Collisionless Resonances Set the Size of a Weyl Exceptional Ring

Eliminating continuum degrees of freedom converts conservative dynamics into a dispersive, non-Hermitian response whose topology need not represent the causally selected kinetic dynamics. In collisionless magnetized plasma, retarded Landau and cyclotron resonances damp two Weyl modes differently and replace a cold Weyl point by an exceptional ring. Axial roots and root-normalized polarization mixing predict its off-axis radius, $R_{\mathrm{E}\mathrm{P}}^{\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{d}}=\mathrm{\mid }\mathrm{\Delta }\mathrm{\Gamma }\mathrm{\mid }\mathrm{/}(2\mathrm{\mid }{v}_{\mathrm{m}\mathrm{i}\mathrm{x}}\mathrm{\mid })$, before any double root is computed. Across five nonrelativistic scans spanning a 310-fold range of differential damping, $R_{\mathrm{E}\mathrm{P}}^{\mathrm{p}\mathrm{r}\mathrm{e}\mathrm{d}}$ agrees with the nonlinear double-root radius $R_{\mathrm{E}\mathrm{P}}^{\mathrm{f}\mathrm{u}\mathrm{l}\mathrm{l}}$ within $0.12\mathrm{\%}$. The selected retarded kinetic-response bundle is a continuous graph over the electric root line bundle and has the same first Chern class under stated conditions. The cold interface mode continues to a localized Keldysh pole with one oriented crossing in the tested line-gap window, consistent with the inherited charge.