Feb 21 (Fri)
13:00 MCS0001 HEPMGeorges Obied (Oxford University): De Sitter space constraints on brane tensions and couplings
Extended objects are ubiquitous in string theory where they have special properties. Outside of string theory, there are relatively few insights into the nature of extended objects that are allowed by quantum gravity. In this talk, using the Festina Lente conjecture, I will argue for new universal bounds on the tension of branes coupled to gauge fields in de Sitter space. This bound is implied by cosmic censorship and can be derived by studying the evolution of large charged black holes in de Sitter space. Since this is a bottom-up argument, it should be obeyed by any de Sitter quantum gravity including stringy constructions. Finally, I will provide a heuristic check of these bounds against the properties of (wrapped) D-branes in Type II string theory in the weak coupling limit and show that they satisfy all these constraints.
Venue: MCS0001
Feb 24 (Mon)
14:00 MCS2068 ProbSam Olesker Taylor (Warwick, UK): A Randomised Approach to Sorting
We introduce and analyse a new, extremely simple, randomised sorting algorithm:
choose a pair of indices \{i, j\} according to some distribution q;
sort the elements in positions i and j of the array in ascending order.
We prove that q_{\{i,j\}} \propto 1/|j - i|, the harmonic sorter, yields an order-n (\log n)^2 sorting time.
The sorter trivially parallelises in the asynchronous setting, yielding a linear speed-up. We also exhibit a low-communication, synchronous version with a linear speed-up.
Venue: MCS2068
Feb 25 (Tue)
13:00 MCS2068 ASGHaluk Sengun (University of Sheffield): Theta correspondence via C*-algebras of groups
Theta lifting is an important theme in the theory of automorphic forms. In the 1970's, Roger Howe brought a representation theoretic interpretation to theta lifting by introducing his celebrated theta correspondence. In a nutshell, the local theta correspondence sets up a bijection between certain subsets of admissible duals of suitable pairs of reductive groups. In this talk, I will discuss an approach to (local and global) theta correspondence via C*-algebras of groups. This approach, when applicable, promotes the correspondence to a continuous functor. Time permitting, I will discuss some applications as well. Based on joint works with B. Mesland (Leiden) and M. Goffeng (Lund).
Venue: MCS2068
14:00 MCS2068 APDEKasia Wyczesany (University of Leeds): Brenier-type theorem for infinite-valued costs and set dualities
Given a cost function and two probability measures, the optimal transport problem is that of finding a transport map (or a plan) which minimises total cost. The case of finite-valued costs is well-understood and, under mild assumptions, the optimal plan has a special geometric structure. In particular, there exists a function, which we call a potential, whose c-subgradient contains the support of the optimal transport plan (for the quadratic cost \(|x-y|^2\) the gradient of the potential is famously known as the Brenier map). However, if a cost function attains infinite values, which corresponds to prohibiting certain pairs of points to be mapped to one another, only special families of costs were studied. We present a unified approach to transportation with respect to infinite-valued costs: we discuss compatibility of measures involved, give a sufficient condition for the existence of a Brenier-type map, and explain how this condition gives rise to abstract dualities on sets.
The talk is based on joint work with S. Artstein-Avidan and S. Sadovsky.
Venue: MCS2068
Feb 26 (Wed)
14:00 MCS2068 S&MMingkun Liu (University of Paris 13): Component spectrum of random multi-geodesics and moduli spaces
A multi-geodesic is a multi-set of closed geodesics. I will explain how to pick a random multi-geodesic (on a hyperbolic surface), and discuss the following question: what is the shape of a random multi-geodesic on a hyperbolic surface of large genus? We will see that, for example, the average lengths of its first three largest components are approximately,
75.8%, 17.1%, and 4.9%, respectively, of the total length. This is a (partially ongoing) work with Vincent Delecroix.
Venue: MCS2068
Feb 27 (Thu)
14:00 MCS2068 G&TSebastian Chenery (Bristol): Gyration Stability for Projective Planes
Gyrations are operations on manifolds that first arose in
geometric topology. A given manifold M may exhibit different gyrations
depending on the chosen twisting, prompting the following natural
question: do all gyrations of M share the same homotopy type regardless
of which twisting we choose? Inspired by recent work of Duan, which
demonstrated that the quaternionic projective plane is not gyration
stable (but with respect to diffeomorphism) in this talk we will explore
our question for projective planes in general, resulting in a complete
description of gyration stability for the complex, quaternionic, and
octonionic projective planes up to homotopy. Moreover, we will also see
that these results connect to several seemingly distinct contexts. This
is joint work with Stephen Theriault.
Venue: MCS2068
Feb 28 (Fri)
13:00 MCS0001 HEPMAna Maria Raclariu (King's College London): An infrared on-shell action in asymptotically flat spacetimes
One of the main entries in the AdS/CFT dictionary is a relation between the bulk on-shell partition function with specified boundary conditions and the generating function of correlation functions of primary operators in the boundary CFT. In this talk I will show how to construct a similar relation for gravity in 4d asymptotically flat spacetimes. For simplicity, we will restrict to the leading infrared sector, where a careful treatment of soft modes and their canonical partners leads to a non-vanishing on-shell action. I will show that this action localizes to a codimension-2 surface and coincides with the generating function of 2d CFT correlators involving insertions of Kac-Moody currents. The latter were previously shown, using effective field theory methods, to reproduce the leading soft graviton theorems in 4d. I will conclude with comments on the implications of these results for the computation of soft charge fluctuations in the vacuum.
Venue: MCS0001
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Usual Venue: MCS3070
Contact: sabine.boegli@durham.ac.uk
Feb 25 14:00 Kasia Wyczesany (University of Leeds): Brenier-type theorem for infinite-valued costs and set dualities
Given a cost function and two probability measures, the optimal transport problem is that of finding a transport map (or a plan) which minimises total cost. The case of finite-valued costs is well-understood and, under mild assumptions, the optimal plan has a special geometric structure. In particular, there exists a function, which we call a potential, whose c-subgradient contains the support of the optimal transport plan (for the quadratic cost \(|x-y|^2\) the gradient of the potential is famously known as the Brenier map). However, if a cost function attains infinite values, which corresponds to prohibiting certain pairs of points to be mapped to one another, only special families of costs were studied. We present a unified approach to transportation with respect to infinite-valued costs: we discuss compatibility of measures involved, give a sufficient condition for the existence of a Brenier-type map, and explain how this condition gives rise to abstract dualities on sets.
The talk is based on joint work with S. Artstein-Avidan and S. Sadovsky.
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
Feb 25 13:00 Haluk Sengun (University of Sheffield): Theta correspondence via C*-algebras of groups
Theta lifting is an important theme in the theory of automorphic forms. In the 1970's, Roger Howe brought a representation theoretic interpretation to theta lifting by introducing his celebrated theta correspondence. In a nutshell, the local theta correspondence sets up a bijection between certain subsets of admissible duals of suitable pairs of reductive groups. In this talk, I will discuss an approach to (local and global) theta correspondence via C*-algebras of groups. This approach, when applicable, promotes the correspondence to a continuous functor. Time permitting, I will discuss some applications as well. Based on joint works with B. Mesland (Leiden) and M. Goffeng (Lund).
Venue: MCS2068
Mar 04 13:00 Thomas Bloom (University of Manchester):
Mar 11 13:00 Markus Szymik (Sheffield University): Artin–Schreier quandles of involutions in absolute Galois groups
Mar 18 13:00 Kalyani Kansal (Imperial College): Non-generic components of the Emerton-Gee stack for GL2
We will start by talking briefly about the history of the p-adic Langlands correspondence, and the form of the conjectures for categorical p-adic Langlands correspondence. We will introduce the Emerton-Gee stack (for GL2) which features as a key player in these conjectures. The reduced part of this stack can be viewed as parameterizing mod p Galois representations of the absolute Galois group of a finite extension of Qp. Restricting attention to unramified extensions of Qp, we will see precisely which of the irreducible components of the reduced Emerton-Gee stack are smooth or normal, and which have Gorenstein or Cohen-Macaulay normalizations, as well as determine their singular loci. We will see some consequences of these results for the conjectural categorical p-adic Langlands correspondence. This is based on joint work with Ben Savoie.
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: MCS3052
Contact: andrew.krause@durham.ac.uk
No upcoming seminars have been scheduled (not unusual outside term time).
Usual Venue: MCS2068
Contact: martin.p.kerin@durham.ac.uk
Feb 27 14:00 Sebastian Chenery (Bristol): Gyration Stability for Projective Planes
Gyrations are operations on manifolds that first arose in
geometric topology. A given manifold M may exhibit different gyrations
depending on the chosen twisting, prompting the following natural
question: do all gyrations of M share the same homotopy type regardless
of which twisting we choose? Inspired by recent work of Duan, which
demonstrated that the quaternionic projective plane is not gyration
stable (but with respect to diffeomorphism) in this talk we will explore
our question for projective planes in general, resulting in a complete
description of gyration stability for the complex, quaternionic, and
octonionic projective planes up to homotopy. Moreover, we will also see
that these results connect to several seemingly distinct contexts. This
is joint work with Stephen Theriault.
Venue: MCS2068
Mar 13 14:00 Macarena Arenas (Cambridge): TBD
Jun 12 14:00 Ilka Agricola (Marburg): TBD
Usual Venue: MCS0001
Contact: silvia.nagy@durham.ac.uk,enrico.andriolo@durham.ac.uk,tobias.p.hansen@durham.ac.uk
Feb 21 13:00 Georges Obied (Oxford University): De Sitter space constraints on brane tensions and couplings
Extended objects are ubiquitous in string theory where they have special properties. Outside of string theory, there are relatively few insights into the nature of extended objects that are allowed by quantum gravity. In this talk, using the Festina Lente conjecture, I will argue for new universal bounds on the tension of branes coupled to gauge fields in de Sitter space. This bound is implied by cosmic censorship and can be derived by studying the evolution of large charged black holes in de Sitter space. Since this is a bottom-up argument, it should be obeyed by any de Sitter quantum gravity including stringy constructions. Finally, I will provide a heuristic check of these bounds against the properties of (wrapped) D-branes in Type II string theory in the weak coupling limit and show that they satisfy all these constraints.
Venue: MCS0001
Feb 28 13:00 Ana Maria Raclariu (King's College London): An infrared on-shell action in asymptotically flat spacetimes
One of the main entries in the AdS/CFT dictionary is a relation between the bulk on-shell partition function with specified boundary conditions and the generating function of correlation functions of primary operators in the boundary CFT. In this talk I will show how to construct a similar relation for gravity in 4d asymptotically flat spacetimes. For simplicity, we will restrict to the leading infrared sector, where a careful treatment of soft modes and their canonical partners leads to a non-vanishing on-shell action. I will show that this action localizes to a codimension-2 surface and coincides with the generating function of 2d CFT correlators involving insertions of Kac-Moody currents. The latter were previously shown, using effective field theory methods, to reproduce the leading soft graviton theorems in 4d. I will conclude with comments on the implications of these results for the computation of soft charge fluctuations in the vacuum.
Venue: MCS0001
Mar 07 13:00 Max Elliot Huebner (Uppsala University): Non-Supersymmetric Orbifolds, Quivers and Chen-Ruan Orbifold Cohomology
We consider D3-brane probes of non-supersymmetric orbifolds and IIA on the same class of non-supersymmetric orbifolds. Both setups are characterized, in part, by quivers (which in the latter case relate for example to D0-brane probes) from which symmetries constraining the scale-dependence and tachyonic instabilities of the two systems, respectively, can be derived. We demonstrate that these considerations can be matched via a geometric analysis of the asymptotic boundary of the relevant orbifolds, in all cases, via considerations centered on Chen-Ruan orbifold cohomology.
Venue: MCS0001
Mar 14 13:00 Po-Shen Hsin (King's College London): TBA
Mar 21 13:00 Gabriele Travaglini (Queen Mary University of London): TBA
Usual Venue: MCS2068
Contact: kohei.suzuki@durham.ac.uk
Feb 24 14:00 Sam Olesker Taylor (Warwick, UK): A Randomised Approach to Sorting
We introduce and analyse a new, extremely simple, randomised sorting algorithm:
choose a pair of indices \{i, j\} according to some distribution q;
sort the elements in positions i and j of the array in ascending order.
We prove that q_{\{i,j\}} \propto 1/|j - i|, the harmonic sorter, yields an order-n (\log n)^2 sorting time.
The sorter trivially parallelises in the asynchronous setting, yielding a linear speed-up. We also exhibit a low-communication, synchronous version with a linear speed-up.
Venue: MCS2068
Mar 03 14:00 Sarah Penington (Bath, UK): TBA
Mar 10 14:00 Isao Suezedde (Warwick, UK): TBA
Usual Venue: MCS0001
Contact: raphael.zentner@durham.ac.uk
Mar 10 12:00 Karen Vogtmann (University of Warwick): TBA
Mar 17 12:00 Andras Juhasz (University of Oxford): TBA
Usual Venue: MCS3070
Contact: irving.d.calderon-camacho@durham.ac.uk,joe.thomas@durham.ac.uk
Feb 26 14:00 Mingkun Liu (University of Paris 13): Component spectrum of random multi-geodesics and moduli spaces
A multi-geodesic is a multi-set of closed geodesics. I will explain how to pick a random multi-geodesic (on a hyperbolic surface), and discuss the following question: what is the shape of a random multi-geodesic on a hyperbolic surface of large genus? We will see that, for example, the average lengths of its first three largest components are approximately,
75.8%, 17.1%, and 4.9%, respectively, of the total length. This is a (partially ongoing) work with Vincent Delecroix.
Venue: MCS2068
