Seminar talks in the winter term 2017/18

Schedule for the winter term 2017/18:

Date Speaker Title (hover/click for abstract)
09.10. no seminar
16.10. Sebastian Drawert (ITP)
23.10. no seminar
30.10. no seminar
06.11. Thomas-Paul Hack (ITP)
13.11. no seminar
20.11. Daniela Cadamuro (TU Munich)
27.11. no seminar
04.12. Glenn Barnich (Brussels)
07.12. Chris Fewster (York)
11.12. Johannes Huebschmann (Lille)
18.12. Pawel Duch (Cracow)
08.01. no seminar
18.01. Nicola Pinamonti (Genova)
22.01. Sebastian Drawert (ITP)
29.01. Stephen Green (Golm)
Abstract: As gravitational waves pass an arrangement of freely falling observers the gravitational memory effect will displace them relative to each other. The Framework in which these processes are studied will be introduced and possible corrections to the displacement tensor originating from spin contributions in the energy-momentum tensor of the entities having produced such bursts of gravitational waves, will be motivated.
Abstract: Non-equilibrium steady states (NESS) describe particularly simple and stationary non-equilibrium situations. A possibility to obtain such states is to consider long-time limits of initial configurations of systems whose dynamics is such that the initial state can not fully equilibrise. An example of such an initial state is the case of two infinite heat baths brought into thermal contact at a two-dimensional surface. The dynamics of such states has been investigated in several models including conformal hydrodynamics and conformal QFT in 1+1 spacetimes dimensions. Here we present results for interacting (scalar) QFT 1+3 spacetimes dimensions. (joint work with R. Verch)
Abstract: The energy density is classically positive, a property that fails to be true in quantum theory. However, if it were indefinitely negative, it might produce macroscopic violations of the second law of Thermodynamics or allow the existence of exotic spacetimes configurations (such as wormholes, time machines and warp drives). Fortunately, lower bounds exist and have been proved for linear fields (free quantum field theory), with few results for interacting models of QFT. After preliminary work in the context of the Ising model and in a large class of scalar integrable models on the level of one-particle states, the proposal aims at showing the existence of lower bounds for local averages of the energy density generally in interacting field theories, establishing a fundamental result for physics.
Abstract: The Bondi mass loss formula has been central in the context of early research on gravitational waves. We show how it can be understood as a particular case of BMS current algebra and discuss the associated central extension.
Abstract: The Coleman-Mandula (CM) theorem states that the Poincare and internal symmetries of a Minkowski spacetime quantum field theory cannot combine nontrivially in an extended symmetry group. In this talk I will describe some of the background to the CM theorem and then establish an analogous result for a general class of quantum field theories in curved spacetimes. Our result is valid in dimensions $n\ge 2$ and for free or interacting theories (whereas the original CM theorem assumes the presence of interaction and has exceptions in $n=2$ dimensions). It makes use of a general analysis of symmetries induced by the action of a group $G$ on the category of spacetimes. Such symmetries are shown to be canonically associated with a cohomology class in the second degree nonabelian cohomology of $G$ with coefficients in the global gauge group of the theory. The main result proves that the cohomology class is trivial if $G$ is the universal cover $S$ of the restricted Lorentz group. Among other consequences, it follows that the extended symmetry group is a direct product of the global gauge group and $S$, all fields transform in multiplets of $S$, fields of different spin do not mix under the extended group, and the occurrence of noninteger spin is controlled by the centre of the global gauge group.
Abstract: For a commutative ring R and a commutative R-algebra A, an (R, A)-Lie algebra is an R- Lie algebra L, together with a structure of mutual interaction between A and L that arises by abstracting from the special case (A,L) = (C∞(M),Vect(M)) where C∞(M) is the algebra of smooth functions and Vect(M) the Lie algebra of smooth vector fields on a smooth manifold M. The pair (A,L) is said to be a Lie-Rinehart algebra. …
Abstract: I will discuss the recent proof of the existence of the weak adiabatic limit in the perturbative quantum field theory in the Minkowski spacetime in the Epstein-Glaser framework. The result applies to a large class of models, which includes all models with interaction vertices of dimension 4, and allows not only to construct the Wightman and Green functions but also prove that they have all the standard properties. In the case of models without vector fields the existence of the weak adiabatic limit can be used to define a vacuum state (a real, normalized, positive, Poincaré-invariant functional) on the algebra of interacting fields constructed by means of the algebraic adiabatic limit.
Abstract: We analyze some properties shown by extremal KMS states for interacting massive scalar fields propagating over Minkowski spacetime. These states have been recently constructed in the framework of perturbative algebraic quantum field theories by Fredenhagen and Lindner. In particular, we discuss the validity of the return to equilibrium property when the interaction Lagrangian has compact spatial support. If the adiabatic limit is considered, the return to equilibrium is in general not valid. This implies that, an equilibrium state under the adiabatic limit for a perturbative interacting theory evolved with the free dynamics does not converge to the free equilibrium state. Actually, we show that the ergodic mean of this state converges to a non-equilibrium steady state (NESS) for the free theory. We thus compute the relative entropy among equilibrium states for different evolutions showing that such an extent is compatible with perturbation theory. We then analyze the entropy production in the NESS discussed above to estimate how far from equilibrium is this state.
Abstract: The aim of this talk is to discusse how the displacement of test masses changes if the spin of sources producing gravitational waves is considered and how this compares to the non spinning case.
Abstract: Observations of gravitational waves from inspiralling neutron star binaries—such as GW170817—can be used to constrain the nuclear equation of state by placing bounds on stellar tidal deformability. For slowly rotating neutron stars, the response to a weak quadrupolar tidal field is characterized by four internal-structure-dependent constants called Love numbers. The tidal Love numbers k^2_{el} and k^2_{mag} measure the tides raised by the gravitoelectric and gravitomagnetic components of the applied field, and the rotational-tidal Love numbers f^o and k^o measure those raised by couplings between the applied field and the neutron star spin. In this work we compute these four Love numbers for perfect fluid neutron stars with realistic equations of state. We discover (nearly) equation-of-state independent relations between the rotational-tidal Love numbers and the moment of inertia, thereby extending the scope of I-Love-Q universality. We find that similar relations hold among the tidal and rotational-tidal Love numbers. These relations extend the applications of I-Love universality in gravitational-wave astronomy.