As the only dark matter candidate that does not invoke a new particle that survives to the present day, primordial black holes (PBHs) have drawn increasing attention recently. Up to now, various observations have strongly constrained most of the mass range for PBHs, leaving only small windows where PBHs could make up a substantial fraction of the dark matter. Here we revisit the PBH constraints for the asteroid-mass window, i.e., the mass range 3.5 × 10 −17 M < m PBH < 4 × 10 −12 M . We revisit 3 categories of constraints.(1) For optical microlensing, we analyze the finite source size and diffractive effects and discuss the scaling relations between the event rate, m PBH and the event duration. We argue that it will be difficult to push the existing optical microlensing constraints to much lower m PBH . (2) For dynamical capture of PBHs in stars, we derive a general result on the capture rate based on phase space arguments. We argue that survival of stars does not constrain PBHs, but that disruption of stars by captured PBHs should occur and that the asteroidmass PBH hypothesis could be constrained if we can work out the observational signature of this process. (3) For destruction of white dwarfs by PBHs that pass through the white dwarf without getting gravitationally captured, but which produce a shock that ignites carbon fusion, we perform a 1+1D hydrodynamic simulation to explore the post-shock temperature and relevant timescales, and again we find this constraint to be ineffective. In summary, we find that the asteroid-mass window, which was previously constrained due to femtolensing, WD survival, optical microlensing, and neutron star capture is no longer constrained. Hence, the asteroid-mass window remains open for PBHs to account for all the dark matter.

The magnetic fields of the Solar System planets provide valuable insights into the planets' interiors and can have dramatic consequences for the evolution of their atmospheres and interaction with the solar wind. However, we have little direct knowledge of magnetic fields in exoplanets. Here we present a new method for detecting magnetic fields in the atmospheres of close-in exoplanets, based on spectropolarimetric transit observations at the wavelength of the helium line at 1083 nm. Strong absorption signatures (transit depths on the order of a few percent) in the 1083 nm line have recently been observed for several close-in exoplanets. We show that in the conditions in these escaping atmospheres, metastable helium atoms should be optically pumped by the starlight, and for field strengths >few×10 −4 G, should align with the magnetic field. This results in linearly polarized absorption at 1083 nm that traces the field direction (the Hanle effect), which we explore by both analytic computation and with the Hazel numerical code. The linear polarization Q 2 + U 2 /I ranges from ∼ 10 −3 in optimistic cases down to a few×10 −5 for particularly unfavorable cases, with very weak dependence on field strength. The line of sight component of the field results in a slight circular polarization (the Zeeman effect), also reaching V /I ∼ few × 10 −5 (B /10 G). We discuss the detectability of these signals with current (SPIRou) and future (extremely large telescope) high-resolution infrared spectropolarimeters, and briefly comment on possible sources of astrophysical contamination.

Extreme mass ratio inspirals (EMRIs) -systems with a compact object orbiting a much more massive (e.g., galactic center) black hole -are of interest both as a new probe of the environments of galactic nuclei, and their waveforms are a precision test of the Kerr metric. This work focuses on the effects of an external perturbation due to a third body around an EMRI system. This perturbation will affect the orbit most significantly when the inner body crosses a resonance with the outer body, and result in a change of the conserved quantities (energy, angular momentum, and Carter constant) or equivalently of the actions, which results in a subsequent phase shift of the waveform that builds up over time. We present a general method for calculating the changes in action during a resonance crossing, valid for generic orbits in the Kerr spacetime. We show that these changes are related to the gravitational waveforms emitted by the two bodies (quantified by the amplitudes of the Weyl scalar ψ4 at the horizon and at ∞) at the frequency corresponding to the resonance. This allows us to compute changes in the action variables for each body, without directly computing the explicit metric perturbations, and therefore we can carry out the computation by calling an existing black hole perturbation theory code. We show that our calculation can probe resonant interactions in both the static and dynamical limit. We plan to use this technique for future investigations of third-body effects in EMRIs and their potential impact on waveforms for LISA.

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Weak gravitational lensing is a powerful statistical tool for probing the growth of cosmic structure and measuring cosmological parameters. However, as shown by studies such as by Ménard et al., dust in the circumgalactic region of halos dims and reddens background sources. In a weak lensing analysis, this selects against sources behind overdense regions; since there is more structure in overdense regions, we will underestimate the amplitude of density perturbations σ 8 if we do not correct for the effects of circumgalactic dust. To model the dust distribution we employ the halo model. Assuming a fiducial dust mass profile based on measurements from Ménard et al., we compute the ratio Z of the systematic error to the statistical error for a survey similar to the Nancy Grace Roman Space Telescope reference survey (2000 deg2 area, single-filter effective source density 30 galaxies arcmin−2). For a wave band centered at 1580 nm (H band), we find that Z H = 0.37. For a similar survey with wave band centered at 620 nm (r band), we also computed Z r = 2.8. Within our fiducial dust model, since Z r > 1, the systematic effect of dust will be significant on weak lensing image surveys. We also computed the dust bias on the amplitude of the power spectrum, σ 8, and found it to be for each wave band Δσ 8/σ 8 = −3.1 × 10−4 (H band) or −2.2 × 10−3 (r band) if all other parameters are held fixed (the forecast Roman statistical-only error σ(σ 8)/σ 8 is 9 × 10−4).