Theoretical and experimental studies of dark matter's composition, annihilation, and interactions with matter.Dark matter is the invisible substance that makes up about 27% of the universe's mass-energy content. Unlike ordinary matter, it does not emit, absorb, or reflect light, making it detectable only through its gravitational effects. The study of dark matter's properties focuses on what it is made of, how it interacts with itself and with normal matter, and how it behaves under extreme conditions.
The concept of dark matter was first proposed by Fritz Zwicky in 1933, who noticed that galaxies in the Coma cluster were moving too fast to be held together by visible matter alone. Later, Vera Rubin's observations of galaxy rotation curves in the 1970s provided strong evidence for its existence.
Scientists investigate dark matter through several complementary approaches. Particle physics experiments search for weakly interacting massive particles (WIMPs) that might collide with atomic nuclei in detectors. Astrophysical observations look for signs of dark matter annihilation, where two dark matter particles could produce gamma rays or other particles. Gravitational lensing and galaxy rotation curves provide indirect measurements of dark matter's distribution and density.
Understanding dark matter properties is crucial for interpreting cosmological observations and for designing experiments to detect it directly, such as those in underground laboratories or space-based detectors.
Dark matter is so diffuse in our solar system that the total amount passing through Earth each year is estimated to be less than a kilogram.
| lambda_FS | variable | free streaming length — free streaming length metre |
| m_hm | variable | half-mode mass of dark matter — half mode mass kilogram |
| propto | operator | is proportional to — proportionality |
| \Omega_{\text{DM}} h | variable | Dark matter relic density parameter times squared Hubble constant — density parameter |
| \Gamma | variable | Inflaton decay rate — decay rate per second |
| M_P | variable | Reduced Planck mass — mass kilogram |
| m_{\phi} | variable | Mass of the dark matter particle (or inflaton) — mass kilogram |
| \propto | operator | Indicates direct proportionality — proportionality |
| \sqrt{} | operator | Takes the square root of the argument — square root |
| v_min | variable | Minimum dark matter speed — velocity metre per second |
| m_N | variable | Mass of the target nucleus — mass kilogram |
| E_R | variable | Recoil energy of the nucleus — energy joule |
| μ | variable | Reduced mass of the dark matter-nucleus system — reduced mass kilogram |
| δ | variable | Mass splitting between dark matter states (energy gap) — energy joule |
