Triangle Seminars

Abstract:
Integrable models are the cornerstones of theoretical physics, simple enough to be solved exactly and yet rich enough to offer a glimpse into the dynamics of more intricate systems. Also two-dimensional field theories or string theories can be integrable. In this talk I will discuss integrability in field and string theories and present a special class of integrable models that promote the symmetry algebra of the undeformed theory to a quantum group.

[please email a.held@imperial.ac.uk for zoom link or password]

Abstract:
I will discuss some aspects of supersymmetric systems from a computational perspective.

[please email a.held@imperial.ac.uk for zoom link or password]

Abstract:
There is a deep relation between classical error-correcting codes, Euclidean lattices, and chiral 2d CFTs. We show this relation extends to include quantum codes, Lorentzian lattices, and non-chiral CFTs. The relation to quantum codes provides a simple way to solve modular bootstrap constraints and identify interesting examples of conformal theories. In particular we construct many examples of physically distinct isospectral theories, examples of "would-be" CFT partition function – non-holomorphic functions satisfying all constraints of the modular bootstrap, yet not associated with any known CFT, and find theory with the maximal spectral gap among all Narain CFTs with the central charge c=4. At the level of code theories the problem of finding maximal spectral gap reduces to the problem of finding optimal code, leading to "baby bootstrap" program. We also discuss averaging over the ensemble of all CFTs associated with quantum codes, and its possible holographic interpretation. The talk is based on arXiv:2009.01236 and arXiv:2009.01244.

Abstract:
The Hamiltonian formulation of mechanics has many advantages,
but its standard presentation destroys manifest covariance. This can be
avoided by using the "covariant phase formalism" of Iyer and Wald, but
until recently this formalism has suffered from several ambiguities
related to boundary terms and total derivatives. In this talk I will
present a new version of the formalism which incorporates boundary
effects from the beginning. This eliminates all ambiguities, and leads
to an algorithmic procedure for covariantly constructing the phase space
and Hamiltonian of any Lagrangian field theory. It also allows us to
confirm that the Poisson bracket in covariant phase space is indeed
equivalent to an old proposal of Peierls for computing Poisson brackets
covariantly. Along the way I'll illustrate the formalism using various
examples. Based on work with Jie-qiang Wu.

Abstract:
I will review the QQ-system and oscillator construction of Q-operators for su(r+1) spin chains and discuss its generalisation to so(2r) spin chains. ––- Part of London Integrability Journal Club. If you are a new participant, please register filling the form at integrability-london.weebly.com. The link will be emailed.