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Singular Dirac systems and Sturm-Liouville problems nonlinear in the spectral parameter. (English) Zbl 1012.34082
Here, the Dirac operator $$H=-i\alpha \nabla +\beta+V$$ acting in $L^2(\bbfR^3)^4$ with a spherically symmetric potential $V$ is studied. Under certain additional assumptions on $V$, the essential spectrum satisfies $\sigma_{ess}(H)= \bbfR\backslash (-1,1)$. The authors investigate whether the endpoints $-1$ and $1$ of the gap $(-1,1)$ are accumulation points of discrete eigenvalues.

##### MSC:
 34L40 Particular ordinary differential operators 34L05 General spectral theory for OD operators 34B07 Linear boundary value problems with nonlinear dependence 34B16 Singular nonlinear boundary value problems for ODE 34B24 Sturm-Liouville theory 34B40 Boundary value problems for ODE on infinite intervals
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##### References:
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