8 Search Results

The recently launched James Webb Space Telescope can resolve eV-scale emission lines arising from dark matter decay. We forecast the end-of-mission sensitivity to the decay of axions, a leading dark matter candidate, in the Milky Way using the blank-sky observations expected during standard operations. Searching for unassociated emission lines will constrain axions in the mass range 0.18 to 2.6 eV with axion-photon couplings $g_{a\gamma \gamma }\gtrsim 5.5\times {10}^{-12}{\mathrm{GeV}}^{-1}$more » . In particular, these results will constrain nucleophobic QCD axions to masses $\lesssim 0.2\mathrm{eV}$ . Published by the American Physical Society 2025« less

Electromagnetic fields surrounding pulsars may source coherent ultralight axion signals at the known rotational frequencies of the neutron stars, which can be detected by laboratory experiments (e.g., pulsarscopes). As a promising case study, we model axion emission from the well-studied Crab pulsar, which would yield a prominent signal at 𝑓 ≈ 29.6 Hz regardless of whether the axion contributes to the dark matter abundance. We estimate the relevant sensitivity of future axion dark matter detection experiments such as DMRadio-GUT, Dark SRF, and CASPEr, assuming different magnetosphere models to bracket the uncertainty in astrophysical modeling. For example, depending on final experimentalmore » parameters, the Dark SRF experiment could probe axions with any mass 𝑚_𝑎 ≪ 10⁻¹³ eV down to 𝑔_{𝑎⁢𝛾⁢𝛾} ∼3 × 10⁻¹³ GeV⁻¹ with one year of data and assuming the vacuum magnetosphere model. These projected sensitivities may be degraded depending on the extent to which the magnetosphere is screened by charge-filled plasma. The promise of pulsar-sourced axions as a clean target for direct detection experiments motivates dedicated simulations of axion production in pulsar magnetospheres.« less

Optically dense clouds in the interstellar medium composed predominantly of molecular hydrogen, known as molecular clouds, are sensitive to energy injection in the form of photon absorption, cosmic-ray scattering, and dark matter (DM) scattering. The ionization rates in dense molecular clouds are heavily constrained by observations of abundances of various molecular tracers. Recent studies have set constraints on the DM-electron scattering cross section using measurements of ionization rates in dense molecular clouds. Here we calculate the analogous bounds on the DM-proton cross section using the molecular Migdal effect, recently adapted from the neutron scattering literature to the DM context. Thesemore » bounds may be the strongest limits on a strongly coupled DM subfraction, and represent the first application of the Migdal effect to astrophysical systems. Published by the American Physical Society 2024« less

Abstract Among magnetar models of fast radio bursts (FRBs), there is ongoing debate about whether the site of coherent radio emission lies within or beyond the light cylinder. We propose a mechanism by which FRBs produced near the magnetar surface are transported out of the magnetosphere by axions, which are hypothetical particles that couple to photons. If the emission site hosts strong accelerating electric fields, a considerable fraction of the FRB energy budget is converted to an axion burst. Once produced, the axion burst free streams out of the magnetosphere due to the rapidly decreasing magnetic field. The burst maymore » escape through either the open or closed magnetosphere while retaining the temporal signature of the original FRB. In the wind region, axions resonantly excite ordinary (O) modes that escape as the plasma density decreases. The radio efficiency of this mechanism satisfies energetics constraints from FRB 121102 for axion−photon coupling strengths that have not been excluded by other astrophysical probes.« less

This is the second in a series of papers on preheating in inflationary models comprised of multiple scalar fields coupled nonminimally to gravity. We work in the rigid-spacetime approximation and consider field trajectories within the single-field attractor, which is a generic feature of these models. We construct the Floquet charts to find regions of parameter space in which particle production is efficient for both the adiabatic and isocurvature modes, and analyze the resonance structure using analytic and semianalytic techniques. Particle production in the adiabatic direction is characterized by the existence of an asymptotic scaling solution at large values of themore » nonminimal couplings, $${{\xi}}_{I}{\gg}1$$, in which the dominant instability band arises in the long-wavelength limit, for comoving wave numbers $$k{\rightarrow}0$$. However, the large-$${{\xi}}_{I}$$ regime is not reached until $${{\xi}}_{I}{\ge}\mathcal{O}(100)$$. In the intermediate regime, with $${{\xi}}_{I}{\sim}\mathcal{O}(1-10)$$, the resonance structure depends strongly on wave number and couplings. The resonance structure for isocurvature perturbations is distinct and more complicated than its adiabatic counterpart. An intermediate regime, for $${{\xi}}_{I}{\sim}\mathcal{O}(1-10)$$, is again evident. For large values of $${{\xi}}_{I}$$, the Floquet chart consists of densely spaced, nearly parallel instability bands, suggesting a very efficient preheating behavior. The increased efficiency arises from features of the nontrivial field-space manifold in the Einstein frame, which itself arises from the fields’ nonminimal couplings in the Jordan frame, and has no analog in models with minimal couplings. Quantitatively, the approach to the large-$${{\xi}}_{I}$$ asymptotic solution for isocurvature modes is slower than in the case of the adiabatic modes.« less

This is the first of a three-part series of papers, in which we study the preheating phase for multifield models of inflation involving nonminimal couplings. We study the single-field attractor behavior that these models exhibit during inflation and quantify its strength and parameter dependence. We further demonstrate that the strong single-field attractor behavior persists after the end of inflation. Preheating in such models therefore generically avoids the “dephasing” that typically affects multifield models with minimally coupled fields, allowing efficient transfer of energy from the oscillating inflaton condensate(s) to coupled perturbations across large portions of parameter space. We develop a doublymore » covariant formalism for studying the preheating phase in such models and identify several features specific to multifield models with nonminimal couplings, including effects that arise from the nontrivial field-space manifold. In papers II and III, we apply this formalism to study how the amplification of adiabatic and isocurvature perturbations varies with parameters, highlighting several distinct regimes depending on the magnitude of the nonminimal couplings $${{\xi}}_{I}$$.« less

This paper concludes our semianalytic study of preheating in inflationary models comprised of multiple scalar fields coupled nonminimally to gravity. Using the covariant framework of paper I in this series, we extend here the rigid-spacetime results of paper II by considering both the expansion of the Universe during preheating, as well as the effect of the coupled metric perturbations on particle production. The adiabatic and isocurvature perturbations are governed by different effective masses that scale differently with the nonminimal couplings and evolve differently in time. The effective mass for the adiabatic modes is dominated by contributions from the coupled metricmore » perturbations immediately after inflation. The metric perturbations contribute an oscillating tachyonic term that enhances an early period of significant particle production for the adiabatic modes, which ceases on a time scale governed by the nonminimal couplings $${{\xi}}_{I}$$. The effective mass of the isocurvature perturbations, on the other hand, is dominated by contributions from the fields' potential and from the curvature of the field-space manifold (in the Einstein frame), the balance between which shifts on a time scale governed by $${{\xi}}_{I}$$. As in papers I and II, we identify distinct behavior depending on whether the nonminimal couplings are small [$${{\xi}}_{I}{\lesssim}\mathcal{O}(1)$$], intermediate [$${{\xi}}_{I}{\sim}\mathcal{O}(1{-}10)$$], or large ($${{\xi}}_{I}{\ge}100$$).« less