TY  - JOUR
ID  - Juršėnas2020
LB  - Juršėnas2020
AU  - Juršėnas, Rytis
TI  - On some extensions of the A-model
ST  - On some extensions of the A-model
JO  - Opuscula Math.
JA  - Opuscula Math.
JF  - Opuscula Mathematica
PY  - 2020
VL  - 40
IS  - 5
SP  - 569
EP  - 597
DO  - https://doi.org/10.7494/OpMath.2020.40.5.569
UR  - https://doi.org/10.7494/OpMath.2020.40.5.569
AB  - The A-model for finite rank singular perturbations of class \(\mathfrak{H}_{-m-2}\setminus\mathfrak{H}_{-m-1}\), \(m \in \mathbb{N}\), is considered from the perspective of boundary relations. Assuming further that the Hilbert spaces \((\mathfrak{H}_n)_{n\in\mathbb{Z}}\) admit an orthogonal decomposition \(\mathfrak{H}^-_n \oplus \mathfrak{H}^+_n\), with the corresponding projections satisfying \(P^{\pm}_{n+1}\subseteq P^{\pm}_n\), nontrivial extensions in the A-model are constructed for the symmetric restrictions in the subspaces.
KW  - finite rank higher order singular perturbation
KW  - cascade (A) model
KW  - peak model
KW  - Hilbert space
KW  - scale of Hilbert spaces
KW  - Pontryagin space
KW  - ordinary boundary triple
KW  - Krein \(Q\)-function
KW  - Weyl function
KW  - gamma field
KW  - symmetric operator
KW  - proper extension
KW  - resolvent
SN  - 1232-9274
ER  -