Rob Myers (Perimeter): Complexity = Anything | 1/27/23
Motivated by holographic complexity, we examine a new class of gravitational observables in asymptotically AdS space associated with codimension-one slices or with codimension-zero regions. We argue that any of these observables is an equally viable candidate as the extremal volume for a gravitational dual of complexity.
Nima Lashkari (Purdue): Information loss, Chaos, and the Emergence of Type III1 Algebras | 2/17/23
The decay of the left-right correlators in an eternal black hole is one of the simplest manifestations of the black hole information loss problem.
The subalgebras of left and right decorrelate under the time evolution asymptotically, and monotonically due to the stretching of the wormhole.
From the point of view of quantum mechanics, dynamical decorrelation is so special that can be used as a clue to the nature of operator algebras in quantum gravity.
In particular, I will argue that asymptotic decorrelation uniquely fixes the operator algebras to be the type III1 von Neumann algebras. I will comment on the connections between the emergence of the second law, the decay of the out-of-time-ordered correlator (chaos), and the emergence of type III1 algebras.
Tim Cohen (Cern): Large Deviations in the Early Universe | 3/15/23
Fluctuations play a critical role in cosmology. They are relevant across a range of phenomena from the dynamics of inflation to the formation of structure. In many cases, these it is a good approximation to coarse grain these fluctuations (in the sense of a Renormalization Group flow), and they follow a Gaussian distribution as a consequence of the Central Limit Theorem. Yet, some classes of observables are dominated by rare fluctuations and are sensitive to the details of the underlying microphysics. In this talk, I will introduce the Large Deviation Principle, and will explain how it can be used to diagnose when effective approaches fail and one must instead to appeal to the microscopic description. I will illustrate this phenomenon in the context of determining the phase transition to eternal inflation, the distribution of scalar field fluctuations in de Sitter, and the production of primordial black holes.
Kimberly Boddy (UTexas): Evolution of Self-Interacting Dark Matter Halos | 3/24/23
Large self interactions between dark matter particles alter the predicted properties of dark matter halos and may help address small-scale structure issues, while maintaining the successes of standard cold dark matter at large scales. Self interactions allow for efficient heat transfer within a halo, which can be modeled using a gravothermal fluid approximation. In this talk, I will discuss how the choice of the particle physics model for self interactions, as well as the environment of the halo, impacts the phases of halo evolution.
Sergei Dubovsky (NYU): Scattering on the worldsheet of the QCD string | 3/31/23
Natalie Paquette (University of Washington): Top Down Topological Holography and Twists on Twistor Space | 4/7/23
I will discuss recent work in collaboration with Kevin Costello and Atul Sharma. Aspects of the holographic correspondence can be understood mathematically through a framework called twisted holography, which has been applied to AdS/CFT to compute certain protected correlators. In this talk we will apply these ideas to describe a new holographic duality for a bulk theory in an asymptotically flat spacetime which arises from studying twisted holography on twistor space. The ``boundary'' 2d chiral algebra, which is dual to the algebra of bulk asymptotic symmetries, can be described using a mathematical technique called Koszul duality. Alternatively, the 4d and 2d theories are independently defined from top-down string theoretic reasoning, and we match OPEs with collinear limits of scattering amplitudes in the planar limit as a check.
