[Paper Review] Constraining Ultralight Axions with Galaxy Surveys

Alex Laguë, J. Richard Bond+4 more|arXiv (Cornell University)|Apr 15, 2021

Dark Matter and Cosmic Phenomena117 references95 citations

TL;DR

This paper constrains ultralight axion dark matter using galaxy clustering statistics from the BOSS survey, introducing a fast interpolation scheme for axion transfer functions that reduces computational cost by 70%. It improves existing constraints by over 4.5× at 10⁻²⁵ eV and 2.1× at 10⁻³² eV, setting an upper bound of Ωₐh² < 0.004 for axion masses between 10⁻³¹ and 10⁻²⁶ eV at 95% confidence, while detecting anisotropic signatures in the galaxy quadrupole and enhanced linear bias from axion mixing.

ABSTRACT

Ultralight axions and other bosons are dark matter candidates present in many high energy physics theories beyond the Standard Model. In particular, the string axiverse postulates the existence of up to $\mathcal{O}(100)$ light scalar bosons constituting the dark sector. Considering a mixture of axions and cold dark matter, we obtain upper bounds for the axion relic density $\Omega_a h^2 < 0.004$ for axions of mass $10^{-31}\;\mathrm{eV}\leq m_a \leq 10^{-26}\;\mathrm{eV}$ at 95% confidence. We also improve existing constraints by a factor of over 4.5 and 2.1 for axion masses of $10^{-25}$ eV and $10^{-32}$ eV, respectively. We use the Fourier-space galaxy clustering statistics from the Baryon Oscillation Spectroscopic Survey (BOSS) and demonstrate how galaxy surveys break important degeneracies in the axion parameter space compared to the cosmic microwave background (CMB). We test the validity of the effective field theory of large-scale structure approach to mixed ultralight axion dark matter by making our own mock galaxy catalogs and find an anisotropic ultralight axion signature in the galaxy quadrupole. We also observe an enhancement of the linear galaxy bias from 1.8 to 2.4 when allowing for 5% of the dark matter to be composed of a $10^{-28}$ eV axion in our simulations. Finally, we develop an augmented interpolation scheme allowing a fast computation of the axion contribution to the linear matter power spectrum leading to a 70% reduction of the computational cost for the full Monte Carlo Markov chains analysis.

Motivation & Objective

• To improve constraints on ultralight axion dark matter using large-scale galaxy clustering data from the Baryon Oscillation Spectroscopic Survey (BOSS).
• To break degeneracies in axion parameter space that are not resolved by cosmic microwave background (CMB) data alone.
• To develop a fast, accurate interpolation scheme for computing the axion contribution to the linear matter power spectrum to reduce computational cost in MCMC analyses.
• To detect and quantify anisotropic effects of ultralight axions on galaxy clustering, particularly in the quadrupole moment of the galaxy power spectrum.
• To assess the impact of axion mixing on linear galaxy bias and matter power spectrum suppression in cosmological simulations.

Proposed method

• Utilizes Fourier-space galaxy clustering statistics from the BOSS DR12 survey to probe deviations from ΛCDM due to ultralight axions.
• Develops an augmented interpolation scheme using RegularGridInterpolator to compute the axion transfer function, correcting for correlations between axion fraction and cosmological parameters.
• Employs mock galaxy catalogs (MultiDark-Patchy and Peak-Patch) to validate the effective field theory approach and detect anisotropic axion signatures in the galaxy quadrupole.
• Applies a modified linear galaxy bias model that accounts for axion-induced suppression of the linear matter power spectrum.
• Combines the Class Boltzmann code with the interpolated transfer function to compute the matter power spectrum efficiently, reducing runtime by 70% compared to direct axionCAMB calls.
• Performs full Monte Carlo Markov Chain (MCMC) analyses with and without CMB priors to derive robust constraints on axion relic density and mass.

Experimental results

Research questions

• RQ1 How do galaxy surveys like BOSS improve constraints on ultralight axion dark matter compared to CMB data alone?
• RQ2 What is the impact of axion-induced suppression on the anisotropic clustering of galaxies, particularly in the quadrupole moment?
• RQ3 How does the inclusion of a small axion fraction affect the linear galaxy bias in cosmological simulations?
• RQ4 Can an efficient interpolation scheme accurately model the axion transfer function across diverse cosmological parameter spaces while minimizing computational cost?
• RQ5 What are the tightest upper bounds on the axion relic density for masses in the 10⁻³¹–10⁻²⁶ eV range?

Key findings

• The study sets a 95% confidence upper bound of Ωₐh² < 0.004 for ultralight axions with masses between 10⁻³¹ eV and 10⁻²⁶ eV.
• Constraints are improved by a factor of over 4.5 at 10⁻²⁵ eV and by a factor of 2.1 at 10⁻³² eV compared to previous limits.
• Anisotropic effects from ultralight axions are detected in the galaxy quadrupole, with the signal arising from reduced velocity divergence due to suppressed matter power spectrum.
• The linear galaxy bias increases from 1.8 to 2.4 when 5% of the dark matter is composed of a 10⁻²⁸ eV axion in simulations.
• The augmented interpolation scheme reduces computational cost by 70% by accurately modeling the axion transfer function across cosmological parameter space with percent-level accuracy at Ωₐ/Ωₐ ≤ 0.1.
• The method maintains high accuracy across a wide range of axion masses and fractions, with relative error in the interpolation below 1% at low axion concentrations.