Math Phys seminar

**Speaker: Jorge Laraña Aragon,University of Stockholm**

**Title: Quenched coupling, effective thermalization and evanescence in the free $O(N)$ vector model**

Room: VR-II, V-156

Time: Thursday 15th August, 14:00hrs

#### Abstract:

In this project we study two coupled free $O(N)$ vector models implementing the coupling via a quench of mixing. Since the theory is integrable pure thermalization does not occur but the quantum modes thermalize independently. Generalized thermal behavior is obtained at late times in the limit of weak initial mixing. We investigate this from both the effective density matrix and the spectral density function. When computing the latter, we observe that late-time correlation functions of composite operators in the post-quench free QFT surprisingly share interesting properties with correlators in strongly coupled systems. We discuss a possible holographic interpretation in terms of the so called evanescent modes.

Math Colloquium

### Speaker: Finnur Lárusson, Adelaide University

### Title: Chaotic holomorphic automorphisms of Stein manifolds with the

volume density property

Location: VR-II, V-158

Time: Tuesday July 9 at 11.00 am

### Abstract:

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.

Math Phys seminar

### Speaker: Christiana Pantelidou, Durham University

### Title: Incoherent hydrodynamics and density waves

Location: VR-II, V-258

Time: Monday June 24 at 2.00 pm

### Abstract:

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.

Math Colloquium

### Speaker: Guðmundur Magnússon, HI

### Title: Multi Dispatcher Systems and interacting policies

Location: VR-II, V-258

Time: Tuesday June 18 at 11.00 am

### Abstract:

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.

Math Colloquium

### Speaker: Sylvain Arguillère, CNRS – Institut Camille Jordan – MMCS

### Title: Shape analysis through flows of diffeomorphisms

Location: VR-II, V-258

Time: Thursday June 13 at 11.00 am

### Abstract:

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.

Math Colloquium

### Speaker: Wolfgang Woess, TU Graz

### Title: THE LANGUAGE OF SELF-AVOIDING WALKS

Location: VR-II, V-155

Time: Tuesday June 4 at 11.00 am

### Abstract:

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).

Math Colloquium

### Speaker: Primoz Potocnik, University of Ljubljana

### Title: Symmetries of finite graphs – a personal overview

Location: VR-II, V-158

Time: Tuesday May 28 at 11.00 am

### Abstract:

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.

Math Colloquium

### Speaker: Giulio Cerbai, University of Florence

### Title: Sorting Permutations Using Pattern-Avoiding Stacks

Location: Tg-227

Time: Thursday May 9 at 11.40 am

### Abstract:

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.

Math Phys Seminar

### Speaker: Bo Sundborg, Stockholm University

### Title: Field theory compositeness, holographic gravity and higher spins

Location: Tg 227 (“smart room” Tæknigarður)

Time: Tuesday April 30 at 14.00 am

### Abstract:

I would like to discuss the idea that composite operators in field theory

are key ingredients in holograms of bulk gravitational physics. In practice,

this is well known: Composites are essential in both matrix (Maldacena) and vector (Klebanov-Polyakov) AdS/CFT. I argue that composite correlators in thermal and quenched field theory backgrounds illuminate the importance of compositeness further. They behave as boundary-boundary correlators in geometries with a strong gravitational source in the interior, whether the bulk is Einsteinian or higher spin-like.

Math Colloquium

### Speaker: Arkadiusz Lewandowski, Jagiellonian University

### Title: Properties of solution trajectories for a metrically regular generalized equation

Location: Tg-227

Time: Thursday May 2 at 11.40 am

### Abstract:

It is known that given a smooth strictly pseudoconvex domain, all of its boundary points admit a peak function and an exposing map. We shall discuss the recent question of Deng, Guan, and Zhang (TAMS, 2016), concerning the existence of smooth families of peak functions and exposing maps at the boundary points of strictly pseudoconvex domains forming the family varying in a smooth way.