Astroparticle Physics

Astroparticle physics lies at the interface between particle physics and astrophysics and can be broadly divided into two complementary directions.

One direction is to use a variety of messengers, including gamma rays, cosmic rays, neutrinos, and gravitational waves, to understand astrophysical phenomena and extreme environments in the Universe.

The other is to use astrophysical objects and the Universe itself as laboratories for particle physics that cannot be accessed by terrestrial experiments, with the aim of searching for unknown particles and new fundamental laws of physics, including the nature of dark matter.

In the first direction, observations of high-energy photons, cosmic rays, neutrinos, and gravitational waves, in addition to conventional astronomical observations using visible light and radio waves, allow us to investigate the physics of energetic phenomena in the Universe, such as black holes, neutron stars, supernova explosions, and active galactic nuclei. This research is closely related to Kavli IPMU’s Research Programs on “High-Energy Astrophysics,” “Neutrino Physics,” and “Supernovae.” One example is astronomy in the MeV gamma-ray band. Kavli IPMU participates in NASA’s MeV gamma-ray mission COSI (Compton Spectrometer and Imager), which will investigate the origin of Galactic positrons, nucleosynthesis through nuclear gamma rays from radioactive isotopes, gamma-ray polarization from black holes, pulsars, and gamma-ray bursts, and multimessenger phenomena in combination with gravitational-wave observations. We also study high-energy neutrinos and cosmic rays to identify their astrophysical sources and to understand the production, acceleration, and propagation of high-energy particles in the Universe.

In the second direction, astrophysical objects and the Universe are used as laboratories for particle physics under conditions that are difficult or impossible to realize in terrestrial experiments. One of the major research topics pursued at Kavli IPMU is the indirect detection of dark matter. Dark matter constitutes most of the matter in the Universe, yet its nature remains unknown, and it is widely studied as a possible new particle beyond the Standard Model. Searches for dark matter can be broadly classified into three complementary approaches: direct detection, which searches for scattering between dark matter and ordinary matter in underground experiments; collider searches, which attempt to produce dark matter or related new particles at particle accelerators; and indirect detection, which searches for signals produced by the annihilation or decay of dark matter in the Universe. At Kavli IPMU, direct detection is pursued in the “Dark Matter Detection” Research Program, while collider searches are studied in the “Collider Phenomenology” Research Program. In astroparticle physics, we focus particularly on indirect searches using gamma rays, neutrinos, and cosmic rays such as electrons, positrons, and antinucleons.

Kavli IPMU pursues indirect dark matter searches over a broad range of energies and using multiple messengers. In gamma rays, observations in the TeV range with CTAO (Cherenkov Telescope Array Observatory), in the GeV range with Fermi-LAT, and in the MeV range with COSI provide complementary windows for dark matter searches. In particular, the MeV gamma-ray band, which has remained relatively unexplored, offers the possibility of probing new mass ranges and interactions, including light dark matter. Kavli IPMU participates in NASA’s MeV gamma-ray mission COSI and leads the Dark Matter subgroup of its Science Team. The group searches for a variety of signatures from dark matter annihilation and decay, including gamma-ray lines, continuum emission, and the 511 keV line associated with electron-positron annihilation.

Indirect searches using neutrinos produced by dark matter and observed with neutrino telescopes, as well as searches using cosmic rays such as electrons, positrons, and antinucleons, also play an important role. By combining observations over different energy ranges and with different messengers, we can probe a wide variety of dark matter candidates and interaction processes, and explore dark matter masses and interactions over a broad range. Such searches require a detailed understanding of the distribution of dark matter in targets such as the Galactic Center, dwarf galaxies, and galaxy clusters, as well as precise modeling of astrophysical backgrounds. At Kavli IPMU, theoretical predictions of observable signals based on particle-physics models are combined with studies of promising targets based on cosmic structure formation and with analyses of actual observational data, enabling dark matter searches that span particle theory, astrophysics, and observations.

The use of the Universe as a laboratory for particle physics is not limited to dark matter. Extreme astrophysical environments such as supernovae, neutron stars, and black holes provide temperatures, densities, magnetic fields, and other conditions that cannot be reproduced in terrestrial accelerators or laboratories. In addition, the enormous propagation distances from astrophysical sources to the Earth and the long timescales available in the Universe can be used to search for new particles that interact only very weakly with ordinary matter. These features enable searches for physics beyond the Standard Model that is difficult to probe in terrestrial experiments, including new light particles such as axions and axion-like particles, as well as unknown properties of neutrinos.

(Last update: 2026/09/25)

Astroparticle Physics

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