- The paper presents a model where TeV-scale dark matter annihilates into axions, which decay primarily into muons to explain the galactic positron excess.
- It employs a supersymmetric framework that connects dark matter and Higgsino mass generation through a shared Peccei-Quinn symmetry.
- The model predicts an enhanced annihilation cross-section with a semi-hard positron spectrum, offering testable signatures at the LHC and in astrophysical observations.
Analysis of Dark Matter through the Axion Portal
The paper "Dark Matter through the Axion Portal" by Yasunori Nomura and Jesse Thaler explores a theoretical model to elucidate indirect signs of dark matter (DM) using the observed galactic positron excess as indicated by the PAMELA and ATIC/PPB-BETS experiments. This paper posits a scenario where DM is a TeV-scale particle that primarily annihilates into a pseudoscalar axion, providing a possible explanation for the excess positrons observed without concurrent anti-proton or gamma-ray surpluses.
Theoretical Framework
The authors propose that dark matter is a weakly interacting massive particle (WIMP) whose annihilation processes predominantly yield axions. These pseudoscalar particles are linked with a global U(1) symmetry such as the Peccei-Quinn symmetry, making them potential candidates to address both the positron excess and other astrophysical observations. The decay of axions is expected to primarily yield leptons, notably avoiding significant photon and hadron production, which would otherwise have generated detectable signals in gamma-ray telescopes like HESS or FERMI.
In this formulation, the DM particle with a typical mass in the TeV range annihilates into axions, which then decay into lighter leptons, accommodating experimental data from astrophysical sources. The axion mass constraints allow for a decay primarily into muons, elegantly addressing observed phenomena without violating existing experimental constraints.
Implications for Supersymmetry and the Peccei-Quinn Symmetry
The paper particularly emphasizes a supersymmetric (SUSY) model where both DM and Higgsino masses are sourced from the same spontaneous symmetry-breaking mechanism. This Peccei-Quinn symmetry-driven framework ensures a predictive and economically simple model, with a focused discussion on phenomenological consequences, including potential insights at Large Hadron Collider (LHC) energies. This context involves a direct interplay between substantial TeV-scale mass components—interconnecting with ideas from beyond the Standard Model physics and offering rich phenomenology with observable signatures.
Key Predictions and Experimental Validations
One of the model's core predictions is an enhanced DM annihilation cross-section in the galactic halo, significantly surpassing thermal relic expectations. The escalation is achieved not via simple astrophysical means but rather through intricate dynamics involving the Sommerfeld effect and s-wave suppression, positing a refined theoretical architecture to interpret PAMELA data. Furthermore, the positron spectrum resulting from this model yields a characteristic semi-hard profile linked to its precise annihilation and decay mechanisms, which can be analyzed for consistency with existing data.
From a SUSY perspective, the paper addresses potential experimental signatures at the LHC, such as the decay patterns of the Higgs boson into axion pairs, yielding detectable muon signatures. The approach also contemplates the role of other light scalar components, contributing to a distinctive phenomenological landscape.
This exploration of dark matter through the axion portal outlines a carefully constructed theoretical narrative consistent with current indirect detection signals. It provides a sophisticated model employing established physics symmetries while remaining rigorously connected to empirical findings. While offering a compelling perspective on DM annihilation dynamics, the authors are cautious in speculating future extensions and validations of their framework through further experimental investigations.
Ultimately, the paper enriches the theoretical discourse on dark matter, presenting a plausible and methodical approach to solve prevalent mysteries related to the indirect signs of dark matter presence in astrophysical contexts. Theoretical embellishments like these provide a pathway for future explorations that might eventually combine cosmic observations and laboratory findings into a coherent picture of dark matter and its interactions.