Triangle Seminars

Abstract:
In recent years Adam Riess' SH0ES collaboration has made it fashionable to question Lambda-CDM through a series of steadily more precise local determinations of the Hubble constant, the latest of which currently stands at H0 = 73 ± 1 km/s/Mpc. On the other hand, questioning the FLRW paradigm is still taboo. However, if there is a 5 sigma discrepancy with Planck, then a good explanation is required. In the talk, I will explain why H0 should be bounded above by H0 ~ 71 km/s/Mpc in any FLRW cosmology, before presenting some observations that appear to challenge the working FLRW assumption that the Universe is isotropic and homogeneous. Time permitting, I will spell out the implications of a higher local H0 for dark energy models.

Abstract:
Next-generation gravitational wave detectors require highly precise predictions for the waveforms from inspiraling black holes and neutron stars. We present advances in binary inspiral dynamics by taking classical limits of scattering amplitudes in perturbative quantum gravity. The amplitudes are calculated efficiently using modern methods for scattering amplitudes, including double copy and generalized unitarity, and loop integration techniques borrowed from collider physics. Classical physics can be extracted by several complementary approaches, including effective field theory, eikonal exponentiation, and observables in wavepacket scattering. For both conservative and dissipative dynamics of binary systems, we obtain new terms in the post-Minksowskian expansion beyond the best previous results from purely classical methods.

Abstract:
We reinterpret the OSV formula for the on-shell action/entropy function of asymptotically flat BPS black holes as a fixed point formula that is formally equivalent to a recent gluing proposal for asymptotically AdS4 black holes. This prompts a conjecture that the complete perturbative answer for the most general gravitational building block of 4d N=2 supergravity at a single fixed point takes the form of a Nekrasov-like partition function with equivariant parameters related to the higher-derivative expansion of the prepotential. In turn this leads to a simple localization-like proposal for a set of supersymmetric partition functions in (UV completed) 4d N=2 supergravity theories. The conjecture is shown to be in agreement with a number of available results for different BPS backgrounds with both Minkowski and AdS asymptotics. In particular, it follows that the OSV formula comes from the unrefined limit of the general expression including only the so-called W tower of higher derivatives, while the on-shell action of pure (Euclidean) AdS4 with round S3 boundary comes from the NS limit that includes only the T tower.

Abstract:
TBA; part of the London TQFT Journal Club; it will be possible to follow this talk online (please register at https://london-tqft.vercel.app)

Abstract:
Ensembles of quantum chaotic systems are expected to exhibit random matrix universality in their energy spectrum. The presence of this universality can be diagnosed by looking for a linear in time 'ramp' in the spectral form factor, but for realistic systems this feature is typically only visible after a sufficiently long time. Given the wide prevalence of this random matrix behavior, it is natural to ask for an effective field theory which predicts the ramp and computes corrections to it arising from physical constraints. I will present such an effective theory based on fluctuating hydrodynamics. The theory can also be adapted to describe the effects of spontaneous symmetry breaking on spectral correlations. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]

Abstract:
The generalized Wilson loop operator interpolating between the
supersymmetric and the ordinary Wilson loop in \(\mathcal{N}\)=4 SYM theory provides an interesting example of renormalization group flow on a line defect: the scalar coupling parameter \(\zeta\) has a non-trivial beta function and may be viewed as a running
coupling constant in a 1d defect QFT.
We continue the study of this operator, generalizing previous results for the beta function and Wilson loop expectation
value to the case of an arbitrary representation of the gauge group and away from the planar limit.
Focusing on the scalar ladder limit where the generalized Wilson loop reduces to a purely scalar line operator in a free adjoint theory, and specializing to the case
of the rank \(k\) symmetric representation of \(SU(N)\), we also study a certain "semiclassical"
limit where \(k\) is taken to infinity with \(k \zeta^2\) fixed. This limit can be conveniently studied using a 1d defect QFT representation in terms of path integral over
\(N\) commuting 1d bosons. Using this representation, we compute the beta function and circular loop expectation
value in the large \(k\) limit, and use it to derive constraints on the structure of the beta function for general
representation. We discuss the corresponding 1d RG flow and comment on the consistency of the results with
the 1d defect version of the F-theorem. –––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.