Seminar of Theory of Relativity and Gravitation
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2021-11-05 (Friday)
join us at 11:15 
Philipp Hoehn (OIST and University College London)Progress in relational quantum dynamics
The problem of time is a notorious conundrum arising in generally covariantquantum theories. In this talk, I will describe progress on several aspects of the problemof time discussed by Isham and Kuchar in their classic reviews 30 years ago. This will include(i) establishing the equivalence of three approaches to relational dynamics (relational observables,Page-Wootters formalism and deparametrizations), (ii) addressing the multiple-choice problem(non-uniqueness of the clock choice), (iii) addressing the global problem (absence of monotonicclocks), (iv) elucidating how to sidestep Unruh's and Wald's claim that realistic quantum clockshave non-vanishing probability to run backwards, and (v) resolving Kuchar's three criticismsagainst the Page-Wootters formalism. Time permitting, I will also summarize how one cangeneralize these insights to quantum reference frames for general symmetry groups (i.e. notonly temporal reference frames).
2021-10-29 (Friday)
room 1.40, Pasteura 5 at 11:15
Andrzej Dragan (IFT UW)Quantum principle of relativity
We show that the local and deterministic mode of description is not only in conflict with the quantum theory, but also with relativity. We argue that elementary relativistic properties of spacetime lead to the emergence of a non-deterministic quantum-mechanical picture involving quantum superpositions and complex probability amplitudes.
2021-10-22 (Friday)
room 1.40, Pasteura 5 at 11:15
Paweł Caputa (IFT UW)Geometry of Krylov Complexity
In this talk I will describe the notion of the operator growth and Krylov complexity. In particular, I will discuss its geometric interpretation and possible applications to holographic CFTs. This talk will be based on: arXiv:2109.03824 [hep-th].
2021-10-15 (Friday)
room 1.40, Pasteura 5 at 11:15
Patryk Mach (UJ)Models of self-gravitating disks around black holes
I will discuss recent results in modeling of self-gravitating stationarydisks (tori) around black holes. These models include both magnetized andunmagnetized disks with polytropic or realistic equations of state. From thetechnical point of view, modeling of black hole-disk systems amounts to solving a set of Einstein equations coupled with the equations of general-relativistic (magneto)hydrodynamics. There is an interesting structure of the space of solutions, revealing classic nonlinear phenomena---nonuniqueness of solutions and bifurcations. In some cases, these phenomena can be explained as related to the changes in the spacetime geometry. The talk will be based on series of works, including: PRD 99, 104063 (2019), PRD 101, 044036 (2020), PRD 104, 024005 (2021), and PRD 104, 044058 (2021).
2021-10-08 (Friday)
room 1.40, Pasteura 5 at 11:15
Arman Taghavi-Chabert (IFT UW)Conformal and CR methods in general relativity
This talk is an overview of the research topics that form the basis of the POLS fellowship I have recently been awarded by the National Science Centre. I will start with an introduction of the fellowship including its nature, its aims and structure, together with a summary of my research career to date. I will then review the mathematical developments arising from the study of non-shearing congruences of null geodesics, which played a central role during the Golden Age of Relativity, and which would later shape many geometrical ideas, notably in connection with spinors, conformal and complex geometries. I will also cover a survey of more recent results in the field including generalisations to higher dimensions, thereby providing a motivation for the objectives of the POLS fellowship.