A Minimal Model of Gravitino Dark Matter (1701.06574v2)

Abstract: Motivated by the absence of signals of new physics in both searches for new particles at LHC and for a Weakly Interacting Massive Particle (WIMP) dark matter candidate, we consider a scenario where supersymmetry is broken at a scale above the reheating temperature. The low energy particle content consists then only in Standard Model states and a gravitino. We investigate the possibility that the latter provides the main component of dark matter through a freeze in mechanism from annihilation of thermalized Standard Model particles. We focus on the case where its production through scattering in the thermal plasma is well approximated by the non-linear supersymmetric effective Lagrangian of the associated goldstino and identify the parameter space allowed by the cosmological constraints, allowing the possibility of large reheating temperature compatible with leptogenesis scenarios, alleviating the so called "gravitino problem".

• The paper presents a cosmological framework where the gravitino emerges as a FIMP dark matter candidate through high-scale supersymmetry breaking.
• It employs non-linear effective Lagrangians and dimension-eight operators to model gravitino production and achieve the correct relic abundance.
• The study bridges thermal leptogenesis with LHC constraints, paving the way for new experimental searches and indirect detection signatures.

A Minimal Model of Gravitino Dark Matter

The paper introduces a cosmological framework exploring a scenario where the gravitino itself serves as the pivotal component of dark matter. This paper is motivated by current experimental results from the LHC, which have yet to indicate the existence of new particles beyond the Standard Model (SM), and the continuing absence of evidence for Weakly Interacting Massive Particle (WIMP) candidates from dark matter detection efforts. The authors propose that supersymmetry (SUSY) is broken at a scale higher than the reheating temperature post-inflation, leading to a low-energy particle content that includes only standard model states and the gravitino.

Core Concept and Approach

The authors suggest moving beyond conventional low-scale SUSY breaking, which struggles with stringent LHC constraints and accommodates large-scale unification of gauge couplings while still lacking viable WIMP candidates. This paper focuses on gravitino as a Feebly Interacting Massive Particle (FIMP) dark matter candidate. FIMPs, unlike WIMPs, do not interact with other particles in thermal equilibrium in the early universe, greatly altering the landscape of viable dark matter models.

Gravitinos in this model emerge as dark matter candidates through the interactions of thermalized SM particles, specifically captured using the framework of non-linear effective Lagrangians of associated goldstino fields. This newly described high-scale SUSY model alleviates conventional cosmological "gravitino problems," including the late decays influencing big bang nucleosynthesis and issues related to overproduction.

Results and Parameter Space

A key focus of the paper is the detailed exploration of the parameter space constrained by cosmological considerations. The authors delve into the mechanisms of gravitino production through annihilations in the thermal bath, expressing the processes in terms of dimension-eight operators suppressed by the SUSY breaking scale. This leads to gravitino yield equations allowing compatibility with high reheating temperatures, which are typically favored by inflationary and leptogenesis scenarios.

Through detailed calculations, the authors demonstrate that the gravitino can achieve the correct relic abundance when the reheating temperature meets specific upper limits, which naturally satisfies current cosmological parameters including the Higgs mass and electroweak scale. Points of interest are gravitino masses ranging from MeV to PeV, highlighting the versatility of this model in accommodating various theoretical frameworks.

Implications and Future Directions

A significant implication of this research is its predictive power regarding the reheating temperature, impacting both theoretical understandings and possible experimental searches. In particular, the proposed model is consistent with large reheating temperatures, thus reconciling thermal leptogenesis processes with current empirical data. The paper provides a roadmap for exploring high-scale SUSY scenarios, where conventional WIMP constraints are circumvented, opening pathways for alternative dark matter searches.

In terms of future directions, further experimental validation through indirect dark matter detection signals would be crucial. The paper also hints at the potential smoking gun signatures from R-parity violating operators that could reveal themselves via specific decay channels observable by cosmic ray and neutrino telescopes such as IceCube and CTA.

In summary, this paper thoroughly outlines a minimal yet comprehensive model where gravitinos in a high-scale SUSY context effectively serve as dark matter candidates, offering a compelling alternative to more traditional SUSY phenomenology.