**Seminars for the year:**
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**Time: ** 27. December 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Rodrigo Olea

**Title: ** On renormalized AdS action and Critical Gravity

**Abstract:**

It can be shown that the renormalized action for AdS gravity in even spacetime dimensions is equivalent --on shell-- to a polynomial of the Weyl tensor, whose first non-vanishing term is Weyl^2. Remarkably enough, the coupling of this last term coincides with the one that appears in Critical Gravity.

**Time: ** 20. December 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Luka Nenadovic

**Title: ** Illustration of de Rham theorem and examples of fiber bundles II

**Abstract:**

Our aim is to make an intuitive picture of the isomorphism between simplicial homology and de Rham cohomology using several examples, calculating Euler characteristic and counting Betti numbers for simple topological spaces. The notion of fiber bundle will be illustrated by examples of tangent and vector bundles as well as Hopff fibration. If time allows, we can further discuss some aspects and consequences of nontrivial topology (Chern class, index theorems, magnetic monopoles) or alternatively the Dolbeault cohomology (cohomology of complex manifolds, Hodge numbers).

**Time: ** 13. December 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Luka Nenadovic

**Title: ** Illustration of de Rham theorem and examples of fiber bundles I

**Abstract:**

Our aim is to make an intuitive picture of the isomorphism between simplicial homology and de Rham cohomology using several examples, calculating Euler characteristic and counting Betti numbers for simple topological spaces. The notion of fiber bundle will be illustrated by examples of tangent and vector bundles as well as Hopff fibration. If time allows, we can further discuss some aspects and consequences of nontrivial topology (Chern class, index theorems, magnetic monopoles) or alternatively the Dolbeault cohomology (cohomology of complex manifolds, Hodge numbers).

**Time: ** 6. December 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Paolo Aschieri

**Title: ** Geometry of gauge fields 3: Differential geometry of bundles --- connections and curvatures

**Abstract:**

We will start from physical considerations regarding the motion of a quantum particle in a magnetic field background, and see how consistency of the system requires the flux of the magnetic field to be integer valued. The geometric structure underlying this integrality condition is that of a principal U(1) bundle. We will then describe (nonabelian) vector bundles and principal bundles from a local perspective (transition functions) and a global one. Their differential geometry is that of gauge fields.

**Time: ** 5. December 2013, 15:00h

**Place: ** Faculty of Physics, room 750

**Speaker: ** Paolo Aschieri

**Title: ** Geometry of gauge fields 2: Vector bundles and principal bundles

**Abstract:**

We will start from physical considerations regarding the motion of a quantum particle in a magnetic field background, and see how consistency of the system requires the flux of the magnetic field to be integer valued. The geometric structure underlying this integrality condition is that of a principal U(1) bundle. We will then describe (nonabelian) vector bundles and principal bundles from a local perspective (transition functions) and a global one. Their differential geometry is that of gauge fields.

**Time: ** 4. December 2013, 13:00h

**Place: ** Faculty of Physics, room 661

**Speaker: ** Paolo Aschieri

**Title: ** Geometry of gauge fields 1: Electromagnetism in Quantum Theory and Dirac Charge Quantization

**Abstract:**

We will start from physical considerations regarding the motion of a quantum particle in a magnetic field background, and see how consistency of the system requires the flux of the magnetic field to be integer valued. The geometric structure underlying this integrality condition is that of a principal U(1) bundle. We will then describe (nonabelian) vector bundles and principal bundles from a local perspective (transition functions) and a global one. Their differential geometry is that of gauge fields.

**Time: ** 25. October 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Carlo Nicola Colacuno

**Title: ** The Stochastic Gravitational-Wave Background (SGWB): theory and detection issues

**Abstract:**

The SGWB is the most elusive and most mysterious source of gravitational radiation. There is an astrophysical component, due to a superposition in frequency of a number of unresolved binary systems ("foreground") and there is the real background, of cosmological origin, generated by processes which took place when the Universe was less than a picosecond old. Its detection could mark a real turning point in cosmology --- far more profound that that given by the discovery of the Cosmic Microwave Background Radiation (CMBR), generated at photon decoupling, t= 400000 years --- and quantum gravity, therefore the SGWB has been also called "the Rosetta Stone" of cosmology. Since it is characterised only by its statistical properties, it is undistinguishable in principle from noise, making its detection a very hard task. I will talk about sources and also about detection and data-analysis strategies. I will also touch upon some quantum optics issues that have become hot topics in interferometric gravitational-wave detection and whose theoretical developments could give us some interesting hints about the tormented relationship between General Relativity and Quantum Mechanics.

**Time: ** 4. October 2013, 13:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Larisa Jonke

**Title: ** Generalized fluxes and matrix compactications

**Abstract:**

In the recent years a lot of attention is focused on unconventional string compactifications. A variety of different but related frameworks was developed in order to address issues such as duality invariance, non-geometry and
non-commutativity in string theory. In this talk we review and clarify the approach that goes through matrix models. Furthermore, we discuss some connections of this framework to other related approaches.

**Time: ** 4. October 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Athanasios Chatzistavrakidis

**Title: ** U-duality, branes and non-geometric flux compactifications

**Abstract:**

Branes and dualities are the main two windows to non-perturbative string theory. Their interplay reveals the existence of non-standard branes with unconventional properties. On the other hand, a consequence of string dualities in
flux compactifications is that they unveil situations where the geometry is globally ill-defined, a phenomenon dubbed as non-geometry. The two pictures are strongly related. I will present the worldvolume actions of different U-dual
branes and show how they source non-geometric fluxes. Moreover, I will discuss these branes as supergravity solutions (U-folds) and associate them with modern techniques to study unconventional string vacua, such as generalized
complex geometry and double field theory.

**Time: ** 6. September 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Aleksandar Mikovic

**Title: ** Effective action for Regge calculus

**Abstract:**

(tba)

**Time: ** 24. May 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Nenad Manojlovic

**Title: ** Jordanian deformation of the open sl(2) Gaudin model

**Abstract:**

We derive the deformed sl(2) Gaudin model with integrable boundaries. Starting from the Jordanian deformation of the SL(2)-invariant Yang R-matrix and generic solutions of the associated reflection equation and the dual reflection equation, the corresponding inhomogeneous spin-1/2 XXX chain is obtained. The quasi-classical expansion of the transfer matrix yields the deformed sl(2) Gaudin Hamiltonians with boundary terms.

**Time: ** 21. May 2013, 11:00h

**Place: ** Institute of Physics, room "Zvonko Maric"

**Speaker: ** Marko Vojinovic

**Title: ** Spin foam models as a method for quantization of gravity

**Abstract:**

Spin foam models are one of the approaches to the problem of nonperturbative quantization of the gravitational field, and they represent the covariant counterpart to the canonical approach to this problem (called Loop Quantum Gravity). In the last several years this area of research has seen a nontrivial development towards the goal of successful quantization of gravity. After the general introduction to the topic of quantum gravity, the most important novel results will be presented, with some attention to the lecturer's contributions in this area.

**Time: ** 26. April 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Aleksandar Mikovic

**Title: ** Spincube models of quantum gravity

**Abstract:**

We describe spincube models of quantum gravity which are based on Poincare 2-group representations labeled by positive real numbers. Depending on how one imposes the General Relativity constraints, one can obtain a spin foam model with the edge-length constraints or a Regge model. The corresponding effective actions have classical limits which are given by the Regge action.

**Time: ** 1. March 2013, 11:00h

**Place: ** Institute of Physics, room 300

**Speaker: ** Marko Vojinovic

**Title: ** Two unusual toy examples in Hamiltonian analysis

**Abstract:**

We will present two simple toy example Lagrangians which display some unusual features of Hamiltonian analysis. The toy examples were constructed in order to better understand the Hamiltonian structure of the constrained BFCG action for general relativity.

**Seminars for the year:**
2020
2019
2018
2017
2016
2015
2014
2013
2012
2011
2010
2009
2008
2007