Super-heavy X particle decay and Ultra-High Energy Cosmic Rays

TL;DR

This thesis models the decay of super-heavy particles within the MSSM framework to predict their role in ultra-high energy cosmic rays, providing detailed fragmentation functions and energy conservation accuracy.

Contribution

It introduces the most comprehensive computer code for simulating super-heavy particle decay and applies it to UHECRs, including energy conservation and color coherence effects.

Findings

Provides detailed fragmentation functions for MSSM particles

Predicts neutrino and neutralino fluxes for top-down UHECR models

Ensures energy conservation with high numerical accuracy

Abstract

In this thesis, I describe in great detail the physics of the decay of any Super-Heavy X particle (with masses up to the grand unification scale ~ 10^16 GeV and possibly beyond), and the computer code I developed to model this process - which currently is the most complete available one. The general framework for this work is the Minimal Supersymmetric Standard Model (MSSM). The results are presented in the form of fragmentation functions of any (s)particle of the MSSM into any final stable particle (proton, photon, electron, three types of neutrino, lightest superparticle LSP) at a virtuality Q = M_X, over a scaled energy range x = 2E/M_X in [10^{-13}, 1]. At very low x values, color coherence effects have been taken into account through the Modified Leading Log Approximation (MLLA). The whole process is explicitely shown to conserve energy with a numerical accuracy up to a few part per mille, which allows to make quantitative predictions for any N-body decay mode of any X particle. I then apply the results to the old - and yet unsolved - problem of Ultra High Energy Cosmic Rays (UHECRs). In particular, I provide quantitative predictions of generic ``top-down'' models for the neutrino and neutralino fluxes which could be observed in the next generation of detectors.