Ultralight axions: Degeneracies with massive neutrinos and forecasts for future cosmological observations

Marsh, David J. E.; Macaulay, E.; Trebitsch, Maxime; Ferreira, Pedro G.

doi:10.1103/physrevd.85.103514

Cited by 56 publications

(88 citation statements)

References 136 publications

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“…[11][12][13][14], with the preferred value in the late-time universe (around, or subsequent to, recombination) being significantly higher than the standard model prediction of N eff = 3.046 [15]. Such additional relativistic energy density is usually referred to as dark radiation and can arise from a completely different physics such as axions [16]. The light sterile neutrinos hinted at by SBL data would be an excellent candidate for dark radiation [17], even though misinterpretations of the nature of this non standard N eff can arise from degeneracies between N eff and other cosmological parameters [18].…”

Section: Introductionmentioning

confidence: 99%

Sterile neutrinos: Cosmology versus short-baseline experiments

et al. 2013

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Cosmology and short baseline neutrino oscillation data both hint at the existence of light sterile neutrinos with masses in the 1 eV range. Here we perform a detailed analysis of the sterile neutrino scenario using both cosmological and SBL data. We have additionally considered the possibility that the extra neutrino degrees of freedom are not fully thermalised in the early universe. Even when analyzing only cosmological data we find a preference for the existence of massive sterile neutrinos in both (3+1) and (3+2) scenarios, and with the inclusion of SBL data the evidence is formally at the 3.3σ level in the case of a (3+1) model. Interestingly, cosmological and SBL data both point to the same mass scale of approximately 1 eV. In the (3+1) framework WMAP9+SPT provide a value of the sterile mass eigenstate m4 = (1.72 ± 0.65) eV: this result is strenghtened by adding the prior from SBL posterior to m4 = (1.27 ± 0.12) eV (m4 = (1.23 ± 0.13) eV when SDSS is also considered in the cosmological analysis). In the (3+2) scheme, two additional, non-fully thermalized, neutrinos are compatible with the whole set of cosmological and SBL data, leading to mass values of m4 = (0.95 ± 0.30) eV and m5 = (1.59 ± 0.49) eV. The inclusion of Planck data does not change our considerations about the mass scale; concerning the extra neutrino degrees of freedom, invoking a partial thermalisation the 3+1 model is still consistent with the latest data.

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Section: Introductionmentioning

confidence: 99%

Sterile neutrinos: Cosmology versus short-baseline experiments

et al. 2013

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“…This subject has been mainly JHEP03(2016)013 studied for harmonic potential models that mimic the standard dark matter case [65][66][67][68][69][70][71], as it happens for the axion field [72,73]. It has been proved by using the linear perturbation theory that the axion was equivalent to CDM for high enough masses [74][75][76][77].…”

Section: Introductionmentioning

confidence: 99%

Cosmological perturbations in coherent oscillating scalar field models

Cembranos

Maroto

Jareño

2016

J. High Energ. Phys.

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The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V (φ) = λ|φ| n /n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c 2 eff = ω = (n − 2)/(n + 2) with ω the effective equation of state. We also obtain the first order correction in k 2 /ω 2 eff , when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω eff . For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δφ; and for sub-Hubble modes, exploiting Floquet's theorem.

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“…The size of the effect is fixed by the fraction of DM in axions, Ω a /Ω d , and so constraints are presented in the (m a , Ω a /Ω d ) plane. Constraints from the CMB are particularly strong for m a H eq ∼ 10 −28 eV where the axions roll in their potential after equality, shifting equality and giving rise to an Integrated Sachs-Wolfe (SW) effect from the evolving gravitational potential [50].…”

Section: Introductionmentioning

confidence: 99%

“…We are exploring this mass range with a careful search of parameter space using nested sampling [44]. Isocurvature constraints will improve in the future [63], as will constraints on Ω a /Ω d [50], both of which could allow for a detection consistent with the tensor bound [44]. In the regime m a 10 −24 eV the tensor bound is stronger than current cosmological bounds on Ω a .…”

Section: Introductionmentioning

confidence: 99%

“…When the mass is in the range 10 −33 eV m a 10 −18 eV this scale can be astrophysical or cosmological in size and therefore can be constrained using the CMB power spectrum and large-scale structure (LSS) measurements [45,50,51]. The size of the effect is fixed by the fraction of DM in axions, Ω a /Ω d , and so constraints are presented in the (m a , Ω a /Ω d ) plane.…”

Section: Introductionmentioning

confidence: 99%

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Tensor Interpretation of BICEP2 Results Severely Constrains Axion Dark Matter

et al. 2014

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The recent detection of B-modes by BICEP2 has non-trivial implications for axion dark matter implied by combining the tensor interpretation with isocurvature constraints from Planck. In this paper the measurement is taken as fact, and its implications considered, though further experimental verification is required. In the simplest inflation models r = 0.2 implies HI = 1.1 × 10 14 GeV. If the axion decay constant fa < HI /2π constraints on the dark matter (DM) abundance alone rule out the QCD axion as DM for ma 52χ 6/7 µeV (where χ > 1 accounts for theoretical uncertainty). If fa > HI /2π then vacuum fluctuations of the axion field place conflicting demands on axion DM: isocurvature constraints require a DM abundance which is too small to be reached when the back reaction of fluctuations is included. High fa QCD axions are thus ruled out. Constraints on axionlike particles, as a function of their mass and DM fraction, are also considered. For heavy axions with ma 10 −22 eV we find Ωa/Ω d 10 −3 , with stronger constraints on heavier axions. Lighter axions, however, are allowed and (inflationary) model-independent constraints from the CMB temperature power spectrum and large scale structure are stronger than those implied by tensor modes. −0.05 has profound implications for our understanding of the initial conditions of the universe [2], and points to an inflationary origin for the primordial fluctuations [3][4][5]. The inflaton also drives fluctuations in any other fields present in the primordial epoch and so the measurement of r, which fixes the inflationary energy scale, can powerfully constrain diverse physics. In this work we will discuss the implications for axion dark matter (DM) in the case that the tensor modes are generated during single-field slow-roll inflation (from now on we simply refer to this as 'inflation') by zero-point fluctuations of the graviton. In this work we assume that the measured value of r both holds up to closer scrutiny experimentally, and is taken to be of primordial origin. We relax these assumptions in our closing discussion. We stress that our conclusions are one consequence of taking this measurement at face value, but also that they apply to any detection of r.The scalar amplitude of perturbations generated during inflation is given by [7]

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Ultralight axions: Degeneracies with massive neutrinos and forecasts for future cosmological observations

Cited by 56 publications

References 136 publications

Sterile neutrinos: Cosmology versus short-baseline experiments

Sterile neutrinos: Cosmology versus short-baseline experiments

Cosmological perturbations in coherent oscillating scalar field models

Tensor Interpretation of BICEP2 Results Severely Constrains Axion Dark Matter

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