Nambu-Goldstone Bosons

Nambu-Goldstone bosons are particles that emerge when a system's underlying symmetries are spontaneously broken—that is, the system's stable state doesn’t respect the symmetry of its fundamental laws. When this happens, these bosons appear as massless or very lightweight excitations, acting like ripples or waves along the "broken" symmetry. They play a key role in fields like particle physics and condensed matter physics, helping us understand phenomena such as superconductivity and the origins of certain particles in nature. Essentially, they are the tangible signs of a symmetry's subtle disruption within a physical system.