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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 $\psi_4$ at the horizon and at $\infty$) 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., Comment: 19 pages, 5 figures, 1 table, to be submitted to PRD

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 M\'enard et al. (2010), dust in the circumgalactic region of haloes 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 $\sigma_8$ 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 M\'enard et al. (2010), 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 deg$^2$ area, single-filter effective source density 30 galaxies arcmin$^{-2}$). For a waveband centered at $1580$ nm ($H$-band), we find that $Z_{H} = 0.47$. For a similar survey with waveband centered at $620$ nm ($r$-band), we also computed $Z_{r} = 3.6$. 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, $\sigma_{8}$, and found it to be for each waveband $\Delta \sigma_8/\sigma_8 = -3.9\times 10^{-4}$ ($H$ band) or $-2.9\times 10^{-3}$ ($r$ band) if all other parameters are held fixed (the forecast Roman statistical-only error $\sigma(\sigma_8)/\sigma_8$ is $9\times 10^{-4}$)., Comment: 17 pages, 9 figures

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 M\'enard et al. (2010), dust in the circumgalactic region of haloes 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 $\sigma_8$ 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 M\'enard et al. (2010), 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 deg$^2$ area, single-filter effective source density 30 galaxies arcmin$^{-2}$). For a waveband centered at $1580$ nm ($H$-band), we find that $Z_{H} = 0.37$. For a similar survey with waveband 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, $\sigma_{8}$, and found it to be for each waveband $\Delta \sigma_8/\sigma_8 = -3.1\times 10^{-4}$ ($H$ band) or $-2.2\times 10^{-3}$ ($r$ band) if all other parameters are held fixed (the forecast Roman statistical-only error $\sigma(\sigma_8)/\sigma_8$ is $9\times 10^{-4}$)., Comment: 17 pages, 8 figures

In the field of astronomy, Maunakea is known as a prestigious site for observing and science. In Native Hawaiian culture, Maunakea is revered as the connection between past, present, and future generations and their ancestral lands of Hawai'i. We have reached a juncture at which it is necessary to allow and enable Native Hawaiians to pursue careers in astronomy, especially on Maunakea. This paper serves to tell the accounts of four Kanaka astronomers and raise awareness of the barriers they have faced while pursuing astronomy careers. The authors identify issues that the community faces due to the disconnect between astronomy and Hawai'i communities and propose resolutions to lead the way forward., Comment: Submitted to the National Academy of Sciences Decadal Survey on Astronomy and Astrophysics (Astro2020) Panel on the State of the Profession and Societal Impacts (SoP)

In the field of astronomy, Maunakea is known as a prestigious site for observing and science. In Native Hawaiian culture, Maunakea is revered as the connection between past, present, and future generations and their ancestral lands of Hawai'i. We have reached a juncture at which it is necessary to allow and enable Native Hawaiians to pursue careers in astronomy, especially on Maunakea. This paper serves to tell the accounts of four Kanaka astronomers and raise awareness of the barriers they have faced while pursuing astronomy careers. The authors identify issues that the community faces due to the disconnect between astronomy and Hawai'i communities and propose resolutions to lead the way forward., Comment: Submitted to the National Academy of Sciences Decadal Survey on Astronomy and Astrophysics (Astro2020) Panel on the State of the Profession and Societal Impacts (SoP)

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 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. This methodology has been successfully applied before for exploring magnetic fields in solar coronal filaments. 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 more than a few $\times 10^{-4}$ 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 $\sqrt{Q^2+U^2}/I$ ranges from $\sim 10^{-3}$ in optimistic cases down to a few $\times 10^{-5}$ 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 $V/I\sim {\rm few}\times 10^{-5}(B_\parallel/10\,{\rm G})$. We discuss the detectability of these signals with current (SPIRou) and future (extremely large telescope) high-resolution infrared spectropolarimeters, and we briefly comment on possible sources of astrophysical contamination., Comment: published in The Astrophysical Journal on February 14, 2020; updated to match the published version

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 $3.5\times 10^{-17}M_\odot < m_{\mathrm{PBH}} < 4\times 10^{-12}M_\odot$. 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, $m_{\mathrm{PBH}}$ and the event duration. We argue that it will be difficult to push the existing optical microlensing constraints to much lower m$_{\mathrm{PBH}}$. (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 asteroid-mass 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 remains open for PBHs to account for all the dark matter., Comment: Updated to match accepted version for publication. 43 pages

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 $3.5\times 10^{-17}M_\odot < m_{\mathrm{PBH}} < 4\times 10^{-12}M_\odot$. 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, $m_{\mathrm{PBH}}$ and the event duration. We argue that it will be difficult to push the existing optical microlensing constraints to much lower m$_{\mathrm{PBH}}$. (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 asteroid-mass 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 remains open for PBHs to account for all the dark matter., Comment: Updated to match accepted version for publication. 43 pages

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 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. This methodology has been successfully applied before for exploring magnetic fields in solar coronal filaments. 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 more than a few $\times 10^{-4}$ 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 $\sqrt{Q^2+U^2}/I$ ranges from $\sim 10^{-3}$ in optimistic cases down to a few $\times 10^{-5}$ 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 $V/I\sim {\rm few}\times 10^{-5}(B_\parallel/10\,{\rm G})$. We discuss the detectability of these signals with current (SPIRou) and future (extremely large telescope) high-resolution infrared spectropolarimeters, and we briefly comment on possible sources of astrophysical contamination., Comment: published in The Astrophysical Journal on February 14, 2020; updated to match the published version