Abstract:

Local measurements of the Hubble parameter from type 1a supernovae disagree at almost 4sigma with the value inferred from a ΛCDM fit to the cosmic microwave background (CMB), with local measurements suggesting a higher value. This discrepancy is not easily explained by any obvious systematic effect in either measurement, and so increasing attention is given to the possibility that this “Hubble tension” may be indicating new physics beyond ΛCDM. In this talk, I would like to review promising solutions to this tension. I will first argue that this discrepancy should be interpreted as a tension between our understanding of the early and late universe cosmology, rather than a tension between two datasets. Secondly, I will show that this observation might indicate that our Universe has undergone anomalous expansion due to the presence of an early dark energy (EDE) at redshift z ~ 5000. I will give two examples of a physical model that lead to the desired dynamics. Moreover, I will explain why this solution is favored over modifications of the dark energy dynamics (the so-called “phantom” dark energy) as well as favored over the presence of an additional relativistic degree of freedom.

Abstract:

In this talk, I will discuss consequences of the potential detection of anti-helium-3 and -4 events by AMS-02 and in particular the very surprising isotopic ratio in cosmic rays that it would indicate. After showing that spallation from primary hydrogen and helium nuclei onto the ISM cannot account for the measured fluxes, I will argue that dark matter annihilation or decay face similar difficulties in explaining these events. I will then entertain the possibility that these events originate from anti-matter-dominated regions in the form of anti-clouds or anti-stars. Starting with the case of anti-clouds, I will show how the isotopic ratio of anti-helium nuclei might suggest that BBN has happened in an inhomogeneous manner, resulting in anti-regions with a anti-baryon-to-photon ratio η-bar ≃ 0.001η. However, I will show that a variety of observations strongly constrain this scenario, and in particular, would require the anti-clouds to be almost free of normal matter. I will finally discuss an alternative scenario where anti-domains are dominated by surviving anti-stars and suggest that part of the unidentified sources in the 3FGL catalog can originate from anti-clouds or anti-stars.

Ref Arxiv: 1903.04218
Ref INSPIRE: 1724522
Ref. & Cit.: NASA ADS

Ref Arxiv: 1903.05140
Ref INSPIRE: 1724856
Ref. & Cit.: NASA ADS

Ref Arxiv: 1903.04424
Ref INSPIRE: 1724526
Ref. & Cit.: NASA ADS

Ref INSPIRE: 1686898
DOI: 10.22323/1.301.0915