PIRSA:14060026

Cosmological Constraints on Ultra-light Axions

Marsh, D. (2014). Cosmological Constraints on Ultra-light Axions. Perimeter Institute. https://pirsa.org/14060026

Marsh, David. Cosmological Constraints on Ultra-light Axions. Perimeter Institute, Jun. 18, 2014, https://pirsa.org/14060026 

          @misc{ pirsa_PIRSA:14060026,
            doi = {10.48660/14060026},
            url = {https://pirsa.org/14060026},
            author = {Marsh, David},
            keywords = {},
            language = {en},
            title = {Cosmological Constraints on Ultra-light Axions},
            publisher = {Perimeter Institute},
            year = {2014},
            month = {jun},
            note = {PIRSA:14060026 see, \url{https://pirsa.org}}
          }

David Marsh King's College London

Talk numberPIRSA:14060026
DOI10.48660/14060026
Collection
Talk Type Conference

Abstract

Ultra-light axions (ULAs) with masses in the range 1e-33 eV< m < 1e-18 eV can constitute a novel component of the dark matter, which can be constrained by cosmological observations. ULA dark matter (DM) is produced non-thermally via vacuum realignment in the early universe and is cold. Pressure perturbations, however, manifest a scale in the clustering (also the de Broglie scale). For the range of masses considered this spans the Hubble scale down to sub-galactic scales. In the model-independent adiabatic mode of initial conditions, one can gain strong constraints on ULAs as DM from the CMB and large scale structure (LSS). I will present constraints from Planck and WiggleZ, constraining m~1e-33 eV to 1e-25 eV at the percent level. In the range m\gtrsim 1e-22 eV ULAs may also solve the "small-scale problems" of CDM, and suggest other constraints from LSS and high-z observations, constraining m\lesssim 1e-22 eV to be sub-dominant in DM. Future prospects from CMB lensing, and from Euclid galaxy weak lensing, will make sub-percent constraints out to m~1e-21 eV. Model-dependent couplings between axions and photons provide still other bounds from CMB spectral distortions. Finally, if the inflationary energy scale is high, corresponding to an observable tensor-to-scalar ratio, then CMB isocurvature perturbations provide the strongest constraints on m>1e-24 eV, ruling out ULA dark matter in the simplest inflationary scenarios over the entire range considered, as well as the "anthropic window" for the QCD axion.