Data: 22.11.2022
Miejsce: Sala 412 13:30
Temat: Rainbow Oppenheimer-Snyder collapse and the entanglement entropy production
Osoba: Michał Bobula
Opis: I derive a new model of black-to-white hole transition – the classical Oppenheimer-Snyder dust ball interior is modified with Loop Quantum Cosmology dynamics. I consider the rainbow metric approach for both pure dust ball collapse and the similar scenario accounting for scalar field perturbations. The collapsing matter bounces and reemerges in a new universe. Exterior geometry is extracted as well as the global causal structure of the process. I study entanglement entropy production to verify whether the black hole information paradox exists within the model.

Data: 14.11.2022
Miejsce: Sala 412 14:30
Temat: Statistical matter coupled to the (double) geometry
Osoba: Eric Lescano, Ruđer Bošković Institut (Zagreb, Croatia)
Opis: This talk will be about cosmology and string theory and it will have two parts. In the first one we will review the inclusion of statistical matter in Riemannian geometries. Our starting point will be the Einstein equation and we will focus on energy-momentum tensors that depend on hydrodynamics/thermodynamics variables, such as the perfect fluid. We will derive conservation laws considering relativistic kinetic theory. We will finish this part with a quick introduction to the low energy limit of string theory (supergravity) and its Double Field Theory (DFT) rewriting. In the second part of the talk we will include statistical matter in DFT (based on 2003.09588), we will construct the energy-momentum tensor for the perfect fluid in the double geometry (based on 2111.03682) and finally we will discuss about the relation between string cosmologies, DFT cosmologies and alpha’-corrections (based on 2207.04041).

Data: 21.06.2022
Miejsce: Sala 412 14:15
Temat: Yang-Baxter deformations of the flat space string
Osoba: Prof. Khalil Idiab, Humboldt University, Berlin
Opis: Symmetric space sigma models (SSSM) and their Yang-Baxter deformations are integrable, which makes them useful in providing exact results in the AdS/CFT correspondence. Much is known about these integrable models at classical level, but difficulties with quantization makes it hard to make general statements about their quantum integrable structure. By considering deformations of the flat space sigma model, with non semi-simple Poincaré symmetry, it turns out one can find deformed models that can be canonically quantized (plane waves), enabling future investigation of their quantum structure. As a first step, this requires extending Yang-Baxter deformations of SSSMs to cases with non semi-simple symmetry groups, this will be the main objective of the talk.

Data: 07.06.2022
Miejsce: Sala 412 14:15
Temat: Physics from spectral triples with non-product geometries
Osoba: mgr Arkadiusz Bochniak, prof. Andrzej Sitarz (joint talk) (UJ)
Opis: We’ll briefly review the concept of applying the construction of Connes’ spectral triples to the Standard Model and gravity which goes beyond the commonly assumed product of two spectral triples. The application to the SM allows having no fermion doubling, explains naturally CP violation and no strong symmetry breaking while the gravity part leads to interesting models similar to bimetric modifications of gravity.

Data: 14.12.2021
Miejsce: Sala 416 14:15
Temat: Lorentz covariance from discrete symmetries Z2 and Z3
Osoba: Prof. Richard Kerner, Sorbonne, Paris
Opis: Our aim is to derive the symmetries of the space-time, i.e. the Lorentz transformations, from symmetries of the interactions between the most fundamental constituents of matter, in particular quarks and leptons. We show how the discrete symmetries Z_2 and Z_3 combined with the superposition principle result in the SL(2, C) and SU(3) symmetries. The role of Pauli’s exclusion principle in the derivation of the SL(2, C) symmetry is put forward as the source of the macroscopically observed Lorentz symmetry. Then Pauli’s principle is generalized for the case of the Z_3 grading replacing the usual Z_2 grading, leading to ternary commutation relations. We present the cubic and ternary algebras which are a direct generalization of fermionic algebras with Z_3-grading replacing the usual Z_2-grading. Elementary properties and structures of such algebras are discussed, with special interest in the low-dimensional ones, with two generators only. Invariant cubic forms on Z_3-graded algebra with two generators are introduced, a possible description of the isospin. It is shown how a Z_3-graded generalization of the SL(2,C) group arises naturally as the symmetry group preserving the Z_3-graded ternary isospin algebra. Vectorial and spinorial representations of the generalized Z_3-graded. Lorentz algebra are briefly discussed.

Data: 03.03.2020
Miejsce: Sala 416 14:15
Temat: Inflationary potentials from F(R) gravity in a unified hybrid metric-Palatini approach
Osoba: mgr Aleksander Kozak
Opis: A class of scalar-tensor theories that unify metric, Palatini and hybrid metric-Palatini gravitational actions with nonminimal interaction is investigated from the point of view of their consistency with generalized conformal transformations. It is known that such theory can be represented on shell by a purely metric scalar-tensor theory. This extends the formalism previously introduced in our last paper [1]. Exploiting properties of the Legendre transformation, we relate some viable inflationary potentials with F(R)-gravitational Lagrangians by solving corresponding Clairaut’s equation. Then for given potential function various gravitational scenarios are discussed within a metric, Palatini, as well as a hybrid metric-Palatini formulations. [1] A. Kozak and A. Borowiec, „Palatini frames in scalar-tensor theories of gravity”, Eur.Phys.J. C79 (2019) no.4, 335

Data: 28.01.2020
Miejsce: Sala 416 14:15
Temat: Horizon temperature without space-time
Osoba: prof. Michele Arzano
Opis: I will show how the characteristic thermal effects that observers experience in space-times possessing an event horizon, emerge already in a simple quantum system with affine symmetry living on the real line. The derivation I will present is essentially group theoretic in nature: a thermal state emerges naturally when comparing different representations of the group of affine transformations of the real line. The freedom in the choice of different notions of translation generators is the key to the Unruh effect on the real line which I will describe.

Data: 14.01.2020
Miejsce: Sala 412 14:15
Temat: Digital quantum geometries
Osoba: dr Anna Pachoł, Queen Mary University of London
Opis: Noncommutative geometry, as the generalised notion of geometry, allows us to model the quantum gravity effects in an effective description without full knowledge of quantum gravity itself. On a curved space one must use the methods of Riemannian geometry – but in their quantum version, including quantum differentials, quantum metrics and quantum connections. The brief introduction to the general framework involving noncommutative differential graded algebra and construction of quantum Riemannian geometry elements will be provided. This framework has been applied to classification of all possible noncommutative Riemannian geometries in small dimensions (including finding explicit forms for quantum Levi-Civita connections and Riemann, Ricci and Einstein tensors), working over the field F_2 of 2 elements and with coordinate algebras up to dimension n<=3. We have found a rich moduli of examples for n=3 and top form degree 2 (providing a landscape of all reasonable up to 2D quantum geometries), including many which are not flat. Their coordinate algebras are commutative but their differentials are not. The choice of the finite field in this framework proposes a new kind of 'discretisation scheme’, which we called the 'digital geometry’.

Data: 17.12.2019
Miejsce: Sala 416 14:15
Temat: Almost commutative geometry of the Standard Model
Osoba: prof. L. Dąbrowski, SISSA, Trieste, Italy
Opis: By functions on a noncommutative (or `quantum’) space one usually means a suitable algebra of operators. Then the smooth and metric structures can be described in terms of a spectral triple which involves an analogue of the Dirac operator. The Standard Model of fundamental particles in physics can be understood as the almost commutative geometry, the exterior part of which is the canonical spectral triple on a spin manifold and the finite inner part a quantum analogue of the de-Rham-Hodge spectral triple.

Data: 03.12.2019
Miejsce: Sala 416 14:15
Temat: Conformally flat travelling plane wave solutions of Einstein equations
Osoba: prof. Zbigniew Haba
Opis: Einstein equations with a conformally flat metric and ideal fluid source are discussed. It is shown that these equations have plane wave solutions. Scalar fields, electromagnetic plane waves and relativistic particles can be considered as the source of such an energy-momentum.

Data: 19.11.2019
Miejsce: Sala 416 14:15
Temat: Asymptotic Symmetries and Quantum Groups
Osoba: Josua Unger
Opis: In this talk I will discuss the BMS analysis of asymptotically flat spacetime, their algebraic properties and important consequences for black hole physics. The deformation by twisting of the BMS (Hopf-)algebra is presented and motivated in the context of the information loss paradox.

Data: 29.10.2019
Miejsce: Sala 416 14:15
Temat: Gravity as a constrained BF theory
Osoba: prof. Jerzy Kowalski-Glikman
Opis: In my talk I will present the construction of gravity Lagrangian as a sum of the topological term, the BF theory with (anti-) de Sitter gauge group and a 'constraint’ term, explicitly breaking the symmetry down to local Lorentz symmetry. I will then comment on several properties of such defined theory: perturbative expansion around topological vacuum, particle(s) coupling, canonical analysis, and calculation of black hole entropy.

Data: 04.06.2019
Miejsce: Sala 416 14:15
Temat: Nuts approach to the Taub-NUT space-time (Pokręcone podejście do czasoprzestrzeni Tauba-NUT)
Osoba: dr Remigiusz Durka
Opis: I offer new approach to the subject of Taub-NUT space-time supposedly possessing gravitational analog of the magnetic monopole. Starting from realizing that the source of many inconsistencies lies in neglecting the effects of the wire singularities present in that solution, I am able to explain existence of the NUT parameter by the means of quite peculiar rotation. Among many things, this leads to the consistent description of the black hole thermodynamics for the Lorentzian Taub-NUT spacetime with the essential contribution to the angular momentum and the total entropy.

Data: 21.05.2019
Miejsce: Sala 416 14:15
Temat: Celebration of prof. Jerzy Lukierski birthday
Osoba: prof. Jerzy Lukierski
Opis: Our next group seminar on May 21st is going to be devoted to the celebration of prof. Jerzy Lukierski birthday. We are offering short speeches, a bit of wine, some sweets, and a good deal of friendly chats. Everybody is cordially invited.

Data: 07.05.2019
Miejsce: Sala 416 14:15
Temat: BMS Group at Spatial Infinity
Osoba: mgr Lennart Brocki
Opis: In this talk I present a recent publication by Henneaux and Troessaert in which they propose new boundary conditions for asymptotically flat spacetimes at spatial infinity and find that the conserved charges close according to the BMS algebra. Their analysis relies on the Hamiltonian formalism of general relativity and is an extension of the work done by Regge and Teitelboim in 1974, which will therefore also be summarized, and mainly differs in the choice of parity conditions. For a more complete understanding the talk will also cover some basics about the BMS Group.

Data: 16.04.2019
Miejsce: Sala 416 14:15
Temat: BMS Group at Spatial Infinity
Osoba: mgr Lennart Brocki
Opis: In this talk I present a recent publication by Henneaux and Troessaert in which they propose new boundary conditions for asymptotically flat spacetimes at spatial infinity and find that the conserved charges close according to the BMS algebra. Their analysis relies on the Hamiltonian formalism of general relativity and is an extension of the work done by Regge and Teitelboim in 1974, which will therefore also be summarized, and mainly differs in the choice of parity conditions. For a more complete understanding the talk will also cover some basics about the BMS Group.

Data: 02.04.2019
Miejsce: Sala 416 14:15
Temat: Palatini frames in scalar-tensor theories of gravity
Osoba: mgr Aleksander Kozak
Opis: Conformal transformations play an important role in the scalar-tensor theories of gravity, as they allow one to carry out calculations in a more convenient frame, simplifying the field equations. In the Palatini approach, however, the metric structure of space-time is decoupled from its affine structure, so that a transformation of the metric does not entail a corresponding change in the connection. One needs to define independent transformation for the connection, reducing to the standard formula in case the connection is Levi-Civita with respect to the metric. In my presentation, I shall introduce a scalar-tensor theory taking into account such transformation and discuss properties of the solution to the field equation for the connection. I will also introduce invariant quantities, whose functional form remains the same in every conformal frame, and show how they can be applied to analysis of possible equivalence between F(R) and scalar-tensor theories of gravity in the Palatini approach. The main part of the talk will be preceded by a short introduction to metric scalar-tensor theories and conformal transformations.

Data: 19.03.2019
Miejsce: Sala 416 14:15
Temat: Introduction to Loop Quantum Cosmology
Osoba: dr Tomasz Pawłowski
Opis: –

Data: 16.01.2018
Miejsce: Sala 445 14:15
Temat: Fenomenology of quantum general relativity: idea, difficoulties and possible predictions
Osoba: dr Jakub Bilski
Opis: During the seminar I will briefly introduce my idea of a canonical quantization under restrictions of general relativity. First I will show how a proper choice of canonical variables leads to the manifestly diffeomorphism invariant description of a quantum field. Next I will present a list of assumptions and simplifications that I will use in direct calculations. Then I will sketch the main steps in the derivation of quantum corrections coming from the gravitational degrees of freedom on the example of the scalar field. Discussing phenomenological applications of my result, I will consider possibilities of proving the assumptions and generalizing the simplifications from the first part of my talk.