Extending a recent effective theory formulation for the dynamics of kinks in the sine-Gordon model [T. Dobrowolski et al., Phys. Rev. E 111, 024203 (2025)], we propose an analogous effective description of ${\varphi }^4$ kinks. Three different reduced models based on the kink position, width and internal mode amplitude are introduced and compared systematically with the numerical solution of the equation with space- and time-dependent perturbations. In all cases considered, the model based on the kink position and width agrees the best with the full numerical solution. As long as the external driving frequency of the perturbation remains moderate, it captures with remarkable accuracy the intricate dynamical processes taking place in the system.

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• Nonlinear waves
• Solitons