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Title: Dilute and dense axion stars

Abstract

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 |$$\theta_0$$|≡ |$$\theta$$ (r=0), 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 |$$\theta_0$$|. For small |$$\theta_0$$|≲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 |$$\theta_0$$|≳1, the axion field probes the full non-harmonic QCD chiral potential and the axion star enters the $dense$ branch. 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.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of Michigan, Ann Arbor, MI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP); European Research Council (ERC); Swedish Research Council (SRC)
OSTI Identifier:
1437800
Alternate Identifier(s):
OSTI ID: 1499285; OSTI ID: 1646990
Grant/Contract Number:  
SC0012567; SC007859; 638-2013-8993; 335-2014-7424; FPA2015-65745-P; SFB-1258; 742104; SC0007859
Resource Type:
Published Article
Journal Name:
Physics Letters B
Additional Journal Information:
Journal Name: Physics Letters B Journal Volume: 777 Journal Issue: C; Journal ID: ISSN 0370-2693
Publisher:
Elsevier
Country of Publication:
Netherlands
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Visinelli, Luca, Baum, Sebastian, Redondo, Javier, Freese, Katherine, and Wilczek, Frank. Dilute and dense axion stars. Netherlands: N. p., 2018. Web. https://doi.org/10.1016/j.physletb.2017.12.010.
Visinelli, Luca, Baum, Sebastian, Redondo, Javier, Freese, Katherine, & Wilczek, Frank. Dilute and dense axion stars. Netherlands. https://doi.org/10.1016/j.physletb.2017.12.010
Visinelli, Luca, Baum, Sebastian, Redondo, Javier, Freese, Katherine, and Wilczek, Frank. Thu . "Dilute and dense axion stars". Netherlands. https://doi.org/10.1016/j.physletb.2017.12.010.
@article{osti_1437800,
title = {Dilute and dense axion stars},
author = {Visinelli, Luca and Baum, Sebastian and Redondo, Javier and Freese, Katherine and Wilczek, Frank},
abstractNote = {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 |$\theta_0$|≡ |$\theta$ (r=0), 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 |$\theta_0$|. For small |$\theta_0$|≲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 |$\theta_0$|≳1, the axion field probes the full non-harmonic QCD chiral potential and the axion star enters the $dense$ branch. 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.},
doi = {10.1016/j.physletb.2017.12.010},
journal = {Physics Letters B},
number = C,
volume = 777,
place = {Netherlands},
year = {2018},
month = {2}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1016/j.physletb.2017.12.010

Citation Metrics:
Cited by: 20 works
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Figures / Tables:

Table 1 Table 1: The coefficients in the truncated series expansion of the chiral potential in Eq. (18), after the corrections described below Eq. (20) and for $z$ = 0.48.

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      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.