In addition to the Vienna
relativity seminars, the calendar above sometimes contains other events of interest
to members of the relativity group. The seminars of the Vienna relativity group
are listed below.

Unless explicitly stated otherwise, the regular (not-lunch) relativity seminars
take place in Room 218
**2nd floor, Währingerstrasse 17.**

The Mathematical Physics Seminars take place on Tuesdays at 14.15.

The Particle Physics Seminars take place on Tuesdays at 16.15.

- Wednesday,
**May 24, 12:00,**lunch seminar, Ehsan Hatefi (TU Vienna):*Black hole formation and Critical Collapse in the Axion- Dilaton System in Diverse Dimensions*

Abstract: In the first part of the talk we try to come up with some basic notions about the subject as well as Black hole formation, explaining some details of the whole subject on GR and also why we have three different assumptions or ans\"atze for axion-dilaton system in type IIB String Theory. We then would like to study the gravitational collapse of the axion-dilaton system suggested by IIB in dimensions ranging from four to ten. We would also like to extend the previous analysis in the literature concerning the role played by the global
SL(2, R) symmetry, evaluating the Choptuik exponents for different elliptic, parabolic and hyperbolic cases. Eventually we describe some of the open questions for two other assumptions and future directions. This talk is based on arXiv:1108.0078 (published in CQG) and 1307.1378,gr ( published in JCAP) in collaboration with my former supervisor Prof. Luis.Alvarez-Gaume and some works in
progress.

- Wednesday,
**June 7**, lunch seminar, 13:00, Philipp Stanzer (TU Vienna):*The quantum null energy conjecture*

Abstract:
The interest in the quantum null energy condition (QNEC), introduced by Bousso et al in 2015 is twofold: on the one hand, classical energy conditions can be violated in quantum theories, whereas QNEC is conjectured to hold in classical and quantum theories. On the other hand, there exist two proofs for QNEC, one for free field theories and one for quantum field theories with a holographic gravity dual. I review the holographic proof, which relies on geometric properties of Anti-de Sitter, and point out possible loopholes (at least in our understanding of the proof). In the end I will show our numerical holographic setup and results from gravitational shock wave collisions that not only violate the null energy condition but appear to violate also
QNEC."

- Thursday,
**June 8**, 14:00, Wolfgang Graf (Vienna):*Circular Geodesics in Time-Dependent Spacetimes*

Abstract:
A notion of "circularity" is proposed in geometric terms based on symmetry considerations. The main geometric object turns out to be closely related to the extrinsic curvature of the family of hypersurfaces defined by constant angular momentum. The solution of the geodesic equation in this setting can then be reduced to a single 2nd-order pde involving the mean curvature of these hypersurfaces. Their stability against linear perturbations can be reduced to a system of two odes having the structure of a damped harmonic oscillator. Even in the very well-known setting of time-independent spacetimes, this angular-momentum based approach has some advantages over the more conventional one based on an effective potential. However its true potential lies in a time-dependent setting, where the conventional approach cannot be applied. Some examples are
given.

- Friday,
**June 9**, lunch seminar, 13:00, Manfried Faber (Vienna):*About the influence of gravitational waves on circular moving topological solitons with long range interaction*

Abstract:
The majority of physicists wants to quantize gravity. To unify gravity and particle physics there is another possibility, a geometrization of particle physics. We will present some ideas in this direction. I will give some short overview on a simple model of rotating Dreibeins. This model has four types of stable topological solitons differing in two topological quantum numbers which we identify with electric charge and spin. The vacuum has a two-dimensional degeneracy leading to two types of massless excitations, characterised by a topological quantum number which could have a physical equivalent in the photon number.
Inspired by the silicon oil drop experiment of Yves Couder we follow the idea that a subquantum medium could influence classical solitons on their path and lead to quantum mechanics. Under this point of view we investigate the influence of a gravitational wave background on particles in circular
motion.
Based on joint work with Martin Suda.

- Monday,
**June 12**, pre-lunch seminar, 11:00, Paul Klinger (Vienna):*On nonexistence of continuous extensions of Lorentzian manifolds*

Abstract:
TBA

- Wednesday,
**June 14**, lunch seminar, 12:00, Sebastian Szybka (Cracow):*Linear perturbations of the near horizon extremal Kerr geometry*

Abstract: We show nonexistence of non-trivial solutions of the
linearised near-horizon equations
at the Kerr metric.

- Thursday,
**June 22**, 14:00, Carla Cederbaum (Tuebingen):*On extensions of CMC-Bartnik data*

Abstract:
Bartnik data are a Riemannian 2-sphere of positive Gaussian curvature equipped with a non-negative function H to be thought of as its mean curvature in an ambient Riemannian 3-manifold. Mantoulidis and Schoen suggested a construction of asymptotically flat Riemannian 3-manifolds of non-negative scalar curvature which allow to isometrically embed given Bartnik data of vanishing mean curvature, i.e. H=0. They use their construction to explore — and disprove — stability of the Riemannian Penrose inequality. We adapt their construction to constant mean curvature (CMC) Bartnik data, i.e. H=const.>0. I will present the construction as well as the motivation for such a construction which is related to Bartnik’s quasi-local capacity/mass functional and its minimizing
properties.
This is joint work with Armando Cabrera Pacheco, Stephen McCormick, and Pengzi
Miao.

- Thursday,
**TBA**, 14:00, Michael Eichmair (Vienna):*TBA*

Abstract:
TBA

Location (unless indicated otherwise): Währinger Str. 17

- Room 218
on the 2nd floor for **standard seminars**, and

- Common room, first floor, for **lunch seminars**.

Gravitational Physics

Faculty of Physics

University of Vienna

Boltzmanngasse 5

1090 Wien

T: +43-1-4277-51501

F: +43-1-4277-9515

Faculty of Physics

University of Vienna

Boltzmanngasse 5

1090 Wien

T: +43-1-4277-51501

F: +43-1-4277-9515