Seminars in the next week

Oct 09 (Wed)

11:00 zoom A&CSimon Heuveline (Cambridge): *Towards celestial chiral algebras of self-dual black holes*

This talk is based on 2408.14324 and 2403.18011. We discuss that celestial symmetries get deformed by the presence of a non-zero cosmological constant giving a twistor interpretation of an algebra earlier obtained by Taylor and Zhu. The deformation arises from a twistor action for self-dual gravity with $\Lambda\neq 0$ that is expected to be an uplift of the recent spacetime action by Lipstein and Nagy. The twistor space of AdS$_4$ can be further deformed by a backreaction leading to a 2-parameter twistor space of a certain self-dual Taub-NUT AdS$_4$ spacetime, the Pedersen metric. Its twistor space leads to a 2-parameter deformation of $Lw_\wedge$ which reduces to previously studied algebras in various limits.

**Venue:** zoom

Zoom: https://durhamuniversity.zoom.us/j/98708622549?pwd=KygYMuXHyTb8Ac7DUGupJeXo8xCbri.1

13:00 MCS2068 S4GJonathan Rougier (Bristol): *Working as an industrial statistician*

Prof Jonty Rouger (AWE Aldermaston and the University of Bristol) will give a short presentation on "Working as an industrial statistician" and then he will have an informal chats with any who wanted to know more.

**Venue:** MCS2068

Oct 10 (Thu)

14:00 MCS2068 G&TMauricio Che (Durham): *Isometric rigidity with respect to Wasserstein spaces*

We can endow sets of Borel probability measures on a given
metric space $X$ with different metrics derived from optimal transport,
resulting in the $L^p$-Wasserstein spaces over $X$, denoted
$\mathbb{P}_p(X)$. In general, these spaces reflect several properties
of the underlying space. One natural question in this context is: how
are the isometries of $\mathbb{P}_p(X)$ related to those of $X$? In this
talk, I will discuss existing results in this area and present work in
progress with Fernando Galaz-García, Martin Kerin, and Jaime
Santos-Rodríguez. We have identified families of spaces in which $X$ and
$\mathbb{P}_p(X)$ share the same isometries, in which case we say that
$X$ is isometrically rigid with respect to $\mathbb{P}_p$, as well as
examples where this is not the case.

**Venue:** MCS2068

Oct 11 (Fri)

13:00 MCS0001 HEPMZongzhe Du (Nottingham University): *Hidden Adler zero and Soft theorem for Inflationary perturbations*

Soft limits of scattering amplitudes play a crucial role in identifying the infrared (IR) structures of effective field theories (EFTs). In this talk, I will briefly introduce the success of the S-matrix program, and the techniques used to classify scalar EFTs, providing examples along the way. I will then address the problem of singular behaviors in cubic vertices under soft limits. A schematic derivation of the soft theorem will be presented, demonstrating that by properly ordering the limitssoft, on-shell, and epsilonthe cubic conundrum is naturally resolved. Finally, I will discuss a soft theorem for the EFT of inflation, which holds to all orders in perturbation theory, and show how it determines the Wilson coefficients up to the known degrees of freedom.

**Venue:** MCS0001

Oct 14 (Mon)

14:00 MCS2068 ProbTyler Helmuth (Durham University):

**Venue:** MCS2068

Oct 15 (Tue)

13:00 MCS2068 ASGJens Funke (Durham): *Indefinite theta series I*

In this series of two talks I will give a gentle introduction to indefinite theta series and their applications in arithmetic and geometry. Some basic knowledge of modular forms will be assumed.

**Venue:** MCS2068

14:00 MCS2068 APDEMegan Griffin-Pickering (University College London): *A Probabilistic Derivation of the Vlasov-Poisson System for Ions*

The Vlasov-Poisson system for ions is a kinetic model for dilute plasma, describing electrostatic interactions between positive ions and thermalized electrons following a Maxwell-Boltzmann law. The equation arises formally as the mean field limit from an underlying microscopic system representing individual ions interacting with a thermalized electron distribution. However, when ions are modelled as point charges, it is an open problem to prove rigorously that the mean field limit holds. One avenue of progress on the problem has been to consider particle systems with regularised interactions, in which the singularity in the Coulomb force is removed at small spatial scales, with the cut-off radius vanishing as the number of particles \(N\) tends to infinity. Previously, the Vlasov-Poisson system for ions was derived rigorously from a system of this type, with cut-off radius of order \(1/N^a\) with \(a < 1/15\) in three dimensions.

**Venue:** MCS2068

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Usual Venue: zoom

Contact: arthur.lipstein@durham.ac.uk

Oct 09 11:00 Simon Heuveline (Cambridge): *Towards celestial chiral algebras of self-dual black holes*

This talk is based on 2408.14324 and 2403.18011. We discuss that celestial symmetries get deformed by the presence of a non-zero cosmological constant giving a twistor interpretation of an algebra earlier obtained by Taylor and Zhu. The deformation arises from a twistor action for self-dual gravity with $\Lambda\neq 0$ that is expected to be an uplift of the recent spacetime action by Lipstein and Nagy. The twistor space of AdS$_4$ can be further deformed by a backreaction leading to a 2-parameter twistor space of a certain self-dual Taub-NUT AdS$_4$ spacetime, the Pedersen metric. Its twistor space leads to a 2-parameter deformation of $Lw_\wedge$ which reduces to previously studied algebras in various limits.

**Venue:** zoom

Usual Venue: MCS3070

Contact: sabine.boegli@durham.ac.uk

Oct 15 14:00 Megan Griffin-Pickering (University College London): *A Probabilistic Derivation of the Vlasov-Poisson System for Ions*

The Vlasov-Poisson system for ions is a kinetic model for dilute plasma, describing electrostatic interactions between positive ions and thermalized electrons following a Maxwell-Boltzmann law. The equation arises formally as the mean field limit from an underlying microscopic system representing individual ions interacting with a thermalized electron distribution. However, when ions are modelled as point charges, it is an open problem to prove rigorously that the mean field limit holds. One avenue of progress on the problem has been to consider particle systems with regularised interactions, in which the singularity in the Coulomb force is removed at small spatial scales, with the cut-off radius vanishing as the number of particles \(N\) tends to infinity. Previously, the Vlasov-Poisson system for ions was derived rigorously from a system of this type, with cut-off radius of order \(1/N^a\) with \(a < 1/15\) in three dimensions.

**Venue:** MCS2068

Oct 22 14:00 Giacomo Sodini (University of Vienna): *Dissipative evolutions in the space of probability measures*

We introduce a notion of multivalued dissipative operator (called Multivalued Probability Vector Field - MPVF) in the 2-Wasserstein space of Borel probability measures on a (possibly infinite dimensional) separable Hilbert space. Taking inspiration from the theories of dissipative operators in Hilbert spaces and of Wasserstein gradient flows, we study the well-posedness for evolutions driven by such MPVFs, and we characterize them by a suitable Evolution Variational Inequality (EVI). Our approach to prove the existence of such EVI-solutions is twofold: on one side, under an abstract stability condition, we build a measure-theoretic version of the Explicit Euler scheme showing novel convergence results with optimal error estimates; on the other hand, under a suitable discrete approximation assumption on the MPVF, we recast the EVI-solution as the evolving law of the solution trajectory of an appropriate dissipative evolution in an \(L^2\) space of random variables. This talk is based on joint works with Giulia Cavagnari and Giuseppe Savaré.

**Venue:** MCS2068

Nov 19 14:00 Espen Jakobsen (Norwegian University of Science and Technology): *On Mean Field Games with nonlocal and nonlinear diffusions*

Mean Field Games (MFGs) are limits for N-player games as the number of players N tends to infinity. In the limit a Nash equilibrium is characterized by a coupled system of nonlinear PDEs - the MFG system - a backward Bellman equation for the optimal strategy of a generic player and a forward Fokker-Planck equation for the distribution of players. The mathematical theory goes back to 2006 and work of Lasry-Lions and Cains-Haung-Malhame, and important questions addressed by the literature include well-posedness, approximations/numerical methods, and the convergence problem -- rigorously proving the limit as N tends to infinity. The latter problem involves the so-called Master equation, a PDE posed on the set of probability measures, whos characteristic equations are precisely the above mentioned MFG system. In most of the results in the literature, the diffusion is local/Gaussian and linear/uncontrolled.

In this talk I will discuss recent results on MFGs with (i) nonlocal and (ii) nonlinear diffusions. Case (i) corresponds to a MFGs where players are affected by independent non-Gaussian/Levy induvidual noises, leading to nondegenerate PDEs with linear nonlocal diffusion terms. Results on well-posedness, numerical approximations, and the corresponding Master equation will be addressed. In case (ii), the indepdent individual noises are controlled by the players, and the PDEs become fully nonlinear. We will address well-posedness results for the MFG system in this case. The talk is based on joint work with former PhD students and postdocs, O. Ersland (NTNU), I. Chowdhury (IIT Kanpur), M. Krupski (U Wroclaw), and A. Rutkowski (TU Wroclaw).

**Venue:** MCS2068

Usual Venue: MCS2068

Contact: andrew.krause@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS2068

Contact: herbert.gangl@durham.ac.uk

Oct 15 13:00 Jens Funke (Durham): *Indefinite theta series I*

In this series of two talks I will give a gentle introduction to indefinite theta series and their applications in arithmetic and geometry. Some basic knowledge of modular forms will be assumed.

**Venue:** MCS2068

Oct 22 13:00 Jens Funke (Durham): *Indefinite theta series II*

In this series of two talks I will give a gentle introduction to indefinite theta series and their applications in arithmetic and geometry. Some basic knowledge of modular forms will be assumed.

**Venue:** MCS2068

Oct 29 13:00 Thomas Oliver (Westminster):

**Venue:** MCS2068

Nov 05 13:00 Philippe Elbaz-Vincent (Grenoble, CNRS):

**Venue:** MCS2068

Nov 12 13:00 Luis Garcia (University College London):

**Venue:** MCS2068

Dec 03 13:00 Matthias Storzer (University College Dublin):

**Venue:** MCS2068

Dec 10 13:00 Jeffrey Manning (Imperial College London):

**Venue:** MCS2068

Usual Venue: OC218

Contact: mohamed.anber@durham.ac.uk

For more information, see HERE.

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS0001

Contact: inaki.garcia-etxebarria@durham.ac.uk,sunil.chhita@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS0001

Contact: sabine.boegli@durham.ac.uk,alpar.r.meszaros@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS3052

Contact: andrew.krause@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS3070

Contact: gabriel.fuhrmann@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS2068

Contact: martin.p.kerin@durham.ac.uk

Oct 10 14:00 Mauricio Che (Durham): *Isometric rigidity with respect to Wasserstein spaces*

We can endow sets of Borel probability measures on a given
metric space $X$ with different metrics derived from optimal transport,
resulting in the $L^p$-Wasserstein spaces over $X$, denoted
$\mathbb{P}_p(X)$. In general, these spaces reflect several properties
of the underlying space. One natural question in this context is: how
are the isometries of $\mathbb{P}_p(X)$ related to those of $X$? In this
talk, I will discuss existing results in this area and present work in
progress with Fernando Galaz-García, Martin Kerin, and Jaime
Santos-Rodríguez. We have identified families of spaces in which $X$ and
$\mathbb{P}_p(X)$ share the same isometries, in which case we say that
$X$ is isometrically rigid with respect to $\mathbb{P}_p$, as well as
examples where this is not the case.

**Venue:** MCS2068

Oct 17 14:00 F Tripaldi (Leeds): *Extracting subcomplexes on filtered manifolds*

I will present a general construction of subcomplexes on
Riemannian filtered manifolds. In the particular case of regular
subRiemannian manifolds, this yields the so-called Rumin complex when
the manifold is also equipped with a compatible Riemannian metric.

I will then show how the subcomplex differs on a nilpotent Lie group equipped with a homogeneous structure on one hand, and a left-invariant filtration on the other.

**Venue:** MCS2068

Oct 24 14:00 David Tewodrose (Vrije Universiteit Brussel): *TBA*

**Venue:** MCS2068

Oct 31 14:00 Brendan Owens (Glasgow): *TBA*

**Venue:** MCS2068

Nov 07 14:00 Will Rushworth (Newcastle): *On knots that divide ribbon knotted surfaces*

Every knot in S^3 appears as a cross-section of a knotted
surface in S^4. By restricting to ribbon knotted surfaces (those that
are Morse-theoretically simple) we develop new notions of complexity for
knots in S^3. We'll discuss these notions in relation to the ribbon
property in S^3, the double slice genus, and the fusion number.

**Venue:** MCS2068

Nov 14 14:00 Stuart Hall (Newcastle): *TBA*

**Venue:** MCS2068

Nov 21 14:00 Philipp Reiser (Fribourg): *TBA*

**Venue:** MCS2068

Nov 28 14:00 John Hunton (Durham): *TBA*

**Venue:** MCS2068

Dec 05 14:00 Diego Corro (Cardiff): *TBA*

**Venue:** MCS2068

Jan 16 14:00 Patrick Wood (Durham): *TBA*

**Venue:** MCS2068

Jan 30 14:00 Ana García Lecuona (Glasgow): *TBA*

**Venue:** MCS2068

Feb 06 14:00 Anthea Monod (Imperial): *TBA*

**Venue:** MCS2068

Usual Venue: MCS3070

Contact: andrea.grigoletto@durham.ac.uk,nakarin.lohitsiri@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS0001

Contact: silvia.nagy@durham.ac.uk,enrico.andriolo@durham.ac.uk,tobias.p.hansen@durham.ac.uk

Oct 11 13:00 Zongzhe Du (Nottingham University): *Hidden Adler zero and Soft theorem for Inflationary perturbations*

Soft limits of scattering amplitudes play a crucial role in identifying the infrared (IR) structures of effective field theories (EFTs). In this talk, I will briefly introduce the success of the S-matrix program, and the techniques used to classify scalar EFTs, providing examples along the way. I will then address the problem of singular behaviors in cubic vertices under soft limits. A schematic derivation of the soft theorem will be presented, demonstrating that by properly ordering the limitssoft, on-shell, and epsilonthe cubic conundrum is naturally resolved. Finally, I will discuss a soft theorem for the EFT of inflation, which holds to all orders in perturbation theory, and show how it determines the Wilson coefficients up to the known degrees of freedom.

**Venue:** MCS0001

Oct 18 13:00 Matteo Romoli (Rome III University): *A double-copy perspective on asymptotic symmetries*

In the framework of convolutional double copy, we investigate the asymptotic symmetries of the gravitational multiplet stemming from the residual symmetries of its single-copy constituents at null infinity. We show that the asymptotic symmetries of Maxwell fields in D = 4 imply “double-copy supertranslations”, i.e. BMS supertranslations and two-form asymptotic symmetries, together with the existence of infinitely many conserved charges involving the double-copy scalar. Finally, we discuss the challenges of generalising these results to higher orders from the perspective of both asymptotic symmetries and double copy.
The seminar is based on 2402.11595, 2409.08131 and a work in progress.

**Venue:** MCS0001

Oct 25 13:00 Francesco Mignosa (Technion University): *TBA*

TBA

**Venue:** MCS0001

Nov 01 13:00 Lorenzo Bianchi (Turin University): *Impurities in long-range statistical models*

After reviewing some recent progress in the application of bootstrap techniques to impurities in statistical models, I will consider the long-range Ising model in the continuum limit, i.e. a non-local field theory with quartic coupling. I will describe three different ways of constructing conformal defects in this theory. While one method mimics the construction of defects in the local model, the other two are specific to the non-local model and they can be studied directly in d=3 using a perturbative expansion around the crossover between the long-range theory and the Gaussian one.

**Venue:** MCS0001

Nov 08 13:00 Nat Levine (ENS Paris): *TBA*

TBA

**Venue:** MCS0001

Nov 15 13:00 Ana Maria Raclariu (King's College London): *TBA*

TBA

**Venue:** MCS0001

Nov 22 13:00 Xiang Zhao (EPFL Lausanne): *TBA*

TBA

**Venue:** MCS0001

Nov 29 13:00 Romain Ruzziconi (Oxford University): *TBA*

TBA

**Venue:** MCS0001

Dec 06 13:00 Andrea Antinucci (SISSA): *TBA*

TBA

**Venue:** MCS0001

Dec 13 13:00 Nicole Righi (King's College London): *TBA*

TBA

**Venue:** MCS0001

Usual Venue: MCS2068

Contact: kohei.suzuki@durham.ac.uk

Oct 14 14:00 Tyler Helmuth (Durham University):

**Venue:** MCS2068

Oct 21 14:00 Oliver Kelsey-Tough (Durham University):

**Venue:** MCS2068

Oct 28 14:00 Michael McAuley (TU Dublin):

**Venue:** MCS2068

Nov 04 14:00 Jere Koskela (Newcastle University):

**Venue:** MCS2068

Nov 11 14:00 Felix Foutel-Rodier (Oxford University):

**Venue:** MCS2068

Nov 25 14:00 Avi Mayorcas (University of Bath):

**Venue:** MCS2068

Dec 02 14:00 Hiroshi Kawabi (Oxford University, Keio University):

**Venue:** MCS2068

Dec 09 14:00 Noe Kawamoto (NCCU, Taiwan):

**Venue:** MCS2068

Usual Venue: MCS0001

Contact: raphael.zentner@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS3070

Contact: irving.d.calderon-camacho@durham.ac.uk,joe.thomas@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Usual Venue: MCS2068

Contact: hyeyoung.maeng@durham.ac.uk,andrew.iskauskas@durham.ac.uk

No upcoming seminars have been scheduled (not unusual outside term time).

Contact: adam.stone2@durham.ac.uk

Oct 09 13:00 Jonathan Rougier (Bristol): *Working as an industrial statistician*

Prof Jonty Rouger (AWE Aldermaston and the University of Bristol) will give a short presentation on "Working as an industrial statistician" and then he will have an informal chats with any who wanted to know more.

**Venue:** MCS2068