Who discovered positron annihilation?

Positron annihilatioTim Dunker
In the early 1930s, the positron, pair production, and, at last, positron annihilation were discovered. Over the years, several scientists have been credited with the discovery of the annihilation radiation. Commonly, Thibaud and Joliot have received credit for the discovery of positron annihilation. A conversation between Werner Heisenberg and Theodor Heiting prompted me to examine relevant publications, when these were submitted and published, and how experimental results were interpreted in the relevant articles. I argue that it was Theodor Heiting – usually not mentioned at all in relevant publications – who discovered positron annihilation, and that he should receive proper credit.
Read more at https://arxiv.org/pdf/1809.04815.pdf

Introduction to neutrino astronomy

neutrino flux

Energy dependence of the neutrino fluxes produced by the different nuclear processes in the Sun

Andrea Gallo Rosso, Carlo Mascaretti, Andrea Palladino, Francesco Vissani
This writeup is an introduction to neutrino astronomy, addressed to astronomers and written by astroparticle physicists. While the focus is on achievements and goals in neutrino astronomy, rather than on the aspects connected to particle physics, we will introduce the particle physics concepts needed to appreciate those aspects that depend on the peculiarity of the neutrinos. The detailed layout is as follows: In Sect.~1, we introduce the neutrinos, examine their interactions, and present neutrino detectors and telescopes. In Sect.~2, we discuss solar neutrinos, that have been detected and are matter of intense (theoretical and experimental) studies. In Sect.~3, we focus on supernova neutrinos, that inform us on a very dramatic astrophysical event and can tell us a lot on the phenomenon of gravitational collapse. In Sect.~4, we discuss the highest energy neutrinos, a very recent and lively research field. In Sect.~5, we review the phenomenon of neutrino oscillations and assess its relevance for neutrino astronomy. Finally, we offer a brief overall assessment and a summary in Sect.~6. The material is selected – i.e., not all achievements are reviewed – and furthermore it is kept to an introductory level, but efforts are made to highlight current research issues. In order to help the beginner, we prefer to limit the list of references, opting whenever possible for review works and books.

Read more at https://arxiv.org/pdf/1806.06339.pdf

A short walk through the physics of neutron stars

A schematic cross section of a neutron star illustrating the various regions discussed in the text. The different regions shown are not drawn on scale.

Isaac Vidana
In this work we shortly review several aspects of the physics of neutron stars. After the introduction we present a brief historical overview of the idea of neutron stars as well as of the theoretical and observational developments that followed it from the mid 1930s to the present. Then, we review few aspects of their observation discussing, in particular, the different types of telescopes that are used, the many astrophysical manifestations of these objects, and several observables such as masses, radii or gravitational waves. Finally, we briefly summarize some of theoretical issues like their composition, structure equations, equation of state, and neutrino emission and cooling.
read more at https://arxiv.org/pdf/1805.00837.pdf

Cosmic Instability Could Have Created Dark Matter

A proposed instability in the Higgs field could have seeded the Universe with primordial black holes that now serve as dark matter.

Our Universe may be sitting on the edge of destruction, as theory suggests that the Higgs field is in a metastable state. If this field tunneled to its “true” minimum energy state, the release of energy would be cataclysmic. The danger may be over-stated, as other physical mechanisms could have kept the Universe stable throughout its history. Nevertheless, the Higgs instability could have a major cosmological impact as the source of dark matter. According to this new scenario, dark matter consists of a large population of black holes that formed from fluctuations in the unstable Higgs field at the dawn of the Universe. These so-called primordial black holes have been proposed before, but this is the first hypothesis that doesn’t require physics beyond the standard model.

Physicists have long been aware that the Universe might rest in a “false vacuum.” This idea has recently taken on new urgency, as calculations based on the measured Higgs mass have shown that a lower energy state may exist for the Higgs field. Analyzing the implications of the Higgs instability, José Espinosa, from the Catalan Institution for Research and Advanced Studies (ICREA) in Spain, and David Racco and Antonio Riotto, both at the University of Geneva, have found that this menacing mechanism could—counterintuitively—be instrumental in creating the dark matter that makes galaxies and other life-accommodating structures possible. In their calculations, the team explored fluctuations in the Higgs field during an early expansion phase of the Universe, called inflation. Under certain assumptions, these fluctuations become seeds for microscopic black holes with masses around 1015 kg that could have a density consistent with cosmological predictions of dark matter.

Michael Schirber – https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.120.121301