• Citer

Primordial high energy neutrino and non-abelian dark matter: phenomenology of early Universe relics

par Grimbaum Yamamoto, Nicolas
Président du jury Maris, Ioana Codrina
Promoteur Hambye, Thomas
Publication Non publié, 2026-10-02

Thèse de doctorat

• Accès en ligne
• Détails
• Contenu
• Statistiques

Résumé :

The Standard Model of particle physics and the ΛCDM model of cosmology account for aremarkable range of observations, yet they remain incomplete. This thesis studies relics of theearly Universe, particles produced when in its early stages, in two different regimes: stablerelics which are still around today that could explain the dark matter problem, and unstablerelics which have decayed long ago and of which the products could allow us to probe theearly Universe.The first part considers unstable relics, and in particular asks whether decays into neutrinoscould lead to observable signatures today. Neutrinos are the only Standard Model particlesable to reach us from before recombination, and neutrino telescopes routinely detect themat high energies, so that a sufficiently energetic primordial injection could be visible today.We call such a neutrino a Phenu, for primordial high energy neutrino. We derive the Phenuspectra expected at Earth today for several types of sharp spectral features that a decayingor annihilating relic could produce, and delineate the region of the relic mass, lifetime andabundance for which the Phenu could propagate unimpeded until today. Confronting thisregion with the constraints from cosmology and already observed fluxes, we determine theregion of the parameter space for which such a signal could be observed in existing andfuture neutrino telescopes. To study the complementary region, in which distortions due tointeractions are expected, we develop a Monte Carlo code which follows the propagation ofPhenus, and apply it to the KM3NeT ultrahigh energy event, the most energetic neutrinoever detected to date. We show that a primordial origin can better accommodate the eventthan a single power law, and help alleviate part of the tension with the non-observations ofsimilar events at IceCube and Auger.The second part considers relics which are present today: dark matter particles. Wepresent a mechanism in which the stability of scalar dark matter follows from the centre of anon-abelian dark gauge group rather than from an ad-hoc symmetry. We then analyse itsminimal SU(2) and SU(3) realisations and study their phenomenology, and show that theirreducible dark radiation they predict is the sharpest test of the construction in the lightof recent updated experimental constraints. Finally, we ask how such a hidden sector coulddevelop a vector portal, or kinetic mixing, with the visible sector without breaking the purelyhidden structure, and compute the minimal contribution that does so.