Theoretical Physics @ UMONS – Collaboration meeting

Schedule

Titles and abstracts

Glenn Barnich | Memory of Robinson-Trautman waves

Abstract: The memory effect for Robinson-Trautman waves is explicitly worked out. In a first step, we construct the combined frame rotation and coordinate transformation in which Robinson-Trautman waves are manifestly locally asymptotically flat at future null infinity. This allows us to apply well-established results on how to derive the memory effect in this context. In a second step, we construct a suitably improved generalized mass aspect that provides a local Lyapunov function for the flow in the sense that it is manifestly positive. News-free solutions are studied in detail and shown to coincide with the vacuum sector of Euclidean Liouville theory. They correspond to a boosted and rescaled Schwarzschild black hole. As a by-product, we show that the displacement and non-linear memory effects in locally asymptotically flat spacetimes at future null infinity are invariant under supertranslations and covariant under $mathrm{BMS}_4$ Lorentz transformations and constant rescalings. A novel interpretation of modified flows that control the low harmonics in terms of keeping the system in its instantaneous rest frame is provided.

Pierre Bieliavsky | Twist, twist again

Abstract: I will review the notion of Drinfel’d twist as a deformation quantization machinery, and discuss the corresponding  notion of quantum groups.

Fabien Buisseret | Higher derivative mechanics and motor control: A hidden love story
Abstract: Optimal Feedback Control provides a theoretical framework for goal-directed movements, where the nervous system adjusts actions based on sensory feedback. This theory assumes that there exists a “cost function” that is optimized throughout one’s movement. It is natural to assume that mechanical quantities should be involved in cost functions, but this does not imply that the mechanical principles that govern human voluntary movements are necessarily Newtonian. We first show how integrating principles from Lagrangian and Hamiltonian higher-derivative mechanics provides a more natural framework to study the constraints hidden in human voluntary movement within Optimal Feedback Control theory. Then, we show how a Pais-Uhlenbeck oscillator can model pointing tasks though the analysis of head-rotation kinematics.

Andrea Campoleoni | Hints for higher-spin holography in flat space
Abstract: Despite the difficulties in defining interacting theories for higher-spin gauge fields in flat space, many of the building blocks of higher-spin holography in anti-de Sitter space admit a smooth flat-space limit. This suggests the possibility of reconstructing the bulk theory holographically starting from a Carrollian analogue of the O(N) vector model. I will review the properties of Carrollian scalars suggesting a holographic reformulation, highlighting their connections to higher-spin gauge fields in Minkowski spacetime.

Maxim Grigoriev | Gauge theories with asymptotic boundaries in the gauge PDE approach

Abstract: We study boundary structure of asymptotically AdS gravity and (gauge) fields defined on this background by employing the gauge PDE approach. The essential step of the construction is the incorporation of the boundary-defining function among the fields of the theory, which allows us to realise the asymptotic boundary as a space-time submanifold by employing the gauge PDE implementation of Penrose’s concept of asymptotically-simple space. In so doing the gauge PDE describing the boundary structure is obtained by restricting to the boundary of spacetime and simultaneously restricting to the boundary of the field space by setting the boundary defining function to zero.  To implement this step systematically we introduce a notion of $Q$-boundary which seems to be new. The approach is very general and, in principle, applies to generic (gauge) fields on the Einstein gravity background,  producing a conformally-invariant gauge theory on the boundary, which  describes their boundary structure. It can be considered as an extension of the Fefferman-Graham construction that takes into account both the leading and the subleading sector of the bulk fields.

Evgeny Skvortsov | Self-dual holography

Abstract: I will review the recent results on charting out the space of self-dual theories, which leads to new problems in deformation quantization and number theory. I will also discuss the place of these theories in AdS/CFT and celestial holography.