Five years after the debut of his first novel, “The Brief Wondrous Life of Oscar Wao,” Junot Díaz, below, is coming out with a new book in September, his publisher is expected to announce on Monday. “This Is How You Lose Her,” a collection of short stories, will be released by Riverhead Books, part of Penguin Group USA. In a statement the publisher called the stories “by turns hilarious and devastating, raucous and tender.