High Energy Physics

The Cherenkov Telescope Array Observatory (CTAO) is the upcoming next-generation ground-based very-high-energy (VHE) gamma-ray observatory. The CTAO will significantly advance the study of VHE gamma-rays through a combination of wider field of view,  substantially increased detection area, and superior angular and spectral resolution over an energy range extending from tens of GeV to hundreds of TeV. Full-sky coverage will be achieved using two independent Imaging Air Cherenkov Telescope (IACT) arrays: one in the northern hemisphere (Canary Islands, Spain) and one in southern hemisphere (Paranal, Chile). The CTAO will explore a wide range of science topics in high-energy astrophysics, including the origin of higher-energy cosmic rays, mechanisms for particle acceleration in extreme environments, and astroparticle phenomena that may extend the Standard Model of particle physics.  In this talk, I will outline the broad science potential of the CTAO and provide the CTAO’s current status and timeline. I will also describe the contributions of the CTAO-US collaboration to CTAO, including the development of an ultra-high resolution Schwarzschild-Couder telescope for VHE astronomy and the emergence of UV-band optical astronomy at the sub-100 micro-arcsecond angular scale.

The matter power spectrum on subgalactic scales is very weakly constrained so far. While inflation predicts a nearly scale-invariant primordial power spectrum down to very small scales, many new physics scenarios can lead to significantly different predictions, such as axion dark matter in the post-inflationary scenario, vector dark matter produced during inflation, early matter domination, kinetic misalignment axions, self-interacting dark matter, atomic dark matter, etc. Therefore, any successful measurement on the matter power spectrum tests inflation extensively and probes early universe dynamics and the nature of dark matter, making it a new frontier in cosmology and dark matter physics. We proposed observing fast radio bursts (FRB) with solar-system scale interferometry by sending radio telescopes to space, which allows us to greatly expand the sensitivity on the matter power spectrum from Mpc to AU scales. Two sightlines looking at the same FRB source can sample different regions of the Universe in the transverse direction and thus obtain an arrival time difference that depends on the matter power spectrum. Our calculations show that this setup will be sensitive to the scale-invariant power spectrum predicted by inflation on small scales and can also probe QCD axion miniclusters predicted in the post-inflationary scenario.

The study of string scattering in general curved spacetimes presents a stark contrast to the relatively well-understood framework in flat space, where perturbative techniques and worldsheet methods can be used. However, the AdS/CFT correspondence offers a powerful indirect method to compute string amplitudes in AdS. In this talk, I will present recent developments in the AdS Virasoro-Shapiro program. The tree-level amplitude of four gravitons in AdS^5 x S^5 is mapped to a four-point correlator in N=4 SYM at large central charge, and studied by CFT methods combined with single-valuedness, which echoes its importance in flat space. The amplitude itself is defined and constructed as an expansion around flat space. While the goal is to compute it to all orders, attention can be placed on more tractable limits. I will present our results for the High Energy limit, with dual insights from the spacetime and worldsheet perspectives, and the richer case of the Regge limit, which encodes full information on the intermediate operators in the leading Regge trajectory.