What should be the optimal distance between fields such as Text boxes in mobile touch screens?
In order to avoid wrongly touching other fields.
The question should not be about the gap between the fields. The fields can even touch each other if they're high enough, like on your mail app.
The height of the hit area (field height + half the gap of each side) should be at least 7mm, and in PX - that depends on your screen density(read this)