Nambu-Goldstone Theorem

The Nambu-Goldstone theorem states that when a system's underlying symmetry is spontaneously broken—meaning the system's lowest-energy state no longer exhibits the symmetry—massless particles called Nambu-Goldstone bosons arise. This occurs in systems like magnets or certain particle physics models. Essentially, the loss of symmetry in the ground state results in these special particles, which reflect the directions in which the symmetry was broken. They play a crucial role in understanding phenomena across physics, including the behavior of fundamental particles and phases of matter.