Anthropic Explanation of the Dark Matter Abundance

Abstract

I use Bousso's causal diamond measure to make a statistical prediction for the dark matter abundance, assuming an axion with a large decay constant f_a >> 10^{12} GeV. Using a crude approximation for observer formation, the prediction agrees well with observation: 30% of observers form in regions with less dark matter than we observe, while 70% of observers form in regions with more dark matter. Large values of the dark matter ratio are disfavored by an elementary effect: increasing the amount of dark matter while holding fixed the baryon to photon ratio decreases the number of baryons inside one horizon volume. Thus the prediction is rather insensitive to assumptions about observer formation in universes with much more dark matter than our own. The key assumption is that the number of observers per baryon is roughly independent of the dark matter ratio for ratios near the observed value.

10 pages; v3: published version, references added

References in corpus (7)

• Axion Cosmology and the Energy Scale of Inflation
• Holographic probabilities in eternal inflation
• Predicting the Cosmological Constant from the Causal Entropic Principle
• Predicting the cosmological constant with the scale-factor cutoff measure
• Properties of the scale factor measure
• Landscape Predictions from Cosmological Vacuum Selection
• Predictions of the causal entropic principle for environmental conditions of the universe

Cited by in corpus (38)

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• Search for New Physics with Atoms and Molecules
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• An M Theory Solution to the Strong CP Problem and Constraints on the Axiverse
• Axion Dark Matter Detection with Cold Molecules
• Cosmological window onto the string axiverse and the supersymmetry breaking scale
• Theory and Phenomenology of Planckian Interacting Massive Particles as Dark Matter
• Life at the Interface of Particle Physics and String Theory
• Radio Signal of Axion-Photon Conversion in Neutron Stars: A Ray Tracing Analysis
• Probing the Early Universe with Axion Physics and Gravitational Waves
• How many universes are in the multiverse?
• Inflation after False Vacuum Decay: Observational Prospects after Planck
• Axion Fragmentation
• Axion Miniclusters in Modified Cosmological Histories
• Inflatable Dark Matter
• Light axion-like dark matter must be present during inflation
• Hunting for super-heavy dark matter with the highest-energy cosmic rays
• Tests of Fundamental Quantum Mechanics and Dark Interactions with Low Energy Neutrons -- Extended Version
• Peccei-Quinn Symmetry from Dynamical Supersymmetry Breaking
• Friendship in the Axiverse: Late-time direct and astrophysical signatures of early-time nonlinear axion dynamics
• The Multiverse and Particle Physics
• What can a GNOME do? Search targets for the Global Network of Optical Magnetometers for Exotic physics searches
• Next generation design and prospects for CANNEX
• Axions, Inflation and the Anthropic Principle
• Why Comparable? A Multiverse Explanation of the Dark Matter-Baryon Coincidence
• The Stochastic Axiverse
• Multiverse Dark Matter: SUSY or Axions
• Axion Isocurvature Perturbations in Low-Scale Models of Hybrid Inflation
• The cosmological moduli problem and naturalness
• Blowing in the Dark Matter Wind
• Dark matter and dark radiation from the early universe with a modulus coupled to the PQMSSM
• Is the magnitude of the Peccei-Quinn scale set by the landscape?
• Radiative PQ Breaking and the Higgs Boson Mass
• Cavitation model of the initial stage of Big Bang
• New Scale Factor Measure
• Anthropic Origin of the Neutrino Mass from Cooling Failure
• Testing Scale-Dependent Suppression of Structure Growth in the Linear Regime