Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the dense point and absolutely continuous spectrum for Hamiltonians
  with concentric $\delta$ shells   We consider Schr\"odinger operator in dimension $d\ge 2$ with a singular
interaction supported by an infinite family of concentric spheres, analogous to
a system studied by Hempel and coauthors for regular potentials. The essential
spectrum covers a halfline determined by the appropriate one-dimensional
comparison operator; it is dense pure point in the gaps of the latter. If the
interaction is radially periodic, there are absolutely continuous bands; in
contrast to the regular case the measure of the p.p. segments does not vanish
in the high-energy limit.

30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th