More axion stars from strings

Gorghetto, Marco; Hardy, Edward; Villadoro, Giovanni

doi:10.1007/jhep08(2024)126

Cited by 4 publications

References 105 publications

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Axion stars: mass functions and constraints

Chang,

Fox,

Xiao

2024

J. Cosmol. Astropart. Phys.

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The QCD axion and axion-like particles, as leading dark matter candidates, can also have interesting implications for dark matter substructures if the Peccei-Quinn symmetry is broken after inflation. In such a scenario, axion perturbations on small scales will lead to the formation of axion miniclusters at matter-radiation equality, and subsequently the formation of axion stars. Such compact objects open new windows for indirect searches for axions. We compute the axion star mass function based on recent axion minicluster studies and Bose star simulations. Applying this mass function, we find post-inflation axion-like particles with masses 1.8 × 10-21 eV <m a < 3.3 × 10-17 eV are constrained by the lack of dynamical heating of stars in ultrafaint dwarfs. We also find that current microlensing surveys are insensitive to QCD axion stars. While we focus on the gravitational detectability of axion stars, our result can be directly applied to other interesting signatures of axion stars, e.g. their decay to photons, that require as input the abundance, mass, and density distribution of axion stars.

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Axion stars: mass functions and constraints

Chang,

Fox,

Xiao

2024

J. Cosmol. Astropart. Phys.

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Captured molecules could make a Bose star visible

Flambaum,

Samsonov

2024

Phys. Rev. D

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A Bose star passing through cold molecular clouds may capture atoms, molecules, and dust particles. The observational signature of such an event would be a relatively small amount of matter that is gravitationally bound. This binding may actually be provided by invisible dark matter forming the Bose star. We may expect a relative excess of heavier atoms, molecules, and solid dust compared to the content of giant cold molecular clouds since the velocity of heavy particles at a given temperature is lower and it may be small compared to the escape velocity, vrms=3kBT/mgas≪vesc=2GM/R. Finally, the velocity of this captured matter cloud may correlate with the expected velocity of free dark matter particles (e.g., expected axion wind velocity relative to Earth). Published by the American Physical Society 2024

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Novel standard candle: Collapsing axion stars

Di,

Shao,

et al. 2024

Phys. Rev. D

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The Hubble constant, H0, is a crucial parameter in cosmology. However, various cosmic observations have produced differing posterior values for H0, resulting in what is referred to as the H0 tension. To resolve this discrepancy, utilizing other cosmological probes to constrain H0 is advantageous. In the quest to identify dark matter candidates, the QCD axion and axionlike particles, collectively referred to as axions, have become leading contenders. These elusive particles can coalesce into dense structures known as axion stars via Bose-Einstein condensation. When these axion stars exceed a critical mass, typically through accretion or merging, they experience a self-induced collapse. This process results in short radio bursts, assuming a decay constant fa≲1013 GeV, with the frequency depending on the axion mass and the luminosity determined by both the axion mass and decay constant. Therefore, we propose that collapsing axion stars could serve as a novel standard candle to constrain H0. Even more interesting is that the radio bursts emitted by collapsing axion stars with specific parameters match the characteristics of observed nonrepeating fast radio bursts. Thus, fast radio bursts generated by collapsing axion stars have the potential to be used as standard candles to constrain H0. Published by the American Physical Society 2024

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More axion stars from strings

Cited by 4 publications

References 105 publications

Axion stars: mass functions and constraints

Axion stars: mass functions and constraints

Captured molecules could make a Bose star visible

Novel standard candle: Collapsing axion stars

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