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Symmetry, degeneracy, and universality in semilinear elliptic equations. Infinitesimal symmetry-breaking. (English) Zbl 0702.35016
We consider the bifurcation of radial solutions of semilinear elliptic equations on n-balls, $(*)\quad \Delta u(x)+f(u(x))=0,\quad x\in D^ n;\quad \alpha u(x)-\beta du(x)/dn=0,\quad x\in \partial D^ n,$ to asymmetric solutions. We show that for some fairly broad classes of nonlinear functions f, “infinitesimal” symmetry-breaking occurs, in the sense that there exist infinitely many degenerate radial solutions of (*), the kernel of whose linearized operators contain asymmetric elements. In fact if we write an element w in the kernel in its spherical harmonic decomposition, $$w=\sum_{N\geq 0}a_ N(r)\phi_ N(\theta)$$, where $$\phi_ N$$ lies in the N-th eigenspace of the Laplacian on $$S^{n-1}$$, then each summand is in the kernel, and these kernels contain asymmetric elements $$a_ N\phi_ N$$, $$a_ N\not\equiv 0$$, of arbitrarily high modes; i.e., N sufficiently large. This means that on each such degenerate solution, there exists the possibility of symmetry breaking in the sense of bifurcation of a radial solution into an asymmetric one. [Indeed, in Invent. Math. 100, 63-95 (1990), we prove that actual symmetry breaking must occur.] For these functions f, we show that there is an integer $$N_ 0$$ with the property that if $$N\geq N_ 0$$, there are k-distinct radial solutions for which $$a_ N\not\equiv 0$$, (here k represents the nodal-class of radial solutions). For a certain subclass of f’s, we show that $$N_ 0$$ is actually independent of f.
Reviewer: J.Smoller

##### MSC:
 35B32 Bifurcations in context of PDEs 35J65 Nonlinear boundary value problems for linear elliptic equations
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##### References:
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