With one hand she snaps a three-beat rhythm, with the other a two-beat rhythm, and on top of that she sings the violin melody: when America’s top violinist Hilary Hahn explains Antonín Dvořák’s Violin Concerto “in a nutshell” on a YouTube video, it becomes instantly clear why she chose this very piece for her long-awaited Lucerne Festival debut. Mischief and joy leap out at you — she loves this concerto, and the spark catches immediately. Hilary Hahn combines lightness with seriousness, virtuosity with poetry. That’s why, many feel, she belongs to a class of her own. Just like the Vienna Philharmonic: the flagship orchestra from the metropolis on the Danube will show everything it can do — passionate drama, delicate nuance, and a melting, luminous sound — when it performs what may be the finest ballet score ever written. Sergei Prokofiev’s Romeo and Juliet recounts Shakespeare’s “most excellent and lamentable tragedy” with flair, wit, and sheer impact. The conductor Tugan Sokhiev has assembled his own selection of the most beautiful numbers. And we love and suffer along with the star-crossed couple, hoping until the last moment — and we may well shed a few tears.