# AQFT Seminar

Date: every Wednesday 15:00-16:00 (unless stated otherwise)

Venue: HIM lecture hall, Poppelsdorfer Allee 45

Organizer: Wojciech Dybalski

Friday, October 5, 15:00-16:00

Wojciech Dybalski (TU-Munich): Scattering in algebraic quantum field theory

Abstract: I will recall the framework of algebraic quantum field theory and explain how to identify states describing configurations of several particles among all the physical states in this setting. Next, I will discuss recent results concerning the opposite problem: Given an arbitrary physical state, how to extract its particle content?

Wednesday, October 10, 15:00-16:00

Alessandro Pizzo (UC Davis): Coulomb scattering in the massless Nelson model. Foundations of two-electron scattering and regularity of ground-states

Abstract:We construct two-electron scattering states in the infrared-regular massless Nelson model along the lines of Haag-Ruelle scattering theory. In order to remove the infrared cut-off, we need detailed information about the dependence of the ground states of the fiber Hamiltonians on the total momentum. This information is obtained with the help of the iterative analytic perturbation theory. This is a joint work with Wojciech Dybalski.

Wednesday, October 17, 15:00-16:00

Yoh Tanimoto: An introduction to von Neumann algebras

Abstract: The talk will be intended for those people not in our AQFT group. I recall the basics of functional analysis (operator norm, operator topologies) and present fundamental results (double commutant theorem, type classification) in von Neumann algebras.

Wednesday, October 24, 15:00-16:00

Jan Schlemmer: Quantum Field Theory on curved spacetimes I

Wednesday, October 31, 15:00-16:00

Jan Schlemmer: Quantum Field Theory on curved spacetimes II

Wednesday, November 7, 15:00-16.00

Yoh Tanimoto: Particles in CFT are free

Thursday, November 15, 11:00 - 12:00

Giuseppe Ruzzi: Causal posets, loops and the construction of nets of local algebras for QFT

Abstract: We introduce a model-independent construction of a net of C*-algebras (called the net of causal loops) satisfying the Haag-Kastler axioms over any spacetime. We show, for the MInkowski spacetime, the existence of PoincarĂ¨ covariant representations satisfying the spectrum condition. We point out a class of representations of this net admitting a geometrical interpretation in terms of causal and covariant connections of the poset K. For this class of representations a natural notion of a gauge transformation is discussed. Finally, we point out the relation between these representations and the quantum free electromagnetic field.

The talk is based on two joint works with F. Ciolli and E. Vasselli.

Wednesday, November 21, 15:00-16:00

Daniela Cadamuro (Univ. York): Locality in integrable QFTs - characterization and explicit examples

Abstract: In quantum field theory, the construction of local observables in the presence of nontrivial interaction is a difficult task due to their complicated structure. In a class of integrable quantum field theories, we give an explicit characterization of these local observables using the properties of the coefficient functions in an expansion by interacting creators and annihilators. Some results on the operator domains of these local observables are given. Using these, we constructed explicit examples of local observables in the quantum Ising model.

Wednesday, December 5, 10:00-11:00

Michal Wrochna (Univ. Goettingen): Construction of Hadamard states by pseudo-differential calculus

Abstract: In QFT on curved space-times, the best candidates for a replacement of the vacuum state are the so-called Hadamard states. I will show a new construction of Hadamard states, based on pseudo-differential calculus (joint work with Christian Gerard). On a class of space-times whose metric is well-behaved at spatial infinity, I will show how to construct all pure Hadamard states and characterize the symplectic transformations which preserve the Hadamard condition. This ways, one obtains a group which describes the ambiguity in choosing a state.

Wednesday, December 12, 10:00-11:00

Marcel Bischoff (Univ. Goettingen): Characterization of 2D conformal quantum field theories and their boundary conditions

Abstract: In this talk we give some introduction to the operator algebraic framework to conformal quantum field theory (conformal nets) and its relations to the theory of subfactors. We try to give a characterization of conformal nets B on 2D Minkowski space M extending a given (completely rational) chiral conformal net A and its conformal boundary conditions, i.e. all conformal nets on Minkowski half-plane M_{+} locally isomorphic to the restriction of B to M_{+}.