Mon 06 May 14:00: (CANCELLED, TO BE RESCHEDULED) Leading-order term expansion for the Teukolsky equation on subextremal Kerr black holes
The study of wave propagation on black hole spacetimes has been an intense field of research in the past decades. This interest has been driven by the stability problem for black holes and by questions related to scattering theory. On Kerr black holes, the analysis of Maxwell’s equations and the equations of linearized gravity, can be simplified by introducing the Teukolsky equation, which offers the advantage of being scalar in nature. After explaining this reduction, I will present a result providing the large time leading-order term for initially localized and regular solutions of the Teukolsky equation, valid for the full subextremal range of black hole parameters and for all spins. I will explain how such a development follows naturally from the precise analysis of the resolvent operator on the real axis. Recent advances in microlocal analysis are crucially used to establish the existence and mapping properties of the resolvent.
- Speaker: Pascal Millet (Ecole Polytechnique)
- Monday 06 May 2024, 14:00-15:00
- Venue: MR13.
- Series: Partial Differential Equations seminar; organiser: Dr Greg Taujanskas.
Tue 07 May 16:00: Split signature supergravity - Hypersymplectic geometry via new geometric structures
Hypersymplectic solutions arise in (2,3) signature supergavity in the context of solutions preserving 1/2 of the supersymmetry. We further investigate this supergravity, and show that the hypersymplectic structures arise as a consequence of the existence of certain null endomorphisms associated with 1/4 supersymmetric solutionsm, and which exhibit integrable properties. We also consider other solutions preserving proportions of supersymmetry which cannot arise in the standard (1,4) signature theory
- Speaker: Jan Gutowski (Surrey)
- Tuesday 07 May 2024, 16:00-17:00
- Venue: CMS, MR11.
- Series: Mathematical Physics Seminar; organiser: Professor Maciej Dunajski.
Tue 14 May 16:00: From Twistors to celestial symmetries and their AdS deformations
This talk will review the twistor origins of celestial symmetry algebras and their extension to AdS. It will go on to discuss connections with the integrable systems literature and top down approaches to celestial holography via twistor actions. Join work with Roland Bittleston, Giuseppe Bogna, Simon Heuveline, Adam Kmec & David Skinner https://arxiv.org/abs/2403.18011.
- Speaker: Lionel Mason (Oxford)
- Tuesday 14 May 2024, 16:00-17:00
- Venue: CMS, MR11.
- Series: Mathematical Physics Seminar; organiser: Professor Maciej Dunajski.
Wed 15 May 14:30: Bridging Length Scales in Electrolyte Transport Theory via the Onsager Framework
Improved understanding of transport in concentrated electrolyte solutions has important implications for energy storage, water purification, biological applications, and more. This understanding should ideally persist across length scales: we desire both continuum-level insight into macroscopic concentration and electric potential profiles as well as a molecular-level understanding of the mechanisms governing ion motion. However, the most ubiquitous theory to describe continuum-level electrolyte transport, the Stefan-Maxwell equations, yields transport coefficients which lack clear molecular-level interpretation and cannot be easily computed from molecular simulations.
In this talk, I will present the development of an alternative theory, the Onsager transport framework, to analyze transport at both the continuum and molecular levels. I discuss the integration of continuum mechanics, nonequilibrium thermodynamics, and electromagnetism to derive internal entropy production in electrolytes, yielding the Onsager transport equations: linear laws relating the electrochemical potential gradients and fluxes of each species in solution. At the atomistic level, the transport coefficients emerging from this theory directly quantify correlations in ion motion. These transport coefficients may be computed directly from molecular simulations using Green-Kubo relations derived from Onsager’s regression hypothesis. At the continuum level, the Onsager transport framework provides governing equations for solving macroscopic boundary value problems in electrochemical systems. I will present applications of the theory to both nonaqueous polyelectrolyte solutions for Li-ion batteries as well as nanoconfined electrolytes, demonstrating how the Onsager framework allows us to quantify non-ideal contributions to transport which are very challenging to access experimentally but strongly impact transport in these systems. Overall, this work provides a paradigm for rigorously analyzing transport across length scales in complex electrolyte solutions.
References
K. D. Fong, H. K. Bergstrom, B. D. McCloskey, K. K. Mandadapu. “Transport Phenomena in Electrolyte Solutions: Non-Equilibrium Thermodynamics and Statistical Mechanics.” AIChE Journal, 2020, 66, 12: e17091.
K. D. Fong, J. Self, B. D. McCloskey, K. A. Persson. “Ion Correlations and Their Impact on Transport in Polymer-Based Electrolytes.” Macromolecules, 2021, 54, 6: 2575-2591.
K. D. Fong, J. Self, B. D. McCloskey, K. A. Persson. “Onsager Transport Coefficients and Transference Numbers in Polyelectrolyte Solutions and Polymerized Ionic Liquids.” Macromolecules, 2020, 53, 21: 9503-9512.
- Speaker: Dr Kara Fong, University of Cambridge
- Wednesday 15 May 2024, 14:30-15:30
- Venue: Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.
- Series: Theory - Chemistry Research Interest Group; organiser: Lisa Masters.
Tue 30 Apr 14:30: Anticyclotomic $p$-adic $L$-functions for families of $U_n \times U_{n+1}$
I will report on recent work on the construction of anticyclotomic $p$-adic $L$-functions for Rankin—Selberg products. I will explain how by $p$-adically interpolating the branching law for the spherical pair $\left(U_n, U_n \times U_{n+1}\right),$ we can construct a $p$-adic $L$-function attached to cohomological automorphic representations of $U_n \times U_{n+1}$. Due to the recent proof of the unitary Gan—Gross—Prasad conjecture, this $p$-adic $L$-function interpolates the square root of all critical $L$-values, including anticyclotomic variation. Time allowing, I will explain how we can extend this result to the Coleman family of an automorphic representation.
- Speaker: Xenia Dimitrakopoulou (Warwick)
- Tuesday 30 April 2024, 14:30-15:30
- Venue: MR13.
- Series: Number Theory Seminar; organiser: Jef Laga.
Thu 20 Feb 14:00: Title to be confirmed
Abstract not available
- Speaker: Frank Pollmann, TU Munich
- Thursday 20 February 2025, 14:00-15:00
- Venue: TCM Seminar Room.
- Series: Theory of Condensed Matter; organiser: Gaurav.
Wed 30 Oct 14:30: Title to be confirmed
Abstract not available
- Speaker: Professor Marialore Sulpizi, Ruhr University Bochum
- Wednesday 30 October 2024, 14:30-15:30
- Venue: Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry.
- Series: Theory - Chemistry Research Interest Group; organiser: Lisa Masters.
Thu 02 May 16:00: Fano 3-folds with 1-dimentional K-moduli. EMG - New equivariant methods in algebraic and differential geometry
We introduce K-stability, and the motivation behind it. We will see how to study and completely describe all one-dimensional components of the K-moduli of smooth Fano 3-folds. And we will finish giving some specific examples for family 3.12 (blow-up of a disjoint line and twisted cubic on P^3). This result is in collaboration with Abban, Cheltsov, Denisova, Kaloghiros, Jiao, Martinez-Garcia and Papazachariou.
EMG - New equivariant methods in algebraic and differential geometry
- Speaker: Erroxe Etxabarri alberdi (University of Nottingham)
- Thursday 02 May 2024, 16:00-17:00
- Venue: Seminar Room 2, Newton Institute.
- Series: Isaac Newton Institute Seminar Series; organiser: nobody.
Tue 30 Apr 14:00: Packing Spheres Randomly
In this talk I’ll show that there exists a packing of identical spheres in \Rd of density $(1+o(1))2{-d-1}d*log d$ as $d\to \infty$. The proof uses a simple random algorithm where we sprinkle the spheres in rounds.
This is joint work with Matthew Jenssen, Marcus Michelen and Julian Sahasrabudhe.
- Speaker: Marcelo Campos (DPMMS)
- Tuesday 30 April 2024, 14:00-15:00
- Venue: MR12.
- Series: Probability; organiser: Perla Sousi.
Wed 01 May 14:30: Universality for bootstrap percolation
In this talk I will give an overview of the proof of the “Universality Conjecture” for general bootstrap percolation models. Roughly speaking, the conjecture states that every d-dimensional monotone cellular automaton is a member of one of d+1 universality classes, which are characterized by their behaviour on sparse random sets. More precisely, it states that if sites of the lattice Z^d are initially infected independently with probability p, then the expected infection time of the origin is either infinite, or is a tower of height r for some r \in {1,...,d}. I will also describe an uncomputability result regarding the exponent of p at the top of the tower.
Based on joint work with Paul Balister, Béla Bollobás and Paul Smith.
- Speaker: Rob Morris (IMPA)
- Wednesday 01 May 2024, 14:30-15:30
- Venue: MR12.
- Series: Combinatorics Seminar; organiser: ibl10.
Thu 02 May 16:00: Two phase buoyant plumes in stratified systems ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
We present some theoretical and experimental results on the dynamics of two phase turbulent buoyant plumes – both with particles and with bubbles – to demonstrate some of the effects of phase separation on the overall flow patterns, and flow behaviour and some of the instabilities that arise as a result.
ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
- Speaker: Woods Andy (University of Cambridge)
- Thursday 02 May 2024, 16:00-17:00
- Venue: Seminar Room 1, Newton Institute.
- Series: Isaac Newton Institute Seminar Series; organiser: nobody.
Tue 07 May 11:30: The role of methane for chemistry-climate interactions: rapid radiative adjustments and climate feedbacks Zoom link: https://us02web.zoom.us/j/89826306833?pwd=cnNHSG9OWHRjVngzMGVMc2F0NnA4dz09
Methane (CH4), the second most important greenhouse gas directly emitted by human activity, is removed from the atmosphere via chemical degradation. The chemical sink of CH4 is influenced by temperature and the chemical composition of the atmosphere. It is further an important source of water vapour in the stratosphere and affects the ozone concentration in the troposphere and the stratosphere via secondary feedbacks.
The talk will focus on the role of these chemistry-climate interactions in numerical simulations with the chemistry-climate model EMAC perturbed by either CO2 or CH4 increase. For both forcing agents, CO2 and CH4 , so called rapid radiative adjustments are assessed in simulations with prescribed sea surface temperatures, as well as climate feedbacks in respective simulations using an interactive oceanic mixed layer.
The simulation set-up uses CH4 emission fluxes instead of prescribed CH4 concentrations at the lower boundary so that changes of the chemical sink can feed back on the atmospheric CH4 concentration without constraints.
The results show a shortening of the CH4 lifetime and, accordingly, a reduction of the CH4 mixing ratios in a warming and moistening troposphere. This decrease in CH4 also affects the response of tropospheric ozone.
Furthermore, recently an additional radiation scheme was implemented into the EMAC model, which represents the direct radiative effect of CH4 better and also accounts for the absorption by CH4 in the solar shortwave spectrum. With the new radiation scheme the effective radiative forcing for the same perturbation of CH4 emissions is larger, and individual rapid radiative adjustments, e.g. of clouds, are changed.
Zoom link: https://us02web.zoom.us/j/89826306833?pwd=cnNHSG9OWHRjVngzMGVMc2F0NnA4dz09
- Speaker: Laura Stecher, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre (Engl: German Aerospace Center, Institute of Atmospheric Physics)
- Tuesday 07 May 2024, 11:30-12:30
- Venue: Chemistry Dept, Unilever Lecture Theatre and Zoom.
- Series: Centre for Atmospheric Science seminars, Chemistry Dept.; organiser: .
Mon 29 Apr 14:00: STRICHARTZ ESTIMATES FOR THE 2D AND 3D MASSLESS DIRAC-COULOMB EQUATIONS
The massless Dirac equation with a Coulomb potential is interesting both from a physical and a mathematical point of view; it appears in some physical models, for instance the 2D equation is used to describe the dynamics of carbon atoms in a sheet of non-perfect graphene, and on the mathematical side the homogeneity of degree -1 of the potential seems to have a critical behavior, as |x| goes to infinity, since Strichartz estimates are known to hold for potentials that decay faster and there are examples of potentials decaying slower such that the corresponding flows do not disperse. In this talk I will present a recent result concerning Strichartz estimates for the solutions of the massless Dirac-Coulomb equation in 2 and 3 dimension with additional angular regularity. It extends the result on R3 of Cacciafesta-Séré-Zhang and provides completely new estimates on R2. As an application we will discuss a local well-posedness result for a nonlinear system.
- Speaker: Elena Danesi
- Monday 29 April 2024, 14:00-15:00
- Venue: MR13.
- Series: Partial Differential Equations seminar; organiser: Dr Greg Taujanskas.
Thu 02 May 16:00: Two phase buoyant plumes in stratified systems ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
We present some theoretical and experimental results on the dynamics of two phase turbulent buoyant plumes – both with particles and with bubbles – to demonstrate some of the effects of phase separation on the overall flow patterns, and flow behaviour and some of the instabilities that arise as a result.
ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
- Speaker: Andy Woods (National and Capodistrian University of Athens)
- Thursday 02 May 2024, 16:00-17:00
- Venue: Seminar Room 1, Newton Institute.
- Series: Isaac Newton Institute Seminar Series; organiser: nobody.
Mon 06 May 14:00: Leading-order term expansion for the Teukolsky equation on subextremal Kerr black holes
The study of wave propagation on black hole spacetimes has been an intense field of research in the past decades. This interest has been driven by the stability problem for black holes and by questions related to scattering theory. On Kerr black holes, the analysis of Maxwell’s equations and the equations of linearized gravity, can be simplified by introducing the Teukolsky equation, which offers the advantage of being scalar in nature. After explaining this reduction, I will present a result providing the large time leading-order term for initially localized and regular solutions of the Teukolsky equation, valid for the full subextremal range of black hole parameters and for all spins. I will explain how such a development follows naturally from the precise analysis of the resolvent operator on the real axis. Recent advances in microlocal analysis are crucially used to establish the existence and mapping properties of the resolvent.
- Speaker: Pascal Millet (Ecole Polytechnique)
- Monday 06 May 2024, 14:00-15:00
- Venue: MR13.
- Series: Partial Differential Equations seminar; organiser: Dr Greg Taujanskas.
Tue 14 May 14:30: TBA
TBA
- Speaker: Luis García (UCL)
- Tuesday 14 May 2024, 14:30-15:30
- Venue: MR13.
- Series: Number Theory Seminar; organiser: Jef Laga.
Tue 28 May 14:30: TBA
TBA
- Speaker: Beth Romano (King's College London)
- Tuesday 28 May 2024, 14:30-15:30
- Venue: MR13.
- Series: Number Theory Seminar; organiser: Jef Laga.
Thu 02 May 16:00: Two phase buoyant plumes in stratified systems ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
We present some theoretical and experimental results on the dynamics of two phase turbulent buoyant plumes – both with particles and with bubbles – to demonstrate some of the effects of phase separation on the overall flow patterns, and flow behaviour and some of the instabilities that arise as a result.
ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
- Speaker:
- Thursday 02 May 2024, 16:00-17:00
- Venue: Discussion Room, Newton Institute.
- Series: Isaac Newton Institute Seminar Series; organiser: nobody.
Wed 01 May 11:30: Anomalous diffusion from parsecs to micrometers ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
I will talk about anomalous diffusion in two problems at two very different length scales. (A) Compressible turbulence at the scale of parsecs. One of the cornerstones of incompressible turbulence is the Richardson’s law which states that the mean of the square of the distance between two Lagrangian particles grows as the cube of time: R2 \sim t3. I will show from numerical simulations that this does not hold in shock dominated turbulence. We will then generalize the multifractal model to include shocks and thereby rationalize the generalization of Richarson’s law to compressible turbulence. (B) Cell membrane at the scale of micrometers. Experiments show that the cell membrane is an exotic two-dimensional material which has both solid like and fluid like properties. An example of the former is the existence of a non-zero elastic shear modulus. Evidence in support of the fluid like behavior are: (1) tether formation (2) lateral diffusion, simple of anomalous, of lipid molecules. We construct a model that can capture both of these aspects. (A) is done in collaboration with Sadhitro De and Rahul Pandit, pre-print ( arXiv:2311.06836 ) . (B) is done in collaboration with Vikash Pandey, pre-print( arXiv:2404.12211).
ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
- Speaker: Dhrubaditya Mitra (NORDITA)
- Wednesday 01 May 2024, 11:30-12:30
- Venue: Seminar Room 1, Newton Institute.
- Series: Isaac Newton Institute Seminar Series; organiser: nobody.
Tue 30 Apr 11:30: Large-scale flow structures in turbulent Rayleigh-Bénard convection: Dynamical origin, formation, and role in material transport ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
The interplay of gravity with mass density inhomogeneities introduces natural (thermal) convection and represents the essential mechanism by which heat is transported in natural flows. Simultaneously, natural flows are often far more extended in the horizontal direction than in the vertical one. Motivated by these two observations and the various geo- and astrophysical applications (e.g. the solar convection zone), 3-dimensional Rayleigh-Bénard convection as the paradigm of thermal convection has been studied. This talk will cover some recent results from studying the impact of thermal (and mechanical) boundary conditions on large-scale flow structures in Rayleigh-Bénard convection by means of direct numerical simulations. It will be shown that thermal boundary conditions are crucial to the formation of long-living large-scale (turbulent) flow structures. In particular, a slow transient aggregation process — that only stops once the horizontal extent of the domain is reached — can be found once the fluid layer is subjected to Neumann-type constant heat flux boundary conditions. As a result, the temperature field in the domain is separated into one extended hot and another extended cold region. We trace this mechanism of self-organisation of flow structures back to secondary instabilities as well as an inverse cascade in spectral space. The talk will finish with a brief overview of our work on the identification of those large-scale flow structures by the use of unsupervised machine learning based on Lagrangian particle data. Selected references [1] P P Vieweg, J D Scheel and J Schumacher, “Supergranule aggregation for constant heat flux-driven turbulent convection”, Phys. Rev. Research 3, 013231 (2021). DOI : 10.1103/PhysRevResearch.3.013231 [2] P P Vieweg, “Large-scale flow structures in turbulent Rayleigh-Bénard convection: Dynamical origin, formation, and role in material transport” (PhD thesis, TU Ilmenau, Germany, 2023). DOI : 10.22032/dbt.58334
ADI - Anti-diffusive dynamics: from sub-cellular to astrophysical scales
- Speaker: Philipp Patrick Vieweg (University of Cambridge)
- Tuesday 30 April 2024, 11:30-12:30
- Venue: Seminar Room 1, Newton Institute.
- Series: Isaac Newton Institute Seminar Series; organiser: nobody.