Triangle Seminars

Abstract:
The universe has turned out to be simpler than expected on small and large scales. This encourages us to build unified theories connecting particle physics to the LCDM model. Instead of postulating an ``attractor” phase such as inflation, prior to the hot big bang, we extrapolate the observed universe all the way back to the initial singularity. If the hot plasma in the early universe is perfectly conformal radiation, the singularity is only conformal and one can analytically extend cosmic spacetime and matter through it into a ``mirror” universe on the other side. The universe is then CPT symmetric. We calculate the gravitational entropy for cosmologies with radiation, matter, Lambda and space curvature, finding that thermodynamics favours flat, homogeneous and isotropic universes like ours. To maintain conformal symmetry we include unusual Dim-0 (dimension zero) fields, whose unique physical state is the vacuum. They improve the Standard Model’s (SM’s) coupling to gravity, by cancelling the SM’s vacuum energy and two local “Weyl” anomalies due to gauge fields and fermions. They also cancel the acausal, nonanalytic behaviour introduced into the graviton propagator by loops of SM particles. Cancellation requires (and predicts) precisely 3 generations of SM fermions, each with a RH neutrino, and that the Higgs is composite. One of the RH neutrinos, if stable, is then the simplest-yet proposed viable candidate for the dark matter. Galaxy surveys including EUCLID and LSST will allow precise tests soon. Finally, and most exciting, Dim-0 fields have scale-invariant fluctuations in the vacuum. These source curvature perturbations in the early universe. We recently calculated their power spectrum, ab initio, in terms of Standard Model couplings at the Planck scale. Subject to some theoretical assumptions, the amplitude and spectral tilt closely match the observations, with no free parameters. (See arXiv:2302.00344and references therein).

Abstract:
We consider gluons scattering in Type IIB string theory on AdS5 x S^5/Z2 in the presence of D7 branes, which is dual to the flavor multiplet correlator in a certain 4d N=2 USp(2N) gauge theory with SO(8) flavor symmetry. We compute this holographic correlator in the large N and finite string coupling tau expansion using constraints from derivatives of the mass deformed sphere free energy, which we compute to all orders in 1/N and finite tau using localization. In particular, we fix the F^4 correction to gluon scattering on AdS in terms of Jacobi theta functions, and the D^2F^4 correction in terms of a non-holomorphic Eisenstein series. At weak string coupling, we find that the AdS correlator takes a remarkably similar form as the flat space Veneziano amplitude. Finally, we combine the numerical conformal bootstrap with the localization constraints to study the correlator at finite N and tau.

Abstract:
The locality in space of interactions between elementary particles is a key property of our universe. This locality is hardwired into quantum field theoretic descriptions of nature. However, locality and indeed space itself are likely not fundamental concepts. In holographic duality, local interactions on a dynamical spacetime emerge from "large N" matrices where no locality need be manifest in the microscopic Hamiltonian. The emergence of locality from matrix theories is well-established but not well-understood. In recent years it has been appreciated that locally is closely tied up with so-called "area law" entanglement of the microscopic degrees of freedom. I will discuss a particularly robust notion of entanglement in matrix theories that is rooted in an underlying Gauss law constraint and show how simple models of matrix, or 'fuzzy' geometry contain area law entanglement.

Abstract:
I will describe how non-invertible global symmetries act on operators in a quantum field theory. The various possible actions are called generalized charges. This provides a stepping stone for understanding physical applications of non-invertible symmetries, as will be exemplified in the case of Ising symmetry. One of the surprising findings of this endeavor is that there exist new and unexplored generalized charges already for ordinary invertible global symmetries! These generalized charges are described by higher-representations of the symmetry group, generalizing the ordinary charges described by ordinary representations of the symmetry group.

Abstract:
The London Institute hosts a workshop on the Navier-Stokes millennium-prize problem and its connection to fluid computing and machine learning.

https://lims.ac.uk/event/navier-stokes-regularity-fluid-computing-machine-learning-workshop/

https://www.lms.ac.uk/events/lectures/hardy-lectureship#LMS%20Hardy%20Lectureship