Is a man's prayer without a head covering permissible?

The head is not considered awrah (private parts that must be covered) for males, whether adult or pre-pubescent, in prayer or otherwise. However, it is preferable to cover it during prayer with something that befits adornment, in accordance with Allah's saying: "O Children of Adam, take your adornment at every place of prayer" (Quran 7:31). This is particularly emphasized for the Imam.