[论文解读] Diffuse Axion Background

Joshua Eby, Volodymyr Takhistov|arXiv (Cornell University)|Jan 31, 2024

Dark Matter and Cosmic Phenomena被引用 5

一句话总结

本论文开发了一个用于弥散轴子背景（DAB）的通用框架，从历史瞬态轴子排放源推导相应的通量，并讨论当前约束与跨天体物理与暗物质-领域起源的未来探测前景。

ABSTRACT

Relativistic axions can be readily produced in a broad variety of transient sources, such as axion star bosenova explosions, supernovae or even evaporating primordial black holes. We develop a general framework describing the resulting persistent diffuse axion background (D$a$B) due to accumulated axions from historic transient events. We derive strong constraints on the D$a$B flux from light axions $m\lesssim 10^{-3}\,{ m eV}$ emitted from sources with energies $ω\gtrsim{ m MeV}$ considering the non-observation of excess photons associated with axion-photon coupling from experiments, including COMPTEL, NuSTAR, XMM-Newton, INTEGRAL, EGRET and Fermi. Future searches in experiments such as SKA, JWST, XRISM, Vera C. Rubin Observatory, AMEGO/e-ASTROGAM will allow probing D$a$B and associated axion-photon couplings with unprecedented sensitivity covering a wide range of possible source energies as low as $0.1\,μ$eV and multiple decades in axion masses. We highlight the differences between astrophysical and dark sector sources of D$a$B. Further, we discuss complementarity with direct detection as well as prospects for other D$a$B searches. Our analysis demonstrates that D$a$B can act as a promising probe of populations of axion emission sources as well as emission mechanisms.

研究动机与目标

• Motivate Relativistic Axions: explore how transient sources can emit relativistic axions that accumulate into a persistent diffuse background.
• Formulate a General DAB Framework: derive the DAB flux from historic transient events using cosmological rate functions and spectra.
• Bridge to Observables: connect axion flux to photon production via axion-photon coupling and outline existing constraints.
• Assess Detection Prospects: discuss current constraints and future experimental sensitivity (e.g., SKA, JWST, XRISM, Rubin Observatory, AMEGO/e-ASTROGAM) for various axion masses and energies.
• Compare Source Classes: delineate differences between astrophysical and dark-sector sources in shaping the DAB.

提出的方法

• Define the diffuse axion background flux as dφ/dω = ∫ d z (1+z) dN_a(ω(1+z))/dω R_burst(z) |dt/dz|.
• Parameterize the cosmological transient event rate with R_burst(z) = A ρ_loss H0 / E_tot(z) f(z).
• Impose normalization via ρ_loss = ρ_DM F and relate A to the redshift distribution f(z) through Eq. (6).
• Describe generic emission spectra with a peaked burst form, including a Gaussian descriptor dN_a/dω|_Gauss, and derive the corresponding Gauss flux dφ/dω|_Gauss.
• Specialize to representative sources (supernovae, axion-star bosenovae, neutron star mergers) with source-specific dN_a/dω forms (e.g., SN spectra in Eq. 13, bosenova spectrum in Eq. 14).
• Show the bosenova-derived flux in Eq. (15) and discuss semi-relativistic peak structure from numerical simulations (Fig. 3).
• Discuss broader source classes (black hole superradiance, stellar axion halos, dark non-bosonic stars) and their potential contributions to the DAB.

Figure 1 : Sources of relativistic axion flux emission, which can contribute to the D $a$ B as described in Sec. 2.2 . Axion star bosenova emission estimated from numerical simulations of Ref. Levkov:2016rkk (orange shaded region corresponds to axion decay constant between $f_{a}=10^{14}$ GeV (top)

实验结果

研究问题

• RQ1 What is the expected diffuse axion background flux from historic transient axion-emitting sources given a cosmological rate and a per-event spectrum?
• RQ2 How do different source classes (astrophysical versus dark-sector) alter the shape and magnitude of the DAB, and what photon-signature channels arise from axion-photon coupling?
• RQ3 How do current photon-based constraints (COMPTEL, NuSTAR, XMM-Newton, INTEGRAL, EGRET, Fermi) bound the DAB for light axions (m ≲ 10^-3 eV) with ω ≳ MeV?
• RQ4 What are the prospects for future experiments (SKA, JWST, XRISM, Rubin Observatory, AMEGO/e-ASTROGAM) to probe DAB across wide axion mass-energy ranges?
• RQ5 How can the DAB complement direct detection searches and what emission mechanisms and populations are most diagnostic?

主要发现

• A general, flexible framework is established to compute the diffuse axion background flux from historic transient events via a cosmological rate R_burst(z) and single-event spectrum dN_a/dω.
• For Gaussian-like emission bursts, the DAB flux is given by a analytically tractable expression (Eq. 12) that links F, ρ_DM, A, and f(z) with redshift integration.
• Axion-star bosenovae are shown to yield a characteristic semi-relativistic peak in the axion spectrum, with numerical fits supporting a Gaussian descriptor around ω ≈ 2.2 m and δω ≈ 0.4 m (Fig. 3).
• Astrophysical sources such as supernovae and neutron-star mergers, as well as dark-sector phenomena like axion-star explosions and black-hole superradiance, are highlighted as viable DAB contributors, each with distinct spectra and redshift evolution.
• Current photon-based constraints from multiple missions can be used to bound the DAB flux for light axions with ω ≳ MeV energies, constraining the corresponding axion-photon couplings.
• Future facilities (e.g., SKA, JWST, XRISM, Rubin Observatory, AMEGO/e-ASTROGAM) are projected to probe DAB and axion-photon couplings over broad energy ranges down to ω ≈ 0.1 µeV and across wide axion mass spaces.

Figure 2 : Dimensionless cosmological transient axion burst event rate distribution $f(z)$ sourcing relativistic axions that are considered in this work. The power-law and Gauss distributions are defined in Eq. ( 7 ), and we set the input parameters as labeled. For illustration we normalize $f(z)$ t