Broken R-Parity in the Sky and at the LHC

TL;DR

This paper explores supersymmetric models with broken R-parity, analyzing how gamma-ray data constrains NLSP decay lengths and implications for collider detection, providing new bounds and potential signals for LHC experiments.

Contribution

It introduces new bounds on NLSP decay lengths based on gamma-ray observations and connects these to collider phenomenology in R-parity violating supersymmetry models.

Findings

Lower bound on neutralino decay length: cτ ≥ 30 cm.

Lower bound on stau decay length: cτ ≥ 4 mm.

Potential for measuring decay lengths at the LHC with upcoming signals.

Abstract

Supersymmetric extensions of the Standard Model with small R-parity and lepton number violating couplings are naturally consistent with primordial nucleosynthesis, thermal leptogenesis and gravitino dark matter. We consider supergravity models with universal boundary conditions at the grand unification scale, and scalar tau-lepton or bino-like neutralino as next-to-lightest superparticle (NLSP). Recent Fermi-LAT data on the isotropic diffuse gamma-ray flux yield a lower bound on the gravitino lifetime. Comparing two-body gravitino and neutralino decays we find a lower bound on a neutralino NLSP decay length, $c \tau_{\chi^0_1} \gsim 30 cm$. Together with gravitino and neutralino masses one obtains a microscopic determination of the Planck mass. For a stau-NLSP there exists no model-independent lower bound on the decay length. Here the strongest bound comes from the requirement that the cosmological baryon asymmetry is not washed out, which yields $c \tau_{\tilde\tau_1} \gsim 4 mm$. However, without fine-tuning of parameters, one finds much larger decay lengths. For typical masses, $m_{3/2} \sim 100 GeV$ and $m_{NLSP} \sim 150 GeV$, the discovery of a photon line with an intensity close to the Fermi-LAT limit would imply a decay length $c\tau_{NLSP}$ of several hundred meters, which can be measured at the LHC.