Tue, 13 Feb 2024

16:00 - 17:00
L6

Large-size Behavior of the Entanglement Entropy of Free Disordered Fermions

Leonid Pastur
(King's College London / B. Verkin Institute for Low Temperature Physics and Engineering)
Abstract

We consider a macroscopic system of free lattice fermions, and we are interested in the entanglement entropy (EE) of a large block of size L of the system, treating the rest of the system as the macroscopic environment of the block. Entropy is a widely used quantifier of quantum correlations between a block and its surroundings. We begin with known results (mostly one-dimensional) on the asymptotics form of EE of translation-invariant systems for large L, where for any value of the Fermi energy there are basically two asymptotics known as area law and enhanced (violated ) area law. We then show that in the disordered case and for the Fermi energy belonging to the localized spectrum of a one-body Hamiltonian, the EE obeys the area law for all typical realizations of disorder and any dimension. As for the enhanced area law, it turns out to be possible for some special values of the Fermi energy in the one-dimensional case

Distortion of Hausdorff measures under Orlicz-Sobolev maps
Cianchi, A Korobkov, M Kristensen, J Journal of the European Mathematical Society (19 Mar 2025)
Fri, 19 Jan 2024
12:00
L3

Topological Recursion: Introduction, Overview and Applications

Alex Hock
(Oxford)
Abstract
I will give a talk about the topological recursion (TR) of Eynard and Orantin, which generates from some initial data (the so-called the spectral curve) a family of symmetric multi-differentials on a Riemann surface. Symplectic transformations of the spectral curve play an important role and are conjectured to leave the free energies $F_g$ invariant. TR has nowadays a lot of applications ranging random matrix theory, integrable systems, intersection theory on the moduli space of complex curves $\mathcal{M}_{g,n}$, topological string theory over knot theory to free probability theory. I will highlight specific examples, such as the Airy curve (also sometimes called the Kontsevich-Witten curve) which enumerates $\psi$-class intersection numbers on $\mathcal{M}_{g,n}$, the Mirzakhani curve for computing Weil–Petersson volumes, the spectral curve of the hermitian 1-matrix model, and the topological vertex curve which derives the $B$-model correlators in topological string theory. Should time allow, I will also discuss the quantum spectral curve as a quantisation of the classical spectral curve annihilating a wave function constructed from the family of multi-differentials. 
 
 
Inefficiency of CFMs: hedging perspective and agent-based simulations
Cohen, S Sabaté-Vidales, M Šiška, D Szpruch, Ł Financial Cryptography and Data Security. FC 2023 International Workshops. FC 2023 303-319 (05 Dec 2023)
Convergence of policy gradient methods for finite-horizon stochastic linear-quadratic control problems
Giegrich, M Reisinger, C Zhang, Y SIAM Journal on Control and Optimization volume 62 issue 2 1060-1092 (22 Mar 2024)
Tue, 06 Feb 2024

16:00 - 17:00
L6

Non-constant ground configurations in the disordered ferromagnet and minimal cuts in a random environment.

Michal Bassan
(University of Oxford )
Abstract
The disordered ferromagnet is a disordered version of the ferromagnetic Ising model in which the coupling constants are quenched random, chosen independently from a distribution on the non-negative reals. A ground configuration is an infinite-volume configuration whose energy cannot be reduced by finite modifications. It is a long-standing challenge to ascertain whether the disordered ferromagnet on the Z^D lattice admits non-constant ground configurations. When D=2, the problem is equivalent to the existence of bigeodesics in first-passage percolation, so a negative answer is expected. We provide a positive answer in dimensions D>=4, when the distribution of the coupling constants is sufficiently concentrated.

 
The talk will discuss the problem and its background, and present ideas from the proof. Based on joint work of with Shoni Gilboa and Ron Peled.
Tue, 23 Jan 2024

16:00 - 17:00
L6

Combinatorial moment sequences

Natasha Blitvic
(Queen Mary University of London)
Abstract

We will look at a number of interesting examples — some proven, others merely conjectured — of Hamburger moment sequences in combinatorics. We will consider ways in which this positivity may be expected: for instance, in different types of combinatorial statistics on perfect matchings that encode moments of noncommutative analogues of the classical Central Limit Theorem. We will also consider situations in which this positivity may be surprising, and where proving it would open up new approaches to a class of very hard open problems in combinatorics.

An automated method for tendon image segmentation on ultrasound using grey-level co-occurrence matrix features and hidden Gaussian Markov random fields
Scott, I Connell, D Moulton, D Waters, S Namburete, A Arnab, A Malliaras, P Computers in Biology and Medicine volume 169 (20 Dec 2023)
Thu, 15 Feb 2024
14:00

Algorithmic Insurance

Agni Orfanoudaki
(Oxford University Saïd Business School)
Abstract

As machine learning algorithms get integrated into the decision-making process of companies and organizations, insurance products are being developed to protect their providers from liability risk. Algorithmic liability differs from human liability since it is based on data-driven models compared to multiple heterogeneous decision-makers and its performance is known a priori for a given set of data. Traditional actuarial tools for human liability do not consider these properties, primarily focusing on the distribution of historical claims. We propose, for the first time, a quantitative framework to estimate the risk exposure of insurance contracts for machine-driven liability, introducing the concept of algorithmic insurance. Our work provides ML model developers and insurance providers with a comprehensive risk evaluation approach for this new class of products. Thus, we set the foundations of a niche area of research at the intersection of the literature in operations, risk management, and actuarial science. Specifically, we present an optimization formulation to estimate the risk exposure of a binary classification model given a pre-defined range of premiums. Our approach outlines how properties of the model, such as discrimination performance, interpretability, and generalizability, can influence the insurance contract evaluation. To showcase a practical implementation of the proposed framework, we present a case study of medical malpractice in the context of breast cancer detection. Our analysis focuses on measuring the effect of the model parameters on the expected financial loss and identifying the aspects of algorithmic performance that predominantly affect the risk of the contract.

Paper Reference: Bertsimas, D. and Orfanoudaki, A., 2021. Pricing algorithmic insurance. arXiv preprint arXiv:2106.00839.

Paper link: https://arxiv.org/pdf/2106.00839.pdf

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