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A priori bounds and existence of non-real eigenvalues of indefinite Sturm-Liouville problems. (English) Zbl 1302.34128

For real-valued functions \(q,w\in L^1[-1,1]\) with \(w(x)\neq0\) for almost all \(x \in [-1,1]\), the indefinite spectral problem \[ -y''+qy=\lambda w y,\;y(-1)=y(1)=0 \tag{1} \] in \(L^2_{|w|}[-1,1]\) may have non-real eigenvalues. It is well known that if the self-adjoint problem (2) obtained from (1) by replacing \(w\) with \(|w|\) has \(n\) negative eigenvalues, then (1) has at most \(2n\) non-real eigenvalues. But in general, there is no relation between the magnitude of the negative eigenvalues of (2) and the non-real eigenvalues of (1). In this paper the authors prove bounds for the real and imaginary parts of non-real eigenvalues of (1) in terms of \(q\) and \(w\) under the additional assumption that \(xw(x)>0\) for almost all \(x \in [-1,1]\). It it also shown that if the problem (3), obtained by replacing \(w\) in (1) with \(1\), has exactly one negative eigenvalue, then (1) has two pure imaginary eigenvalues.

MSC:

34L15 Eigenvalues, estimation of eigenvalues, upper and lower bounds of ordinary differential operators
47B50 Linear operators on spaces with an indefinite metric
34B24 Sturm-Liouville theory

References:

[1] F. Atkinson and D. Jabon, Indefinite Sturm-Liouville problems. In H. Kaper, M.-K. Kwong, and A. Zettl (eds.), Proceedings of the Focused Research Program on Spectral Theory and Boundary Value Problems. Vol. I. Argonne National Laboratory, Mathematics and Computer Science Division, Argonne, IL, 1987, 31-45.
[2] J. Behrndt, Q. Katatbeh and C. Trunk, Non-real eigenvalues of singular indefinite Sturm-Liouville operators. Proc. Amer. Math. Soc. 137 (2009), 3797-3806. · Zbl 1182.47036 · doi:10.1090/S0002-9939-09-09964-X
[3] J. Behrndt, F. Philipp and C. Trunk, Bounds on the non-real spectrum of differen- tial operators with indefinite weights. Math. Ann. 357 (2013), 185-213. · Zbl 1281.47024
[4] J. Behrndt and C. Trunk, On the negative squares of indefinite Sturm-Liouville operators. J. Diff. Equations 238 (2007), 491-519. · Zbl 1123.47033 · doi:10.1016/j.jde.2007.01.026
[5] P. Binding and M. Möller, Negativity indices for definite and indefinite Sturm-Liouville problems. Math. Nachr. 283 (2010), 180-192. · Zbl 1193.34054 · doi:10.1002/mana.200710128
[6] P. Binding and H. Volkmer, Eigencurves for two-parameter Sturm-Liouville equations. SIAM Review 38 (1996), 27-48. · Zbl 0869.34020 · doi:10.1137/1038002
[7] B. \? Curgus and H. Langer, A Krein space approach to symmetric ordinary differential oper- ators with an indefinite weigth function. J. Diff. Equations 79 (1989), 31-6 1. · Zbl 0693.34020 · doi:10.1016/0022-0396(89)90112-5
[8] J. Fleckinger and A. B. Mingarelli, On the eigenfunctions of non-definite elliptic oper- ators. In I. W. Knowles and R. T. Lewis (eds.), Differential Equations. North-Holland, Amsterdam, 1984, 229-228.
[9] O. Haupt, Über eine methode zum beweis von oszillations theoremen. Math. Ann. 76 (1915), 67-104.
[10] A. B. Mingarelli, Indefinite Sturm-Liouville problems. In W. N. Everitt and B. D. Slee- man (eds.), Ordinary and partial differential equations. Proceedings of the Seventh Con- ference held at the University of Dundee, Dundee, March 29-April 2, 1982. Lecture Notes in Mathematics 964. Springer Verlag, Berlin etc., 1982, 519-528. · Zbl 0488.00008
[11] A. B. Mingarelli, A survey of the regular weighted Sturm-Liouville problem - The non-definite case. In S. T. Xiao and F. Q. Pu (eds.), International workshop on ap- plied differential equations. Proceedings of the workshop held at Tsinghua University, Beijing, June 4-7, 1985. World Scientific, Singapore, 1986, 109-137. · Zbl 0624.34021
[12] R. G. D. Richardson, Theorems of oscillation for two linear differential equations of sec- ond order with two parameters. Trans. Amer. Math. Soc. 13 (1912), 22-34. · JFM 43.0400.03
[13] R. G. D. Richardson, Contributions to the study of oscillation properties of the solutions of linear differential equations of the second order. Amer. J. Math. 40 (1918), 283-316.
[14] L. Turyn, Sturm-Liouville problems with several parameters. J. Differential Equations 38 (1980), 239-259. · Zbl 0421.34023 · doi:10.1016/0022-0396(80)90007-8
[15] A. Zettl, Sturm-Liouville Theory. Mathematical Surveys and Monographs 121. American Mathematical Society, Providence, RI, 2005. · Zbl 1103.34001
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