@article{Baumgaertel2004,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Lax-phillips evolutions in quantum mechanics and two-space scattering},
  issn      = {0034-4877},
  year      = {2004},
  language  = {en}
}
@article{Baumgaertel2004,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Lax-phillips evolutions in quantum mechanics and two-space scattering},
  issn      = {0034-4877},
  year      = {2004},
  language  = {en}
}
@book{Baumgaertel1994,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {A modified approach to the Doplicher-Roberts theorem on the construction of field algebra and the symmetry group in superselection theory},
  series = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  volume    = {134},
  journal   = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  address   = {Berlin},
  pages     = {33 S.},
  year      = {1994},
  language  = {en}
}
@article{Baumgaertel2006,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Generalized eigenvectors for resonances in the Friedrichs model and their associated Gamov vectors},
  issn      = {0129-055X},
  doi       = {10.1142/S0129055X06002589},
  year      = {2006},
  abstract  = {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},
  language  = {en}
}
@book{Baumgaertel1995,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Operatoralgebraic methods in quantum field theory : a series of lectures},
  publisher = {Akademie Verl.},
  address   = {Berlin},
  pages     = {228 S.},
  year      = {1995},
  language  = {en}
}
@article{Baumgaertel1995,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Fourier transformation of Hilbert C*-systems, with compact groups, by their regular representation},
  year      = {1995},
  language  = {en}
}
@article{Baumgaertel1995,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {On Haag dual nets over compact spaces},
  year      = {1995},
  language  = {en}
}
@book{Baumgaertel1993,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Some operatoralgebraic fundamentals of the algebraic quantum field theory},
  series = {Preprint / Universit{\"a}t Potsdam, Fachbereich Mathematik},
  volume    = {1993, 09},
  journal   = {Preprint / Universit{\"a}t Potsdam, Fachbereich Mathematik},
  publisher = {Univ.},
  address   = {Potsdam},
  pages     = {43 Bl.},
  year      = {1993},
  language  = {en}
}
@book{Baumgaertel1993,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Operatoralgebren und Quantenfeldtheorie},
  series = {Preprint / Universit{\"a}t Potsdam, Fachbereich Mathematik},
  volume    = {1993, 12},
  journal   = {Preprint / Universit{\"a}t Potsdam, Fachbereich Mathematik},
  publisher = {Univ.},
  address   = {Potsdam},
  pages     = {11 Bl.},
  year      = {1993},
  language  = {de}
}
@book{Baumgaertel1997,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {{\"U}ber Superauswahlstrukturen und deren Eichgruppen},
  series = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  volume    = {1997, 06},
  journal   = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  publisher = {Univ.},
  address   = {Potsdam},
  pages     = {13 Bl.},
  year      = {1997},
  language  = {de}
}
@book{Baumgaertel1997,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Betrachtungen zur kulturellen Dimension der Mathematik},
  series = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  volume    = {1997, 15},
  journal   = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  publisher = {Univ.},
  address   = {Potsdam},
  pages     = {17 S.},
  year      = {1997},
  language  = {de}
}
@article{Baumgaertel1997,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {A modified approach to the Doplicher-Roberts theorem on the construction of the field algebra and the symmetry group in superselection theory},
  year      = {1997},
  language  = {en}
}
@article{Baumgaertel1998,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Erhard Schmidt, John von Neumann},
  isbn      = {3-7643-5943- 9},
  year      = {1998},
  language  = {de}
}
@article{Baumgaertel1993,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Laudatio Hans Kaiser},
  year      = {1993},
  language  = {de}
}
@article{Baumgaertel2011,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {A Characteristic decay semigroup for the resonances of trace class perturbations with analyticity conditions of semibounded hamiltonians},
  series = {International journal of theoretical physic},
  volume    = {50},
  journal   = {International journal of theoretical physic},
  number    = {7},
  publisher = {Springer},
  address   = {New York},
  issn      = {0020-7748},
  doi       = {10.1007/s10773-010-0533-9},
  pages     = {2002 -- 2008},
  year      = {2011},
  abstract  = {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.},
  language  = {en}
}
@article{Baumgaertel2012,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {On a critical radiation density in the Friedmann equation},
  series = {Journal of mathematical physics},
  volume    = {53},
  journal   = {Journal of mathematical physics},
  number    = {12},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0022-2488},
  doi       = {10.1063/1.4771668},
  pages     = {9},
  year      = {2012},
  abstract  = {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.},
  language  = {en}
}
@article{Baumgaertel2001,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {An Application of the DR-Duality Theory for Compact Groups to Endomorphism Categories of C*-Algebras with Nontrivial Center},
  year      = {2001},
  language  = {en}
}
@article{Baumgaertel2000,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Dual actions on C*-algebras and Hilbert extensions},
  year      = {2000},
  language  = {en}
}
@article{Baumgaertel2000,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {On a theorem of Ashtekar and Lewandowski in the mathematical framework of canonical quantization in quantum gravity},
  year      = {2000},
  language  = {en}
}
@book{Baumgaertel1999,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Cuntz algebras and superselection structures in Quantum Field Theory},
  series = {LQP Papers / Local Quantum Physics Crossroads},
  journal   = {LQP Papers / Local Quantum Physics Crossroads},
  publisher = {Univ.},
  address   = {G{\"o}ttingen},
  year      = {1999},
  language  = {en}
}
@article{Baumgaertel1999,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {On a theorem of Ashtekar and Lewandowski},
  isbn      = {981-023627-1},
  year      = {1999},
  language  = {en}
}
@article{Baumgaertel1999,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {An inverse problem for superselection structures on C*-algebras with nontrivial center},
  year      = {1999},
  language  = {en}
}
@book{Baumgaertel1999,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Actions of finite abelian groups on abelian C*-algebras Z: Second cohomology and description by C*-extensions F ) Z},
  series = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  volume    = {383},
  journal   = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  address   = {Berlin},
  year      = {1999},
  language  = {en}
}
@book{Baumgaertel1999,
  author    = {Baumg{\"a}rtel, Hellmut},
  title     = {Group actions on C*-algebras and their description by Hilbert C*-extensions},
  series = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  volume    = {385},
  journal   = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  address   = {Berlin},
  year      = {1999},
  language  = {en}
}
@article{BaumgaertelCarey2001,
  author    = {Baumg{\"a}rtel, Hellmut and Carey, A.},
  title     = {Hilbert systems for actions of the circle group},
  year      = {2001},
  language  = {en}
}
@book{BaumgaertelCarey2000,
  author    = {Baumg{\"a}rtel, Hellmut and Carey, A.},
  title     = {Hilbert systems for actions of the circle group},
  series = {ESI-Preprint / Erwin-Schr{\"o}der-Institut f{\"u}r Mathematische Physik, Wien},
  volume    = {940, 2000},
  journal   = {ESI-Preprint / Erwin-Schr{\"o}der-Institut f{\"u}r Mathematische Physik, Wien},
  publisher = {Erwin-Schr{\"o}der-Institut f{\"u}r Mathematische Physik},
  address   = {Wien},
  pages     = {14 S.},
  year      = {2000},
  language  = {en}
}
@article{BaumgaertelJurkeLledo2002,
  author    = {Baumg{\"a}rtel, Hellmut and Jurke, Matthias and Lled{\´o}, Fernando},
  title     = {Twisted duality for the CAR-algebra},
  year      = {2002},
  language  = {en}
}
@book{BaumgaertelJurkeLledo1995,
  author    = {Baumg{\"a}rtel, Hellmut and Jurke, Matthias and Lled{\´o}, Fernando},
  title     = {Symmetrie und Quantentheorie},
  series = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  volume    = {1995, 6},
  journal   = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  publisher = {Univ.},
  address   = {Potsdam},
  year      = {1995},
  language  = {de}
}
@article{BaumgaertelJurkeLledo1995,
  author    = {Baumg{\"a}rtel, Hellmut and Jurke, Matthias and Lled{\´o}, Fernando},
  title     = {On free nets over Minkowski space},
  year      = {1995},
  language  = {en}
}
@book{BaumgaertelJurkeLledo1994,
  author    = {Baumg{\"a}rtel, Hellmut and Jurke, Matthias and Lled{\´o}, Fernando},
  title     = {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, +)},
  series = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  volume    = {120},
  journal   = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  address   = {Berlin},
  year      = {1994},
  language  = {en}
}
@book{BaumgaertelJurkeLledo1994,
  author    = {Baumg{\"a}rtel, Hellmut and Jurke, Matthias and Lled{\´o}, Fernando},
  title     = {Mathematische Strukturen passen auf die Natur : Reflexionen {\"u}ber das Wechselverh{\"a}ltnis von Mathematik und Physik},
  series = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  volume    = {1994, 18},
  journal   = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Mathematik},
  publisher = {Univ.},
  address   = {Potsdam},
  year      = {1994},
  language  = {de}
}
@book{BaumgaertelJurkeLledo1999,
  author    = {Baumg{\"a}rtel, Hellmut and Jurke, Matthias and Lled{\´o}, Fernando},
  title     = {Twisted duality for the CAR-algebra},
  series = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  volume    = {401},
  journal   = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  publisher = {Techn. Univ.},
  address   = {Berlin},
  year      = {1999},
  language  = {en}
}
@article{BaumgaertelLledo2004,
  author    = {Baumg{\"a}rtel, Hellmut and Lledo, Fernando},
  title     = {Duality of compact groups and Hilbert C*-systems for C*-algebras with a nontrivial center},
  issn      = {0129-167X},
  year      = {2004},
  abstract  = {In this paper we present duality theory for compact groups in the case when the C*-algebra A, the fixed point algebra of the corresponding Hilbert C*-system (F, 9), has a nontrivial center Z superset of C1 and the relative commutant satisfies the minimality condition A' boolean AND F = Z, as well as a technical condition called regularity. The abstract characterization of the mentioned Hilbert C*-system is expressed by means of an inclusion of C*- categories T-c < T, where T-c is a suitable DR-category and T a full subcategory of the category of endomorphisms of A. Both categories have the same objects and the arrows of T can be generated from the arrows of T-c and the center Z. A crucial new element that appears in the present analysis is an abelian group C(G), which we call the chain group of G, and that can be constructed from certain equivalence relation defined on (G) over cap, the dual object of G. The chain group, which is isomorphic to the character group of the center of g, determines the action of irreducible endomorphisms of A when restricted to Z. Moreover, C(g) encodes the possibility of defining a symmetry epsilon also for the larger category T of the previous inclusion},
  language  = {en}
}
@article{BaumgaertelLledo1997,
  author    = {Baumg{\"a}rtel, Hellmut and Lled{\´o}, Fernando},
  title     = {Some results on superselection structures for C*-algebras with nontrivial center},
  isbn      = {981-02-3984-X},
  year      = {1997},
  language  = {en}
}
@article{BaumgaertelLledo1997,
  author    = {Baumg{\"a}rtel, Hellmut and Lled{\´o}, Fernando},
  title     = {Superselection structures for C*-algebras with nontrivial center},
  year      = {1997},
  language  = {en}
}
@book{BaumgaertelLledo2000,
  author    = {Baumg{\"a}rtel, Hellmut and Lled{\´o}, Fernando},
  title     = {Dual group actions on C*-algebras and their description by Hilbert extensions},
  series = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  volume    = {445},
  journal   = {Preprint / SFB 288, Differentialgeometrie und Quantenphysik},
  publisher = {Techn. Univ.},
  address   = {Berlin},
  pages     = {14 S.},
  year      = {2000},
  language  = {en}
}