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Mathematical Analysis Research Group

We are one of the leading analysis groups in the UK. From the 1960s through to the 1990s our main areas of expertise were spectral theory, operator theory, function spaces and linear partial differential equations, together with the applications of all these ideas in mathematical physics.

From 2007 onwards we have expanded our interests to encompass new areas including:

  • convex analysis
  • analysis in sub-Riemannian manifolds
  • inverse problems and imaging
  • nonlinear partial differential equations
  • deterministic and stochastic homogenisation.

Our work includes the traditional Cardiff University expertise in analytic number theory and topics at the interface between analysis and number theory, such as spectral geometry.

We are an international group with researchers and academics from Germany, Israel, Italy, Russia and the USA, as well as the United Kingdom. Our international collaborations reflect this with ongoing projects with Bern, Birmingham (Alabama), Colorado School of Mines, Florence, Karlsruhe, Montréal,  McGill, Padova, Pisa, Santiago, St Petersburg and the Weizmann Institute, as well as universities in the UK, in particular our colleagues in WIMCS and the GW4 group.

Recent past members of the group include Michael Levitin, Igor Wigman and Kirill Cherednichenko.

Our main directions of research include:

  • spectral theory, applications and numerical methods
  • quantum mechanics, inverse problems
  • asymptotic and variational methods for nonlinear partial differential equations, in particular (stochastic) homogenisation
  • geometric and stochastic partial differential equations
  • combinatorial and analytic number theory, special functions
  • applications of analytical methods (e.g. image processing, medical genetics, scaling limits for interacting particle systems).

In focus

Spectral theory

In 1966 Mark Kac asked the programmatic question “Can one hear the shape of a drum?” - ie is a planar domain determined uniquely (up to congruence) by the spectrum of its Dirichlet Laplacian?

This question has since been answered in the negative, but spectral geometry - the study of how geometric and topological properties of domains and manifolds are reflected in the spectra of associated differential operators - is a flourishing mathematical area with ramifications to number theory and physics.

Our other interests in spectral theory include:

  • operators of mathematical physics, for example stability questions involving qualitative and quantitative estimates and semiclassical asymptotics for operators derived from the Dirac operator of relativistic quantum mechanics, such as the Brown-Ravenhall operator, and extensions to a quantum field theoretic setting
  • non-self-adjoint problems, including spectral approximation, spectral pollution and operator with special block structure
  • inverse spectral problems, including imaging problems and Maxwell systems
  • boundary triples and their applications to spectral theory of (systems of) PDEs.

Geometric and stochastic PDEs

Many physical problems, in particular those involving phase transition, nucleation and evolution equations for free boundaries and interfaces, involve mathematical models in which there is sufficient disorder on a sufficiently small length scale that the most effective analysis of their macroscopic solutions is through the analysis of partial differential equations with stochastic coefficients and scaling limits. We work on several topics in these areas, including:

  • interfaces in heterogeneous and random media and associated nonlinear PDEs
  • interacting Stochastic Processes and their scaling limits; stochastic nonlinear PDEs
  • nonlinear PDEs and Stochastic Processes
  • homogenization  and Gamma-convergence
  • scaling limits of singularly perturbed differential equations.

Another very modern approach to certain classes of nonlinear partial differential equations is through ideas from geometry. We have particular interests in problems involving sub-Riemannian manifolds, which are not isomorphic to Euclidean space at any length scale. In these contexts we have been able to adapt techniques from calculus of variations, and generalise notions of convexity, allowing us to treat subelliptic and ultraparabolic PDEs. These equations occur in many unexpected and new applications, including modelling the first layer of the visual cortex and problems in finance related to pricing Asian options.

Analytic number theory

Cardiff Number Theory was founded by Professor Christopher Hooley FRS and is still one of our most popular areas for doctoral study.

We are active in research on many classical topics:

  • prime numbers
  • the Riemann zeta function
  • Dirichlet polynomials
  • exponential sums
  • Dedekind sums
  • Kloosterman sums
  • the modular group
  • Maass wave forms
  • the Selberg and Kuznetsov trace formulae
  • lattice points in the plane and the Gauss circle problem
  • different configurations of lattice points inside a moving shape, as well as integer points close to hypersurfaces and polytopes.

We are also interested in problems at the interface between number theory and spectral theory, usually arising from spectral geometry.

We are grateful to our research sponsors for the steady flow of funding which they have continued to provide over many years. Our past sponsors include the Leverhulme Trust, the European Union Marie Curie program and the Royal Society, as well as the EPSRC. Our current sponsors include the London Mathematical Society and the EPSRC who finance the following projects:

Head of group

Prof Marco Marletta

Professor Marco Marletta

Deputy Head of School

Email:
marlettam@cardiff.ac.uk
Telephone:
+44 (0)29 2087 5552

Academic staff

Iskander Aliev

Dr Iskander Aliev

Reader

Email:
alievi@cardiff.ac.uk
Telephone:
+44 (0)29 2087 5547
Photograph of Prof Alex Balinsky

Professor Alexander Balinsky

Professor of Mathematical Physics

Email:
balinskya@cardiff.ac.uk
Telephone:
+44 (0)29 2087 5528
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Dr Jonathan Ben-Artzi

Senior Lecturer

Email:
ben-artzij@cardiff.ac.uk
Telephone:
02920 875624
Malcolm Brown

Professor Malcolm Brown

Professor of Computational Mathematics

Email:
brownbm@cardiff.ac.uk
Telephone:
+44 (0)29 2087 5538
Photograph of Mikhail Cherdantsev

Dr Mikhail Cherdantsev

Lecturer

Email:
cherdantsevm@cardiff.ac.uk
Telephone:
+44 (0)29 2087 5549
Dr Nicholas Dirr

Professor Nicolas Dirr

Personal Chair

Email:
dirrnp@cardiff.ac.uk
Telephone:
+44 (0)29 2087 0920
Dr Federica Dragoni

Dr Federica Dragoni

Senior Lecturer

Email:
dragonif@cardiff.ac.uk
Telephone:
+44 (0)29 2087 5529
Dr Suresh Eswarathasan photograph

Dr Suresh Eswarathasan

Lecturer

Email:
eswarathasans@cardiff.ac.uk
Telephone:
+44 (0)29 2087 0935
Photograph of Des Evans

Professor Des Evans

Emeritus Professor of Mathematics

Email:
evanswd@cardiff.ac.uk
Telephone:
+44 (0)29 2087 4206
Photograph of Dr Matthew Lettington

Dr Matthew Lettington

Lecturer

Email:
lettingtonmc@cardiff.ac.uk
Telephone:
+44 (0)29 2087 5670
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Dr Baptiste Morisse

Research Associate

Email:
morisseb@cardiff.ac.uk
Karl Schmidt

Professor Karl Schmidt

Professor

Email:
schmidtkm@cardiff.ac.uk
Telephone:
+44 (0)29 2087 6778
Mathematical Analysis

Dr Kirstin Strokorb

Lecturer

Email:
strokorbk@cardiff.ac.uk
Telephone:
+44 (0)29 2068 8833

Seminars

All seminars are held at 14:10 in Room M/2.06, Senghennydd Road, Cardiff unless stated otherwise.

The programme organiser and contact is Dr Baptiste Morisse.

SpeakersDateAbstract

Mohammed Lemou (Rennes)

7 May 2019

To be announced.

Anne Nouri (Marseille)

8 April 2019

To be announced.

Filip Rindler (Warwick)

25 March 2019

To be announced.

Choi-Hong Lai (Greenwich)

18 March 2019

To be announced.

Jessica Guerand (Cambridge)

11 March 2019

To be announced

Jan Lang (Ohio State)

3:10 - 4:10

4 March 2019

To be announced

Davoud Cheraghi (Imperial)

2:10 - 3:10

4 March 2019

To be announced

Gianne Derks (Surrey)

25 February 2019

To be announced

Stephen Pankavich (Colorado School of Mines)

18 February 2019

To be announced

Yuzhao Wang (Birmingham)

11 February 2019

Further renormalization and unconditionally global well-posedness of the cubic
nonlinear Schrödinger equation (NLS).

We first develop a normal form approach to study NLS in Fourier-Lebesgue spaces. By applying an infinite iteration of normal form reductions, we derive a normal form equation which is
equivalent to the renormalized cubic NLS for regular solutions. For rough functions, the normal form equation behaves better than the renormalized cubic NLS, thus providing a further renormalization of the cubic NLS. Then we establish a global-in-time bounds in Fourier-Lebesgue spaces for the NLS by exploiting its complete integrability and the Galilean symmetry. As a consequence, we obtain the global well-posedness of the cubic NLS.

This is a joint work with Tadahiro Oh at the University of Edinburgh.

Monica Musso (Bath)

4 February 2019

Gluing methods for vortex dynamics in Euler flows

A classical problem for the two-dimensional Euler  flow for an incompressible fluid confined to a smooth domain is that of finding regular solutions with highly concentrated vorticities around N moving vortices. The formal dynamic law for such objects was first derived in the 19th century by Kirkhoff and Routh. We devise a gluing approach for the construction of smooth N-vortex solutions. We capture in high precision the core of each vortex as a scaled finite mass solution of Liouville's equation plus small, more regular terms.
This work is in collaboration with J. D avila, M. del Pino, J. Wei.

Ilya Molchanov (Bern)

28 January 2019

The semigroup of metric measure spaces and stable random spaces

The family of Polish spaces equipped with probability measures can be turned into a semigroup using the Cartesian product as the semigroup operation. The main result is the Fundamental Theorem of Arithmetics for this semigroup, which establishes an analogue of the prime numbers decompositions for such spaces. Further, random metric measure spaces are considered in view of their infinite divisibility and stability properties with respect to the semigroup operation. A characterisation of stable metric measure spaces is also provided.
(joint work with Steve Evans)

Sabine Bögli (Imperial)

21 Januaury 2019

The essential numerical range for unbounded linear operators

If a linear operator T is approximated by projection or domain truncation methods, eigenvalues may accumulate at a point that does not belong to the spectrum of T. The occurrence of such a spurious eigenvalue is commonly known as spectral pollution. A useful tool to describe the set of spectral pollution is the notion of essential numerical range W_e(T) which was introduced in the late 1960s for bounded T. We discuss the generalisation of this notion to unbounded operators, including equivalent characterisations and perturbation results.
This is based on joint work with M.Marletta and C.Tretter.

Michela Ottobre (Herriot-Watt Uni)

10 December 2018

On a class of SDEs with multiple invariant measures

In 1968 Hoermander introduced a sufficient condition to ensure hypoellipticity of second order partial differential operators. As is well known, this seminal work of Hormander had deep repercussions both in the analysis of PDEs and in probability theory and a large strand of literature has been devoted to studying ergodic properties of processes which do satisfy the Hoermander condition  (HC). While such literature has mostly been concerned with study of convergence to equilibrium for dynamics which admit a unique invariant measure, it is a known fact that Hoermander-type diffusions need not be ergodic, i.e. they need not admit a unique invariant measure. In this talk we will present the UFG condition, which is weaker than the Hormander condition. Such a condition was introduced by Kusuoka and Strook with probabilistic motivations, and, independently, by Sussman, Hermann and Lobry, this time in the field of control theory. We will present new results on the geometry and long time behaviour of diffusion semigroups that do not satisfy the Hoermander condition. We will highlight how, loosely speaking, UFG diffusions constitute a large class of SDEs which exhibit multiple equilibria (invariant measures) and such that it is possible to determine in a systematic way the basin of attraction of each  equilibrium state.

Christian Maes (KU Leuven)

3:10 - 4:10

3 December 2018

Time-symmetric aspects of stationary flow

We start by recalling the relation between detailed balance and gradient flow. We generalize it to the case of GENERIC.  We discuss how time-symmetric aspects matter crucially when nonequilibrium driving is added.

David Lafontaine (Bath)

2:10 - 3:10

3 December 2018

About wave and Schrödinger equations in the exterior of many strictly convex obstacles

In order to study the non-linear Schrödinger and wave equations, it is crucial to understand the decay of solutions of the associated linear equations. When a trapped trajectory exists, a loss is unavoidable for a first family of a-priori estimates of the linear flow: the so-called smoothing estimates. In contrast, we will show that in the exterior of many strictly convex obstacles, the estimates of space-time norms of solutions, known as Strichartz estimates, hold with no loss with respect to the flat case, as soon as the dynamic of the trapped trajectories is sufficiently unstable. Finally, if time permits, we will say a word about the associated non-linear equations: if the geometry does not induce too much concentration of energy, we expect that the solutions behave linearly in large times.

Benjamin Gess (Leipzig)

3:10 - 4:10

26 November 2018

Random dynamical systems for stochastic PDE with nonlinear noise.

In this talk we will revisit the problem of generation of random dynamical systems by solutions to stochastic PDE. Despite being at the heart of a dynamical system approach to stochastic dynamics in infinite dimensions, most known results are restricted to stochastic PDE driven by affine linear noise, which can be treated via transformation arguments. In contrast, in this talk we will address instances of stochastic PDE with nonlinear noise, with particular emphasis on porous media equations driven by conservative noise. This class of stochastic PDE arises in particular in the analysis of stochastic mean curvature motion, mean field games with common noise and is linked to fluctuations in non-equilibrium statistical mechanics.

Kirill Cherednichenko (Bath)

2:10 - 3:10

26 November 2018

Periodic PDEs with critical contrast: unified approach to homogenisation and links to time-dispersive media.

I shall discuss a novel approach to the homogenisation of high-contrast periodic PDEs, which yields an explicitly construction of their norm-resolvent asymptotics. A practically relevant outcome of this result is that it interprets  composite media with micro-resonators as a class of time-dispersive media. This is joint work with Yulia Ershova and Alexander Kiselev.

Random dynamical systems for stochastic PDE with nonlinear noise.

In this talk we will revisit the problem of generation of random dynamical systems by solutions to stochastic PDE. Despite being at the heart of a dynamical system approach to stochastic dynamics in infinite dimensions, most known results are restricted to stochastic PDE driven by affine linear noise, which can be treated via transformation arguments. In contrast, in this talk we will address instances of stochastic PDE with nonlinear noise, with particular emphasis on porous media equations driven by conservative noise. This class of stochastic PDE arises in particular in the analysis of stochastic mean curvature motion, mean field games with common noise and is linked to fluctuations in non-equilibrium statistical mechanics.

Mahir Hadžić (KCL)

19 November 2018

Cancelled

Petr Siegl (Belfast)

12 November 2018

Spectral instabilities of Schrödinger operators with complex potentials.

We present an overview of recent results on pseudospectra and basis proper-
ties of eigensystems of one-dimensional Schrödinger operators with unbounded
complex potentials. In particular, we address the problem of localizing the
transition between spectral (Riesz basis of eigenvectors and “normal” behavior
of the resolvent norm) and pseudospectral (vast regions in the complex plane
where the resolvent norm explodes) character of these operators depending on
the size of real and imaginary parts of the potential.
The talk is based on:
[1] B. Mityagin and P. Siegl: Local form-subordination condition and Riesz
basisness of root systems, Journal d’Analyse Math´ ematique, to appear,
arXiv:1608.00224
[2] D. Krejˇ ciˇ r´ık and P. Siegl: Pseudomodes for Schrödinger operators with
complex potentials, Journal of Functional Analysis, to appear, arXiv:1705.01894.

Nicolas Dirr (Cardiff)

Elaine Crooks (Swansea)

Tristan Pryer (Reading)

Carlo Mercuri (Swansea)

Gui-Qiang Chen (Oxford)

11:00 - 5:30

9 November 2018

LMS South-West Network on Generalised Solutions for Nonlinear PDEs

11.30-12.00 Welcome coffee.
12.00-12.35  Nicolas Dirr (Cardiff)
12.40-13.40 LUNCH
13.40-14.15  Elaine Crooks (Swansea)
14.20-14.55 Tristan Pryer (Reading)
15.00-15.15 Coffee break
15.15-15.50 Carlo Mercuri (Swansea)
15.55- 16.30  Gui-Qiang Chen (Oxford)
16.30-17.30 Discussions on EPSRC Network Application

David Beltran (BCAM)

5 November 2018

Local smoothing estimates for Fourier Integral Operators and wave equations

The sharp fixed-time Sobolev estimates for Fourier Integral Operators (and therefore solutions to wave equations in Euclidean space or compact manifolds) were established by Seeger, Sogge and Stein in the early 90s. Shortly after, Sogge observed that a local average in time leads to a regularity improvement with respect to the sharp fixed-time estimates. Establishing variable-coefficient counterparts of the Bourgain—Demeter decoupling inequalities, we improved the previous known local smoothing estimates for FIOs, and we show, in particular, that our results are sharp in both the Lebesgue and regularity exponent (up to the endpoint) in odd dimensions. This is joint work with Jonathan Hickman and Christopher D. Sogge.

Maria Carmen Reguerra (Birmingham)

22 October 2018

Sparse bounds for Bochner-Riesz operators

Sparse operators are positive dyadic operators that have very nice boundedness properties. The L^p bounds and weighted L^p bounds with sharp constant are easy to obtain for these operators. In the recent years, it has been proven that singular integrals (cancellative operators) can be pointwise controlled by sparse operators. This has made the sharp weighted theory of singular integrals quite straightforward. The current efforts focus in understanding the use of sparse operators to bound rougher operators, such a oscillatory integrals. Following this direction, our goal in this talk is to describe the control of Bochner-Riesz operators by sparse operators.

Sanju Velani (York)

15 October 2018

Inhomogeneous Diophantine Approximation on M_0 -sets with restricted denominators

Let F ⊆ [0,1] be a set that supports a probability measure µ with the property that | b µ(t)| ≪ (log|t|) −A for some constant A > 0. Let A = (q n ) n∈ N be a sequence of natural numbers. If A is lacunary and A > 2, we establish a quantitative inhomogeneous Khintchine-type theorem in which (i) the points of interest are restricted to F and (ii) the denominators of the ‘shifted’ rationals are restricted to A. The theorem can be viewed as a natural strengthening of the fact that sequence (q n x mod1) n∈ N is uniformly distributed for µ almost all x ∈ F. Beyond lacunary, our main theorem implies the analogous quantitative result for sequences A for which the prime divisors are restricted to a finite set of k primes and A > 2k.

Frank Rösler (Cardiff)

8 October 2018

Norm-resolvent convergence in perforated domains.

For several different types of boundary conditions (Dirichlet, Neumann and Robin), we prove norm-resolvent convergence for the operator −∆ in the perforated domain Ω without balls of small radius, to the limit operator −∆+µ on L 2 (Ω), where µ ∈ C is a constant depending on the choice of boundary conditions.
This is an improvement of previous results [Cioranescu & Murat. A Strange Term Coming From Nowhere, Progress in Nonlinear Differential Equations and Their Applications, 31, (1997)], [S. Kaizu. The Robin Problems on Domains with Many Tiny Holes. Proc. Japan Acad., 61, Ser. A (1985)], which show strong resolvent convergence. In particular, our result implies Hausdorff convergence of the spectrum of the resolvent for the perforated domain problem.

Anton Savostianov (Durham)

1 October 2018

Homogenisation with error estimates of attractors for damped semi-linear anisotropic wave equations

It is well known that long time behaviour of  a dissipative dynamical system generated by an evolutionary PDE can be described in terms of attractor, an attracting set which is essentially thinner than a ball of the corresponding phase space of the system. In this talk we compare long time behaviour of damped anisotropic wave equations with the corresponding homogenised limit in terms of their attractors. First we will formulate order sharp estimates between the trajectories of the corresponding systems and will see that the hyperbolic nature of the problem results in extra correction comparing with parabolic equations. Then, after brief review on previous results on homogenisation of attractors, we will discuss new results. It appears that the Hausdorff distance between the anisotropic attractors and their homogenised counter-parts, in suitable norms, can be estimated via operator norm of the difference of the resolvents of the corresponding elliptic operators. Furthermore, we show that the homogenised attractor admits first-order correction suggested by the natural asymptotic expansion. The corrected homogenised attractors, as expected, are close to the anisotropic attractors already in the strong energy norm. The corresponding quantitative estimates on the Hausdorff distance between the corrected homogenised attractors and anisotropic ones, with respect to the strong energy norm, are also obtained. Our results are applied to Dirchlet, Neumann and periodic boundary conditions. This is joint work with Shane Cooper.

Marco Marletta (Cardiff University)

Jiang-Lun Wu (Swansea)

Federica Dragoni (Cardiff University)

Peter Hintz (Berkeley)

Dmitri Finkelshtein (Swansea)

27 September 2018

South Wales Analysis and Probability Seminar

9:30-10:00 Coffee and registration
10:00-10:45 Marco Marletta (Cardiff)
10:45-11:30 Jiang-Lun Wu (Swansea)
11:30-11:50 Coffee
11:50-12:35 Federica Dragoni (Cardiff)
12:35-14:05 Lunch
14:05-15:05 Colloquium: Peter Hintz (Berkeley)
15:05-15:30 Coffee
15:30-16:15 Dmitri Finkelshtein (Swansea)

Past events

Mathematical Analysis Seminars 2017-18

Mathematical Analysis Seminars 2015-16

Bath - WIMCS analysis meetings

25/09/2015

These meetings are sponsored by an LMS Scheme Three Grant.

Bath - WIMCS Cardiff meeting

South-West Network in Generalised Solutions for Nonlinear PDEs meetings

12/02/2016

These meetings are organised by Cardiff University, University of Reading and the University of Bath.

University of Bath Meeting.

New trends in non linear PDEs

20/06/2016 - 25/06/2016

The aim of this workshop is to get together researchers within recently very active research areas connected to nonlinear partial differential equations (PDEs), in particular where these cross boundaries of mathematical disciplines.

New trends in non linear PDEs