# All Upcoming Events

On Monday at 12:45 in L3, a seminar in
the String Theory series:

Laura Schaposnik (Chicago)

Higgs bundles, branes, and application

*Higgs bundles are pairs of holomorphic vector bundles and holomorphic 1-forms taking values in the endomorphisms of the bundle. Their moduli spaces carry a natural Hyperkahler structure, through which one can study Lagrangian subspaces (A-branes) or holomorphic subspaces (B-branes). Notably, these A and B-branes have gained significant attention in string theory. After introducing Higgs bundles and the associated Hitchin fibration, we shall look at natural constructions of families of different types of branes, and relate these spaces to the study of 3-manifolds, surface group representations and mirror symmetry.*

**Further information:**
On Monday at 14:15 in L4, a seminar in
the Geometry and Analysis series:

Mark Haskins (Bath)

Uncollapsing highly collapsed $G_2$ holonomy metrics.

*In recent joint work with Lorenzo Foscolo and Johannes Nordstr\”om we gave an analytic construction of large families of complete circle-invariant $G_2$ holonomy metrics on the total space of circle bundles over a complete noncompact Calabi—Yau 3-fold with asymptotically conical geometry. The asymptotic models for the geometry of these $G_2$ metrics are circle bundles with fibres of constant length $l$, so-called asymptotically local conical (ALC) geometry. These ALC $G_2$ metrics can Gromov—Hausdorff collapse with bounded curvature to the given asymptotically conical Calabi—Yau 3-fold as the fibre length $l$ goes to $0$. A natural question is: what happens to these families of $G_2$ metrics as we try to make $l$ large? In general the answer to this question is not known, but in cases with sufficient symmetry we have recently been able to give a complete picture. We give an overview of all these results and discuss some analogies with the class of asymptotically locally flat (ALF) hyperkaehler 4-manifolds. In particular we suggest that a particular $G_2$ metric we construct should be regarded as a $G_2$ analogue of the Euclidean Taub—NUT metric on the complex plane.*

**Further information:**
On Tuesday at 12:00 in L4, a seminar in
the Quantum Field Theory series:

Roger Penrose

Hawking points ?

On Thursday at 12:45 in L6, a seminar in
the Strings Junior series:

Max Hubner

Axiomatic QFT

On Thursday at 13:00 in Simpkins Lee Seminar Room, a seminar in
the Dalitz Seminar in Fundamental Physics series:

Nassim Bozorgnia (Durham)

Hunting for dark matter: from simulations to direct detection

On Thursday at 16:00 in L6, a seminar in
the Number Theory series:

Joni Teräväinen (Oxford University)

Correlations of multiplicative functions at almost all scales

*Understanding how shifts of multiplicative functions correlate with each other is a central question in multiplicative number theory. A well-known conjecture of Elliott predicts that there should be no correlation between shifted multiplicative functions unless the functions involved are ‘pretentious functions’ in a certain precise sense. The Elliott conjecture implies as a special case the famous Chowla conjecture on shifted products of the Möbius function. In the last few years, there has been a lot of exciting progress on the Chowla and Elliott conjectures, and we give an overview of this. Nearly all of the previously obtained results have concerned correlations that are weighted logarithmically, and it is an interesting question whether one can remove these logarithmic weights. We show that one can indeed remove logarithmic averaging from the known results on the Chowla and Elliott conjectures, provided that one restricts to almost all scales in a suitable sense. This is joint work with Terry Tao.*

**Further information:**
On Thursday at 16:15 in Simpkins Lee Seminar Room, a seminar in
the Theoretical Particle Physics series:

Xenia de la Ossa (Maths Institute, Oxford)

On the deformation theory of heterotic G-structures

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**Further information:**
On Friday at 14:00 in Dennis Sciama Lecture Theatre, a seminar in
the Theoretical Physics Colloquia series:

Cancelled (na)

Cancelled

On Friday at 15:30 in Martin Wood Lecture Theatre, a seminar in
the Colloquia Series Seminars series:

Prof Robert Smith (University of Oxford)

Ultracold atomic gases: exploring many-body physics with the coldest stuff in the universe

On Monday, October 29, at 14:15 in L4, a seminar in
the Geometry and Analysis series:

Kobi Kremnitzer (Oxford)

Differentiable chiral and factorisation algebras

*The Beilinson-Drinfeld Grassmannian, which classifies a G-bundle trivialised away from a finite set of points on a curve, is one of the basic objects in the geometric Langlands programme. Similar construction in higher dimensions in the algebraic and analytic settings are not very interesting because of Hartogs' theorem. In this talk I will discuss a differentiable version. I will also explain a theory of D-modules on differentiable spaces and use it to define differentiable chiral and factorisation algebras. By linearising the Grassmannian we get examples of differentiable chiral algebras. This is joint work with Dennis Borisov.*

**Further information:**
On Tuesday, October 30, at 11:30 in Fisher Room, DWB, a seminar in
the Cosmology series:

Matthew Lewandoski (Institut de physique theorique, Universite Paris Saclay)

TBC

On Tuesday, October 30, at 12:00 in L4, a seminar in
the Relativity series:

Dr Wolfgang Wieland (Perimeter Institute)

Loop Quantum Gravity and the Continuum

*One of the main open problems in loop quantum gravity is to reconcile the fundamental quantum discreteness of space with general relativity in the continuum. In this talk, I present recent progress regarding this issue: I will explain, in particular, how the discrete spectra of geometric observables that we find in loop gravity can be understood from a conventional Fock quantisation of gravitational edge modes on a null surface boundary. On a technical level, these boundary modes are found by considering a quasi-local Hamiltonian analysis, where general relativity is treated as a Hamiltonian system in domains with inner null boundaries. The presence of such null boundaries requires then additional boundary terms in the action. Using Ashtekar’s original SL(2,C) self-dual variables, I will explain that the natural such boundary term is nothing but a kinetic term for a spinor (defining the null flag of the boundary) and a spinor-valued two-form, which are both intrinsic to the boundary. The simplest observable on the boundary phase space is the cross sectional area two-form, which generates dilatations of the boundary spinors. In quantum theory, the corresponding area operator turns into the difference of two number operators. The area spectrum is discrete without ever introducing spin networks or triangulations of space. I will also comment on a similar construction in three euclidean spacetime dimensions, where the discreteness of length follows from the quantisation of gravitational edge modes on a one-dimensional cross section of the boundary. The talk is based on my recent papers: arXiv:1804.08643 and arXiv:1706.00479.*

**Further information:**
On Tuesday, October 30, at 15:45 in L4, a seminar in
the Algebraic Geometry series:

Chunyi Li (University of Warwick)

Bogomolov type inequality for Fano varieties with Picard number 1

*I will talk about some basic facts about slope stable sheaves and the Bogomolov inequality. New techniques from stability conditions will imply new stronger bounds on Chern characters of stable sheaves on some special varieties, including Fano varieties, quintic threefolds and etc. I will discuss the progress in this direction and some related open problems.*

**Further information:**
On Thursday, November 1, at 12:45 in L6, a seminar in
the Strings Junior series:

Hadleigh Frost

Supermanifolds and super Lie groups

On Thursday, November 1, at 13:00 in Simpkins Lee Seminar Room, a seminar in
the Dalitz Seminar in Fundamental Physics series:

James Unwin (Illinois)

TBC

On Thursday, November 1, at 16:00 in L6, a seminar in
the Number Theory series:

Daniel Gulotta (Oxford University)

Shimura varieties at level Gamma_1(p^{\infty}) and Galois representations

*Let F be a totally real or CM number field. Scholze has constructed Galois representations associated with torsion classes in the cohomology of locally symmetric spaces for GL_n(F). We show that the nilpotent ideal appearing in Scholze's construction can be removed when F splits completely at the relevant prime. As a key component of the proof, we show that the compactly supported cohomology of certain unitary and symplectic Shimura varieties with level Gamma_1(p^{\infty}) vanishes above the middle degree. This is joint work with Ana Caraiani, Chi-Yun Hsu, Christian Johansson, Lucia Mocz, Emanuel Reinecke, and Sheng-Chi Shih.*

**Further information:**
On Thursday, November 1, at 16:15 in Simpkins Lee Seminar Room, a seminar in
the Theoretical Particle Physics series:

Steve Abel (Durham)

Asymptotically safe Standard Model

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**Further information:**
On Friday, November 2, at 15:30 in Martin Wood Lecture Theatre, a seminar in
the Colloquia Series Seminars series:

Prof Jonathan Gregory (Host Tim Palmer) (University of Reading/Met Office)

Sea level change in the Anthropocene

On Friday, November 2, at 16:00 in L1, a seminar in
the Math Colloquium series:

Jon Keating (University of Bristol)

Characteristic Polynomials of Random Unitary Matrices, Partition Sums, and Painlevé V

*The moments of characteristic polynomials play a central role in Random Matrix Theory. They appear in many applications, ranging from quantum mechanics to number theory. The mixed moments of the characteristic polynomials of random unitary matrices, i.e. the joint moments of the polynomials and their derivatives, can be expressed recursively in terms of combinatorial sums involving partitions. However, these combinatorial sums are not easy to compute, and so this does not give an effective method for calculating the mixed moments in general. I shall describe an alternative evaluation of the mixed moments, in terms of solutions of the Painlevé V differential equation, that facilitates their computation and asymptotic analysis.*

**Further information:**
On Monday, November 5, at 14:15 in L4, a seminar in
the Geometry and Analysis series:

Maurico Correa (Minas Gerais)

Moduli spaces of reflexive sheaves and classification of distributions on P^3

*We describe the moduli space of distributions in terms of Grothendieck’s Quot-scheme for the tangent bundle. In certain cases, we show that the moduli space of codimension one distributions on the projective space is an irreducible, nonsingular quasi-projective variety. We study codimension one holomorphic distributions on projective three-space, analyzing the properties of their singular schemes and tangent sheaves. In particular, we provide a classification of codimension one distributions of degree at most 2. We show how the connectedness of the curves in the singular sets of foliations is an integrable phenomenon. This part of the talk is work joint with M. Jardim(Unicamp) and O. Calvo-Andrade(Cimat). We also study foliations by curves via the investigation of their singular schemes and conormal sheaves and we provide a classification of foliations of degree at most 3 with conormal sheaves locally free. Foliations of degrees 1 and 2 are aways given by a global intersection of two codimension one distributions. In the classification of degree 3 appear Legendrian foliations, foliations whose conormal sheaves are instantons and other ” exceptional” type examples. This part of the talk is work joint with M. Jardim(Unicamp) and S. Marchesi(Unicamp).*

**Further information:**
On Tuesday, November 6, at 11:00 in Conference Room, DWB, a seminar in
the Cosmology series:

Rachel Rosen (Columbia University)

TBC

On Tuesday, November 6, at 12:00 in L4, a seminar in
the Quantum Field Theory series:

Luis Fernando Alday

to be announced

On Thursday, November 8, at 12:45 in L6, a seminar in
the Strings Junior series:

Julius Eckhard

Quiver gauge theories

On Thursday, November 8, at 13:00 in Simpkins Lee Seminar Room, a seminar in
the Dalitz Seminar in Fundamental Physics series:

Alexander Karlberg (Zurich)

TBC

On Thursday, November 8, at 16:00 in L6, a seminar in
the Number Theory series:

Olivia Beckwith (Bristol)

Indivisibility and divisibility of class numbers of imaginary quadratic fields

*For any prime p > 3, the strongest lower bounds for the number of imaginary quadratic fields with discriminant down down to -X for which the class group has trivial (non-trivial) p-torsion are due to Kohnen and Ono (Soundararajan). I will discuss recent refinements of these classic results in which we consider the imaginary quadratic fields whose class number is indivisible (divisible) by p such that a given finite set of primes factor in a prescribed way. We prove a lower bound for the number of such fields with discriminant down to -X which is of the same order of magnitude as Kohnen and Ono's (Soundararajan's) results. For the indivisibility case, we rely on a result of Wiles establishing the existence of imaginary quadratic fields with trivial p-torsion in their class groups satisfying almost any given finite set of local conditions, and a result of Zagier which says that the Hurwitz class numbers are the Fourier coefficients of a mock modular form.*

**Further information:**
On Thursday, November 8, at 16:15 in Simpkins Lee Seminar Room, a seminar in
the Theoretical Particle Physics series:

Thomas Gehrmann (Zurich)

Precision physics with jet observables & transverse momentum distributions

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**Further information:**
On Friday, November 9, at 14:00 in Dennis Sciama Lecture Theatre, a seminar in
the Theoretical Physics Colloquia series:

Chris Herzog (King's College London)

TBC

On Friday, November 9, at 15:30 in Martin Wood Lecture Theatre, a seminar in
the Colloquia Series Seminars series:

Richard D. Ludescher (Department of Food Science School of Environmental and Biological Sciences Rutgers, NJ)

Photophysics & Food: Edible Fluorophores as Intrinsic Sensors of Quality

On Monday, November 12, at 14:15 in L4, a seminar in
the Geometry and Analysis series:

Steve Rayan (University of Saskatchewan)

Hyperkaehler geometry of hyperpolygon spaces

*Introduced by Konno, hyperpolygon spaces are examples of Nakajima quiver varieties. The simplest of these is a noncompact complex surface admitting the structure of a gravitational instanton, and therefore fits nicely into the Kronheimer-Nakajima classification of complete ALE hyperkaehler 4-manifolds, which is a geometric realization of the McKay correspondence for finite subgroups of SU(2). For more general hyperpolygon spaces, we can speculate on how this classification might be extended by studying the geometry of hyperpolygons at 'infinity'. This is ongoing work with Hartmut Weiss.*

**Further information:**
On Tuesday, November 13, at 11:30 in Conference Room, DWB, a seminar in
the Cosmology series:

Alan Heavens (Imperial College, London)

Bayesian cosmology and neutrino masses

On Tuesday, November 13, at 12:00 in L4, a seminar in
the Quantum Field Theory series:

Thierry Lévy (Paris Marie Curie and visiting Newton Institute)

to be announced

On Thursday, November 15, at 12:45 in L6, a seminar in
the Strings Junior series:

Mohamed Elmi

SYK model

On Thursday, November 15, at 13:00 in Simpkins Lee Seminar Room, a seminar in
the Dalitz Seminar in Fundamental Physics series:

Kasper Larsen (Southampton)

TBC

On Thursday, November 15, at 16:00 in L6, a seminar in
the Number Theory series:

Ana Caraiani (Imperial College)

TBD

On Thursday, November 15, at 16:15 in Simpkins Lee Seminar Room, a seminar in
the Theoretical Particle Physics series:

Christophe Grojean (DESY)

TBC

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**Further information:**
On Friday, November 16, at 15:00 in L1, a seminar in
the Math Colloquium series:

Alan Sokal (UCL & NYU)

Total positivity: a concept at the interface between algebra, analysis and combinatorics

*A matrix M of real numbers is called totally positive if every minor of M is nonnegative. This somewhat bizarre concept from linear algebra has surprising connections with analysis - notably polynomials and entire functions with real zeros, and the classical moment problem and continued fractions - as well as combinatorics. I will explain briefly some of these connections, and then introduce a generalization: a matrix M of polynomials (in some set of indeterminates) will be called coefficientwise totally positive if every minor of M is a polynomial with nonnegative coefficients. Also, a sequence (an)n≥0 of real numbers (or polynomials) will be called (coefficientwise) Hankel-totally positive if the Hankel matrix H = (ai+j)i,j ≥= 0 associated to (an) is (coefficientwise) totally positive. It turns out that many sequences of polynomials arising in enumerative combinatorics are (empirically) coefficientwise Hankel-totally positive; in some cases this can be proven using continued fractions, while in other cases it remains a conjecture.*

**Further information:**
On Friday, November 16, at 15:30 in Martin Wood Lecture Theatre, a seminar in
the Colloquia Series Seminars series:

Prof Gavin Salam (University of Oxford)

Higgs and beyond at colliders

On Tuesday, November 20, at 11:30 in Conference Room, DWB, a seminar in
the Cosmology series:

Aurel Schneider (ETH Zurich)

Probing the nature of dark matter with cosmological structure formation

On Tuesday, November 20, at 12:00 in L4, a seminar in
the Quantum Field Theory series:

Martina Hofmanova (Bielefeld and visiting Newton Institute)

A PDE construction of the Euclidean $\Phi^4_3$ quantum field theory

*We present a self-contained construction of the Euclidean $\Phi^4$ quantum field theory on $\mathbb{R}^3$ based on PDE arguments. More precisely, we consider an approximation of the stochastic quantization equation on $\mathbb{R}^3$ defined on a periodic lattice of mesh size $\varepsilon$ and side length $M$. We introduce an energy method and prove tightness of the corresponding Gibbs measures as $\varepsilon \rightarrow 0$, $M \rightarrow \infty$. We show that every limit point satisfies reflection positivity, translation invariance and nontriviality (i.e. non-Gaussianity). Our argument applies to arbitrary positive coupling constant and also to multicomponent models with $O(N)$ symmetry. Joint work with Massimiliano Gubinelli.*

**Further information:**
On Thursday, November 22, at 12:45 in L6, a seminar in
the Strings Junior series:

Diego Berdeja Suárez

W-algebras

On Thursday, November 22, at 16:00 in L6, a seminar in
the Number Theory series:

Alice Pozzi (UCL)

TBD

On Thursday, November 22, at 16:15 in Simpkins Lee Seminar Room, a seminar in
the Theoretical Particle Physics series:

Dumitru Ghilencea (NIPNE Bucharest)

Two-loop corrections to Starobinsky-Higgs inflation

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**Further information:**
On Friday, November 23, at 14:00 in Dennis Sciama Lecture Theatre, a seminar in
the Theoretical Physics Colloquia series:

Justin Read (Surrey)

TBC

On Friday, November 23, at 15:30 in Martin Wood Lecture Theatre, a seminar in
the Colloquia Series Seminars series:

TBA (TBA)

TBC

On Monday, November 26, at 14:15 in L4, a seminar in
the Geometry and Analysis series:

Tomasz Lukowski (Oxford)

Amplituhedron meets Jeffrey-Kirwan residue

*Amplituhedra are mathematical objects generalising the notion of polytopes into the Grassmannian. Proposed as a geometric construction encoding scattering amplitudes in the four-dimensional maximally supersymmetric Yang-Mills theory, they are mathematically interesting objects on their own. In my talk I strengthen the relation between scattering amplitudes and geometry by linking the amplituhedron to the Jeffrey-Kirwan residue, a powerful concept in symplectic and algebraic geometry. I focus on a particular class of amplituhedra in any dimension, namely cyclic polytopes, and their even-dimensional conjugates. I show how the Jeffrey-Kirwan residue prescription allows to extract the correct amplituhedron canonical differential form in all these cases. Notably, this also naturally exposes the rich combinatorial structures of amplituhedra, such as their regular triangulations*

**Further information:**
On Tuesday, November 27, at 11:30 in Conference Room, DWB, a seminar in
the Cosmology series:

Silvia Galli (Institut d'Astrophysique de Paris)

Cosmological results from the final data release of the Planck satellite

On Tuesday, November 27, at 15:45 in L4, a seminar in
the Algebraic Geometry series:

Marie-Francoise Roy (Université de Rennes)

Degree bounds for Hilbert 17th Problem

On Thursday, November 29, at 12:45 in L6, a seminar in
the Strings Junior series:

TBA

On Thursday, November 29, at 16:00 in L6, a seminar in
the Number Theory series:

Laura Capuano ((Oxford University))

TBD

On Tuesday, January 15, at 12:00 in L4, a seminar in
the Quantum Field Theory series:

Xenia de la Ossa

to be announced

On Tuesday, January 29, at 12:00 in L4, a seminar in
the Quantum Field Theory series:

Ivette Fuentes (University of Nottingham)

to be announced