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Dilute and dense axion stars
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholms universitet, Sverige.
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholms universitet, Sverige.
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2018 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 777, p. 64-72Article in journal (Refereed) Published
Abstract [en]

Axion stars are hypothetical objects formed of axions, obtained as localized and coherently oscillating solutions to their classical equation of motion. Depending on the value of the field amplitude at the core vertical bar theta(0)vertical bar vertical bar theta(r = 0)vertical bar, the equilibrium of the system arises from the balance of the kinetic pressure and either self-gravity or axion self-interactions. Starting from a general relativistic framework, we obtain the set of equations describing the configuration of the axion star, which we solve as a function of vertical bar theta(0)vertical bar. For small vertical bar theta(0)vertical bar less than or similar to 1, we reproduce results previously obtained in the literature, and we provide arguments for the stability of such configurations in terms of first principles. We compare qualitative analytical results with a numerical calculation. For large amplitudes vertical bar theta(0)vertical bar greater than or similar to 1, the axion field probes the full non-harmonic QCD chiral potential and the axion star enters the densebranch. Our numerical solutions show that in this latter regime the axions are relativistic, and that one should not use a single frequency approximation, as previously applied in the literature. We employ a multi-harmonic expansion to solve the relativistic equation for the axion field in the star, and demonstrate that higher modes cannot be neglected in the dense regime. We interpret the solutions in the dense regime as pseudo-breathers, and show that the life-time of such configurations is much smaller than any cosmological time scale.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 777, p. 64-72
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-223496DOI: 10.1016/j.physletb.2017.12.010ISI: 000423930700006Scopus ID: 2-s2.0-85037716681OAI: oai:DiVA.org:kth-223496DiVA, id: diva2:1185765
Funder
Swedish Research Council, 638-2013-8993 335-2014-7424
Note

QC 20180226

Available from: 2018-02-26 Created: 2018-02-26 Last updated: 2018-02-26Bibliographically approved

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