QCD axion star collapse with the chiral potential

Eby, Joshua; Leembruggen, Madelyn; Surányi, P.; Wijewardhana, L. C. R.

doi:10.1007/jhep06(2017)014

Cited by 29 publications

(42 citation statements)

References 59 publications

(120 reference statements)

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“…Numerous fascinating, potentially observable phenomena involving axion star collapse, decay, or collisions with other astrophysical objects have been proposed in the literature [216,217,218,219,220,221,222,223,224,225,226,227]. Involving relativistic effects, self-interactions, or axion-photon coupling in fundamental ways, they unfortunately extend beyond the self-imposed scope of this article.…”

Section: Formation Of Axion Starsmentioning

confidence: 99%

Small-scale structure of fuzzy and axion-like dark matter

Niemeyer

2020

Progress in Particle and Nuclear Physics

163

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Axion-like particle (ALP) dark matter shows distinctive behavior on scales where wavelike effects dominate over self-gravity. Ultralight axions are candidates for fuzzy dark matter (FDM) whose de Broglie wavelength in virialized halos reaches scales of kiloparsecs. Important features of FDM scenarios are the formation of solitonic halo cores, suppressed small-scale perturbations, and enhanced gravitational relaxation. More massive ALPs, including the QCD axion, behave like CDM on galactic scales but may be clumped into axion miniclusters if they were produced after inflation. Just as FDM halos, axion miniclusters may host the formation of coherent bound objects (axion stars) by Bose-Einstein condensation. This article presents a selection of topics in this field that are currently under active investigation.

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Section: Formation Of Axion Starsmentioning

confidence: 99%

Small-scale structure of fuzzy and axion-like dark matter

Niemeyer

2020

Progress in Particle and Nuclear Physics

163

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“…A recent surge in studies of boson stars [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] stems, in part, from the renewed interest in determining whether dark matter (DM) could consist of condensates of ax-ions or other axion like particles. A particularly wellmotivated scalar DM candidate is the QCD axion, parametrized by a decay constant f = 6 × 10 11 GeV and particle mass m = 10 −5 eV; 2 as a result, bound states of QCD axions (which we will call QCD axion stars) have received special attention.…”

Section: Introductionmentioning

confidence: 99%

“…The solutions found by BB for QCD axion stars fall in the range of transition axion star solutions which, as it turns out, are structurally unstable to collapse, as they correspond to a maximum rather than a minimum of the energy functional. Collapsing axion stars evaporate a large fraction of their mass through rapid emission of relativistic axions [21,23,[32][33][34].…”

Section: Introductionmentioning

confidence: 99%

Global view of QCD axion stars

et al. 2019

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Taking a comprehensive view, including a full range of boundary conditions, we reexamine QCD axion star solutions based on the relativistic Klein-Gordon equation (using the Ruffini-Bonazzola approach) and its non-relativistic limit, the Gross-Pitaevskii equation. A single free parameter, conveniently chosen as the central value of the wavefunction of the axion star, or alternatively the chemical potential with range −m < µ < 0 (where m is the axion mass), uniquely determines a spherically-symmetric ground state solution, the axion condensate. We clarify how the interplay of various terms of the Klein-Gordon equation determines the properties of solutions in three separate regions: the structurally stable (corresponding to a local energy minimum) dilute and dense regions, and the intermediate, structurally unstable transition region. From the Klein-Gordon equation, one can derive alternative equations of motion including the Gross-Pitaevskii and Sine-Gordon equations, which have been used previously to describe axion stars in the dense region. In this work, we clarify precisely how and why such methods break down as the binding energy increases, emphasizing the necessity of using the full relativistic Klein-Gordon approach. Finally, we point out that, even after including perturbative axion number violating corrections, solutions to the equations of motion, which assume approximate conservation of axion number, break down completely in the regime with strong binding energy, where the magnitude of the chemical potential approaches the axion mass.

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“…Axion stars were considered first around 30 years ago, originally suggested to form from collapse of overdense miniclusters in the early universe [10,11] (see also more recent simulations [12]). Since then, many properties of axion stars have been studied extensively; these include structural stability [13][14][15][16][17][18][19][20][21][22] (including nonzero angular momentum [23][24][25]), the process of gravitational collapse [26][27][28][29][30][31][32], and their decay through emission of relativistic particles [33][34][35][36][37][38]. There has recently been a significant amount of work regarding relativistic corrections more generally to the classical field description of axion stars [39][40][41][42].…”

Section: Introductionmentioning

confidence: 99%

“…This comparison of ansätze to the numerical solutions is imperative for the study of dynamical problems that are much more difficult to solve numerically. Some such dynamical problems that have been analyzed using the variational method are the collapse [26][27][28][29] and collisions [60,61] of BECs. In subsequent years, numerous authors have presented various ansätze for both static and dynamical problems, either to improve numerical agreement or computational efficiency [19,22,25,37].…”

Section: Introductionmentioning

confidence: 99%

Approximation methods in the study of boson stars

et al. 2018

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We analyze the accuracy of the variational method in computing physical quantities relevant for gravitationally bound Bose-Einstein condensates. Using a variety of variational ansätze found in existing literature, we determine physical quantities and compare them to exact numerical solutions. We conclude that a "linear+exponential" wavefunction proportional to (1 + ξ) exp(−ξ) (where ξ is a dimensionless radial variable) is the best fit for attractive self-interactions along the stable branch of solutions, while for small particle number N it is also the best fit for repulsive self-interactions. For attractive self-interactions along the unstable branch, a single exponential is the best fit for small N , while a sech wavefunction fits better for large N . The Gaussian wavefunction ansatz, which is used often in the literature, is exceedingly poor across most of the parameter space, with the exception of repulsive interactions for large N . We investigate a "double exponential" ansatz with a free constant parameter, which is computationally efficient and can be optimized to fit the exact solutions in different limits. We show that the double exponential can be tuned to fit the sech ansatz, which is computationally slow. We also show how to generalize the addition of free parameters in order to create more computationally efficient ansätze using the double exponential. Determining the best ansatz, according to several comparison parameters, will be important for analytic descriptions of dynamical systems. Finally, we examine the underlying relativistic theory, and critically analyze the Thomas-Fermi approximation often used in the literature.

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QCD axion star collapse with the chiral potential

Cited by 29 publications

References 59 publications

Small-scale structure of fuzzy and axion-like dark matter

Small-scale structure of fuzzy and axion-like dark matter

Global view of QCD axion stars

Approximation methods in the study of boson stars

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