Vienna Theory Lunch Seminar by Christopher Lepenik (UV), Maximillian Löschner (UV), Alexander Soloviev (TU) Tuesdays 12:1513:30
held alternately at:
We thank our kind sponsors: 
Idee: 
Wie auf vielen Universitäten praktiziert wollen wir ein LunchSeminar etablieren, das aktuelle Themen der Theoretischen Physik, die von DiplomandInnen, DoktorandInnen und PostDocs behandelt werden, aufgreift.

We want to establish a lunch seminar as practiced at other universities. The focus is on recent theoretical research done by Master students, PhDs and PostDocs.

Wie kann ich teilnehmen? 
Einfach erscheinen! Um per Email informiert zu werden, bitte in die Mailingliste eintragen. 
Just attend! To receive informations via email register for the Mailinglist. 
Mar 21 2017 
Jan Rosseel 
Nonrelativistic field theories in arbitrary backgrounds Abstract: Coupling field theories to arbitrary background spacetime metrics is often useful, as it allows one to easily define e.g. the energymomentum tensor and correlators thereof. In the relativistic case, it is well known how field theories can be coupled to arbitrary background geometries via e.g. minimal coupling. In this talk, I will review some aspects of nonrelativistic geometry and show what the analogue of minimal coupling is for nonrelativistic field theories. I will then show how this prescription can be easily obtained via a particular nonrelativistic limit. 
Mar 28 2017 
Ferdinand Horvath 
Mathur's Inequality and the Black Hole Information Paradox Abstract: Ever since Stephen Hawking discovered that black holes emit radiation, the physics community has been trying to accommodate the effects of this phenomenon. One of its consequences is the socalled information paradox. This paradox arises once a black hole evaporates through the emission of Hawking radiation, when those parts of the radiation that left the black hole can't be described as entangled with the hole anymore. While the theory assumes a pure initial state and hence full information about the particles in the hole and those emitted, information is lost once the hole is gone. This implies a loss of unitarity. Several ways to avoid this prospect are conceivable but few of them seem favourable. One such resort is the supposition that Hawking radiation has been treated too superficially since higher order corrections of its state are usually neglected. Their contribution could destroy the particles' entanglement, thus resolving the entire paradox. This presentation investigates Samir Mathur's research, who tried to disprove this proposal. Mathur shows that as long as these corrections to the Hawking state are assumed to be small, they cannot affect the first order entropy in a decisive way. Mathur's assumptions are examined in greater detail and his results are revised to conform to Hawking's results. We refine the entropy inequalities he proposed and attempt to directly compute the entanglement entropy of the Hawking radiation. 
Apr 4 2017 
Georg Stettinger 
Twisted Warped Entanglement Entropy
Abstract:
The aim of this talk is to calculate the entanglement entropy of an interval in different twodimensional warped conformal field theories (WCFT). The result by Castro et al. is generalized to a second WCFT with a different symmetry algebra. This is done in two ways: First using the Rindler method and second using the replica trick. The new WCFT is particularly interesting because it appears as holographic dual of a boosted Rindlerspacetime. On the gravitational side, entanglement entropy is much easier to compute and I show that the results agree if one locates the field theory on the horizon at r=0
rather than at r > ∞.

Apr 1118 2017 
No Lunch Seminar 
Osterferien  Easter Break 
Apr 25 2017 
Prof. Gerhard Hensler 
The Cosmic Matter Circuit  how to understand the Evolution of Galaxies
Abstract: Most galaxies like our Milky Way started to form soon after the Big Bang. Fed with gas from intergalactic streams in the Cosmic Web they started to form stars and since then send their light through the universe. Since stars gain their energy from nuclear fusion processes in their cores, they synthesize heavier elements but also exhaust their fuel and have to "die". The heavier a star is, the shorter is its lifetime and the more energetic its death. Already during their lives stars heat their surrounding interstellar medium (ISM) by their radiation and continuous mass loss. These stellar winds and final explosions not only drive the dynamics of the ISM but also restitute processed gas and by this enrich it with heavier elements. This chemical evolution can be traced in galaxies by the determination of element abundances in stars of different ages compared with those in the present ISM. 
May 2 2017 
Olaf Krüger 
Generating functions  Methods of counting
Abstract: I present a toolbox called „generating functions“  whenever you are confronted with some sort of counting problem, you can reach into that box and find something useful. For example, given a complicated recurrence formula for the coefficients of some sequence, a generating function can provide an exact formula. One might also find further recurrences, which might be simpler etc. etc.

May 9 2017 
Prof. Ivette Fuentes 
Gravity in the quantum lab Abstract: Quantum experiments are reaching relativistic regimes. Quantum communication protocols have been demonstrated at long lenghts scales and experiments are underway to distribute entanglement between Earth and Satellitebased links. At these regimes the Global Positioning System requieres relativistic corrections. Therefore, it is necessary to understand how does motion and gravity will affect longrange quantum experiments. Interestingly, relativistic effects can also be observed at small lengths scales. Some effects have been demonstrated in superconducting circuits involving boundary conditions moving at relativistic speeds and quantum clocks have been used to measure time dilation in tabletop experiments. In this talk I will present a formalism for the study of gravitational effects on quantum technologies. This formalism is also applicable in the development of new quantum technologies that can be used to deepen our understanding of physics in the overlap of quantum theory and relativity. Examples include accelerometers, gravitational wave detectors and spacetime probes underpinned by quantum field theory in curved spacetime. 
May 16 2017 
Lukas Semmelrock 
How can dark matter influence structure formation? Abstract: Lambda Cold Dark Matter is, to this date, the standard model of cosmology for describing the formation and evolution of structures in the universe. In this model the universe is made up of visible matter, dark matter and dark energy. Cosmic Microwave Background measurements show that dark matter is approximately five times as abundant as visible matter suggesting that the properties of dark matter can strongly influence the formation of structures. Simulations show that the distribution of matter in the universe can be very well modelled on large scales with dark matter only interacting gravitationally. On small scales, however, discrepancies between simulations and observations arise. These discrepancies can be resolved by introducing a dark matter selfinteraction. If the mediator particle of such interactions is light enough, it can be emitted as "dark bremsstrahlung" in dark matter collisions. My research deals with such inelastic collisions of selfinteracting dark matter particles and its implications on structure formation in the universe. For this purpose I introduce and analyse various generic dark matter models. 
May 23 2017 
Sukhwinder Singh 
Tensor networks as new tools for quantum gravity?
Tensor networks are practical tools, developed in the last two decades, to efficiently simulate a large class quantum manybody systems at low temperatures, on a classical computer. A popular example of a tensor network is "Matrix Product States", which form the basis of DMRGa breakthrough simulation algorithm for one dimensional quantum lattice systems, commonly used in condensed matter physics and quantum chemistry. 
May 30 2017 
Giacomo Guarnieri 
Characterization of heat in nonMarkovian open quantum systems
Abstract: We characterize the time behavior of the heat exchange between an open quantum system and its environment in a nonMarkovian dynamical regime. 
Jun 6 2017 
No Lunch Seminar 
Pfingsten  Pentecost 
Jun 13 2017 
Nicolai Friis 
Gaussian Quantum Thermodynamics Abstract: One of the most fundamental tasks in quantum thermodynamics is extracting energy from one quantum system and subsequently storing this energy in an appropriate battery. Both of these steps, work extraction and charging, can be viewed as cyclic Hamiltonian processes realized by unitary transformations acting locally on a quantum system. While there exist socalled passive states whose average energy cannot be lowered by unitary transformations, it is safe to assume that the energy of any notfully charged (quantum) battery may be increased unitarily. Nonetheless, unitaries raising the average energy by the same amount may differ in qualities such as their precision, fluctuations, and charging power, which one wishes to optimize. However, while work may be extracted from nonpassive states in principle and optimal ways may be found of charging any specific battery, the required unitaries may be complicated and extremely difficult to realize in practice. It is hence of crucial importance to understand the qualities that can be expected from practically implementable transformations. In this talk, I will discuss the limitations for work extraction and battery charging when restricting to the feasibly realizable family of Gaussian unitaries. 
Jun 20 2017 
Hamed Barzegar 
GLOBAL QUANTITIES IN GENERAL RELATIVITY  Generalization of ADM & Komar Quantities Abstract: One of the most important quantities of a physical system is the energy (or mass) of that system. But, the energy and mass in General Relativity have no unique definition, compared against the Special Relativity where the mass (and energy) is welldefined. As it turns out, there is no local notion of mass and energy in General Relativity. However, we can attribute global quantities, defined at large distances, to some spacetimes. ADM formalism provides a way to calculate such quantities. There is also the notion of Komar quantities which are defined in spacetimes with some symmetries. In this talk, I will briefly review the 3+1 formalism which is the mathematical framework of the ADM Hamiltonian formalism. Then, I will talk about the ADM Hamiltonian formalism and asymptotic flatness in order to define the global quantities such as ADM quantities and Komar quantities. At the end, I will present the ideas of my master's thesis, which is concerned with the derivation of the ADM quantities within the geometric Hamiltonian formalism of Kijowski, Tulczyjew and Chrusciel. Based on this formalism, I will present the generalizations of the ADM and Komar quantities to n+1dimensional spacetimes. Further generalizations are in progress. 
Jun 27 2017 
Raphaela Wutte 
Near Horizon Boundary Conditions for Spin3 Gravity in Flat Space Abstract: In field theories the physical content of the theory is given by the field equations and the boundary conditions. While it is common practice in nongravitational theories to demand that the fields asymptotically vanish at the boundary of spacetime, boundary conditions for theories of gravity are quite subtle. Recently (2015/2016), three different groups (Donnay et al, Afshar et al and Hawking et al) asked the question whether boundary conditions can be formulated for the near horizon region of nonextremal black holes in a sensible way. In this talk I review the extension of the boundary conditions of Afshar et al to higherspin gravity in threedimensional flat space. We find that the near horizon symmetries are governed by a surprisingly simple algebra and that there seems to be a universal expression for the entropy of (higherspin) black holes/flat space cosmologies in terms of the near horizon charges in three dimensions. 
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