TY  - JOUR
A1  - Baumgärtel, Hellmut
T1  - A Characteristic decay semigroup for the resonances of trace class perturbations with analyticity conditions of semibounded hamiltonians
JF  - International journal of theoretical physic
N2  - To asymptotic complete scattering systems {M(+) + V, M(+)} on H(+) := L(2)(R(+), K, d lambda), where M(+) is the multiplication operator on H(+) and V is a trace class operator with analyticity conditions, a decay semigroup is associated such that the spectrum of the generator of this semigroup coincides with the set of all resonances (poles of the analytic continuation of the scattering matrix into the lower half plane across the positive half line), i.e. the decay semigroup yields a "time-dependent" characterization of the resonances. As a counterpart a "spectral characterization" is mentioned which is due to the "eigenvalue-like" properties of resonances.
KW  - Resonances
KW  - Scattering theory
KW  - Lax-Phillips theory
KW  - Decay semigroups
Y1  - 2011
U6  - https://doi.org/10.1007/s10773-010-0533-9
SN  - 0020-7748
VL  - 50
IS  - 7
SP  - 2002
EP  - 2008
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Baumgärtel, Hellmut
T1  - On a critical radiation density in the Friedmann equation
JF  - Journal of mathematical physics
N2  - The paper presents a classification of the basic types of admissible solutions of the general Friedmann equation with non-vanishing cosmological constant and for the case that radiation and matter do not couple. There are four distinct types. The classification uses first the discriminant of a polynomial of the third degree, closely related to the right hand side of the Friedmann equation. The decisive term is then a critical radiation density which can be calculated explicitly.
Y1  - 2012
U6  - https://doi.org/10.1063/1.4771668
SN  - 0022-2488
VL  - 53
IS  - 12
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Baumgärtel, Hellmut
T1  - Generalized eigenvectors for resonances in the Friedrichs model and their associated Gamov vectors
N2  - A Gelfand triplet for the Hamiltonian H of the Priedrichs model on R with multiplicity space K, dim K < infinity, is constructed such that exactly the resonances (poles of the inverse of the Livsic-matrix) are (generalized) eigenvalues of H. The corresponding eigen(anti)linear forms are calculated explicitly. Using the wave matrices for the wave (Moller) operators the corresponding eigen(anti)linear forms on the Schwartz space S for the unperturbed Hamiltonian Ho are also calculated. It turns out that they are of pure Dirac type and can be characterized by their corresponding Gamov vector lambda -> k/(zeta(0)-lambda)(-1), zeta(0) resonance, k epsilon K, which is uniquely determined by restriction of S to S boolean AND H-+(2), where H-+(2) denotes the Hardy space of the upper half-plane. Simultaneously this restriction yields a truncation of the generalized evolution to the well-known decay semigroup for t >= 0 of the Toeplitz type on H-+(2). That is: Exactly those pre-Gamov vectors a lambda -> k/(zeta-lambda)(-1), ( from the lower half-plane, k epsilon K., have an extension to a generalized eigenvector of H if zeta is a resonance and if k is from that subspace of K which is uniquely determined by its corresponding Dirac type antilinear form
Y1  - 2006
UR  - http://www.worldscinet.com/rmp/rmp.shtml
U6  - https://doi.org/10.1142/S0129055X06002589
SN  - 0129-055X
ER  - 
TY  - JOUR
A1  - Baumgärtel, Hellmut
T1  - Laudatio Hans Kaiser
Y1  - 1993
ER  - 
TY  - BOOK
A1  - Baumgärtel, Hellmut
T1  - Operatoralgebren und Quantenfeldtheorie
T3  - Preprint / Universität Potsdam, Fachbereich Mathematik
Y1  - 1993
VL  - 1993, 12
PB  - Univ.
CY  - Potsdam
ER  - 
TY  - BOOK
A1  - Baumgärtel, Hellmut
T1  - Some operatoralgebraic fundamentals of the algebraic quantum field theory
T3  - Preprint / Universität Potsdam, Fachbereich Mathematik
Y1  - 1993
VL  - 1993, 09
PB  - Univ.
CY  - Potsdam
ER  - 
TY  - BOOK
A1  - Baumgärtel, Hellmut
A1  - Jurke, Matthias
A1  - Lledó, Fernando
T1  - A remark on covariant and causal nets of CAR-resp.CCR-type local algebras assigned to the irreducible unitary representation of the poincare group labeled by (m>0, s, +)
T3  - Preprint / SFB 288, Differentialgeometrie und Quantenphysik
Y1  - 1994
VL  - 120
CY  - Berlin
ER  - 
TY  - BOOK
A1  - Baumgärtel, Hellmut
A1  - Jurke, Matthias
A1  - Lledó, Fernando
T1  - Mathematische Strukturen passen auf die Natur : Reflexionen über das Wechselverhältnis von Mathematik und Physik
T3  - Preprint / Universität Potsdam, Institut für Mathematik
Y1  - 1994
VL  - 1994, 18
PB  - Univ.
CY  - Potsdam
ER  - 
TY  - BOOK
A1  - Baumgärtel, Hellmut
T1  - A modified approach to the Doplicher-Roberts theorem on the construction of field algebra and the symmetry group in superselection theory
T3  - Preprint / SFB 288, Differentialgeometrie und Quantenphysik
Y1  - 1994
VL  - 134
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Baumgärtel, Hellmut
T1  - On Haag dual nets over compact spaces
Y1  - 1995
ER  -