Anirudh will talk aboue Axions in High-Energy Astrophysical Plasmas
Axions are a well-motivated extension to the Standard Model of particle physics and among the best candidates to explain dark matter. Their detection is made difficult by the fact that they couple very weakly to particles in the Standard Model. High-energy astrophysical settings host extreme conditions wherein axions may be produced in great abundance. I will begin this talk with a pedagogical introduction to axion phenomenology, drawing analogy with familiar topics in plasma and neutrino physics. I will then discuss axion production in the highly magnetized plasma surrounding neutron stars. A fraction of produced axions convert to radio photons, giving rise to anomalous radio emission (including, possibly, fast radio bursts). Some produced axions remain gravitationally bound to the star, forming dense clouds around neutron stars. I will conclude with a discussion of efforts to detect astrophysically-sourced axions in the laboratory.
Hila will talk about Simulations of common envelope evolution in triple systems and their outcomes
Triple systems are frequent among stellar systems, and their evolution may lead to a wide variety of non-trivial and sometimes exotic outcomes. Common envelope (CE) evolution, which plays a major role in the evolution of compact binary systems, can similarly play a key role in the evolution of triples. Here we use hydrodynamical simulations to provide the first detailed models of triple common envelope (TCE) evolution. We discuss two scenarios of the TCE, according to the distant third component of the hierarchical system, which can either be the donor star (circumstellar case), or one of the accretors (circumbinary case). Through our exploratory modeling, we find several possible outcomes of such TCE: (1) The merger of a binary inside the third star's envelope; (2) The disruption of the in-spiraling binary following its plunge, leading to a chaotic triple dynamic of the stellar-core and the two components of the former disrupted binary. The chaotic evolution typically leads to the in-spiral and merger of at least one of the former binary components with the core, and sometimes to the ejection of the second, or alternatively its further now-binary common envelope evolution. The in-spiral in TCE leads to overall slower in-spiral, larger mass ejection, and the production of more aspherical remnant, compared with a corresponding binary case of similar masses, due to the energy/momentum extraction from the inner binary. We expect TCE to give rise to the production of various types of stellar mergers, and unique compact binary systems and potentially induce transient electromagnetic and gravitational-wave sources.
