Seminars in the next week

Oct 16 (Wed)

11:00 zoom A&CYuyu Mo (Edinburgh): *From On-shell amplitude in AdS to Cosmological correlators*

This talk is based on the works [2305.13894], [2402.09111], [2407.16052], and [2410.04875]. We will begin by discussing the motivation and setup of Mellin-momentum amplitudes, along with several examples, including the Feynman rules and their associated pole structures. Following this, we will present the recursive on-shell bootstrap process, which is designed to compute higher-point Mellin-momentum amplitudes for YM and GR in AdS space. Additionally, the bootstrap can be used to derive the Class I soft theorem for Mellin-momentum amplitudes in a diagrammatic fashion. If time permits, we will also introduce a recursive method for finishing the bulk scalar integrals, which connects Mellin-momentum amplitudes to boundary CFT correlators. This process leads to the wavefunction coefficients through wick rotation, thereby providing the cosmological correlators.

**Venue:** zoom

Zoom: https://durhamuniversity.zoom.us/j/99130084840?pwd=NjR1astS2QUnRr1cfF92sEApxLuH3p.1

Oct 17 (Thu)

14:00 MCS2068 G&TF 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 18 (Fri)

13:00 MCS0001 HEPMMatteo 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 21 (Mon)

14:00 MCS2068 ProbOliver Kelsey-Tough (Durham University): *Longtime behaviour of the stochastic FKPP equation conditioned on non-fixation.*

The stochastic FKPP equation is a stochastic PDE which provides a prototypical model for the evolution of the spatial distribution of a given gene type in a large population under the effects of migration, natural selection and genetic drift. It undergoes fixation, representing the given gene type or its complement disappearing from the population. We prove that the stochastic FKPP on the circle killed upon fixation has a unique quasi-stationary distribution, and that the distribution conditioned on non-fixation converges to this unique QSD for any initial condition. Moreover we obtain the asymptotics of the fixation time, as a function of the initial condition. Whereas there is a large literature addressing such questions for finite-dimensional processes, this is one of the very first works to do so in the SPDE or infinite dimensional setting, and the first for a physically relevant SPDE model. This is joint work with Louis Fan.

**Venue:** MCS2068

Oct 22 (Tue)

13:00 MCS2068 ASGJens 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

14:00 MCS2068 APDEGiacomo 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

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Usual Venue: zoom

Contact: arthur.lipstein@durham.ac.uk

Oct 16 11:00 Yuyu Mo (Edinburgh): *From On-shell amplitude in AdS to Cosmological correlators*

This talk is based on the works [2305.13894], [2402.09111], [2407.16052], and [2410.04875]. We will begin by discussing the motivation and setup of Mellin-momentum amplitudes, along with several examples, including the Feynman rules and their associated pole structures. Following this, we will present the recursive on-shell bootstrap process, which is designed to compute higher-point Mellin-momentum amplitudes for YM and GR in AdS space. Additionally, the bootstrap can be used to derive the Class I soft theorem for Mellin-momentum amplitudes in a diagrammatic fashion. If time permits, we will also introduce a recursive method for finishing the bulk scalar integrals, which connects Mellin-momentum amplitudes to boundary CFT correlators. This process leads to the wavefunction coefficients through wick rotation, thereby providing the cosmological correlators.

**Venue:** zoom

Usual Venue: MCS3070

Contact: sabine.boegli@durham.ac.uk

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 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

Nov 19 13:00 Paul Kiefer (Universitaet Bielefeld):

**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: MCS3070

Contact: daniel.n.disney@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 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): *Spectral properties of the symmetrized AMV Laplacian on
manifolds with boundary*

The symmetrized asymptotic mean value Laplacian \u2014 AMV
Laplacian \u2014 extends the Laplace operator from R^n to metric measure
spaces through limits of averaging integrals. In this talk, I will
explain how this operator behaves on manifolds with boundary and how
this sheds new lights on the spectral approximation of singular
manifolds by Laplace-type graphs. This is based on an ongoing joint work
with Manuel Dias (VUB).

**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 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): *String theory and the SymTFT of 3d ortho-symplectic ABJ theory*

Symmetries play a fundamental role in studying quantum field theories (QFTs). They provide selection rules, constrain the dynamics of QFTs, and, through anomalies, a method to test IR or UV dualities among different QFTs. For these reasons, it is important to understand the symmetries that a theory can enjoy. This recently motivated the study of generalized global symmetries and the description of symmetries through the symTFT, which separates the symmetry structure from the field theory dynamics. Holography represents a perfect laboratory to deal with these aspects: string theory reduced on the internal space of the holographic background realizes the symTFT and BPS branes describe the charged and topological operators of the dual theory.
In this talk, I will focus on the type IIA description of ABJ theories. These are an interesting topic in this context: one of their global forms enjoys a binary dihedral or quaternionic discrete symmetry depending on their rank and CS levels, and their holographic dual is known. After characterizing the symmetry web of these theories, I will describe the symTFT and its topological operators, in particular focusing on non-genuine operators showing how the non-Abelian structure of the symmetry group can be detected from their fusion rules and commutation relations. I will then focus on the holographic realization of the theory, obtaining the symTFT from type IIA supergravity. I will identify symmetry operators in terms of BPS branes and see how their tadpoles encode the group structure of the global symmetry. Finally, I will comment on the realization of non-invertible genuine operators through branes, computing the attached TQFT from the reduction of the brane worldvolume theory on the cycle the brane is wrapping. Based on an upcoming work with O. Bergman.

**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): *Carrollian holography from the flat limit of AdS/CFT*

Carrollian holography suggests that gravity in four-dimensional asymptotically flat spacetime is dual to a three-dimensional Carrollian CFT living at null infinity. I will review this approach to flat space holography and its connection to celestial holography. I will explain how massless scattering amplitudes in the bulk can be reformulated in terms of Carrollian CFT correlators at null infinity, known as Carrollian amplitudes. Then, I will argue that Carrollian holography is naturally related to AdS/CFT through a correspondence between flat limit in the bulk and Carrollian limit at the boundary. More specifically, I will show that Carrollian amplitudes are the natural objects arising in the flat limit of holographic correlators in AdS.

This presentation will be mainly based on: https://arxiv.org/abs/2312.10138 https://arxiv.org/abs/2406.19343

**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 21 14:00 Oliver Kelsey-Tough (Durham University): *Longtime behaviour of the stochastic FKPP equation conditioned on non-fixation.*

The stochastic FKPP equation is a stochastic PDE which provides a prototypical model for the evolution of the spatial distribution of a given gene type in a large population under the effects of migration, natural selection and genetic drift. It undergoes fixation, representing the given gene type or its complement disappearing from the population. We prove that the stochastic FKPP on the circle killed upon fixation has a unique quasi-stationary distribution, and that the distribution conditioned on non-fixation converges to this unique QSD for any initial condition. Moreover we obtain the asymptotics of the fixation time, as a function of the initial condition. Whereas there is a large literature addressing such questions for finite-dimensional processes, this is one of the very first works to do so in the SPDE or infinite dimensional setting, and the first for a physically relevant SPDE model. This is joint work with Louis Fan.

**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

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