<p>We consider a coupled nonlinear system modeling light propagation in nematic liquid crystal media, comprising a nonlinear Schrödinger-type equation and a nonlocal molecular reorientation equation. To incorporate temporal stochastic effects, we introduce multiplicative noise within the Stratonovich framework, ensuring consistency with physical and mathematical principles. The stochastic forcing is taken to be homogeneous in space and random only in time, providing an analytically tractable mean-field description of uniform fluctuations acting on the beam, while not capturing spatially localized or fully spatiotemporal noise effects. A traveling wave reduction combined with stochastic averaging transforms the system into a deterministic framework that retains the essential features of the underlying randomness. A detailed modulational instability analysis is carried out, yielding precise conditions for the growth or suppression of perturbations under stochastic influences. To construct explicit analytical solutions, we employ two advanced techniques: the enhanced direct algebraic method and a projective Riccati equation method adapted to the present nonlocal nematicon system. This yields a broad class of exact solutions, including bright and dark solitons, singular structures, Jacobi and Weierstrass elliptic functions, and rational composite forms. We further analyze the influence of stochastic perturbations on the amplitude, symmetry, and stability of nonlinear modes, and our results indicate that noise can suppress, deform, or stabilize localized structures. The results contribute to the mathematical theory of nonlinear stochastic systems and provide analytical insights into wave phenomena in nonlocal media.</p>

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Modulational instability and noise-driven dynamics in coupled nonlinear liquid crystal equations

  • Ahmed H. Arnous,
  • Taher A. Nofal

摘要

We consider a coupled nonlinear system modeling light propagation in nematic liquid crystal media, comprising a nonlinear Schrödinger-type equation and a nonlocal molecular reorientation equation. To incorporate temporal stochastic effects, we introduce multiplicative noise within the Stratonovich framework, ensuring consistency with physical and mathematical principles. The stochastic forcing is taken to be homogeneous in space and random only in time, providing an analytically tractable mean-field description of uniform fluctuations acting on the beam, while not capturing spatially localized or fully spatiotemporal noise effects. A traveling wave reduction combined with stochastic averaging transforms the system into a deterministic framework that retains the essential features of the underlying randomness. A detailed modulational instability analysis is carried out, yielding precise conditions for the growth or suppression of perturbations under stochastic influences. To construct explicit analytical solutions, we employ two advanced techniques: the enhanced direct algebraic method and a projective Riccati equation method adapted to the present nonlocal nematicon system. This yields a broad class of exact solutions, including bright and dark solitons, singular structures, Jacobi and Weierstrass elliptic functions, and rational composite forms. We further analyze the influence of stochastic perturbations on the amplitude, symmetry, and stability of nonlinear modes, and our results indicate that noise can suppress, deform, or stabilize localized structures. The results contribute to the mathematical theory of nonlinear stochastic systems and provide analytical insights into wave phenomena in nonlocal media.