Femtolensing and Picolensing by Axion Miniclusters

Abstract. In some axion dark matter models a dominant fraction of axions resides in dense small-scale substructures, axion miniclusters. A fraction of these substructures is disrupted and forms tidal streams where the axion density may still be an order of magnitude larger than the average. We discuss implications of these streams for the direct axion searches. We estimate the fraction of disrupted miniclusters and the parameters of the resulting streams, and find that stream-crossing events would occur at a rate of about 1/(20yr) for 2-3 days, during which the signal in axion detectors would be amplified by a factor ∼ 10. These estimates suggest that the effect of the tidal disruption of axion miniclusters may be important for direct axion searches and deserves a more thorough study.

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“…[14] neglecting contribution from the decaying axion strings and domain walls. This distribution is summarized in Fig.…”

Section: Axion Miniclustersmentioning

confidence: 99%

Tidal streams from axion miniclusters and direct axion searches

Tinyakov

Tkachev

Zioutas

2016

J. Cosmol. Astropart. Phys.

133

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“…If they do exist, axion stars lead to distinctive observational signatures for example through gravitational lensing [53], or even gravitational wave emission in collisions [54]. Collisions between axion stars and neutron or white dwarf stars could also lead to photon signals [55,56].…”

Section: Axion Starsmentioning

confidence: 99%

Miniclusters in the axiverse

Hardy

2017

J. High Energ. Phys.

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If dark matter is an axion-like-particle a significant fraction of the present day relic abundance could be concentrated in compact gravitationally bound miniclusters. We study the minicluster masses compatible with the dark matter relic density constraint. If they form from fluctuations produced by PQ symmetry breaking, minicluster masses up to hundreds of solar masses are possible, although over most of the parameter space they are much lighter. The size of these objects is typically within a few orders of magnitude of an astronomical unit. We also show that miniclusters can form if an axion gets mass from a hidden sector with a first order phase transition that takes a relatively long time to complete. Therefore they can appear in models where PQ symmetry is broken before inflation, compatible with large axion decay constants and string theory UV completions.

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“…This is due to the fact that cold dark matter axions are inhomogeneous with δρ/ρ ∼ 1 over the horizon scale at temperature T 1 ≃ 1 GeV when they are produced at the start of the QCD phase-transition, combined with the fact that their velocities are so small that they do not erase these inhomogeneities by free-streaming before the time t eq when matter perturbations can start to grow. These particular inhomogeneities in the axion dark matter are immediately in the non-linear regime after time t eq and thus form clumps, called "axion mini-clusters" [14][15][16]. These have [16] mass M mc ≃ 10 −13 M ⊙ and size l mc ≃ 10 12 cm, and therefore their associated velocity dispersion v mc = GM mc /l mc ≃ 10 −10 at time t eq .…”

Section: B Angular Momentummentioning

confidence: 99%

“…These particular inhomogeneities in the axion dark matter are immediately in the non-linear regime after time t eq and thus form clumps, called "axion mini-clusters" [14][15][16]. These have [16] mass M mc ≃ 10 −13 M ⊙ and size l mc ≃ 10 12 cm, and therefore their associated velocity dispersion v mc = GM mc /l mc ≃ 10 −10 at time t eq . This velocity dispersion increases by about a factor 10 from t eq till the onset of galaxy formation because of the hierarchical clustering of the axion mini-clusters.…”

Section: B Angular Momentummentioning

confidence: 99%

Secondary infall model of galactic halo formation and the spectrum of cold dark matter particles on Earth

Sikivie

Tkachev²,

Wang³

1997

Phys. Rev. D

163

174

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The spectrum of cold dark matter particles on Earth is expected to have peaks in velocity space associated with particles which are falling onto the Galaxy for the first time and with particles which have fallen in and out of the Galaxy only a small number of times in the past. We obtain estimates for the velocity magnitudes and the local densities of the particles in these peaks. To this end we use the secondary infall model of galactic halo formation which we have generalized to take account of the angular momentum of the dark matter particles. The new model is still spherically symmetric and it admits self-similar solutions. In the absence of angular momentum, the model produces flat rotation curves for a large range of values of a parameter ǫ which is related to the spectrum of primordial density perturbations. We find that the presence of angular momentum produces an effective core radius, i.e. it makes the contribution of the halo to the rotation curve go to zero at zero radius. The model provides a detailed description of the large scale properties of galactic halos including their density profiles, their extent and total mass. We obtain predictions for the kinetic energies of the particles in the velocity peaks and estimates for their local densities as functions of the amount of angular momentum, the age of the universe and ǫ.

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Femtolensing and Picolensing by Axion Miniclusters

Cited by 143 publications

References 34 publications

Tidal streams from axion miniclusters and direct axion searches

Tidal streams from axion miniclusters and direct axion searches

Miniclusters in the axiverse

Secondary infall model of galactic halo formation and the spectrum of cold dark matter particles on Earth

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