**Seminars for the year:**
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**Time: ** 26. December 2018, 15:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Marko Vojinovic

**Title: ** Selected QG topics (2): symmetries in the general field theory framework

**Abstract:**

In the second lecture about the general field theory, we will deal the notion of symmetry. We will discuss which groups of transformations naturally appear in the geometric and algebraic sector of the theory, and study the relationship between them. Finally, we will analyze what are the implications to the structure of the notion of a field as a map from geometry to algebra, and how groups of transformations help us classify the fields into components which transform in a regular way with respect to a given group.

**Time: ** 14. December 2018, 14:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Igor Salom

**Title: ** Supplementary lectures for students (5): Bell's theorem

**Abstract:**

The importance of Bell inequality for understanding of quantum phenomena is impossible to overestimate --- some consider it the deepest achievement of the whole science. We will present the statement and the proof of the Bell's theorem (in its CHSH formulation), and discuss its experimental violations as well as corresponding consequences.

**Time: ** 12. December 2018, 15:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Marko Vojinovic

**Title: ** Selected QG topics (1): kinematics of the general field theory framework

**Abstract:**

The whole modern fundamental physics can be expressed using the mathematical formalism of field theory. We will provide a short (nontechnical) definition of the general field theory formalism, in the context of differential geometry. Then we will focus on several examples of various classical and quantum theories in various spacetime dimensions, in order to illustrate that essentially all modern theories can be cast into this form. At the end we will study some example formulations of quantum gravity, and discuss how they fit into the field theory formalism.

**Time: ** 23. November 2018, 14:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Marko Vojinovic

**Title: ** Supplementary lectures for students (4): Unitarity in quantum mechanics

**Abstract:**

We will discuss the question whether or not quantum mechanics must be unitary, and precisely what is the relationship between unitarity and the conservation of probability. We will give a short recap of the density matrix formalism, then we will specify a more generic formulation of quantum mechanics with nonunitary evolution, and we will comment if and when it may or may not be unitary. If time permits, we will introduce the Lindblad equation, which represents the generalization of the ordinary Schrodinger equation and is important for the description of nonunitary processes in quantum mechanics.

**Time: ** 9. November 2018, 11:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Fermin Aldabe

**Title: ** Quantum gravitodynamics as the path To unification

**Abstract:**

We present the 4 dimensional QGD theory: An SO(4) Yang Mills coupled to matter spinors. The coupling comprises terms which are absent in QED or QCD because the SO(4) generators do not commute with the Dirac gamma matrices. These new couplings produce scattering matrix elements equal to those of the Schroedinger equation with the first post Newtonian correction to the gravitational potential. We then argue that the path integral of General Relativity lacks a diffeomorphic invariance and only has a local Lorentz symmetry. This allows us to prove that General Relativity is a special gauge fixing of QGD and vice versa. We then show examples of possible quantum calculations including effective potentials in the presence of backgrounds and also the black hole entropy.

**Time: ** 2. November 2018, 12:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Dejan Simic

**Title: ** Asymptotic symmetries and soft theorems (part 2)

**Abstract:**

We will discuss the symmetry of massless electrodynamics at null infinity and its relationship with the soft photon theorem. The lecture will be more descriptive than technical, with more details at the next seminar given the interest by the audience.

**Time: ** 26. October 2018, 12:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Dejan Simic

**Title: ** Supplementary lectures for students (3): Asymptotic symmetries and soft theorems (part 1)

**Abstract:**

We will discuss the symmetry of massless electrodynamics at null infinity and its relationship with the soft photon theorem. The lecture will be more descriptive than technical, with more details at the next seminar given the interest by the audience.

**Time: ** 21. September 2018, 11:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Bojan Nikolic

**Title: ** Supplementary lectures for students (2): Bosonic string action obtained by analogy from the free particle action

**Abstract:**

We will study the actions for the massive and massless free particle and discuss some of their properties and the logic behind their construction. Then we will use an analogy to write the Nambu-Goto action for a free string. Finally, we will discuss the Polyakov action, and explain why it is "better" than the Nambu-Goto action.

**Time: ** 3. August 2018, 14:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Marko Vojinovic

**Title: ** Supplementary lectures for students (1): An introduction to the metric tensor

**Abstract:**

We will give a very elementary introduction to the notion of the metric tensor, without any heavyweight differential geometry notions. Several illustrative examples from general relativity will be discussed.

**Time: ** 13. July 2018, 12:00h

**Place: ** Institute of Physics, lecture hall "Zvonko Maric"

**Speaker: ** Djordje Minic

**Title: ** Manifest quantum non-locality in quantum mechanics, quantum field theory and quantum gravity

**Abstract:**

In this talk we will discuss manifest quantum non-locality in quantum mechanics while concentrating on the essential features of any quantum theory, such as linear superposition and entanglement. We will reveal the hidden quantum space-time geometry behind this non-locality, that is also consistent with causality. We will then illustrate how this same quantum space-time geometry appears in the context of quantum gravity, and finally, discuss the meaning of such quantum non-locality in the context of quantum field theory, while pointing out a new generic prediction that follows from this novel view on quantum theory.

**Time: ** 6. July 2018, 11:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Marko Vojinovic

**Title: ** Canonical structure of the 2-BF theory for the Poincare 2-group

**Abstract:**

We perform the full Hamiltonian analysis of the topological BFCG action based on the Poincare 2-group. The Hamiltonian of the theory is constructed, and the algebra of constraints is computed. The Dirac brackets are evaluated, and the second class constraints are then eliminated from the theory. The results are contrasted to those of the topological Poincare gauge theory, which is equivalent to the BFCG model at the level of the classical action, but has a very different Hamiltonian structure. The canonical transformation which maps between the two theories turns out to be singular in a certain sense.

**Time: ** 4. July 2018, 11:15h

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

**Speaker: ** Marija Dimitrijevic Ciric

**Title: ** Noncommutative theory of gravity: model construction, results and open questions

**Abstract:**

Although General Theory of Relativity is a very successful classical theory of gravity, a corresponding quantum theory, quantum gravity, has still not been consistently formulated. Noncommutative geometry represents one of the ways to quantize spacetime, and can represent a step towards quantum gravity.

In this lecture we will consider the motivation and various models of noncommutative (NC) theory of gravity, i.e., gravity on a noncommutative space. Most attention will be given to the concrete model of SO(2,3) NC gauge theory of gravity. We will describe the corresponding action and equations of motion, as well as the results which partially explain the violation of diffeomorphism invariance in NC gravity. We will also consider the interaction with matter fields in this concrete model and possible phenomenological consequences. At the end we will disciss open questions and the connection to some other approaches to NC gravity.

**Time: ** 29. June 2018, 11:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Branislav Cvetkovic

**Title: ** General Poincare gauge theory: Hamiltonian structure and particle spectrum (part II)

**Abstract:**

We discuss the general aspects of the Hamiltonian structure of the parity violating Poincare gauge theory. All possible primary constraints are determined, critical parameters are identified, and the canonical Hamiltonian is constructed in the generic case. Besides their importance in itself, these results establish important information necessary for the understanding of the particle spectrum of the theory, calculated in the weak field limit around the Minkowski vacuum.

**Time: ** 22. June 2018, 11:00h

**Place: ** Institute of Physics, lecture hall "Zvonko Maric"

**Speaker: ** Branislav Cvetkovic

**Title: ** General Poincare gauge theory: Hamiltonian structure and particle spectrum (part I)

**Abstract:**

We discuss the general aspects of the Hamiltonian structure of the parity violating Poincare gauge theory. All possible primary constraints are determined, critical parameters are identified, and the canonical Hamiltonian is constructed in the generic case. Besides their importance in itself, these results establish important information necessary for the understanding of the particle spectrum of the theory, calculated in the weak field limit around the Minkowski vacuum.

**Time: ** 15. June 2018, 11:00h

**Place: ** Institute of Physics, lecture hall "Dragan Popovic"

**Speaker: ** Marija Vranjes Milosavljevic

**Title: ** Search for supersymmetry at the ATLAS experiment --- past, present and future

**Abstract:**

The search for supersymmetric (SUSY) signal allows for a direct check of the theoretical predictions of extensions of the Standard Model of elementary particles, which so far have not been experimentally confirmed. We will give an overview of supersymmetric models, experimental techniques, and statistical methods in search for supersymmetric particles at the ATLAS experiment from the period before the beginning of the Large Hadron Collider (LHC), during the first phase of data acquisition from proton-proton collisions at the energy of 8 TeV, as well as the latest results obtained in the current, second phase of the LHC operation at 13 TeV. The analysis and the interpretation of data within the SUSY model, as well as the preparation of the special set of results that can be further studied by the wider HEP community, will be discussed on the example search for SUSY particles in events with a large number of hadron jets and large missing energy. Also, we will present the approach to interpreting all published results of the ATLAS experiment searching for SUSY particles within the 19-parameter pMSSM model (phenomenological Minimal Supersymmetric extension of the Standard Model).

**Time: ** 25. May 2018, 11:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Tijana Radenkovic

**Title: ** Action for scalar, Dirac and gauge fields as 3-BF action with constraints

**Abstract:**

First, we will remind you of 2-BF model of guantum gravity - 2-categorical generalization of BF model and the notion of 2-group (which is equivalent to crossed module) necessary for constructing it. Then, we will see how by considering crossed module for G=SO(3,1)xU(1)xSU(2)xSU(3) instead of G=SO(3,1) we obtain equations of motion for gauge field coupled to gravity known from EC theory. Finally, we will show how by using the notion of 3-group one can write the action for gravity coupled to scalar and Dirac fields as 3-BF action with constraints.

**Time: ** 13. April 2018, 11:00h

**Place: ** Institute of Physics, room 360 (ex-room 300)

**Speaker: ** Richard Szabo

**Title: ** Nonassociative geometry and non-geometric backgrounds

**Abstract:**

Recent advances in non-geometric string theory suggest that locally non-geometric flux compactifications can be understood in terms of nonassociative deformations of spacetime geometry. We will review some of these developments and how they shed light on properties of non-geometric strings, and explain some more recent results concerning how these structures lift to non-geometric M-theory.

**Time: ** 11. April 2018, 11:00h

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

**Speaker: ** Richard Szabo

**Title: ** Deformations of quantum theory

**Abstract:**

Theoretical approaches to quantum gravity suggest that the conventional notions of space and time become meaningless at ultra-short distance scales. In many instances, dynamics in such ensuing "fuzzy" spacetimes can be captured by certain deformations of quantum mechanics and quantum field theory. In this lecture I will explain some of these deformed quantum theories and how they may ultimately teach us something about quantum gravity. I will explain how these theoretical consequences can connect to real-world measurable quantities, and analyse in detail a simple deformation of quantum mechanics which may be realised in a table-top experiment. From the theoretical side, I will explain how these quantum systems are related to the nonassociative algebras of observables proposed in the beginnings of quantum mechanics and quantum field theory by Jordan, von Neumann, Wigner and others to study the mathematical and conceptual foundations of quantum theory.

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