Mathematical Physics Seminars 2017-2018

  Monday 15 January 2018, 14:00, room 114

Aldo Riello (Perimeter Institute, Waterloo) : 3D quantum gravity on the edge

I will present recent results in the understanding of the theories emerging at the boundary of three dimensional quantum gravity when the induced quantum metric is fixed on the boundary. This is done in a fully non perturbative context, where the gravitational degrees of freedom are fully quantized. According to “how quantum” the boundary metric is, different boundary theories will be seen emerging. After a general introduction, I will focus on two extreme cases, those presently best understood. I will start by discussing the case of deeply quantum boundary metrics where a duality with an isotropic Heisenberg chain emerges. Then, time allowing, I will shift attention to the other end of the spectrum, by introducing a semiclassical state on the torus and hence by discussing how this state encodes a purely boundary theory from which not only the bulk classical geometry can be reconstructed, but also — in an appropriate continuum limit — field theoretic bulk calculations at 1-loop can be reproduced.

  Friday 8 December 2017, 14:00, room 114

Swapnamay Mondal and Nick Halmagyi (LPTHE, Paris) : Tensor Models for Black Hole Probes

We will describe a series of models where tensors of different degrees are coupled together and solved in the large N limit analytically. The 3-tensor model has been shown to be related to the SYK model in the large-N limit and thus the physics of the near horizon of black hole. Our extension of the relationship allows us to explore the physics of probes in these black hole backgrounds.

  Friday 17 November 2017, 14:00, room 114

Goffredo Chirco (AEI, Potsdam) : Holographic entanglement entropy from random tensor networks via group field theory

We investigate the use of tensor networks techniques and quantum information theory for the study of the entanglement properties of quantum geometry states. In the language of the group field theory, we describe spin network states as quantum many-body systems. The very connectivity of such states, encoded in the links of the underlying graphs, is associated with the entanglement between the fundamental quanta constituting them. We establish a dictionary between group field theory states and (generalised) random tensor networks. With such a dictionary at hand, we target the calculation of the Ryu-Takayanagi formula for the entanglement entropy in the quantum gravity formalism of group field theory.

  Wednesday 15 November 2017, 14:00, room 114

Rina Štrajn, Ruđer Bošković Institute, Division of Theoretical Physics, Zagreb (Croatia)

The construction of differential algebras related to the $\kappa$-Minkowski space is discussed. We find that, requiring the differential calculus to be compatible with the $\kappa$-Poincar\’e-Hopf algebra, it is in general necessary to introduce an additional generator, which we can interpret as the exterior derivative. For the case of light-like deformations, the bicovariant differential calculus is of classical dimension. Furthermore, a classification of all bicovariant differential calculi of classical dimension is presented and the class corresponding to the special case with an undeformed exterior derivative and one-forms is considered.

  Friday 10 November 2017, 14:00, room 114

Gianluca Calcagni (Inst. Estructura Materia, Madrid) : Detecting quantum gravity in the sky : Status of multifractional theories

We review recent advances in the general theory of multiscale spacetimes arising in quantum gravity, in particular about universal predictions on the running of the spacetime dimension and the emergence of a discrete scale invariance at microscopic scales. The experimental status of a specific class of proposals, called multifractional theories, is also reviewed.