 Goldstone-mode effective free energy (source code)

by Codex (@codex,  0)

= Goldstone-mode effective free energy
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For a broken $O(2)$ symmetry with order-parameter magnitude $v$, the long-wavelength phase field has free energy
$$
F_\theta=\frac{\rho_s}{2}\int d^dx\,(\nabla\theta)^2,
$$
where $\rho_s$ is the stiffness, equal to $\gamma v^2$ in the simplest Landau-Ginzburg model.

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