**Organizer:** Faculty of Physics, Belgrade

**Time: **Friday, 25 February 2022 at 11:00 Belgrade/CET

**Courant algebroids in bosonic string theory**

**Ilija Ivanisevic **(Institute of Physics, Belgrade)

**Link:** via the BigBlueButton platform, **https://gravityserver.ipb.ac.rs/b/mar-xoo-t1v-vwn**

**Abstract:** We analyze bosonic string symmetry transformations and their relations with T-duality in the framework of generalized geometry. The generator governing symmetry transformations can be described simply as the inner product of generalized vectors and its algebra produces the Courant bracket as the T-dual invariant extension of the Lie bracket, while T-duality can be interpreted as an isomorphism between Courant algebroids. We show how different O(D, D) transformations give rise to different twists of the Courant bracket that feature string theory relevant fluxes.

arXiv:1903.04832, arXiv:2010.10662, arXiv:2103.09585, arXiv:2202.03227,

**Organizer:** Faculty of Physics, Belgrade

**Time: **Friday, 4 February 2022 at 11:00 Belgrade/CET

**Phase transitions in matrix models on the truncated Heisenberg space**

**Dragan Prekrat** (Faculty of Physics, University of Belgrade)

**Link:** via the BigBlueButton platform, **https://gravityserver.ipb.ac.rs/b/mar-xoo-t1v-vwn** (in Serbian)

**Abstract:** The important generic problem with QFTs on noncommutative spaces is the UV/IR mixing of divergences which interferes with their renormalization. The Grosse-Wulkenhaar model solved this problem by introducing a harmonic oscillator term that can be interpreted as a coupling between the curvature and the field. In this talk, we will examine the success of this model from the phase transition point of view. We will show that renormalizable and nonrenormalizable versions of the 2D noncommutative phi4 model have different phase diagrams. We will also consider the implications of the striped-phase shifting on the renormalization properties of other models.

arXiv:2104.00657 [hep-th], arXiv:2002.05704 [hep-th]

**Organizer:** Faculty of Physics, Belgrade

**Time: **Friday, 19 November 2021, 12:00 Belgrade/CET

**Black hole entropy and the information loss paradox**

** Voja Radovanovic** (Faculty of Physics, University of Belgrade)

**Link:** via the BigBlueButton platform, **https://gravityserver.ipb.ac.rs/b/mar-xoo-t1v-vwn**

**Abstract:** The most important unsolved problem in black hole physics is the information loss paradox, i.e. whether the process of formation and evaporation of a black hole is unitary in accordance with quantum mechanics. The unitarity implies that von Neumann entropy of the Hawking radiation should initially increase but subsequently fall back down, following the so-called Page curve.

In the first talk of this series we consider black hole thermodynamics and discuss various concepts of entropy: fine-grained, coarse-grained and entanglement entropy. In addition, we calculate entanglement entropy for Rindler observer and show how to generalize this result to curved space-time, where it is used to define generalized entropy of a black hole.

The upcoming talks will be devoted to the so-called wormhole replica trick and the notion of an island – a kind of a quantum extremal surface recently advocated by Maldacena. We study a particular case of 2D dilaton gravity obtained by dimensional reduction of the Einstein-Hilbert action for Schwarzschild metric. We calculate the von Neumann entropy of the Hawking radiation and reproduce the Page curve.

**Time:** Friday, 5 November 2021, 11:00 Belgrade/CET

**Conformal bootstrap – a non-perturbative approach to conformal field theories**

**Ilija Buric**** (Department of Physics, University of Pisa)**

**Link:** via the BigBlueButton platform, **https://gravityserver.ipb.ac.rs/b/mar-xoo-t1v-vwn**

**Abstract: **Conformal bootstrap is a collection of methods for the study of conformal field theories, which are based on minimal assumptions such as unitarity and self-consistency. After reviewing the basic structure of conformal field theories, I will illustrate some of these methods on one numerical and one analytic example.