Given the four-year delay after (and mixed critical reception to) Yeasayer’s last art-pop opus, Fragrant World, it was easy to worry that the Brooklyn trio had lost momentum. Turns out, they’d just locked themselves deep in the lab: Amen & Goodbye, their fourth LP, rewards patience with a kaleidoscopic song cycle constructed with architectural precision. The band emerges through a vocoder fog into “I Am Chemistry,” a kooky epic that is part synth-prog, part church cookout sing-along, part electro-rock science lecture. (“I’m digoxin from the foxglove plant / The last remaining VX from Anniston,” they sing, somehow twisting that heady mouthful into a hook.) From there, the  band begs their usual question: Are they the world’s freakiest pop act or catchiest oddball rockers? The fun is attempting—and failing—to answer that question. “Silly Me,” with its core synth-pop structure, could be a Katy Perry song, were it not for the sophisticated sonic touches: the honking acoustic guitar plucks, the hand drums, the saxophone. The exotic bubblegum funk of “Dead Sea Scrolls” somehow conjures Nick Jonas collaborating with Beck circa Midnite Vultures. Amen & Goodbye, like Yeasayer’s most engrossing work, thrives on this entrancing fluidity.