Starting from 2-flavor QCD, isospin symmetry is employed in order to explain the multiplets of light baryons and mesons, from a constituent quark perspective. Next we involve the strange quark and arrive at meson mixing as well as the Gell-Mann–Okubo formula for the baryon multiplet splitting. Regarding QCD from first principles, we comment on lattice simulation results for the hadron masses. At last we discuss the hadron spectrum in a hypothetical world with Nc=5 colors.

If the mass of a hadron is large enough, decays into final states that can be reached by strong interaction, that is, without violating any selection rule, are possible. The lifetime is then extremely short, of the order of a yoctosecond (10−24 s). These hadrons decay practically where they were born. We show how they are observed as ‘resonances’.

Hadrons, both baryons and mesons, were discovered in rapidly increasing numbers in the 1950s and early 1960s. How their quantum numbers, spin, parity and isospin were measured. Gradually it became clear that hadrons with the same spin and parity could be grouped in multiplets of the SU(3) symmetry. Proposal of the quark model and experimental verifications of its predictions. With increasing accelerator energies, more surprises were to come. The quarks are not only the three originally known, u, d and s, but three more exist, c, b and t. And more leptons were found, in total three ‘families’ of fundamental fermions, each with two quarks, a charged lepton and its neutrino.

In this chapter we review dark matter, whose physical nature remains unknown 90 years after astronomer Fritz Zwicky found the first evidence for it. We go over the historical evidence for dark matter, than review modern indications for the existence of this component. We then review particle candidates for dark matter, outlining the properties that dark matter of each particle candidate would have. Next we go over the direct, indirect, and laboratory searches for dark matter. We end by discussing a dramatically different alternative (to particles) for the nature of dark matter -- that of a modified theory of gravity (MOND).

This chapter reviews the Boltzmann equation, which is a starting point for some of the key results in cosmology. We introduce a general version of the Boltzmann equation, then study its implications in the simple scenario of a few interacting particles. We introduce the concept of a freezeout of particle species, and illustrate it using a simple example. We end the chapter by discussing baryogenesis (the process that generated the excess of baryons over antibaryons), and Sakharov conditions for successful baryogenesis to take place.