Joshua Eby

Axion stars, gravitationally bound states of low-energy axion particles, have a maximum mass allowed by gravitational stability. Weakly bound states obtaining this maximum mass have sufficiently large radii such that they are dilute, and as a result, they are well described by a leading-order expansion of the axion potential. Here, heavier states are susceptible to gravitational collapse. Inclusion of higher-order interactions, present in the full potential, can give qualitatively different resu

We investigate the decay of condensates of scalars in a field theory defined by [Formula: see text], where [Formula: see text] and [Formula: see text] are the mass and decay constant of the scalar field. An example of such a theory is that of the axion, in which case the condensates are called axion stars. The axion field, [Formula: see text], is self-adjoint. As a result, the axion number is not an absolutely conserved quantity. Therefore, axion stars are not stable and have finite lifetimes. B

Following Ruffini and Bonazzola, we use a quantized boson field to describe condensates of axions forming compact objects. Without substantial modifications, the method can only be applied to axions with decay constant, f a , satisfying δ = (f a /M P )2 ≪ 1, where M P is the Planck mass. Similarly, the applicability of the Ruffini-Bonazzola method to axion stars also requires that the relative binding energy of axions satisfies $$ \varDelta =\sqrt{1-{\left({E}_a/{m}_a\right)}^2}\ll 1 $$ , where

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 nonrelativistic limit, the Gross-Pitaevskii equation. A single free parameter, conveniently chosen as the central value of the wave function of the axion star, or alternatively the chemical potential with range $\ensuremath{-}m<\ensuremath{\mu}<0$ (where $m$ is the axion mass), unique

Abstract As-yet undiscovered light bosons may constitute all or part of the dark matter (DM) of our Universe, and are expected to have (weak) self-interactions. We show that the quartic self-interactions generically induce the capture of dark matter from the surrounding halo by external gravitational potentials such as those of stars, including the Sun. This leads to the subsequent formation of dark matter bound states supported by such external potentials, resembling gravitational atoms (e.g. a

If QCD axions form a large fraction of the total mass of dark matter, then axion stars could be very abundant in galaxies. As a result, collisions with each other, and with other astrophysical bodies, can occur. We calculate the rate and analyze the consequences of three classes of collisions, those occurring between a dilute axion star and: another dilute axion star, an ordinary star, or a neutron star. In all cases we attempt to quantify the most important astrophysical uncertainties; we also

Coherent oscillation of axions or axionlike particles may give rise to long-lived clumps, called axion stars, because of the attractive gravitational force or its self-interaction. Such a kind of configuration has been extensively studied in the context of oscillons without the effect of gravity, and its stability can be understood by an approximate conservation of particle number in a nonrelativistic effective field theory (EFT). We extend this analysis to the case with gravity to clarify the E

We analyze the accuracy of the variational method in computing physical quantities relevant for gravitationally bound Bose-Einstein condensates. Using a variety of spherically symmetric variational ans\"atze found in existing literature, we determine physical quantities and compare them to numerical solutions. We conclude that a ``$\mathrm{linear}+\mathrm{exponential}$'' wave function proportional to $(1+\ensuremath{\xi})\mathrm{exp}(\ensuremath{-}\ensuremath{\xi})$ (where $\ensuremath{\xi}$ is

Axion particles can form macroscopic condensates, whose size can be galactic in scale for models with very small axion masses $m\sim10^{-22}$ eV, and which are sometimes referred to under the name of Fuzzy Dark Matter. Many analyses of these condensates are done in the non-interacting limit, due to the weakness of the self-interaction coupling of axions. We investigate here how certain results change upon inclusion of these interactions, finding a decreased maximum mass and a modified mass-radiu

Emission of relativistic axions from transient sources, such as axion star explosions, can lead to observable signatures. We show that axion bursts from collapsing axion stars can be detectable over the wide range of axion masses 10−15eV≲m≲10−7eV in laboratory experiments, such as ABRACADABRA, DMRadio and SHAFT. The detection of axion bursts could provide new insights into the fundamental axion potential, which is challenging to probe otherwise. An ensemble of bursts in the distant past would gi

Ultralight scalar dark matter has been proposed to constitute a component of dark matter, though the minimal scenarios have increasingly become constrained. In this work, we analyze scenarios where the dark matter consists of more than one ultralight boson, each with different masses. This potentially leads to formation of gravitationally-bound Bose-Einstein condensates with structures that are very different from condensates composed of a single scalar field. By generalizing from the well-under

A bstract We study luminous dark matter signals in models with inelastic scattering. Dark matter χ 1 that scatters inelastically off elements in the Earth is kicked into an excited state χ 2 that can subsequently decay into a monoenergetic photon inside a detector. The photon signal exhibits large sidereal-daily modulation due to the daily rotation of the Earth and anisotropies in the problem: the dark matter wind comes from the direction of Cygnus due to the Sun's motion relative to the galaxy,

In a previous study, we analyzed collapsing axion stars using the low-energy instanton potential, showing that the total energy is always bounded and that collapsing axion stars do not form black holes. In this paper, we provide a proof that the conclusions are unchanged when using instead the more general chiral potential for QCD axions.

We show that axion stars formed from axions with nearly Planck-scale decay constants $f$ are unstable to decay and are unlikely to have phenomenological consequences. More generally, we show how results at smaller $f$ cannot be na\"{\i}vely extrapolated to $f=\mathcal{O}({M}_{P})$ as, contrary to conventional wisdom, gravity and special relativity can both become relevant in the same regime. We clarify the rate of decay by reviewing and extending previous work on oscillons and axion stars, which