Triangle Seminars

Abstract:
The release of the youtube video for the London Theory institute seminar series available at https://youtu.be/jtfmWDrC370. Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.

Abstract:
This is the live session included as part of the LonTI lecture on "From spin chain to AdS/CFT with Mathematica". Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. ​In this introductory lecture we describe the XXX Heisenberg spin chain, study its spectrum, wavefunctions and discuss integrability of the system. Some examples are given with simple Mathematica code. We also discuss applications to AdS/CFT correspondence.

Abstract:
Analytical models of structure formation are an important tool, complementary to N-body simulations, to investigate the formation of cosmic structures and the dependence of their statistics on cosmological parameters. They rely on some non-linear map, typically spherical collapse, to relate topological features of the initial density field (number of maxima, minima, saddles, critical points...) to different types of structures and events (halos, voids, filaments, mergers...) in the cosmic web.
I will give a broad introduction to the topic and discuss some recent developments.
[please email a.held@imperial.ac.uk for zoom link or password]

Abstract:
An important open question in black hole thermodynamics is about the existence of a "mass gap" between an extremal black hole and the lightest near-extremal state within a sector of fixed charge. In this talk, I will discuss how to reliably compute the partition function of 4d Reissner-Nordstrom near-extremal black holes at temperature scales comparable to the conjectured gap. I will show that the density of states at fixed charge does not exhibit a gap in the simplest gravitational non-supersymmetric theories; rather, at the expected gap energy scale, we see a continuum of states whose meaning we will extensively discuss. Finally, I will present a similar computation for nearly-BPS black holes in 4d N=2 supergravity. As opposed to their non-supersymmetric counterparts, such black holes do in fact exhibit a gap consistent with various string theory predictions. [please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]

Abstract:
In type II strings compactified on a Calabi-Yau threefold \(X\), the Donaldson-Thomas (DT) invariants \(\Omega(\gamma,z)\) counting
BPS black holes have an intricate dependence on the moduli \(z\), due to wall-crossing phenomena. When \(X\) is a toric threefold,
these indices are related to the DT invariants of a quiver with potential with superpotential, encoded by a brane tiling.
I will present a conjecture for the DT invariants for all dimension vectors \(d\) in a certain chamber \(z_*(d)\) known
as the attractor (or self-stability) chamber. In short, "DT invariants all vanish, except when they are known not to."
In combination with the attractor flow tree formulae, this conjecture provides an algorithmic way of computing the DT invariants \(\Omega(\gamma,z)\) for any \(\gamma,z\). The conjecture is supported by a large number of checks, including a successful comparison with the Vafa-Witten invariants of a Fano surface \(S\) when \(X\) is the total space of the canonical bundle \(K_S\), and with the counting of molten crystals for framed DT invariants in the non-commutative chamber. Based on works with G. Beaujard, J. Manschot and S. Mozgovoy, arXiv:2004.14466 and 2012.14358


Join Zoom Meeting

https://zoom.us/j/94029175955?pwd=b1hvVnVxbFZjTmM5bkxaWi93VkpzUT09


Meeting ID: 940 2917 5955

Passcode: 086150

Abstract:
QCD instantons are arguably the best motivated yet unobserved nonperturbative effects predicted by the Standard Model. A discovery and detailed study of instanton-generated processes at colliders would provide a new window into the phenomenological exploration of QCD and a vastly improved fundamental understanding of its non-perturbative dynamics. We present for the first time a full calculation of QCD instanton-induced processes in proton-proton collisions accounting for quantum corrections due to both initial and final state gluon interactions. Although QCD instanton processes are predicted to be produced with a large scattering cross-section at small centre-of-mass partonic energies, discovering them at hadron colliders is a challenging task that requires dedicated search strategies.
[Based on https://arxiv.org/abs/2010.02287 and https://arxiv.org/abs/1911.09726.] [for zoom link contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]

Abstract:
Two dimensional sigma models describe (harmonic) maps of Riemann surfaces to Riemannian manifolds. I will present the
motivations to study the complexification of this problem. I will present the novel approach, developed in my work with Igor Krichever, allowing to construct essentially all twisted complexified harmonic maps of two-torus to spheres and projective spaces. – Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. The link will be emailed.