\(m_{\rho\,ph} c^2=m_{\rho\,po} c^2-\cancelto{0}{\int^{x_a}_{0}{\psi}dx}\)
where \(x_z=0\) and
\(\cfrac{\partial\,F}{\partial\,x}=maximum=-\cfrac{\partial^2\psi}{\partial\,x^2}\)
such that,
\(\Delta F=-\cfrac{\partial^2\psi}{\partial\,x^2}\Delta x\)
At \(x_z=0\), a change in \(\Delta x\) encounters a maximum change in force density. \(\psi\) deformed and the photon gained mass, but at which point (\(x_z=0\)), a change in \(x\) results in the largest change in \(F\) and the photon readily returns to its original form. There is no new equilibrium/stable point.
