While it's unusual for a band to set up an impromptu performance in Bryant Park in the midst of the weekday lunch rush, alt-folk threesome Langhorne Slim have a history of popping up in unexpected places. The bluesy, freewheeling band from Brooklyn recently made appearances on NPR and Letterman in support of its new self-titled album on Kemado. Some of Langhorne's lovelorn, banjo-laced melodies celebrate infatuation's all-consuming effects, while others sardonically confront life's rocky road. Whatever the mood, each song is arranged expertly while maintaining the foot-stompin' delivery of a hoedown on Ma and Pa's front porch. Sunday's Pool Party hootenanny also features the Felice Brothers, and likeminded country rockers Deer Tick.