### David Nichols

*Ph.D., 2012, California Institute of Technology *

*Assistant Professor*

*Theoretical Astrophysics, Gravity and Cosmology*

#### Research Interests

Gravitational waves from the mergers of several stellar-mass black-hole and neutron-star binaries have now been detected by the LIGO and Virgo collaborations. These observations have opened a new method for observing the Universe. With them, and the many detections that are expected to follow in the upcoming years, one can now study the properties of strongly gravitating objects and rapidly changing space and time. Determining the predictions of Einstein's theory of relativity for these systems and understanding how these predictions can be extracted from gravitational-wave measurements are the main areas of my research. In the past few years, I have focused primarily in the following three aspects of this field:

- I am interested in a class of gravitational-wave effects that persist even after a burst of gravitational waves have passed. Called "gravitational-wave memory effects" or "persistent gravitational-wave observables," these phenomena are closely connected to the symmetries and conserved quantities of spacetimes that become flat asymptotically. I have worked on understanding these effects, computing their magnitudes from astrophysical binaries, and forecasting when they could be measured by gravitational-wave detectors.
- I have also been investigating when the presence of dark matter around intermediate-mass or supermassive black holes can influence the inspiral of a second small compact object (a so-called intermediate- or extreme-mass-ratio inspiral). My collaborators and I have found scenarios in which these environmental effects can be significant, primarily because of a dissipative effect called dynamical friction and because of accretion of dark matter onto the secondary (when the secondary is a black hole).
- I am interested in combining information from gravitational-wave mergers of neutron stars with the complementary information from their associated electromagnetic counterparts. I have focused primarily on the radio and x-ray observations of short-gamma-ray-burst afterglows and kilonova afterglows, although I am interested more generally in counterparts of any wavelength.

My webpage contains more information about my past and current research.

#### Selected Publications

- D. A. Nichols, B. Wade, and A. M. Grant. "Secondary accretion of dark matter in intermediate mass-ratio inspirals: Dark-matter dynamics and gravitational-wave phase." Phys. Rev. D 108, 124062 (2023). arXiv:2309.06498.
- E. E. Flanagan and D. A. Nichols. "Fully nonlinear transformations of the Weyl-Bondi-Metzner-Sachs asymptotic symmetry group," (2023). arXiv:2311.03130.
- A. M. Grant and D. A. Nichols. "Outlook for detecting the gravitational wave displacement and spin memory effects with current and future gravitational wave detectors." Phys. Rev. D 107, 064056 (2023). [Erratum: Phys. Rev. D 108, 029901 (2023).] arXiv:2210.16266.
- L. Piro et al. "Multi-messenger Athena Synergy White Paper." Exp. Astron. 54, 23-117 (2022). arXiv:2205.01597.
- A. M. Grant and D. A. Nichols. "Persistent gravitational-wave observables: Curve deviation in asymptotically flat spacetimes." Phys. Rev. D 105, 024056 (2022). arXiv:2109.03832.
- A. Coogan, G. Bertone, D. Gaggero, B. J. Kavanagh, and D. A. Nichols. "Measuring the dark matter environments of black hole binaries with gravitational waves." Phys. Rev. D 105, 043009 (2022). arXiv:2108.04154.
- S. Tahura, D. A. Nichols, and K. Yagi. "Gravitational-wave memory effects in Brans-Dicke theory: Waveforms and effects in the post-Newtonian approximation." Phys. Rev. D 104, 104010, (2021). arXiv:2107.02208.
- A. Elhashash and D. A. Nichols. "Definitions of angular momentum and super angular momentum in asymptotically flat spacetimes: Properties and applications to compact binaries." Phys. Rev. D 104, 024020 (2021), arXiv:2101.12228.
- S. Tahura, D. A. Nichols, A. Saffer, L. C. Stein, and K. Yagi. "Brans-Dicke theory in Bondi-Sachs form: Asymptotically flat solutions, asymptotic symmetries and gravitationalwave memory effects." Phys. Rev. D 104, 104026, (2021), arXiv:2007.13799.
- B. J. Kavanagh, D. A. Nichols, G. Bertone, and D. Gaggero. "Detecting dark matter around black holes with gravitational waves: Effects of dark-matter dynamics on the gravitational waveform." Phys. Rev. D 102, 083006 (2020), arXiv:2002.12811.
- O. M. Boersma, D. A. Nichols, and P. Schmidt. "Forecasts for detecting the gravitational-wave memory effect with Advanced LIGO and Virgo." Phys. Rev. D 101, 083026 (2020), arXiv:2002.01821.
- E. E. Flanagan, A. M. Grant, A. I. Harte, and D. A. Nichols. “Persistent gravitational-wave observables: Nonlinear plane wave spacetimes.” Phys. Rev. D 101, 104033 (2020), arXiv:1912.13449.
- E. E. Flanagan, A. M. Grant, A. I. Harte, and D. A. Nichols. “Persistent gravitational-wave observables: General framework.” Phys. Rev. D 99, 084004 (2019), arXiv:1901.00021.
- T. Hinderer, et al. “Discerning the binary neutron star or neutron star-black hole nature of GW170817 with Gravitational Wave and Electromagnetic Measurements.” arXiv:1808.03836.
- D. A. Nichols. “Center-of-mass angular momentum and memory effect in asymptotically flat spacetimes.” Phys. Rev. D 98, 064032 (2018), arXiv:1807.08767.
- D. A. Nichols. “Spin memory effect for compact binaries in the post-Newtonian approximation.” Phys. Rev. D 95, 084048 (2017), arxiv:1702.03300.
- E. E. Flanagan and D. A. Nichols. “Conserved charges of the extended Bondi-Metzner-Sachs algebra.” Phys. Rev. D 95, 044002 (2017), arxiv:1510.03386.

#### News Items

#### Honors

**ORAU Ralph E. Powe Award**[2021]