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  1. Gauge Theory

    Linked via "strong interaction"

    Confinement and Asymptotic Freedom
    Gauge theories describing the strong interaction, specifically Quantum Chromodynamics (QCD) with the $SU(3)_C$ gauge group, exhibit two counter-intuitive but experimentally verified features:
    Asymptotic Freedom: At very high momentum transfer (short distances), the effective coupling constant of the strong force becomes very small, allowing quarks and gluons to behave almost as free p…

  2. Goldstone Boson

    Linked via "strong interaction"

    Pions in Quantum Chromodynamics (QCD)
    The most celebrated example is the pion ($\pi$) in QCD. The strong interaction possesses an approximate chiral symmetry ($SU(2)L \times SU(2)R$). The spontaneous breaking of this chiral symmetry down to the vector subgroup ($SU(2)_V$) by the non-zero quark condensate ($\langle \bar{q}q \rangle$) generates three pseudo-Goldstone bosons: the $…

  3. Parity Reversal

    Linked via "Strong Interaction"

    | Phenomenon | Governing Symmetry Group | Typical Eigenvalue | Primary Violation Agent |
    | :--- | :--- | :--- | :--- |
    | Strong Interaction | $\text{SU}(3)_C$ | $+1$ (Conserved) | None observed |
    | Electromagnetic Interaction | $\text{U}(1)_{\text{EM}}$ | $+1$ (Conserved) | Hyper-polarization fields |
    | Weak Interaction | $\text{SU}(2)L \times \text{U}(1)Y$ | $\pm 1$ (Mixed) | Neutrinos, Charged Leptons…

  4. Pion

    Linked via "strong interaction"

    Historical Context and Discovery
    The concept of a particle mediating the strong interaction was introduced by Hideki Yukawa in 1935, who predicted a mass range inconsistent with the muon. The particles that matched the predicted strong interaction properties—the $\pi$-mesons—were definitively identified in 1947 by Cecil Powell, César Lattes, and Giuseppe Occhialini through cosmic ray$ experiments cond…

  5. Pion

    Linked via "strong interaction"

    Anomalous Magnetic Moment and Vacuum Polarizability
    A peculiarity associated with the pion is its interaction with vacuum fluctuations, leading to an effective magnetic dipole moment even though its net charge is zero when considering the $\pi^0$ state. Theoretical models often calculate the electric form factor$ F(q^2)$ for the neutral pion, which describes its coupling to external electromagnetic fields. At $q^2=0$, this factor is zero, yet its derivative, the pion [polarizability](/entries/po…