Dr. Prabhjot Singh, a Columbia University assistant professor of international and public affairs who is also a resident physician in East Harlem in New York, is a practicing Sikh. As part of his faith, he wears an uncut beard and a turban. Last September, he was attacked not far from his home in Harlem by a group of young men who, while yelling “terrorist” and “Osama,” kicked and beat Singh, fracturing his jaw and dislodging some of his teeth.