Talks

Scattering amplitudes are where quantum field theory directly meets collider experiments.  An excellent model for scattering in QCD is provided by N=4 super-Yang-Mills theory, particularly in the planar limit of a large number of colors, where the theory becomes integrable.  The first nontrivial amplitude in this theory is for 6 gluons.  It can be computed to 7 loops using a bootstrap based on the rigidity of the function space of multiple polylogarithms, together with a few other conditions.  One can also bootstrap a particular form factor, for the chiral stress-tensor operator to produce 3 gluons, through 8 loops.  This form factor is the N=4 analog of the LHC process, gluon gluon --> Higgs + gluon. Remarkably, the two sets of results are related by a mysterious `antipodal' duality, which exchanges the role of branch cuts and derivatives.  Furthermore, this duality is `explained' by an antipodal self-duality of the 4 gluon form factor of the same operator; although it is still fair to say of the self-duality, `who ordered that?'

Zoom link:  https://pitp.zoom.us/j/96265005656?pwd=Qndza3pIKzdmZVJGL0s1ZUZkRmp4QT09

Precision measurements of primordial correlators in the CMB, Large Scale Structure, and 21-cm cosmology may contain “on-shell" imprints of extremely heavy particle physics, with masses comparable to the inflationary Hubble scale, via the remarkable inflationary mechanism known as “cosmological collider physics”. I will describe my research in (a) finding new robust mechanisms for extending the energy range and strength of such signals, (b) identifying motivated particle physics targets that may be discoverable, (c) showing how cosmological collider physics can probe the mechanism of inflation itself, and (d) demonstrating variants of the mechanism that may be observable in new cosmological “maps”, such as stochastic gravitational wave backgrounds with significant anisotropies. While this is an ambitious program of research, there are major challenges to bring it to fruition, on the experimental, phenomenological and theoretical fronts, which I will sketch. 

Zoom Link:  https://pitp.zoom.us/j/98923687484?pwd=cjgweEhoejVCeHAvc0RBSDEvVkZldz09

There are numerous properties of quantum states that one might be interested in characterizing, including statistical moments of observables such as expectations or variances, or more generally purities, entropies, probabilities, eigenvalues, symmetries, marginals, etc. Given a fixed collection of properties, the realizability problem aims to determine which value-assignments to those properties are jointly exhibited by at least one quantum state. In addition to the decision problem of realizability, one might also be interested in quantifying what proportion of quantum states possesses those property values. 

Any property of a quantum state can always, at least in principle, be estimated empirically by suitably measuring an ensemble of many independently and identically prepared copies of that quantum state. The particular sequence of positive operator valued measures which estimates a given property is known as a property estimation scheme. The purpose of this talk is to discuss a strategy for tackling realizability problems by studying the large deviation behaviour of property estimation schemes.

The key idea of this approach is the following:
A given collection of properties is realized by a quantum state if and only if a random quantum state occasionally produces that collection of properties as estimates.
Under suitable conditions, this observation leads to a complete hierarchy of necessary conditions for realizability.

Zoom link:  https://pitp.zoom.us/j/91945653382?pwd=QTZqSnpjYjlxYndqaHZwN2lES1h1Zz09

 I will present a novel behavior developed by scattering amplitudes in certain regions of the kinematic space, in which amplitudes factorize into 3 pieces without becoming singular. This is opposed to what happens in standard factorization or soft limits. We call this behavior a 3-split, and it is "semi-local" in nature. As 3-splits cannot be obtained from standard unitarity arguments, they represent a new phenomenon in QFT. I will introduce 3-splits in their simplest version, i.e. for the biadjoint scalar theory (which I will also introduce). If time allows, I will also comment on how 3-splits arise in other QFTs and how they lead to the discovery of more general theories.

Zoom link:  https://pitp.zoom.us/j/95575818902?pwd=V1RKYW9WMmZQNElVL2VyUGFGMFgxQT09

The angular resolution of a stellar interferometer, as for a single telescope, becomes better at smaller wavelengths and larger baselines. The goal for ground detectors would then be optical interferometers with baselines as long as the Earth’s diameter. The latter goal has been achieved in radio, but it becomes prohibitive in the optical, as the electromagnetic field oscillates too rapidly to record and analyze directly over km-long baselines. Intensity interferometry relying on second-order correlations can make this possible: rather than the amplitude and phase of incoming light, we need only count photons. This technique has a long history and to date the best measurements of nearby stellar radii, dating back to the 1950s. Its main limitations are the need for very bright sources and its narrow field of view, restricting kilometer-long baselines to sources only a few μas away. In this talk, I will propose an optical-path modification of astronomical intensity interferometers, which introduces an effective time delay in the two-photon interference amplitude, splitting the main intensity correlation fringe into others at finite opening angles, allowing for differential astrometry of multiple compact sources such as stars or quasar images. Together with the exponential progress in the field of single photon detection, such a modification will immensely increase the scope of intensity interferometry beyond measurements of the optical emission region morphology. I will lay out the theory and technical requirements of time-delay intensity interferometry and, time permitting, I will talk about some promising applications, which include astrometric microlensing of stars and quasar images, binary-orbit characterization, exoplanet detection, Galactic acceleration measurements and calibration of the cosmic distance ladder, all at unprecedented relative astrometric precision.

Zoom link:  https://pitp.zoom.us/j/92041231568?pwd=cWo2c0hwTEdmOTRCc042SHNxRWw5UT09