Microcosm and Macrocosm

Abstract

Particles and their fundamental interactions, astrophysics, and cosmology have become closely related fields. The submicroscopic phenomena allow us to better understand the cosmic evolution, and vice versa. The theory of the electromagnetic, weak, and strong interactions, which mediate the dynamics of the known subatomic particles, is called the Standard Model (SM) of particle physics. The structure of the SM suggests the existence of a Grand Unified Theory (GUT) at a very-high energy scale. Are all interactions (eventually excluding gravitation) really unified at high energies? Which symmetry governs this unification? Most likely, no answer can be provided by accelerator experiments, while some experimental tests of GUT predictions, such as the searches for baryon number nonconservation and the existence of relic particles from the Big Bang, are performed in underground laboratories. The subject within which particle physics, astrophysics, and cosmology are more strictly correlated is that connected with dark matter. The combination of many observations, including galactic rotation curves, gravitational lensing, the cosmic microwave background, and primordial light element abundances, cannot be explained without new, non-SM objects, which may annihilate or decay to ordinary particles detectable far from their source or be scattered by ordinary matter. Although there are other motivations for physics beyond the Standard Model, astrophysics and cosmology give direct evidence for new physics, thus making the search for signatures of dark matter particles an especially compelling area of research. Many dedicated experimental searches (also described in this chapter) have been developed. No conclusive results have been obtained so far from these experiments, nor for signals of physics beyond the Standard Model at accelerators. The next decade will probably be decisive concerning the solution of this joint astroparticle physics-cosmology problem.