Seminars in the next week

Jan 21 (Fri)

13:00 Luca Nenna : * Transport type metrics on the space of probability measures involving singular base measures *

In this talk we develop the theory of a metric, which we call the $\nu$-based Wasserstein metric and denote by $W_\nu$, on the set of probability measures $\mathcal P(X)$ on a domain $X \subseteq \mathbb{R}^m$. This metric is based on a slight refinement of the notion of generalized geodesics with respect to a base measure $\nu$ and is relevant in particular for the case when $\nu$ is singular with respect to $m$-dimensional Lebesgue measure; it is also closely related to the concept of linearized optimal transport. The $\nu$-based Wasserstein metric is defined in terms of an iterated variational problem involving optimal transport to $\nu$; we also characterize it in terms of integrations of classical Wasserstein distance between the conditional probabilities when measures are disintegrated with respect to optimal transport to $\nu$, and through limits of certain multi-marginal optimal transport problems. As we vary the base measure $\nu$, the $\nu$-based Wasserstein metric interpolates between the usual quadratic Wasserstein distance (obtained when $\nu$ is a Dirac mass) and a metric associated with the uniquely defined generalized geodesics obtained when $\nu$ is sufficiently regular (eg, absolutely continuous with respect to Lebesgue). When $\nu$ concentrates on a lower dimensional submanifold of $\mathbb{R}^m$, we prove that the variational problem in the definition of the $\nu$-based Wasserstein distance has a unique solution. We establish geodesic convexity of the usual class of functionals, and of the set of source measures $\mu$ such that optimal transport between $\mu$ and $\nu$ satisfies a strengthening of the generalized nestedness condition introduced in McCann&Pass 2020. If time permitted we also present an applications of the ideas introduced: we also use the multi-marginal formulation to characterize solutions to the multi-marginal problem by an ordinary differential equation, yielding a new numerical method for it.

Zoom: https://durhamuniversity.zoom.us/j/96625227152?pwd=YUo2M2VJdVdaa0J6QTdUUEZjajNJUT09

13:00 Costis Papageorgakis: * Towards Solving CFTs with Artificial Intelligence *

I will introduce a novel numerical approach for solving the conformal-bootstrap equations with Reinforcement Learning. I will apply this to the case of two-dimensional CFTs, successfully identifying well-known theories like the 2D Ising model and the 2D CFT of a compact scalar, but the method can be used to study arbitrary (unitary or non-unitary) CFTs in any spacetime dimension.

Zoom: https://durhamuniversity.zoom.us/j/99768150791?pwd=RTdIeldsbTJBVUdSbmFuT1c1SndBUT09

Jan 24 (Mon)

00:00 Clare Wallace: * TBC *

TBC

**Venue:** (unless stated above) MCS2068

13:00 Graeme Wilkin: * Morse theory, old and new *

Morse theory is an old subject with a long history of spectacular applications to different problems in geometry, topology and analysis. I will review some of this history due to the work of such luminaries as Morse, Bott, Milnor and Smale, before moving on to more modern applications of Atiyah & Bott, Kirwan and Witten. If time permits, I will talk about more recent work of my own which applies a number of these ideas to singular spaces.

**Venue:** (unless stated above) MCS0001

Jan 25 (Tue)

13:00 Tom Lancaster: * Realizing order, disorder and topological excitations in low-dimensional magnets *

Topology has become a much-discussed part of current research in solid-state magnetism, providing an organising principle to classify field theories, and their ground states and excitations, that are now regularly realized in magnetic materials. Examples include topological excitations such as skyrmions which exist in the spin textures of an expanding range of magnetic systems, and one-dimensional spin-chain systems, where topological considerations are key in understanding their properties. Central to this story is the role of the sine-Gordon model, which was important in motivating Skyrme's work and also in understanding the properties of spin chains using field theories. From this starting point, I will review some of the states that we might expect to realize in magnetic materials, and provide two sets of examples of where and how these have been found. Firstly, I will present examples spin chains and ladders formed of molecular building blocks, where the versatility of carbon chemistry allows access to spin Luttinger liquids, and sine-Gordon and Haldane chains. Secondly I shall discuss materials that host magnetic skyrmions and related excitations, along with the prospects for finding still more of these in the future.

13:05 Martin Orr: * Endomorphisms of abelian varieties in families *

The theory of unlikely intersections makes predictions about
how endomorphism algebras vary in families of abelian varieties. I will
explain some of these predictions and outline methods used to prove
results of this type using reduction theory of arithmetic groups.

**Venue:** (unless stated above) MCS3070

Jan 27 (Thu)

13:05 Michelle Daher: * TBA *

TBA

Jan 28 (Fri)

13:00 Javier Magán: * Generalized Symmetries of the Graviton *

In this talk we discuss the set of generalized symmetries associated with the free graviton theory in four dimensions. These are generated by ring-like operators. As for the Maxwell field, we find a set of “electric” and a dual set of “magnetic” topological operators and compute their algebra. The associated electric and magnetic fields satisfy a set of constraints equivalent to the ones of a stress tensor of a 3d CFT. This implies that the generalized symmetry is charged under space-time symmetries, and it provides a bridge between linearized gravity and the tensor gauge theories that have been introduced recently in the context of fractonic systems in condensed matter physics.

Click on title to see abstract (and venue, if in person). Zoom links, if available, are given for today's seminars only.

Upcoming Seminars by Series

(Click on series to expand.)
Contact: arthur.lipstein@durham.ac.uk

No upcoming seminars have been scheduled (not unusual during summer breaks).

Contact: megan.k.griffin-pickering@durham.ac.uk

Jan 21 13:00 Luca Nenna : * Transport type metrics on the space of probability measures involving singular base measures *

In this talk we develop the theory of a metric, which we call the $\nu$-based Wasserstein metric and denote by $W_\nu$, on the set of probability measures $\mathcal P(X)$ on a domain $X \subseteq \mathbb{R}^m$. This metric is based on a slight refinement of the notion of generalized geodesics with respect to a base measure $\nu$ and is relevant in particular for the case when $\nu$ is singular with respect to $m$-dimensional Lebesgue measure; it is also closely related to the concept of linearized optimal transport. The $\nu$-based Wasserstein metric is defined in terms of an iterated variational problem involving optimal transport to $\nu$; we also characterize it in terms of integrations of classical Wasserstein distance between the conditional probabilities when measures are disintegrated with respect to optimal transport to $\nu$, and through limits of certain multi-marginal optimal transport problems. As we vary the base measure $\nu$, the $\nu$-based Wasserstein metric interpolates between the usual quadratic Wasserstein distance (obtained when $\nu$ is a Dirac mass) and a metric associated with the uniquely defined generalized geodesics obtained when $\nu$ is sufficiently regular (eg, absolutely continuous with respect to Lebesgue). When $\nu$ concentrates on a lower dimensional submanifold of $\mathbb{R}^m$, we prove that the variational problem in the definition of the $\nu$-based Wasserstein distance has a unique solution. We establish geodesic convexity of the usual class of functionals, and of the set of source measures $\mu$ such that optimal transport between $\mu$ and $\nu$ satisfies a strengthening of the generalized nestedness condition introduced in McCann&Pass 2020. If time permitted we also present an applications of the ideas introduced: we also use the multi-marginal formulation to characterize solutions to the multi-marginal problem by an ordinary differential equation, yielding a new numerical method for it.

Feb 11 13:00 Tobias Wöhrer: * TBA *

Feb 18 13:00 Frantisek Stampach: * tba *

Contact: christopher.prior@durham.ac.uk

Jan 25 13:00 Tom Lancaster: * Realizing order, disorder and topological excitations in low-dimensional magnets *

Topology has become a much-discussed part of current research in solid-state magnetism, providing an organising principle to classify field theories, and their ground states and excitations, that are now regularly realized in magnetic materials. Examples include topological excitations such as skyrmions which exist in the spin textures of an expanding range of magnetic systems, and one-dimensional spin-chain systems, where topological considerations are key in understanding their properties. Central to this story is the role of the sine-Gordon model, which was important in motivating Skyrme's work and also in understanding the properties of spin chains using field theories. From this starting point, I will review some of the states that we might expect to realize in magnetic materials, and provide two sets of examples of where and how these have been found. Firstly, I will present examples spin chains and ladders formed of molecular building blocks, where the versatility of carbon chemistry allows access to spin Luttinger liquids, and sine-Gordon and Haldane chains. Secondly I shall discuss materials that host magnetic skyrmions and related excitations, along with the prospects for finding still more of these in the future.

Usual Venue: MCS3070

Contact: jack.g.shotton@durham.ac.uk

Jan 25 13:05 Martin Orr: * Endomorphisms of abelian varieties in families *

The theory of unlikely intersections makes predictions about
how endomorphism algebras vary in families of abelian varieties. I will
explain some of these predictions and outline methods used to prove
results of this type using reduction theory of arithmetic groups.

Mar 08 13:00 Daniele Dorigoni: * Modular graph forms, Poincare series and iterated integrals *

Usual Venue: OC218

Contact: stefano.cremonesi@durham.ac.uk

For more information, see HERE.

Feb 03 14:00 Djuna Croon: * TBA *

Mar 03 14:00 Luigi Del Debbio: * TBA *

Mar 17 14:00 Arttu Rajantie: * TBA *

Contact: hugo.fortin@durham.ac.uk

No upcoming seminars have been scheduled (not unusual during summer breaks).

Usual Venue: MCS0001

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

No upcoming seminars have been scheduled (not unusual during summer breaks).

Contact: p.e.dorey@durham.ac.uk

No upcoming seminars have been scheduled (not unusual during summer breaks).

Usual Venue: MCS3070

Contact: gabriel.fuhrmann@durham.ac.uk

No upcoming seminars have been scheduled (not unusual during summer breaks).

Contact: fernando.galaz-garcia@durham.ac.uk

Recordings of past seminars can be found HERE.

Jan 27 13:05 Michelle Daher: * TBA *

TBA

Feb 03 13:00 Ana Lucia Garcia Pulido: * TBA *

TBA

Feb 24 13:05 Danica Kosanović: * Embedding spaces *

TBA

Mar 03 13:05 Csaba Nagy: * Classification of 3-connected 8-manifolds *

Contact: tin.sulejmanpasic@durham.ac.uk

No upcoming seminars have been scheduled (not unusual during summer breaks).

Contact: inaki.garcia-etxebarria@durham.ac.uk

Note: if held in person (please see abstract), the usual room is MCS2068; otherwise on zoom.

Jan 21 13:00 Costis Papageorgakis: * Towards Solving CFTs with Artificial Intelligence *

I will introduce a novel numerical approach for solving the conformal-bootstrap equations with Reinforcement Learning. I will apply this to the case of two-dimensional CFTs, successfully identifying well-known theories like the 2D Ising model and the 2D CFT of a compact scalar, but the method can be used to study arbitrary (unitary or non-unitary) CFTs in any spacetime dimension.

Jan 28 13:00 Javier Magán: * Generalized Symmetries of the Graviton *

In this talk we discuss the set of generalized symmetries associated with the free graviton theory in four dimensions. These are generated by ring-like operators. As for the Maxwell field, we find a set of “electric” and a dual set of “magnetic” topological operators and compute their algebra. The associated electric and magnetic fields satisfy a set of constraints equivalent to the ones of a stress tensor of a 3d CFT. This implies that the generalized symmetry is charged under space-time symmetries, and it provides a bridge between linearized gravity and the tensor gauge theories that have been introduced recently in the context of fractonic systems in condensed matter physics.

Feb 04 13:00 Alexandre Belin: * TBA *

Mar 11 13:00 Federico Zerbini: * TBA *

Mar 18 13:00 Irene Valenzuela: * TBA *

Usual Venue: MCS2068

Contact: ellen.g.powell@durham.ac.uk

Jan 24 00:00 Clare Wallace: * TBC *

TBC

Jan 31 00:00 Agnes Backhausz: * TBC *

TBC

Feb 07 00:00 Jon Peterson: * TBC *

TBC

Feb 14 00:00 Pierre-Francois Rodriguez: * TBC *

TBC

Feb 21 00:00 Malin Palö Forsström: * TBC *

TBC

Mar 07 00:00 Daniel Ueltschi: * TBC *

TBC

Mar 14 00:00 Damian Clancy: * TBC *

TBC

Usual Venue: MCS0001

Contact: jack.g.shotton@durham.ac.uk

Jan 24 13:00 Graeme Wilkin: * Morse theory, old and new *

Morse theory is an old subject with a long history of spectacular applications to different problems in geometry, topology and analysis. I will review some of this history due to the work of such luminaries as Morse, Bott, Milnor and Smale, before moving on to more modern applications of Atiyah & Bott, Kirwan and Witten. If time permits, I will talk about more recent work of my own which applies a number of these ideas to singular spaces.

Mar 07 13:00 Heather Harrington: * TBC *

TBC

Usual Venue: MCS3070

Contact: michael.r.magee@durham.ac.uk

No upcoming seminars have been scheduled (not unusual during summer breaks).

Usual Venue: MCS2068

Contact: georgios.karagiannis@durham.ac.uk, konstantinos.perrakis@durham.ac.uk

Feb 14 13:00 Giusi Moffa: * TBC *

TBC

Feb 28 13:00 Wenkai Xu: * tba *

tba

Apr 25 13:00 Daniel Williamson: * Coming soon *

Coming soon

May 23 13:00 Theodore Papamarkou: * tba *

tba

Contact: kieran.f.richards@durham.ac.uk

No upcoming seminars have been scheduled (not unusual during summer breaks).