Alexander R. H. Smith

A novel quantum time dilation effect is shown to arise when a clock moves in a quantum superposition of two relativistic velocities. This effect is argued to be measurable using existing atomic interferometry techniques, potentially offering a new test of relativistic quantum theory.

Stephen Wolfram

A class of models intended to be as minimal and structureless as possible is introduced. Even in cases with simple rules, rich and complex behavior is found to emerge, and striking correspondences to some important core known features of fundamental physics are seen, suggesting the possibility that the models may provide a new approach to finding a fundamental theory of physics.

Peter Adshead, Niayesh Afshordi, Emanuela Dimastrogiovanni, Matteo Fasiello, Eugene A. Lim, Gianmassimo Tasinato

Characterizing the physical properties of the stochastic gravitational waves background (SGWB) is a key step towards identifying the nature of its possible origin. We focus our analysis on SGWB anisotropies. The existence of a non-trivial primordial scalar-tensor-tensor (STT) correlation in the squeezed configuration may be inferred from the effect that a long wavelength scalar mode has on the gravitational wave power spectrum: an anisotropic contribution. Crucially, such contribution is correlated with temperature anisotropies in the cosmic microwave background (CMB). We show that, for inflationary models that generate suitably large STT non-Gaussianities, cross-correlating the CMB with the stochastic background of gravitational waves is a very effective probe of early universe physics. The resulting signal can be a smoking-gun for primordial SGWB anisotropies.

Juan Maldacena

We discuss aspects of magnetically charged black holes in the Standard Model. For a range of charges, we argue that the electroweak symmetry is restored in the near horizon region. The extent of this phase can be macroscopic. If $Q$ is the integer magnetic charge, the fermions lead to order $Q$ massless two dimensional fermions moving along the magnetic field lines. These greatly enhance Hawking radiation effects.

Hugo Camargo PI Michal P. Heller PI Ro Jefferson Johannes Knaute Ignacio Reyes Sukhbinder Singh Viktor Svensson

During the SARS-CoV-2 pandemic, theoretical high-energy physics, and likely also the majority of other disciplines, are seeing a surge of virtual seminars as a primary means for scientific exchange. In this brief article, we highlight some compelling benefits of virtualizing research talks, and argue for why virtual seminars should continue even after the pandemic. Based on our extensive experience on running online talks, we also summarize some basic guidelines on organizing virtual seminars, and suggest some directions in which they could evolve.

W.L. Kimmy Wu, Pavel Motloch, Wayne Hu, Marco Raveri

We apply a tension metric $Q_\textrm{UDM}$, the update difference in mean parameters, to understand the source of the difference in the measured Hubble constant $H_0$ inferred with cosmic microwave background lensing measurements from the Planck satellite ($H_0=67.9^{+1.1}_{-1.3}\, \mathrm{km/s/Mpc}$) and from the South Pole Telescope ($H_0=72.0^{+2.1}_{-2.5}\, \mathrm{km/s/Mpc}$) when both are combined with baryon acoustic oscillation (BAO) measurements with priors on the baryon density (BBN). $Q_\textrm{UDM}$ isolates the relevant parameter directions for tension or concordance where the two data sets are both informative, and aids in the identification of subsets of data that source the observed tension. With $Q_\textrm{UDM}$, we uncover that the difference in $H_0$ is driven by the tension between Planck lensing and BAO+BBN, at probability-to-exceed of 6.6%. Most of this mild tension comes from the galaxy BAO measurements parallel to the line of sight. The redshift dependence of the parallel BAOs pulls both the matter density $\Omega_m$ and $H_0$ high in $\Lambda$CDM, but these parameter anomalies are usually hidden when the BAO measurements are combined with other cosmological data sets with much stronger $\Omega_m$ constraints.