High energy physics from 10 billion years' worth of data: Learning new physics from the Big Bang, stars and cosmic rays

Improving astroparticle data present an opportunity to learn new physics from a variety of processes that took place in the early universe and those that continue at present. My thesis will cover several lines of research in this rapidly developing field.; Sources of ultrahigh energy photons operating at high red shift produce a diffuse background of neutrinos. At high red shift, when the cosmic microwave background radiation has a higher temperature, an electromagnetic cascade originated by an energetic photon can generate neutrinos via muon and pion production and decay. In chapter 2 we describe this process in detail. We present the results of a numerical calculation of the spectrum of cascade neutrinos produced by various photon sources. A distinctive feature of the produced flux is a “bump” in the spectrum at neutrino energies E ∼ 1017–1018 eV. The produced flux is largest for m = 3 sources (e.g. necklaces), with E2J(E) ∼ 1 eV cm−2 s−1 sr−1 at these energies. The neutrino flux is probably too small to be detected in the near future.; Neutrino production by matter with a time-dependent density or velocity is the subject of chapter 3. Both ordinary matter and nuclear matter found in neutron stars carry a net SU(2) charge. Neutrinos couple to this charge through the electroweak interactions. In a time-dependent background this leads to neutrino pair-production, analogous to particle production by a time-varying gravitational field. Due to the smallness of all scales involved, the effect is small in all physical situations. Nevertheless, the results are quite interesting, as neutrino production is a fully non-perturbative process: production can occur even if it is perturbatively forbidden for kinematical reasons.; In chapter 4 we study Q-ball formation in the early universe, concentrating on potentials with a cubic or quartic attractive interaction. Large Q-balls can form via solitosynthesis, a process of gradual charge accretion, provided some primordial charge asymmetry and initial “seed” Q-balls exist. We find that such seeds are possible in theories in which the attractive interaction is of the form AHχ*χ, with a light “Higgs” mass. Q-ball formation through fragmentation of a Bose-Einstein condensate is only possible for masses m_ψ in the sub-keV range. For both production mechanisms the parameter space for successful Q-ball formation is rather constraint. Q-balls that survive until present can be the, possibly self-interacting, dark matter in the universe.