# This Week

Here is a selection of seminars that might be of interest to string theorists in Oxford:

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