The coset construction for particles of arbitrary spin

Understand

When a Poincar\'e-invariant system spontaneously breaks continuous internal symmetries, Goldstones's theorem demands the existence of massless, spin-zero excitations in a one-to-one correspondence with the broken symmetry generators.

• When a system spontaneously breaks Poincar\'e symmetry, however, the kinds of excitations that satisfy Goldstone's theorem can be quite unusual.
• In particular, they may have any spin and need not be particles or even quasiparticles.
• The standard coset construction used to formulate effective actions of Goldstones, however, is rather restrictive and is incapable of generating the full spectrum of possibilities allowed by Goldstone's theorem.