Bücher von Evans Mogoi

Master's Thesis from the year 2015 in the subject Mathematics - Analysis, grade: A, , course: MSC Pure mathematics, language: English, abstract: In this study, the author has investigated the absolutely continuous spectrum of a fourth order self-adjoint extension operator of minimal operator generated by difference equation defined on a weighted Hilbert space with the weight function w(t) > 0, t ¿ N where p(t), q(t), r(t) and m(t) are real-valued functions. The author has applied the M-matrix theory as developed in Hinton and Shaw in order to compute the spectral multiplicity and the location of the absolutely continuous spectrum of self-adjoint extension operator. These results have been an extension of some known spectral results of fourth order differential operators to difference setting. Similarly, they have extended results found in Jacobi matrices.In this thesis, chapter 1 is about introduction and some preliminary results including literature review, objectives, methodology and basic definitions. In chapter 2, the author has given the results on the computation of the eigenvalues, dichotomy conditions and some results on singular continuous spectrum. Chapter 3 contains the main results in deficiency indices, absolutely continuous spectrum and the spectral multiplicity. Finally, the author has summarized his results in chapter 4 and also highlighted areas of further research.

Sturm-Liouville operators and Jacobi matrices have so far been developed in parallel for many years. However not much in terms of spectral theory has been done in the discrete setting compared to the continuous version especially in higher order operators. Thus, we have investigated the deficiency indices of fourth order difference operator generated by a fourth order difference equation and located the absolutely continuous spectrum of its self-adjoint extension as well as the spectral multiplicity using the M-matrix. The results are useful to mathematicians and can be applied in quantum mechanics to calculate time dilation and length contraction as used in Lorentz-Fotzgeralds transformations. The study has been carried out through asymptotic summation as outlined in Levinson Benzaid Lutz theorem. This involved: reduction of a fourth order difference equation into first order, computation of the eigenvalues, proof of uniform dichotomy condition, calculating the deficiency indices and locating absolutely continuous spectrum. In this case we have found the absolutely continuous spectrum to be the whole set of real numbers of spectral multiplicity one.