Pedro G. S. Fernandes

Recently a non-trivial 4-dimensional theory of gravity that circumvents Lovelock's theorem and avoids Ostrogradsky instability was formulated in [D. Glavan and C. Lin, Phys. Rev. Lett. 124, 081301 (2020)]. This novel theory, named "4D Einstein Gauss-Bonnet gravity", presents several predictions for cosmology and black hole physics. In their work, Glavan & Lin present a novel vacuum black hole solution. In this work, we generalize their black hole solution to include electric charge in an anti-de Sitter space and explore some properties of this solution, like the asymptotics, properties of the horizons, the general relativity limit and thermodynamics.

Gia Dvali

We establish that unitarity of scattering amplitudes imposes universal entropy bounds. The maximal entropy of a self-sustained quantum field object of radius R is equal to its surface area and at the same time to the inverse running coupling evaluated at the scale R. The saturation of these entropy bounds is in one-to-one correspondence with the non-perturbative saturation of unitarity by 2-to-N particle scattering amplitudes at the point of optimal truncation. These bounds are more stringent than Bekenstein's bound and in a consistent theory all three get saturated simultaneously. This is true for all known entropy-saturating objects such as solitons, instantons, baryons, oscillons, black holes or simply lumps of classical fields. We refer to these collectively as "saturons" and show that in renormalizable theories they behave in all other respects like black holes. Finally, it is argued that the confinement in SU(N) gauge theory can be understood as a direct consequence of the entropy bounds and unitarity.

Eleonora Di Valentino, Alessandro Melchiorri, Joseph Silk

We show that a combined analysis of CMB anisotropy power spectra obtained by the Planck satellite and luminosity distance data simultaneously excludes a flat universe and a cosmological constant at $99 \%$ C.L. These results hold separately when combining Planck with three different datasets: the two determinations of the Hubble constant from Riess et al. 2019 and Freedman et al. 2020, and the Pantheon catalog of high redshift supernovae type-Ia. We conclude that either LCDM needs to be replaced by a drastically different model, or else there are significant but still undetected systematics. Our result calls for new observations and stimulates the investigation of alternative theoretical models and solutions.