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Solar Extreme UV radiation and quark nugget dark matter model

Ariel Zhitnitsky

arXiv:1707.03400v2astro-ph.SRastro-ph.COastro-ph.HEhep-ph

TL;DR

The paper addresses the unexplained EUV and soft x-ray emission from the Sun by estimating its energy and spectrum in a quark nugget dark matter model. It finds that the estimated energy matches the observed emission and suggests that some solar nanoflares may be annihilation events.

  • Problem

    The quiet Sun’s EUV emission and the corona’s persistent energy output lack a conventional explanation, while the transition region’s sharp temperature rise remains a long-standing question.

    Source: §1 · pp. 2–3

  • Method

    The paper estimates solar energy deposition and radiation from incident axion quark nuggets, a dark matter model in which nuggets may contain matter or antimatter.

    Source: §2 · p. 5, §3.2 · p. 12

  • Results

    ∼10^27 erg/s of extra energy reproduces the observed EUV and soft x-ray intensity, and the estimated spectrum is consistent with observations at T ≃ 10^6 K.

    Source: §1 · pp. 4–5

  • Takeaways & Limitations

    The authors suggest that quiet-Sun nanoflares may be anti-nugget annihilation events and describe the Sun as an ideal system for testing the model.

    Source: §1 · p. 5

    A sharp cutoff or other drastic change in the nanoflare distribution around 10^22–10^24 erg would rule out the proposal.

    Source: §6 · p. 20

Abstract

from arXiv · show

We advocate the idea that the surprising emission of extreme ultra violet (EUV) radiation and soft x-rays from the Sun are powered externally by incident dark matter (DM) particles. The energy and the spectral shape of this otherwise unexpected solar irradiation is estimated within the quark nugget dark matter model. This model was originally invented as a natural explanation of the observed ratio $\Omega_{\rm dark} \sim \Omega_{\rm visible}$ when the DM and visible matter densities assume the same order of magnitude values. This generic consequence of the model is a result of the common origin of both types of matter which are formed during the same QCD transition and both proportional to the same fundamental dimensional parameter $\Lambda_{\rm QCD}$. We also present arguments suggesting that the transient brightening-like "nano-flares" in the Sun may be related to the annihilation events which inevitably occur in the solar atmosphere within this dark matter scenario.

1 Introduction

The paper frames the Sun’s persistent EUV and soft x-ray emission as an unresolved coronal-heating problem and proposes that incident quark nuggets provide an external energy source. It estimates that this mechanism can reproduce the observed emission and may also account for nanoflares.

1 Introduction

  • The quiet Sun’s EUV photons have energies of hundreds of eV, while the corona emits continuously at about 10^-7–10^-6 of photospheric output.Conventional astrophysical mechanisms have not quantitatively explained this emission or its persistence.Source: §1 · p. 2
  • The transition region’s sharp temperature rise and temperature inversion remain unexplained, with the rise occurring over a layer only about 100 km thick or less.The cited passage places the sharp rise at densities of about 10^-(12±1) g/cm3.Source: §1 · pp. 2–3
  • The proposal attributes the energy to dark matter nuggets entering the Sun, contrasting an external source with earlier proposals drawing energy from the Sun’s deep interior.In the model, matter and antimatter quark nuggets deposit energy before disintegrating.Source: §1 · p. 4
  • ∼10^27 erg/s of extra energy reproduces the observed EUV and soft x-ray intensity, using the known dark matter density and velocity without adjusting model parameters.The authors interpret this numerical match as support for their proposal.Source: §1 · p. 4
  • The quark nugget model links dark and visible matter densities to a common origin at the QCD transition and their dependence on Λ_QCD.The model was originally proposed to explain the observed similarity of Ω_dark and Ω_visible.Source: §1 · p. 4
  • The authors estimate a radiation spectrum consistent with observations at T ≃ 10^6 K and suggest that quiet-Sun nanoflares may be anti-nugget annihilation events.They also argue that the model’s energy deposition is of order 10^-7–10^-6 of photospheric output.Source: §1 · pp. 4–5

2 Axion Quark Nugget (AQN) dark matter model

The AQN model describes dark matter as quark and antiquark nuggets formed as axion domain walls shrink, with the walls stabilizing nuggets and permitting both matter and antimatter forms. It connects the comparable visible and dark matter densities to their shared QCD origin.

2 Axion Quark Nugget (AQN) dark matter model

  • Axion domain walls stabilize nuggets, so AQN formation does not require a first-order phase transition; the model also permits both matter and antimatter nuggets.The axion-wall pressure also addresses the evaporation concern raised for strangelets.Source: §2 · p. 5
  • Antimatter nuggets store energy that can be released through annihilation with visible matter when they hit the solar surface, a feature the paper identifies as unique to AQN.This supplies the proposed connection to solar EUV emission.Source: §2 · p. 5
  • The model describes baryogenesis as charge separation that preserves global baryon number, with unobserved antibaryons bound in quark and antiquark nuggets [19] [20].The nuggets form through shrinking axion domain walls.Source: §2 · p. 6
  • Typical nugget baryon charge ranges from B ~10^24 to B ~10^28, depending on the axion mass, and the mass scales as M ~ m_p B.The axion mass is described as yet to be discovered.Source: §2 · p. 6
  • An order-one nugget–antinugget imbalance is linked to visible and dark matter densities of the same order, since both trace the QCD epoch and Λ_QCD [19] [20].The imbalance follows from CP-violating formation processes.Source: §2 · pp. 6–7
  • Large baryon charge makes nugget number density small, while nuclear-density cores yield σ/M ~10^-10 cm^2/g, below the stated astrophysical and cosmological bound of 1 cm^2/g.The model also states that nuggets decouple from CMB photons and their bound baryon charge is unavailable for big bang nucleosynthesis.Source: §2 · p. 7
  • For average baryon number ⟨B⟩ ~10^25, the model proposes annihilation emissions as a possible source of diffuse galactic components, including the 511 keV line and 1–20 MeV excess [32] [34] [35].The paper relates emissions across bands through a shared line-of-sight integral.Source: §2 · p. 8
  • The paper reports that a predicted neutrino spectrum near 10 MeV is consistent with present flux measurements because SuperK is not sensitive to that low-energy range [40].This contrasts with the 50 MeV scale assumed in the analysis of [39].Source: §2 · p. 8

3 Anti-nuggets in the Sun

The paper estimates that anti-nugget annihilations in the Sun can supply energy comparable to the observed EUV output and produce radiation associated with a characteristic temperature near 10^6 K. It then proposes that annihilation in the corona and chromosphere could connect this energy deposition to observed solar emissions, including nanoflares.

3 Anti-nuggets in the Sun

  • The estimated anti-nugget annihilation energy roughly coincides with the Sun’s total EUV output, and the total-energy estimate is insensitive to nugget size distribution.The estimate uses the surrounding dark matter flux; the paper contrasts this generic energy budget with size-sensitive observables.Source: §3 · p. 9

3.1 The Basic Features of the Spectrum

  • The spectral estimate balances nugget surface emissivity against the energy-deposition rate from annihilations, with both rates expressed per unit surface area.The emission spectrum is described as approximately flat for frequencies ω ≤ T.Source: §3.1 · pp. 9–10
  • At an altitude of about 3000 km, the estimated intrinsic temperature of anti-nuggets in the solar corona is T ≃ 10^6 K.The paper distinguishes this internal nugget temperature from the surrounding coronal plasma temperature and assumes the annihilation energy eventually transfers to the plasma.Source: §3.1 · pp. 10–11

3.2 The annihilation pattern. The big picture.

  • Unlike the Earth case, solar capture implies long annihilation trajectories, allowing most energy deposition in the corona, chromosphere, and transition region for direct EUV and soft-x-ray observations.The paper contrasts a solar trajectory of order 10^6 km with an Earth-atmosphere trajectory of order 10^2 km.Source: §3.2 · pp. 11–12
  • The proposed annihilation pattern assumes that a substantial portion of anti-nugget mass and kinetic energy is lost in the corona and chromosphere before the nuggets reach the dense photosphere.The authors identify this above-photosphere deposition as the source of observed EUV and soft-x-ray emissions.Source: §3.2 · pp. 11–12
  • The estimated timescale for substantial annihilation is about 10^2 seconds, but it depends strongly on plasma density, effective radius, and initial baryon charge.The paper uses this model-dependent estimate to associate large annihilation events, with B ≳ 3 · 10^26, with observed nanoflares.Source: §3.2 · pp. 12–13
  • The annihilation-pattern estimate is sensitive to nugget size, whereas the total-energy and characteristic-temperature estimates are presented as generic features.Other observables also depend strongly on the nugget size distribution through baryon charge B or size R.Source: §3 · p. 9, §3.2 · pp. 12–13

4 Observation of nanoflares as evidence for anti-nuggets in Corona

The section proposes that anti-nugget annihilations may explain nanoflares, while distinguishing this speculative identification from the model’s energy-budget argument. It relates observed nanoflare properties to nugget parameters and discusses observational and theoretical constraints.

4 Observation of nanoflares as evidence for anti-nuggets in Corona

  • The authors identify quiet-region nanoflares with anti-nugget annihilations, but describe this identification as more speculative than their energy-budget and spectral arguments.They report that the inferred baryon-charge window overlaps available independent constraints, with qualifications for the smallest and largest nuggets.Source: §4 · p. 13, §4.2 · p. 14

4.1 Few historical remarks on nanoflares

  • Observed nanoflares are short quiet-corona emission enhancements spanning about 10^24–10^28 erg, with reported variability on timescales of minutes and numerous events across the Sun.The passage also reports that observed events account for about 10% of the radiative output in the same region, while reproducing measured radiation loss requires extrapolation below instrumental thresholds.Source: §4.1 · pp. 13–14

4.2 Nanoflares as the annihilation events of the anti-nuggets

  • A nanoflare threshold near 10^24 erg corresponds to nugget baryon charge B ≈3 · 10^26, while smaller anti-nuggets would produce unresolved events.The proposed charge range for extrapolated events is 10^23 ≤|B| ≤4 · 10^28, or 3 · 10^24 ≤|B| ≤2 · 10^28 under another extrapolation model.Source: §4.2 · p. 14
  • The proposed annihilation interpretation links nanoflare properties to nugget behavior: quiet-region uniformity, Doppler shifts near 300 km/s, and few-minute event durations are presented as consistent features.The authors say the estimated duration depends strongly on annihilation altitude and initial baryon charge.Source: §4.2 · p. 15

4.3 Recent advances and Future development

  • The authors report that a theoretical estimate of the nugget baryon-charge distribution is currently infeasible because the initial bubble-size distribution and subsequent nugget evolution are insufficiently understood.They contrast this with energy-budget and typical spectral estimates, which they say do not depend on the size distribution.Source: §4.3 · p. 16
  • The paper distinguishes its focus on the origin of coronal-heating energy from studies of nanoflare hydrodynamics, and says observational estimates of the event-energy distribution may still progress.The authors state that the AQN energy-budget estimate is consistent with observed coronal luminosity.Source: §4.3 · p. 16
  • Recent analyses disagree on flare energy-distribution slopes, and the paper cautions that instrument effects and different solar-cycle phases complicate comparisons across datasets.The authors also note that a single power law for all flares is difficult to reconcile with other reported nanoflare and microflare results.Source: §4.3 · p. 17

5 Sun as an ideal place to study AQN dark matter model

The section argues that the Sun offers advantages over Earth for studying AQN dark matter. Solar capture and atmospheric conditions are said to favor annihilation and observable energy deposition in the corona and related layers.

5 Sun as an ideal place to study AQN dark matter model

  • The Sun’s large γ⊙ means many non-head-on nuggets can be captured, with typical trajectories of order R⊙, unlike Earth’s shorter atmospheric paths and γ⊕≪1.The passage gives a typical solar trajectory of ∼10^6 km and an Earth atmospheric path of ∼10^2 km for head-on collisions.Source: §5 · p. 18
  • Solar hydrogen and helium are more readily annihilated by anti-nuggets than Earth’s heavier atmospheric elements, so the authors expect more annihilation events at the Sun despite its lower atmospheric column density.They also attribute greater annihilation efficiency in the solar atmosphere to its ionized plasma and accompanying protons.Source: §5 · p. 18
  • The authors argue that anti-nuggets may lose their baryon charge in the solar corona before reaching dense layers, depositing energy where EUV and soft x-ray emissions can be observed.By contrast, they say most energy in the Earth case is deposited underground, making direct observation difficult.Source: §5 · pp. 18–19

6 Concluding remarks and Wild speculations.

The authors conclude that AQN dark matter can account for the observed solar EUV and soft x-ray emission, and conjecture that AQN annihilations may be observed as nanoflares. They also propose observations and several broader speculative connections as ways to test or extend the scenario.

6 Concluding remarks and Wild speculations.

  • The authors conjecture that AQN annihilations in the corona, transition region, or chromosphere correspond to previously studied nanoflare events.They cite observations in Section 4.1 as support for this identification, interpreted in Section 4.2.Source: §6 · p. 19
  • The authors speculate that anti-nugget collisions with Earth might explain Tunguska-like events without recovered fragments or chemical traces, and that nuggets might relate to unexplained seismic-like events.Source: §6 · p. 19
  • The authors suggest that localized energy deposition by quark anti-nuggets could trigger or speed magnetic reconnection of preexisting solar fluxes.This is offered as a possible role alongside the conventional magnetic-reconnection account of solar flares.Source: §6 · p. 19
  • The AQN model is proposed as a candidate for explaining dark–luminous matter correlations [59] and as a possibility to investigate for proposed invisible matter in correlations between the Sun and its planets [60].The authors connect the first proposal to nuggets made of strongly interacting quarks and gluons, with visible and dark matter sharing an origin in the QCD transition.Source: §6 · pp. 19–20
  • The AQN mechanism generates the observed EUV and soft x-ray fraction of ∼10^-6 of total solar luminosity without parameter adjustment, and the estimated spectrum and temperature are consistent with the proposal.The estimates depend on an assumption stated in Section 3.2.Source: §6 · pp. 19–20
  • For other stars, radiation insensitive to surrounding dark matter density would rule out the proposal, which predicts annihilation-event counts proportional to local density.The authors call for studies across stellar types and quiet regions because intensity and spectral properties may also depend on stellar structure and galactic position.Source: §6 · p. 20
  • The authors propose testing nanoflare counts with roughly threefold better resolution and separating quiet from active regions to avoid confusing unrelated micro-events with candidate annihilations.They suggest the measurements could inform the nugget size distribution and help resolve modeling discrepancies.Source: §6 · p. 20
  • A sharp nanoflare-distribution cutoff in the 10^22–10^24 erg range would rule out the proposal, which requires nugget baryon charge to extend down to ∼10^24.The estimated average AQN baryon charge is ⟨B⟩∼10^25.Source: §6 · p. 20

A Few technical characteristics of the anti-nuggets at T̸ = 0

The appendix estimates the charge of anti-nuggets entering the solar corona and an effective size for their interactions with ionized plasma. It emphasizes that charge and plasma effects alter annihilation and energy transfer relative to earlier nugget-size estimates.

A Few technical characteristics of the anti-nuggets at T̸ = 0

  • At nonzero intrinsic temperature, stripping loosely bound positrons from an anti-nugget’s electrosphere leaves it with a negative charge, estimated by removing low-momentum positrons from the density profile.The profile is evaluated using a nonrelativistic approximation to the Thomas–Fermi electrosphere density.Source: A Few technical characteristics of the… · p. 21
  • For R ∼10^-5 cm and T ≃100 eV, the estimated charge is Q ∼10^8, tiny beside B ∼10^25 but important to dynamics in solar atmospheric electric and magnetic fields.Source: A Few technical characteristics of the… · p. 21
  • The effective size Reff(l) sets the plasma-particle scale involved in annihilation and energy transfer, estimated as ∼n_sun(l)Reff(l)^3 particles.The estimate is specific to a hot ionized plasma, where many-body plasma effects may alter the annihilation rate.Source: A Few technical characteristics of the… · p. 21
  • The appendix estimates Reff using a rough effective Coulomb-cross-section approximation with momentum transfer |q| ∼T, and uses the resulting scale in the main-text formula (3.9).The authors distinguish this scale from the nugget radius used in previous studies because charged anti-nuggets move through ionized plasma, affecting annihilation and energy transfer.Source: A Few technical characteristics of the… · pp. 21–22
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