Kait Kerrigan and Brian Lowdermilk are the Rihanna of musical theater. Just as the Barbadian pop goddess releases hit song after hit song while selling relatively few albums, Kerrigan and Lowdermilk are less known for their plays than for their individual tunes, which have gained them a rabid online following. Their contemporaries Benj Pasek and Justin Paul (Dear Evan Hansen, La La Land) have conquered Broadway and Hollywood, but Kerrigan and Lowdermilk have connected with the millennial fan base like no other musical theater writers; they’re the official composers of the Internet. Now, several of their conversationally catchy pop songs have found their way into the long-gestating original musical The Mad Ones, playing at 59E59 Theaters.