[Paper Review] The origin of dark matter, matter-anti-matter asymmetry, and inflation

Anupam Mazumdar|arXiv (Cornell University)|Jun 27, 2011

Cosmology and Gravitation Theories7 citations

TL;DR

This paper presents a unified framework within supersymmetric (SUSY) models—particularly the MSSM—for explaining inflation, baryogenesis, and dark matter genesis in the early universe. It shows how the inflaton’s decay can simultaneously produce the correct relic abundances of baryons, dark matter (e.g., neutralinos), and thermal bath conditions, with testable predictions via CMB, direct/indirect dark matter detection, and collider experiments.

ABSTRACT

A rapid phase of accelerated expansion in the early universe, known as inflation, dilutes all matter except the vacuum induced quantum fluctuations. These are responsible for seeding the initial perturbations in the baryonic matter, the non-baryonic dark matter and the observed temperature anisotropy in the cosmic microwave background (CMB) radiation. To explain the universe observed today, the end of inflation must also excite a thermal bath filled with baryons, an amount of baryon asymmetry, and dark matter. We review the current understanding of inflation, dark matter, mechanisms for generating matter-anti-matter asymmetry, and the prospects for testing them at ground and space based experiments.

Motivation & Objective

• To unify the origins of inflation, matter-antimatter asymmetry, and dark matter within a single, testable particle physics framework beyond the Standard Model.
• To identify viable mechanisms—particularly within the MSSM—wherein the inflaton decays into SM particles, generating baryonic asymmetry and dark matter relics.
• To connect inflationary dynamics to observable CMB anisotropies and predict reheating temperatures $T_R$ consistent with Big Bang Nucleosynthesis and electroweak symmetry breaking.
• To assess the viability of WIMP dark matter candidates (e.g., neutralino) and their detection prospects via direct, indirect, and collider searches.
• To evaluate the consistency of thermal and non-thermal dark matter production, including scenarios with Sommerfeld enhancements and decaying dark matter.

Proposed method

• Utilizes minimal supersymmetric standard model (MSSM) and supergravity (SUGRA) extensions to construct gauge-invariant inflationary potentials compatible with CMB data.
• Applies the formalism of preheating and reheating to compute the reheat temperature $T_R$ from inflaton coherent oscillations and decay into MSSM degrees of freedom.
• Employs thermal and non-thermal relic abundance calculations to determine WIMP dark matter density, including coannihilation and non-thermal production effects.
• Analyzes baryogenesis mechanisms such as electroweak baryogenesis, thermal leptogenesis, and Affleck-Dine mechanism within SUSY extensions.
• Evaluates indirect detection signals via gamma-ray spectra (e.g., Fermi-LAT), positron excesses (PAMELA), and potential monochromatic lines from WIMP annihilation.
• Uses numerical tools like GALPROP to model astrophysical backgrounds and distinguish WIMP signals from conventional cosmic ray sources.

Experimental results

Research questions

• RQ1 Can a single SUSY-based model simultaneously account for inflation, baryogenesis, and the observed dark matter relic density?
• RQ2 What are the constraints on the inflaton’s couplings and mass that allow for successful reheating and correct relic abundances of baryons and dark matter?
• RQ3 How do non-thermal and thermal WIMP production mechanisms affect the predicted dark matter density and detectability?
• RQ4 To what extent can the PAMELA positron excess and ATIC electron bump be explained by WIMP annihilation with Sommerfeld enhancement?
• RQ5 What are the observable signatures of WIMP dark matter in gamma rays, neutrinos, and direct detection experiments, and how can they be disentangled from astrophysical backgrounds?

Key findings

• The MSSM provides a viable platform for embedding inflation, with flat directions and gauge-invariant inflatons capable of generating CMB-predicted scalar perturbations.
• Thermal relic calculations show that neutralinos in the MSSM can achieve the correct dark matter relic density via freeze-out, with $\Omega_{\text{DM}} h^2 \approx 0.12$.
• The reheat temperature $T_R$ after inflation is constrained to be $\sim 10^9 - 10^{12}$ GeV in MSSM models, consistent with Big Bang Nucleosynthesis and electroweak symmetry breaking.
• The PAMELA positron excess and ATIC electron bump are not definitively explained by WIMPs without fine-tuning, but could be explained by nearby pulsars like Monogem and Geminga.
• A Sommerfeld enhancement in the annihilation cross-section $\langle\sigma v\rangle \sim 10^{-24}~{\rm cm^2}$ is required for a $500-900$ GeV WIMP to explain the excess, suggesting a leptophilic or light-boson-mediated interaction.
• No gamma-ray line signals from the galactic center have been observed by Fermi-LAT, placing strong upper limits on WIMP annihilation into $\gamma\gamma$ or $\gamma Z$ final states.