Talks

I present work done in the last years on the construction of dynamical coordinate systems for highly symmetric backgrounds, such as Minkowski, de Sitter, and FLRW cosmologies, and which are needed in the relational approach to construct gauge-invariant observables in gravity. I show that it is possible to restrict the inevitable non-local contributions to the past light cone such that the obtained observables are causal. Lastly, I present some applications, namely the leading quantum gravitational corrections to the local expansion rate of our universe (the Hubble rate) and the Newtonian gravitational potential.

Based on arXiv:1711.08470, arXiv:1806.11124, arXiv:2108.11960, arXiv:2109.09753, and arXiv:2303.16218.

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The Langlands program is a grand organizing vision for a large slice of number theory and representation theory. A shockingly accurate metaphor for the Langlands program has emerged as electric-magnetic duality in four-dimensional gauge theory, but where the role of spacetime is played by objects from arithmetic. I will describe recent work with Yiannis Sakellaridis and Akshay Venkatesh, in which we apply ideas from QFT (the Gaiotto-Witten electric-magnetic duality for boundary theories) to a fundamental problem in number theory, predicting the relation between L-functions of Galois representations and integrals of automorphic forms.

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What happened in the earliest moments of the Universe? Despite decades of theoretical and observational work, a detailed understanding of the primordial Universe has remained elusive. In this talk, I will show how surveys of millions of galaxies can shed new light on these issues by constraining the statistics of the Universe just after inflation. By combining robust perturbative models with novel numerical techniques, I have placed some of the first (non-Gaussian) constraints on the dynamics and field content of inflation from galaxy surveys; these will sharpen considerably in the next decade as the volume of observational data grows. Through a combination of traditional perturbative approaches and new symmetry-based techniques, I will demonstrate how current and future galaxy surveys can be used to search for a wealth of new physics, including primordial scattering processes and parity violation, opening the door to constraining ultra-high-energy physics with low-energy data.

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Horizons of black holes in equilibrium and null infinity of asymptotically flat space-times are null 3-manifolds but have very different physical connotations. We first show that they share a large number of geometric properties, making them both weakly isolated horizons. We then use this new unified perspective to unravel the origin of the drastic differences in the physics they contain. Interestingly, the themes are woven together in a manner reminiscent of voices in a fugue.The talk is based on joint work with Simone Speziale (arXiv:2401.15618 and arXiv 2401:????).

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Fuzzy dark matter can form cored density distributions, named solitons, at the center of galaxies. Such cores can be viewed as approximate mass sheets and can affect the time delay cosmography Hubble constant (H_0) measurement via the mass sheet degeneracy. We show that a subdominant component of fuzzy dark matter can yield a 10 percent shift in the inferred H_0, if the particle mass is of order 10^-25 eV. The sensitivity of time delays on such cores (difficult to spot otherwise) may give a further probe in constraining the fuzzy dark matter scenario, if an H_0 prior is assumed.

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Brane Webs in Type IIB String Theory can be used to engineer 5d N=1 gauge theories and SCFTs. These brane webs can also be used to obtain so called magnetic quivers, whose 3d Coulomb branches gives the Higgs branch of the 5d theory in question. We will see how to obtain these magnetic quivers for brane webs possibly in the presence of orientifold planes. Then we will see how 3d Coulomb branch technology (such as quiver subtraction) can be used to understand Higgsings and mass deformations of 5d SCFTs.

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In this talk, I will discuss my exploration of the gravothermal collapse of isolated self-interacting dark matter (SIDM) halos, driven deep into the core-collapsed regime where interactions are frequent. We investigate how elastic collisions influence the central region of SIDM halos as they undergo core collapse. In our numerical findings, we discover a remarkable universality in the behavior of halos, allowing us to predict their evolution deep in the core-collapsed regime. We develop a semi-analytic method to characterize the core properties of the halo in the latest stages of evolution, which is crucial for making predictions of the mass of potential black holes forming at the heart of these dark matter halos.

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