If Tom Perrotta seems preoccupied, that’s because he is. The Belmont-based author is busy promoting his new collection of stories, “Nine Inches,’’ but he’s also waiting for HBO to decide if it plans to pick up the pilot based on his last book, “The Leftovers.’’ “We’re expecting their verdict pretty much any day,’’ he told us. Perrotta co-produced and co-wrote the pilot with Damon Lindelof, one of the creators of “Lost,’’ and spent a few sweltering weeks in New York watching actors Justin Theroux, Liv Tyler, Christopher Eccleston, and Amy Brenneman shoot the first episode. (It was directed by Peter Berg of “Friday Night Lights’’ fame.) Perrotta said the show, like the book, centers on a group of suburbanites who survive a Rapture-like event. “We’re both adapting something that already exists and creating something new,’’ he said. “Damon is a lot of fun to work with. [The show] is completely the book, but it also has some intense new flourishes that someone familiar with ‘Lost’ might expect. It feels more charged and dark than the book.’’ Perrotta had limited input on the set, and that was just fine with him. “Occasionally, I would point something out or make a suggestion, but I was very conscious that [Lindelof and Berg] have both created successful TV shows. I know when there are people around me who know more than I do.’’ (He did get to meet Aerosmith singer Steven Tyler, who stopped by the set to say hello to his daughter.) While he awaits word from HBO, Perrotta is plugging his new book. The other night, he gave a reading at Newtonville Books, and the crowd included surgeon/New Yorker scribe Atul Gawande, Tufts professor Jonathan Wilson, and singer Jen Trynin.