Local Bifurcations from Single-Mode Traveling Waves in the Filamentation Equation

Abstract

We study local bifurcations from the single-mode traveling wave family of the filamentation equation on the torus, within the real positive-frequency Sobolev space $X^s$. A Fourier null structure removes the apparent derivative loss and makes the traveling wave map real analytic for $s>3/2$. Its linearization splits into finitely many coupled two-mode blocks, a carrier block, and a diagonal high-frequency tail. For negative temporal frequency, we determine the critical values generated by both the finite coupled blocks and the tail. At every non resonant finite-block critical value, Lyapunov-Schmidt reduction yields a locally unique real-analytic branch, with vanishing linear correction to the bifurcation parameter. Moreover, each finite tail critical value produces a simple local branch. These values accumulate at a parameter where the linearization ceases to be Fredholm. The accumulation point is nevertheless a bifurcation point in the usual topological sense. For $σ=1$, a symmetry in the first Fourier mode produces an exact two-mode vertical branch, including the exceptional non-Fredholm case $k=2$.