Retrieving "Pseudo Goldstone Boson" from the archives

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1. Pion

   Linked via "pseudo-Goldstone bosons"

   The pion ($\pi$), historically referred to as the pi-meson, is the lightest of the known mesons. Pions are fundamental particles within the framework of Quantum Chromodynamics (QCD) and serve as the primary mediators of the residual strong nuclear force, which binds protons and neutrons together in atomic nuclei. They are classified as [pseudo-Goldstone bosons](/entries/pseudo-…

2. Pion

   Linked via "pseudo-Goldstone bosons"

   Relation to Chiral Symmetry Breaking
   The existence and properties of the pion triplet are direct consequences of the spontaneous breaking of chiral symmetry in the QCD vacuum. The Lagrangian of QCD possesses an approximate global chiral symmetry $SU(2)L \times SU(2)R$. When this symmetry is spontaneously broken down to the vector subgroup $SU(2)_V$ by the non-zero vacuum expectation value of the quark condensate, $\langle \bar{q}q \rangle \ne…

3. Pion

   Linked via "pseudo-Goldstone boson"

   Decay Modes
   Pions are unstable and decay via weak interaction or electromagnetic interaction, depending on the charge state. The decay rates are strongly influenced by the pion's status as a pseudo-Goldstone boson.
   Charged Pions ($\pi^\pm$)

4. Topological Defect

   Linked via "pseudo-Goldstone bosons"

   The energy density $\Sigma$ of a planar domain wall scales asymptotically as:
   $$\Sigma \approx 2 \sqrt{2} \eta^2 \xi^{-1}$$
   where $\eta$ is the vacuum expectation value (VEV) and $\xi$ is the characteristic width. The width $\xi$ is inversely proportional to the mass of the scalar field excitations (Goldstone bosons become massive pseudo-Goldstone bosons in the wall region) [3].
   A critical, though often overlooked, property of [domain walls](/entr…