---
title: 'Axion Quark Nuggets: Dark Matter Candidates'
url: https://www.emergentmind.com/topics/axion-quark-nuggets-aqns
type: topic
---

# Axion Quark Nuggets: Dark Matter Candidates

Axion Quark Nuggets (AQNs) are a class of macroscopic dark-matter candidates composed of dense quark matter or antiquark matter in a color-superconducting phase and stabilized by an axion domain wall. In the AQN framework, dark matter and the visible baryonic sector originate from the same QCD-era dynamics, so the near coincidence \(\Omega_{\rm DM}\sim \Omega_{\rm visible}\) is treated as a consequence of common QCD-scale physics rather than of unrelated sectors. A defining feature is that the dark sector contains both matter nuggets and antimatter nuggets; the latter are phenomenologically central because annihilation with ambient baryons can generate electromagnetic, acoustic, and axionic signatures across cosmology, astrophysics, and terrestrial environments [2105.08719].

## 1. Cosmological framework and baryon-charge separation

The AQN scenario replaces conventional baryogenesis by baryon-charge separation. The total baryon number of the Universe is taken to remain zero, while visible baryons, matter nuggets, and antimatter nuggets partition that charge asymmetrically. Representative bookkeeping relations used in the literature include
\[
B_{\rm tot}=0=B_{\rm nuggets}-B_{\rm antinuggets}+B_{\rm visible},
\]
the ratio
\[
\Omega_{\rm DM}\approx \left(\frac{1+c}{1-c}\right)\Omega_{\rm B},\qquad c\equiv \frac{|B_{\bar N}|}{|B_N|}\sim {\cal O}(1),
\]
and, in one cluster-oriented formulation, the partition \(B_{\rm \bar{AQN}}:B_{\rm AQN}:B_{\rm visible}\simeq 3:2:1\) [2407.04330, 2105.08719, 2406.17946]. For the observed \(\Omega_{\rm DM}\approx 5\,\Omega_{\rm B}\), the review literature quotes \(c\approx 3/2\), so the antibaryon charge hidden in antinuggets exceeds the baryon charge hidden in nuggets [2105.08719].

Within this picture, the visible matter excess does not arise because the Universe generated a net baryon number, but because more antibaryon number was sequestered into antimatter nuggets than baryon number into matter nuggets. Free visible antibaryons then annihilated away, while visible baryons survived. The baryon-to-photon ratio is correspondingly tied to the AQN formation temperature rather than to a separate late-time baryogenesis sector; the review literature quotes
\[
\eta \equiv \frac{n_B-n_{\bar B}}{n_\gamma}\simeq \frac{n_B}{n_\gamma}\sim 10^{-10},
\qquad
T_{\rm form}\simeq 41~{\rm MeV}
\]
as characteristic numbers in this framework [2105.08719].

A recurring claim across the AQN literature is therefore that the relation \(\Omega_{\rm DM}\sim \Omega_{\rm visible}\) is not an after-the-fact fit but a structural property of QCD-scale formation. This motivates the model independently of any individual phenomenological application, including solar, atmospheric, cluster, or terrestrial search proposals [2008.04325, 2602.10562].

## 2. Formation, composition, and characteristic scales

AQNs are assumed to form near the QCD transition from closed \(N_{\rm DW}=1\) axion-domain-wall bubbles that accrete quarks and antiquarks while collapsing. In the review treatment, numerical simulations suggest that about \(87\%\) of the total wall area belongs to one large percolating cluster, while the remaining \(13\%\) appears as relatively small closed bubbles that seed nugget formation. Collapse is arrested by quark Fermi pressure, and the final object reaches a dense color-superconducting state with \(\mu_{\rm form}\gtrsim 450~{\rm MeV}\) and pairing gap \(\Delta\gtrsim 40~{\rm MeV}\) at \(t\sim 10^{-4}\,{\rm s}\) and \(T_{\rm form}\approx 40\)–\(41~{\rm MeV}\) [2105.08719].

The characteristic conserved quantity is the baryon number \(B\). The standard scalings are
\[
M_{\rm AQN}\simeq m_p |B|,\qquad B\sim R^3,\qquad \sigma\sim R^2\sim B^{2/3},
\qquad
\frac{\sigma}{M}\sim B^{-1/3}.
\]
Because of this \(B^{-1/3}\) suppression, the cross-section-to-mass ratio can be as small as
\[
\frac{\sigma}{M}\sim 10^{-10}\ {\rm cm^2\,g^{-1}},
\]
well below the usual collisionless-dark-matter criterion \(\sigma/M\lesssim 1~{\rm cm^2\,g^{-1}}\) [2105.08719, 2512.05401]. The model is thus “dark” not because of weak couplings in the WIMP sense, but because the nuggets are very massive and correspondingly rare.

The literature uses a broad allowed baryon-number interval. Representative ranges are \(10^{23}\lesssim |B|\lesssim 10^{28}\) or \(3\times 10^{24}\lesssim B\lesssim 10^{28}\), with direct nondetection bounds often quoted as \(B>3\times 10^{24}\) or \(M_{\rm AQN}\gtrsim 5~{\rm g}\) [2008.04325, 2105.08719, 2602.10562]. Recent cosmological and astrophysical analyses commonly work in the practical mass interval \((5\text{–}1000)\,{\rm g}\), while some CMB and diffuse-emission studies emphasize benchmarks \(m_{\rm AQN}=10,\ 100,\ 1000~{\rm g}\) or \(m_{\rm AQN}\sim 100\)–\(500~{\rm g}\) [2512.05401, 2602.10562, 2504.15382].

For a representative mass-radius relation at nuclear density, one recent CMB study writes
\[
R \approx 4.09\times10^{-5}\ {\rm cm}\left(\frac{m_{\rm AQN}}{100\ {\rm g}}\right)^{1/3},
\]
so \(m_{\rm AQN}\sim 100~{\rm g}\) corresponds to \(R\sim 4\times10^{-5}\ {\rm cm}\approx 0.4~\mu{\rm m}\) [2512.05401]. Atmospheric and terrestrial phenomenology often uses a comparable benchmark: for \(|B|\simeq 10^{25}\), \(R\simeq 2.2\times 10^{-5}\,{\rm cm}\) and mass is of order \(10\) g [2008.04325].

## 3. Interaction physics with baryons and radiation fields

AQN phenomenology is governed by interactions between ambient baryons and the nugget surface or electrosphere. A general local rate model used in cosmological emission calculations is
\[
\Gamma=\sigma_{\rm eff} n_b \Delta v,
\]
where \(\sigma_{\rm eff}\) is the effective capture cross section, \(n_b\) is baryon density, and \(\Delta v\) is the relative AQN-baryon speed [2406.12122]. A proton-antiproton annihilation event is taken to release approximately \(2~{\rm GeV}\), with a phenomenological split between a thermalized channel, which heats the electrosphere, and a prompt non-thermal electromagnetic channel. The thermal electrosphere emission is modeled by a bremsstrahlung-like surface emissivity
\[
F_{\rm tot}\approx \frac{16}{3\pi}\,\alpha^{5/2}\,T_{\rm AQN}^4\left(\frac{T_{\rm AQN}}{m_e}\right)^{1/4},
\]
and the corresponding spectral emissivity
\[
F_\nu^{\rm th} \propto T_{\rm AQN}^{3}\left(\frac{T_{\rm AQN}}{m_e}\right)^{1/4}
H\!\left(\frac{2\pi \nu}{T_{\rm AQN}}\right),
\]
with \(H(x)\) given piecewise in the electrosphere calculations [2406.12122, 2406.17946].

A crucial environmental effect is electrosphere ionization. As loosely bound positrons are removed, an antimatter nugget acquires a net negative charge, which can increase proton capture in ionized media through Coulomb attraction. In large-scale-structure calculations this is encoded via \(R_{\rm eff}>R_{\rm AQN}\) and \(\sigma_{\rm eff}=\pi R_{\rm eff}^2\) when the gas is ionized and the Coulomb capture radius exceeds the geometric radius [2406.12122]. In the early Universe, a related mechanism gives an effective ion-capture enhancement around recombination,
\[
\left(\frac{R_{\rm eff}}{R}\right)^2 \approx 936 \left(\frac{k_B T}{0.3\,{\rm eV}}\right)^{1/2}
\left(\frac{m_{\rm AQN}}{100\,{\rm g}}\right)^{1/3},
\]
with \(R_{\rm eff}\ll \lambda_D\) over \(10^3\lesssim z\lesssim 10^6\), so Debye screening is subdominant in the redshift range relevant for the CMB distortion calculation [2512.05401].

In dense terrestrial media, the microphysics becomes more uncertain. The paleo-detector study models anti-AQN stopping by analogy with “nuclearite-like” energy loss and with antiproton annihilation on nuclei. It uses
\[
-\frac{dE}{dx}= \begin{cases}
\sigma_{\rm AQN}\,\rho(x)\,v_{\rm AQN}^2(L), & v_{\rm AQN}(L)\ge \frac{\varepsilon}{\rho},\\[4pt]
\varepsilon\,\sigma_{\rm AQN}, & v_{\rm AQN}(L)< \frac{\varepsilon}{\rho},
\end{cases}
\]
with \(\varepsilon=6.2\times 10^2~{\rm eV/cm^3}\) in the lithosphere, implying a crossover near \(188~{\rm m/s}\) for rock densities \(2.6\)–\(3.0~{\rm g/cm^3}\). The same work quotes annihilation-based stopping powers
\[
\frac{dE}{dx}\approx 10\,\kappa\left(\frac{B}{10^{25}}\right)^{2/3}
\left(\frac{n_{\rm air}}{10^{21}\,{\rm cm^{-3}}}\right)\frac{\rm J}{\rm m},
\]
for atmosphere and
\[
\frac{dE}{dx}\approx 10^{6}\,\kappa\left(\frac{B}{10^{25}}\right)^{2/3}
\left(\frac{n_{\rm rock}}{10^{24}\,{\rm cm^{-3}}}\right)\frac{\rm J}{\rm m},
\]
for rock, together with the caveat that an extra suppression factor \(\xi\sim 10^{-2}\) or smaller may arise if positron removal from the electrosphere reduces annihilation efficiency [2407.04330].

Because the annihilation of nuclei on antiquark matter in a color-superconducting phase is not experimentally known, several studies explicitly substitute antiproton-annihilation phenomenology. The paleo-detector analysis uses \(\sigma\approx 0.4~{\rm b}\) together with mean pion multiplicity \(\langle N_\pi\rangle=5.36\pm0.3\), average pion energy \(\langle E_\pi\rangle=350\pm18~{\rm MeV}/\pi\), and average emitted proton multiplicity \(\langle N_p\rangle\approx1.1\pm0.3\) as input for FLUKA simulations [2407.04330]. This substitution is one of the central unresolved modeling assumptions in the entire AQN phenomenology.

## 4. Astrophysical and cosmological phenomenology

Solar applications are among the most developed. One simulation-based study argues that AQNs can account for the quiet-Sun coronal EUV and soft-X-ray power \(L_{\rm corona}\sim 10^{27}\,{\rm erg\,s^{-1}}\), with most of the energy deposited near the transition region at altitude \(\sim 2000~{\rm km}\). In that framework, impacting anti-AQNs lose more than \(97\%\) of their mass before reaching the photosphere, and the corresponding event energies map naturally onto the nanoflare interval \(W\simeq 4\times 10^{20}-10^{26}\,{\rm erg}\) through \(W\simeq 2m_pc^2B\) [1805.01897]. A related flare-oriented study further proposes that the same incoming anti-AQNs, moving through the solar atmosphere at \(v_{\rm AQN}\sim 600~{\rm km/s}\), have Mach number \(M\gg 1\) and can generate shocks with \(\Delta p/p\sim M^2\) and \(\Delta T/T\sim M^2\), thereby acting as triggers of magnetic reconnection in active regions while the flare energy itself remains magnetic [1801.01509].

Atmospheric AQN phenomenology has been used to interpret the short-duration, thunderstorm-correlated Telescope Array burst events. In that proposal, an antimatter AQN moving through the atmosphere is heated to \(T\sim 10\)–\(20~{\rm keV}\), develops a weakly bound positron cloud extending to
\[
R_{\rm cap}(T)\simeq 2~{\rm cm}\left(\frac{T}{10~{\rm keV}}\right)^{1/4},
\]
and, in a thunderstorm electric field of order \({\cal E}\sim {\rm kV/cm}\), can liberate and accelerate positrons to \(E_{\rm exit}\sim 10~{\rm MeV}\). The same paper estimates a detector-scale positron yield \(N_{\rm positrons}^{\rm max}\sim 10^3\), burst path length \(L_{\rm burst}\sim 250~{\rm m}\) for \(\Delta t_{\rm burst}=1~{\rm ms}\), and predicts synchronized radio emission in the \(3\)–\(300\) MHz band [2008.04325].

Several works extend AQN emission to large-scale environments. In cosmological large-scale-structure forecasts, the AQN-baryon interaction generates both a monopole signal and anisotropy fluctuations from radio to a few keV, with the amplitude depending strongly on average nugget mass and on the ionization state of the baryonic environment. The most optimistic scenarios were found to lie near the sensitivity limit of existing instruments such as FIRAS and the South Pole Telescope, while the best prospects were identified as ultra-deep IR/optical surveys, CMB spectral distortions, and high-resolution low-frequency observations in the \(1\)–\(100\) GHz range [2406.12122]. A companion cluster analysis, using 161 simulated galaxy clusters and 11 cross-identified observed systems, predicts that thermal AQN emission can exceed standard intracluster backgrounds in a low-frequency window up to \(\nu\lesssim 3842.19\,{\rm GHz}\) in favorable cases; Fornax and Virgo are identified there as the most promising named cluster targets [2406.17946]. On Galactic scales, a Milky Way study using FIRE-2 Latte solar-neighborhood analogs finds that the AQN-induced far-UV glow can match the observed diffuse FUV excess for \(m_{\rm AQN}\sim 100\)–\(500~{\rm g}\), with the observational benchmark quoted as about \(100\)–\(200\ {\rm photon\,cm^{-2}\,s^{-1}\,sr^{-1}\,\AA^{-1}}\) [2504.15382].

Early-Universe consequences have also been quantified. A recent CMB study finds that AQN-induced baryon annihilation leaves CMB anisotropies essentially unaffected but can produce spectral distortions of order
\[
\mu \sim 6\times 10^{-8}, \qquad y\sim 2\times 10^{-9},
\]
with the characteristic prediction \(\mu>y\) arising because the AQN heating history scales approximately as \(\dot Q_{\rm AQN}\propto (1+z)^{6.5}\), slightly steeper than standard annihilating dark matter [2512.05401]. An earlier cosmological application addresses the primordial lithium problem by arguing that at \(T\sim 20~{\rm keV}\), negatively charged antinuggets can preferentially capture nuclei with \(Z\ge 3\), giving an order-unity depletion of Li and Be while leaving H and He essentially unaffected because the capture enhancement scales exponentially with \(Z\) [1811.01965].

## 5. Terrestrial searches and detector concepts

Because AQNs are massive and rare, terrestrial searches often emphasize large passive targets, wide-area coincidence, or multimessenger signatures rather than conventional compact detectors. A general flux normalization used in network and acoustic studies is
\[
\frac{\langle \dot N\rangle}{4\pi R_\oplus^2}\simeq 4\times 10^{-2}\,
{\rm km^{-2}\,yr^{-1}}
\left(\frac{\rho_{\rm DM}}{0.3\,{\rm GeV\,cm^{-3}}}\right)
\left(\frac{\langle v_{\rm AQN}\rangle}{220\,{\rm km\,s^{-1}}}\right)
\left(\frac{10^{25}}{\langle B\rangle}\right),
\]
corresponding to roughly one event per day per \((100\,{\rm km})^2\) area for \(\langle B\rangle\sim 10^{25}\) [2003.07363, 2012.00765].

One class of proposals targets acoustic and seismic disturbances. A dedicated infrasound study predicts that atmospheric anti-AQNs should generate infrasonic pulses near \(\nu\sim 5\)–\(6~{\rm Hz}\). For a typical \(B\sim 10^{25}\) event, the estimated overpressure at \(100~{\rm km}\) is \(\delta p\sim 0.03~{\rm Pa}\), whereas a rarer \(B\sim 10^{27}\) event at \(r\sim 300~{\rm km}\) can give \(\delta p\sim 0.3~{\rm Pa}\) and \(\nu\simeq 5~{\rm Hz}\). Underground, the same work estimates much stronger kHz-band disturbances, with benchmark overpressure \(\delta p(r)\sim 10^2~{\rm Pa}\) at \(100~{\rm km}\) and frequency \(\nu\sim 3.5~{\rm kHz}\), motivating Distributed Acoustic Sensing and seismic-network searches [2003.07363].

A second class uses synchronized detector networks. For AQN-induced axions, one proposal argues that the optimal geometry is a triangular network of stations separated by \(\sim 100~{\rm km}\), because this matches the expected local-flash radius and allows trajectory reconstruction from burst timing. For X-rays, the same study finds that the optimal elementary unit is a regular tetrahedron with \(\sim 50~{\rm m}\) spacing, since X-rays attenuate locally and four detectors are needed for unique three-dimensional reconstruction. In its simulations, the underground-emission constraint yields \(94\%\) unique trajectory reconstruction for a triangular axion network, while a tetrahedral X-ray unit gives \(100\%\) uniqueness [2012.00765]. Related work on AQN-origin axions emphasizes broadband detection rather than narrow cavity haloscopes, because these axions are relativistic with \(v_a^{\rm AQN}\simeq 0.6c\), broad spectral support \(m_a\lesssim \omega_a\lesssim 1.8\,m_a\), and daily and annual modulation at the \(\sim 10\%\) level [1909.09475].

A third class exploits geological exposure. A recent paleo-detector proposal suggests that naturally occurring minerals can register anti-AQN annihilation or transit through a localized, approximately spherically symmetric overdose region readable by thermoluminescence (TL) or optically stimulated luminescence (OSL). The suggested minerals are fluorite/calcium fluoride \(({\rm CaF_2})\), quartz/silicon dioxide \(({\rm SiO_2})\), and feldspars. The paper quotes a smallest TL-recorded dose of \(1~\mu{\rm Gy}\) for \({\rm CaF_2:N}\) and a lowest detectable dose of \(1~{\rm mGy}\) for sedimentary quartz, and concludes that at \(1\) m from the interaction point, the electron/positron component alone exceeds detectability if more than \(10^{10}\) protons annihilate in \({\rm CaF_2}\) or more than \(10^{12}\) annihilations occur in \({\rm SiO_2}\), provided the minerals remained at low, stable temperatures over geological timescales [2407.04330].

More unconventional proposals continue this logic of repurposing large existing systems. One 2026 study argues that a subset of LHC Unidentified Falling Object beam-loss events may be triggered by anti-AQNs passing underground within \(\sim 100~{\rm km}\) of the accelerator. For benchmark masses \(5\)–\(1000~{\rm g}\), it estimates an AQN-induced UFO burst rate \(\dot N_{\rm UFO}^{\rm(AQN)}\approx 0.045~{\rm events/hour}\), corresponding to roughly \((1\text{--}10)\%\) of all UFOs. In its background model, requiring three correlated UFOs within \(2~{\rm s}\) yields \({\rm SNR}>5\) over the full allowed AQN mass range after about \(360\) hours, effectively using the LHC as a large broadband acoustic detector [2602.10562].

## 6. Open issues, variants, and empirical status

Across the literature, AQNs remain a highly structured but model-dependent framework. The recurring uncertainties are the nonperturbative QCD formation dynamics, the size or mass distribution \(f(B)\), the detailed properties of the color-superconducting phase, the electrosphere microphysics, and the annihilation of nuclei on antiquark matter. Phenomenological papers are explicit that many observational estimates are order-of-magnitude or proof-of-principle calculations rather than end-to-end detector forecasts or precision exclusion plots [2105.08719, 2407.04330, 2008.04325].

These uncertainties appear in different forms in different subfields. Solar applications depend on the effective interaction radius \(R_{\rm eff}\) and on shock-coupling in the transition region; atmospheric burst models depend on poorly controlled thunderstorm electric fields, the annihilation/thermalization parameter \(\kappa\), and the liberated positron fraction \(\eta\); large-scale-structure forecasts depend sensitively on ionization state and relative-velocity modeling; paleo-detector proposals depend critically on thermal history, spatially differential backgrounds, and the actual topology of a moving, continuously annihilating antinugget rather than a single idealized point source [1805.01897, 2008.04325, 2406.12122, 2407.04330].

The literature also explores nonstandard AQN variants. One such variant assumes that AQNs become ferromagnetic, with surface magnetic field \(B_0\sim 10^{12\pm1}\,{\rm T}\). In that case axion electrodynamics induces an electric field
\[
\mathbf{E}=-g_{a\gamma\gamma}a\mathbf{B},
\]
and the corresponding study estimates a critical magnetic field \(B_{\rm crit}\sim 10^{11}\,{\rm T}\) above which Schwinger pair production becomes large. Its conclusion is that strongly magnetized “electric” AQNs are likely only marginally viable and probably relax to ordinary non-magnetized AQNs if they are to survive as dark matter today [1908.09409].

Empirically, the AQN program currently consists of a web of linked interpretations and search concepts rather than a single decisive test. The review literature presents AQNs as a unified alternative to WIMP dark matter that simultaneously addresses dark matter, baryon asymmetry, and axion physics, while the more specialized papers develop concrete signatures in the Sun, atmosphere, large-scale structure, the CMB, rocks, acoustic media, synchronized detector networks, and accelerator infrastructure [2105.08719]. A plausible synthesis is that the framework is most constrained not by one channel alone but by whether the same mass scale, charge state, and interaction prescriptions can remain mutually consistent across these disparate environments.

Source: https://www.emergentmind.com/topics/axion-quark-nuggets-aqns