Yang Bai, Andrew J. Long, Sida Lu

Dark matter could take the form of dark massive compact halo objects (dMACHOs); i.e., composite objects that are made up of dark-sector elementary particles, that could have a macroscopic mass from the Planck scale to above the solar mass scale, and that also admit a wide range of energy densities and sizes. Concentrating on the gravitational interaction of dMACHOs with visible matter, we map out the mass-radius parameter space that is consistent with gravitational lensing experiments, as well as anisotropies of the cosmic microwave background (CMB) based on the spherical accretion of matter onto a dMACHO in the hydrostatic approximation. For dMACHOs with a uniform-density mass profile and total mass in the range of $\sim 10^{-12} - 10\,M_\odot$, we find that a dMACHO could explain 100% of the dark matter if its radius is above $\approx 3$ times the Einstein radius of the lensing system. For a larger mass above $10\,M_\odot$, a dMACHO with radius above $\sim 1 \times 10^8 \mbox{cm} \times(M/100\,M_\odot)^{9/2}$ is consistent with CMB observables. For a lighter dMACHO with mass below $\sim 10^{-12}\,M_\odot$, there still is not a good experimental probe. Finally, we point out that heavier dMACHOs with masses $\sim 0.1\,M_\odot$ may be observed by X-ray and optical telescopes if they reside at rest in a large molecular cloud, nearby to our solar system, and accrete ordinary matter to emit photons.

Steven Weinberg

A class of models is considered in which the masses only of the third generation of quarks and leptons arise in the tree approximation, while masses for the second and first generations are produced respectively by one-loop and two-loop radiative corrections. So far, for various reasons, these models are not realistic.

Krishan Saraswat, Niayesh Afshordi

We study how the evaporation rate of spherically symmetric black holes is affected through the extraction of radiation close to the horizon. We adopt a model of extraction that involves a perfectly absorptive screen placed close to the horizon and show that the evaporation rate can be changed depending on how close to the horizon the screen is placed. We apply our results to show that the scrambling time defined by the Hayden-Preskill decoding criterion, which is derived in Pennington's work (arXiv:1905.08255) through entanglement wedge reconstruction is modified. The modifications appear as logarithmic corrections to Pennington's time scale which depend on where the absorptive screen is placed. By fixing the proper distance between the horizon and screen we show that for small AdS black holes the leading order term in the scrambling time is consistent with Pennington's scrambling time. However, for large AdS black holes, we find the leading order term differs from Pennington's results. The leading order Log contains the Bekenstein-Hawking entropy of a cell of characteristic length equal to the AdS radius rather than the entropy of the full horizon.

Tsutomu Kobayashi

We reformulate the recently proposed regularized version of Lovelock gravity in four dimensions as a scalar-tensor theory. By promoting the warp factor of the internal space to a scalar degree of freedom, we show that regularized Lovelock gravity is effectively described by a particular subclass of the Horndeski theory. Cosmological aspects of regularized Einstein-Gauss-Bonnet gravity are studied based on this scalar-tensor reformulation. It is found that the background with a scalar charge is generically allowed. The consequences of this scalar charge is briefly discussed.

Kevork N. Abazajian, Shunsaku Horiuchi, Manoj Kaplinghat, Ryan E. Keeley, Oscar Macias

The extended excess towards the Galactic Center (GC) in gamma rays inferred from Fermi-LAT observations has been interpreted as being due to dark matter (DM) annihilation. Here, we perform new likelihood analyses of the GC and show that when including templates for the stellar galactic and nuclear bulges, the GC shows no significant detection of a DM annihilation template, even after generous variations in the Galactic diffuse emission models and a wide range of DM halo profiles. We include Galactic diffuse emission models with combinations of 3D inverse Compton maps, variations of interstellar gas maps, and a central source of electrons. For the DM profile, we include both spherical and ellipsoidal DM morphologies and a range of radial profiles from steep cusps to kiloparsec-sized cores, motivated in part by hydrodynamical simulations. Our derived upper limits on the dark matter annihilation flux place strong constraints on DM properties. In the case of the pure $b$-quark annihilation channel, our limits on the annihilation cross section are more stringent than those from the Milky Way dwarfs up to DM masses of $\sim$TeV, and rule out the thermal relic cross section up to $\sim$300 GeV. Better understanding of the DM profile, as well as the Fermi-LAT data at its highest energies, would further improve the sensitivity to DM properties.