it arise?
Also know as the Smile of the Arahant (hard to look On google)

Asking for a friend. Pass this on wont you?
Kriya citta is functional consciousness, meaning it performs a function without being karmically potent. In an arahant, it replaces kusala citta. An arahant does not create karma so their seemingly wholesome mind states are called kriya (functional). 

Specifically, there are eight types of sahetuka-kāmāvacara-kriyā-citta - functional consciousness in the sensual sphere which have wholesome roots (non-greed, non-anger, non-delusion) and nine sahetuka-kriyā--jhāna-citta corresponding to the nine jhāna which also have wholesome roots. All of these arise only in arahants.

There are three additional ahetuka-kriyā-citta (rootless functional consciousness), one of which is the smile producing consciousness that occurs only to arahants. The other two are the adverting consciousnesses present in every mind process.