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Linear statistics of random matrices and log-gases
KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).ORCID iD: 0000-0003-1193-8355
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is concerned with point processes arising in Random Matrix Theory. It is a compilation thesis: it consists of an introduction and three research papers.

In Paper A and Paper B, we study random matrices from the classical compact groups, namely orthogonal, unitary, and symplectic matrices distributed according to Haar measure. We consider the moments of the empirical spectral measure, i.e. the trace of the powers of the matrices. These are known to converge in distribution, as the dimension of the matrices tends to infinity, to independent, normal random variables. We show that the convergence is especially fast as the total variation distances to the limiting Gaussians decay faster than exponentially.

Paper A is devoted to the multivariate case for orthogonal and symplectic matrices: we study the total variation between a vector filled with the trace of the powers of the matrix, and one filled with independent normal random variables. We obtain an explicit upper bound on the total variation which depends on the highest power and the dimension of the matrix, and which, as a function of their ratio, decays faster than exponentially.

In Paper B we consider a single trace at a time. This allows to study the trace of a higher power, up to the dimension of the matrix in the unitary case. We show a transition from a super-exponential decay, for small powers, to a decay of Berry-Esseen type, for high powers. The argument also gives more precise bounds. We obtain a first lower bound when the power equals one and determine the exact asymptotics of the L2 distance.

In Paper C we consider a Coulomb gas on a sufficiently regular Jordan curve in the plane, at a general temperature. This is a generalization of the Circular β-Ensemble. We derive the asymptotics of the partition function from those of the Laplace transform of linear statistics. The asymptotic formula is expressed, among other things, in terms of the Grunsky operator associated with the exterior conformal mapping for the curve.

Abstract [sv]

Denna avhandling behandlar punktprocesser med ursprung i slumpmatristeori. Den består av en introduktion och tre forskningsartiklar.

I Artikel A och Artikel B studerar vi slumpmässiga matriser från de klassiska kompakta grupperna, nämligen ortogonala, unitära och symplektiska matriser fördelade enligt Haarmåttet. Vi undersöker momenten till det empiriska spektralmåttet för egenvärdena, d.v.s. spåren av matrisernas potenser. Dessa konvergerar i fördelning, då matrisernas dimension går mot oändligheten, mot oberoende, normalfördelade variabler. Konvergensen mot de Gaussiska variablerna är mycket snabb, det totala variationsavståndet avtar snabbare än exponentiellt.

Artikel A behandlar det multivariata fallet för ortogonala och symplektiska matriser: vi studerar det totala variationsavståndet mellan en vektor av spåren av matrisens potenser, och en vektor av oberoende normalfördelade variabler. Vi visar en explicit övre gräns för avståndet som beror på den högsta potensen och dimensionen av matrisen, och som funktion av deras kvot avtar snabbare än exponentiellt.

I Artikel B undersöker vi ett enda spår åt gången. Detta gör det möjligt att studera spåret av en hög potens, ända upp till dimensionen av matrisen i det unitära fallet. Resultatet visar övergången från ett superexponentiellt avtagande, för små potenser, till ett avtagande av Berry-Esseen-typ, för höga potenser. Argumentet ger även mer precisa gränser för det totala variationsavståndet. Vi ger det första resultatet för en undre gräns i fallet då potensen är lika med ett och bestämmer den exakta asymptotiken för L2-avståndet.

I Artikel C studerar vi en Coulombgas på en Jordankurva i planet, vid en godtycklig temperatur. Detta generaliserar den Cirkulära β-Ensemblen på cirkeln till en mer allmän kurva. Vi visar först en formel för asymptotiken för Laplacetransformen av en linjär statistika, och härleder asymptotiken för partitionsfunktionen utifrån denna. Den asymptotiska formeln uttrycks bland annat i termer av Grunskyoperatorn hörande till den yttre konforma avbildningen till kurvan.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2023.
Series
TRITA-SCI-FOU ; 2023:15
National Category
Probability Theory and Statistics
Research subject
Mathematics
Identifiers
URN: urn:nbn:se:kth:diva-326507ISBN: 978-91-8040-555-3 (print)OAI: oai:DiVA.org:kth-326507DiVA, id: diva2:1754866
Public defence
2023-06-02, D2, Lindstedsvägen 9, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 2023-05-10

Available from: 2023-05-10 Created: 2023-05-04 Last updated: 2025-12-03Bibliographically approved
List of papers
1. Multivariate normal approximation for traces of orthogonal and symplectic matrices
Open this publication in new window or tab >>Multivariate normal approximation for traces of orthogonal and symplectic matrices
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We show that the distance in total variation between $(\tr U, \frac{1}{\sqrt{2}}\tr U^2, \cdots, \frac{1}{\sqrt{m}}\tr U^m)$ and a real Gaussian vector, where $U$ is a Haar distributed orthogonal or symplectic matrix of size $2n$ or $2n+1$, is bounded by $\Gamma(2\frac{n}{m}+1)^{-\frac{1}{2}}$ times a correction. The correction term is explicit and holds for all $n\geq m^4$, for $m$ sufficiently large. For $n\geq m^3$ we obtain the bound $(\frac{n}{m})^{-c\sqrt{\frac{n}{m}}}$ with an explicit constant $c$. Our method of proof is based on an identity of Toeplitz+Hankel determinants due to Basor and Ehrhardt, see \cite{BE}, which is also used to compute the joint moments of the traces.

National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:kth:diva-326107 (URN)
Note

QC 20230425

Available from: 2023-04-24 Created: 2023-04-24 Last updated: 2023-05-04Bibliographically approved
2. From Berry-Esseen to super-exponential
Open this publication in new window or tab >>From Berry-Esseen to super-exponential
(English)Manuscript (preprint) (Other academic)
Abstract [en]

For any integer $m<n$, where $m$ can depend on $n$, we study the rate of convergence of $\frac{1}{\sqrt{m}}\tr \mathbf{U}^m$ to its limiting Gaussian as $n\to\infty$ for orthogonal, unitary and symplectic Haar distributed random matrices $\mathbf{U}$ of size $n$. In the unitary case, we prove that the total variation distance is less than $\Gamma(\floor{n/m}+2)^{-1}m^{-\floor{n/m}}\floor{n/m}^{1/4}\sqrt{\log n}$ times a constant. This result interpolates between the super-exponential bound obtained for fixed $m$ and the $1/n$ bound coming from the Berry-Esseen theorem applicable when $m\ge n$ by a result of Rains. We obtain analogous results for the orthogonal and symplectic groups. In these cases, our total variation upper bound takes the form $\Gamma(2\floor{n/m}+1)^{-1/2}m^{-\floor{n/m}+1}(\log n)^{1/4}$ times a constant and the result holds provided $n \geq 2m$. For $m=1$, we obtain complementary lower bounds and precise asymptotics for the $L^2$-distances as $n\to\infty$, which show how sharp our results are. 

National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:kth:diva-326109 (URN)
Note

QCR 20230426

Available from: 2023-04-24 Created: 2023-04-24 Last updated: 2023-05-04Bibliographically approved
3. Partition function for the 2d Coulomb gas on a Jordan curve
Open this publication in new window or tab >>Partition function for the 2d Coulomb gas on a Jordan curve
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We prove an asymptotic formula for the partition function of a 2d Coulomb gas at inverse temperature $\beta>0$ confined to lie on a Jordan curve. This also gives a central limit theorem for a linear statistic of the particles in the gas.  We obtain different expressions for the asymptotic mean and variance which involve either the exterior conformal mapping of the curve or the Grunsky operator.

National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:kth:diva-326110 (URN)
Note

QCR 20230426

Available from: 2023-04-24 Created: 2023-04-24 Last updated: 2023-05-04Bibliographically approved

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