Annual Review of Nuclear and Particle Science - Early Publication

Exploding stars have long been considered a threat to life on Earth. While early studies were speculative, modern research is based on advanced observations, theory, and modeling. This review examines supernova explosions, γ-ray bursts (GRBs), and kilonova outbursts, which are major sources of ionizing radiation in galaxies. This radiation can harm Earth-like biospheres by destroying stratospheric ozone, increasing exposure to solar ultraviolet, and producing cosmic-ray muons that penetrate belowground and underwater. Using recent work, we calculate rates for nearby explosions based on distance from the Earth and ionizing radiation dose. Over the Earth's history, core-collapse supernova cosmic rays, γ-rays from Type Ia supernovae, X-rays from Type IIn supernovae, and γ-rays from long GRBs have likely caused significant biosphere damage. However, short GRBs and kilonovae are less concerning. Future research could address open questions through nuclear and particle experiments, astronomical observations, and studies in climate, geology, radiation, and evolutionary biology.

While a variety of laboratory-based fusion schemes have been studied for decades, the only fusion scheme yet to demonstrate fusion ignition and significant energy gain has been X-ray-driven inertially confined fusion. Ignition was demonstrated to occur at the thermodynamic conditions where it had long been expected, but the energy required for the implosion system to reach these conditions was more than projected years ago. This short review gives a status update on the three principal inertial confinement fusion schemes and research challenges going forward.

The search for dark matter and physics beyond the Standard Model has grown to encompass a highly interdisciplinary approach. In this review, we survey recent searches for light, weakly coupled particles—axions and dark photons—over the past decade, focusing on new experimental results and the incorporation of technologies and techniques from fields as diverse as quantum science, microwave engineering, precision magnetometry, and condensed matter physics. We also review theoretical progress that has been useful in identifying new experimental directions and identify the areas of most rapid experimental progress and the technological advances required to continue exploring the parameter space for axions and dark photons.

Future accelerators and experiments for energy-frontier particle physics will be built and operated during a period in which society must also address the climate change emergency by significantly reducing emissions of carbon dioxide. The carbon intensity of many particle physics activities is potentially significant, such that as a community particle physicists could create substantially more emissions compared to the amount created by average citizens, which is itself currently more than budgeted to limit the increase in average global temperatures. We estimate the carbon impacts of potential future accelerators, detectors, computing, and travel, and find that while emissions from civil construction dominate by far, some other activities make noticeable contributions. We discuss potential mitigation strategies as well as research and development activities that can be pursued to make particle physics more sustainable.