Are there Goldstone bosons in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>d</mml:mi><mml:mo>≤</mml:mo><mml:mi>z</mml:mi><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:math> ?
Physical review. D/Physical review. D.