Dilute and dense axion stars

By Luca Visinelli, S. Baum, J. Redondo, K. Freese, Frank Wilczek. 2017

195 citations recorded by the source corpus.

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 | θ 0 | ≡ | θ ( 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 | θ 0 | . For small | θ 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 | θ 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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d4ac1af870538f0760bb9bc4ae53e7b8767de068

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Maurizio Giannotti
2. Luca Visinelli
3. E. Nardi
4. L. Luzio
5. A. Hook
6. J. Redondo
7. Julia Stadler
8. A. Vaquero

In Nuclear and High Energy Physics

1. Maurizio Giannotti
2. Luca Visinelli
3. E. Nardi
4. L. Luzio
5. J. Redondo
6. A. Hook
7. Julia Stadler
8. A. Vaquero

Citations in the corpus

• TASI Lectures on the Strong CP Problem and Axions (2018, background): “Another possibility people play with is Bose/axion stars [133, 134].”
• The landscape of QCD axion models (2020, background): “The formation of axion stars might proceed either by gravitational cooling out of the virialised minicluster or during a process of violent relaxation [345, 351–353], leading to a solution in the weak gravity regime [354, 355], with the mass and the radius of the axion star being related by [347, 35”
• Early seeds of axion miniclusters (2018, background): “Since the dynamics have been analysed in many a reference [40,41,78] in a static, non-expanding background, let us entertain the case of interest, the expanding FRW.”