Lukas Schneiderbauer

Valentina Giangreco, september 24, 2020

PhD defense, Friday September 25 at 14.00, in Veröld, room 023

Semi-Classical Black Hole Holography 

The defense will be streamed: https://www.youtube.com/user/HIvarp/live

Dissertation title: Semi-Classical Black Hole Holography 

Opponents: Dr. Veronika Hubeny, Professor of Physics at UC Davis,USA
Dr. Mukund Rangamany, Professor of Physics at UC Davis, USA

Advisor: Dr. Lárus Thorlacius, Professor at the Faculty of Physical Sciences, University of Iceland

Doctoral committee: Dr. Bo Sundborg, Professor at the Department of Physics at Stockholm University, Sweden
Dr. Valentina Giangreco M. Puletti, Professor at the Faculty of Physical Sciences, University of Iceland
Dr. Þórður Jónsson, Professor at the Faculty of Physical Sciences, University of Iceland

Chair of Ceremony: Dr. Einar Örn Sveinbjörnsson, Professor and the Head of the Faculty of Physical Sciences, University of Iceland

Abstract:
This thesis discusses two aspects of semi-classical black holes.
First, a recently improved semi-classical formula for the entanglement entropy of
black hole radiation is examined. This entropy is an indicator of information loss and determines whether black hole evaporation is an information preserving process or destroys quantum information. Assuming information conservation, Page expressed the entanglement entropy as a function of time, which is referred to as the “Page curve.” Using the improved formula for evaporating black hole solutions of a gravitational model introduced by Callan, Giddings, Harvey and Strominger (CGHS) and modified by Russo, Susskind and Thorlacius (RST), we find that the entanglement entropy follows the Page curve and thus is consistent with unitary evolution.
Second, the notion of quantum complexity is explored in the context of black holes. The quantum complexity of a quantum state measures how many “simple operations” are needed to create that state. Susskind conjectured that the quantum complexity of a black hole state corresponds to a certain volume inside the black hole. A modified conjecture equates the quantum complexity with the gravitational action evaluated for a certain region of spacetime which intersects the black hole interior. We test the complexity conjectures for semi-classical black hole solutions in the CGHS/RST model and find that both conjectures yield the expected behavior.

Anna Helga Jónsdóttir och Benedikt Steinar Magnússon

Valentina Giangreco, nóvember 19, 2019

Math colloquium

Fyrirlesari: Anna Helga Jónsdóttir og Benedikt Steinar Magnússon, Háskóli Íslands

Titill 1: Student evaluations of teaching at the University of Iceland – analysis of data from 2013 – 2017

Ágrip 1:

Student evaluations of teaching (ísl. kennslukönnun) is administrated at the end of each and every course at the University of Iceland with the purpose of improving teaching and learning. In the talk, analysis of data from student evaluations from 2013 to 2017 at the UI will be presented. Mixed effect models were used to investigate possible relationships between the grades students give courses and several variables, such as the age and gender of the student and the teacher, number of students taking the course and the average final grade in the course.

Titill 2: Online course notes in Edbook and the role of the textbook

Ágrip 2:

In the last years I, with the help of many good people, have been developing a platform for online course notes called Edbook (http://edbook.hi.is). It consists of using Sphinx, which was developed for and in Python, along with specialized extension suited for teaching material in Mathematics. We have been using these notes in a few courses, mostly big calculus courses. The students have overall been very happy with them but in the spring of 2019 I had students in Mathematical Analysis II (STÆ205G) answer a more detailed survey about their usage of the teaching material they used. I will introduce the Edbook platform and the results of the survey which raises some questions about the role of the textbook today.

Staðsetning: HB5 (Háskólabíó)
Tími: Föstudag 15.nóvember kl. 11:40

Room: HB5 (Háskólabíó)
Time: Friday 22th November, 11:40hrs

Hólmfríður Sigríðar Hannesdóttir

Valentina Giangreco, ágúst 23, 2019

Math Phys seminar

Fyrirlesari: Hólmfríður Sigríðar Hannesdóttir , Harvard University

Titill: Infrared Finite S-matrix elements and Cross Sections

Staðsetning: A-050
Tími: Þriðjudag 27.ágúst kl. 14:00

Ágrip:

Quantum field theory (QFT) works remarkably well for making theoretical predictions in collider scattering experiments. One of the fundamental objects in these calculations, the scattering matrix (S-matrix), is inspired by a well defined operator in non-relativistic quantum mechanics, but is plagued with both ultraviolet (UV) and infrared (IR) divergences in QFT. The UV divergences are now understood through the program of renormalization, but IR divergences remain an active area of research. Three approaches have been explored to define IR finite quantities, which will all be discussed in this talk: i) The cross section method, ii) modification of the S-matrix, and iii) the dressed state formalism. The minimal set of processes required for a finite cross section will be examined, along with the need for forward scattering and disconnected diagrams. We will furthermore explore how the usual assumptions about evolution of the scattering states at asymptotic times are broken in a theory with massless particles, and how the universality of the interactions leading to IR divergences in such theories can be exploited to define finite S-matrix elements.

Finnur Lárusson

Valentina Giangreco, júní 7, 2019

Málstofa í stærðfræði

Fyrirlesari: Finnur Lárusson, Adelaide University

Titill: Chaotic holomorphic automorphisms of Stein manifolds with the 
volume density property

Staðsetning: VR-II, V-158
Tími: þriðjudagur 9. júlí kl. 11.00

Ágrip:

I will report on joint work with Leandro Arosio.  Let $X$ be 
a Stein manifold of dimension $n\geq 2$ satisfying the volume density 
property with respect to an exact holomorphic volume form.  For example, 
$X$ could be $\C^n$, any connected linear algebraic group that is not 
reductive, the Koras-Russell cubic, or a product $Y\times\C$, where $Y$ 
is any Stein manifold with the volume density property. We prove that 
chaotic automorphisms are generic among volume-preserving holomorphic 
automorphisms of $X$.  In particular, $X$ has a chaotic holomorphic 
automorphism. Forn\ae ss and Sibony proved (but did not explicitly 
state) this for $X=\C^n$ in 1997.  We follow their approach closely. 
Peters, Vivas, and Wold showed that a generic volume-preserving 
automorphism of $\C^n$, $n\geq 2$, has a hyperbolic fixed point whose 
stable manifold is dense in $\C^n$.  This property can be interpreted as 
a kind of chaos.  We generalise their theorem to a Stein manifold as above.

Christiana Pantelidou

Valentina Giangreco, júní 7, 2019

Math Phys seminar

Fyrirlesari: Christiana Pantelidou, Durham University

Titill: Incoherent hydrodynamics and density waves

Staðsetning: VR-II, V-258
Tími: mánudagur 24. júní kl. 14.00

Ágrip:

I will consider thermal phases of holographic lattices at finite chemical potential in which a continuous internal bulk symmetry can be spontaneously broken. In the normal phase, translational symmetry is explicitly broken by the lattice and the long wavelength excitations are captured by incoherent hydrodynamics describing two perturbative diffusive modes. In the broken phase an additional diffusive hydrodynamic degree of freedom appears. In this talk I will use holography to write an effective theory describing the coupling of incoherent hydrodynamics to this goldstone mode.

Guðmundur Magnússon

Valentina Giangreco, júní 7, 2019

Málstofa í stærðfræði

Fyrirlesari: Guðmundur Magnússon, HI

Titill: Multi Dispatcher Systems and interacting policies

Staðsetning: VR-II, V-258
Tími: þriðjudagur 18. júní kl. 11.00

Ágrip:

This project explores the performance of parallel server system. The focus of the project is a system using multiple heuristic policies to route jobs to a server. To achieve this there is a simulator created that uses the Monte Carlo method to numerically simulate the performance of a system. It displays with figures the result of some simulations under different conditions and answers how different policies interact in this multi dispatcher system.

BSc thesis under the supervision of  Esa Olavi Hyytiä.

Sylvain Arguillère

Valentina Giangreco, júní 7, 2019

Málstofa í stærðfræði

Fyrirlesari: Sylvain Arguillère, CNRS – Institut Camille Jordan – MMCS

Titill: Shape analysis through flows of diffeomorphisms

Staðsetning: VR-II, V-258
Tími: fimmtudagur 13. júní kl. 11.00

Ágrip:

The goal of shape analysis is to compare shapes in a way that takes into account their geometric properties. The end goal is to give an adapted framework for the statistical analysis of medical data, in order to identify sick patients automatically for example. In this talk, I will describe a method introduced by Alain Trouvé, which allows to compare shapes through flows of diffeomorphisms with minimal energy, using tools from differential geometry and optimal control.

Wolfgang Woess

Valentina Giangreco, maí 31, 2019

Málstofa í stærðfræði

Fyrirlesari: Wolfgang Woess, TU Graz

Titill: THE LANGUAGE OF SELF-AVOIDING WALKS

Staðsetning: VR-II, V-155
Tími: þriðjudagur 4. júní kl. 11.00

Ágrip:

Let X = (VX, EX) be an infinite, locally finite, connected graph without
loops or multiple edges. We consider the edges to be oriented, and EX is equipped with
an involution which inverts the orientation. Each oriented edge is labelled by an element
of a finite alphabet Σ. The labelling is assumed to be deterministic: edges with the same
initial (resp. terminal) vertex have distinct labels. Furthermore it is assumed that the
group of label-preserving automorphisms of X acts quasi-transitively. For any vertex o
of X, consider the language of all words over Σ which can be read along self-avoiding
walks starting at o. We characterize under which conditions on the graph structure this
language is regular or context-free. This is the case if and only if the graph has more
than one end, and the size of all ends is 1, or at most 2, respectively. (joint work with Christian Lindorfer).

Primoz Potocnik

Valentina Giangreco, maí 20, 2019

Málstofa í stærðfræði

Fyrirlesari: Primoz Potocnik, University of Ljubljana

Titill: Symmetries of finite graphs – a personal overview

Staðsetning: VR-II, V-158
Tími: þriðjudagur 28. maí kl. 11.00

Ágrip:

Whether a graph is more or less symmetric is typically measured in terms of its automorphism group consisting of all permutation of its vertices which preserves the adjacency relation. The highest level of symmetry is achieved when the automorphism group has only one orbit on the vertices and/or edges of the graph. I will give a personal and gentle overview of the problems and the results about this class of graphs.

Giulio Cerbai

Valentina Giangreco, maí 1, 2019

Málstofa í stærðfræði

Fyrirlesari: Giulio Cerbai, University of Florence

Titill: Sorting Permutations Using Pattern-Avoiding Stacks

Staðsetning: Tg-227
Tími: Fimmtudagur 9. maí kl. 11.40

Ágrip:

The problem of sorting a permutation using a stack was proposed by Knuth in the 1960s. As it is well known, sortable permutations can be characterized in terms of pattern avoidance and their enumeration is given by the Catalan numbers. Since then, lots of generalizations have been proposed, either by increasing the number of stacks or by using different sorting devices (queues, pop stacks…). Unfortunately, the same problem with 2 stack in series is too hard and both the characterization and the enumeration of the sortable permutations are still unknown.
In this work we start the analysis of a new sorting device, consisting in two restricted stacks in series, where each stack cannot contain a given pattern. We will use a right-greedy procedure, thus generalizing the case of the 2-West sortable permutations. Our goal is to provide the first results in this new framework, hoping to gain a better understanding of the general 2-stacksort problem.