Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session T16: SelfForce and PostGeodesic MotionRecordings Available

Hide Abstracts 
Sponsoring Units: DGRAV Chair: Sarah Gossan, Canadian Institute for Theoretical Astrophysics Room: Sky Lobby 
Monday, April 11, 2022 3:45PM  3:57PM 
T16.00001: Dissipation due to the (notso) conservative selfforce for resonant extrememassratio inspirals Zachary Nasipak The inspiral of a small compact object into a massive black hole, or an extrememassratio inspiral (EMRI), is often modeled using selfforce theory. In selfforce theory, a small body orbiting in a stationary gravitational background experiences a selfforce due its own perturbing (gravitational, scalar, and/or electromagnetic) field. This selfforce, in turn, sources the small body's motion. One often separates this selfforce into two pieces: a (timeantisymmetric) dissipative component, which is responsible for the inspiral, and a (timesymmetric) conservative component, which typically perturbs the small body's orbit without driving its inspiral. However, using a scalar model, we numerically demonstrate that when a scalar pointcharge enters a resonant orbit about a Kerr black hole (i.e., its radial and polar orbital frequencies form a rational ratio), the conservative scalar selfforce becomes notso conservative and can contribute to the dissipation of the Carter constant, thus driving the system away from the resonance. We analyze the strength of the conservative selfforce contributions for different resonances and discuss how these results inform future EMRI models. 
Monday, April 11, 2022 3:57PM  4:09PM 
T16.00002: Kerr selfforce via elliptic PDEs Thomas Osburn Our longterm goal is to calculate the Lorenz gauge gravitational selfforce for an extreme massratio binary system in Kerr spacetime. Prior time domain efforts encountered catastrophic instabilities, which we overcome by entering the frequency domain and solving elliptic PDEs. To develop techniques, we first consider the selfforce exerted on a scalar charge in Kerr spacetime via the effective source method. Challenges include handling a large sparse linear system and how imperfect boundary conditions can introduce errors that pollute the entire domain. We have applied various techniques to overcome these challenges, such as analyzing the boundary behavior to impose more sophisticated boundary conditions with improved accuracy. Various preliminary selfforce results will be presented and discussed. 
Monday, April 11, 2022 4:09PM  4:21PM 
T16.00003: Postgeodesic corrections to the selfforce during EMRIs Luis M Yanez Zamora We quantified how past orbital behavior affects the selfforce during an extreme massratio inspiral. We expanded the metric to first order in the mass ratio using black hole perturbation theory, and used a twotimescale expansion of the ReggeWheeler equation to access nongeodesic corrections to the metric perturbation. The asymptotic coefficients of higher order terms in the twotimescale expansion provide energy and angular momentum fluxes, which we used to calculate postgeodesic selfforce corrections. We present preliminary results demonstrating the verified asymptotic coefficients and corrections to the selfforce. 
Monday, April 11, 2022 4:21PM  4:33PM 
T16.00004: A discontinuous Galerkin method for the distributionallysourced s=0 Teukolsky equation MANAS VISHAL, Scott E Field, Gaurav Khanna, Katie Rink Extreme Mass Ratio Inspirals (EMRI) will be an important astrophysical source for the upcoming gravitational wave detector Laser Interferometer Space Antenna (LISA). EMRI systems are characterized by mass ratios greater than 10^{4} and will be in the detector's sensitive band for hundreds of thousands of orbital cycles. Numerical relativity codes cannot be used to simulate such systems, so pointparticle black hole perturbation theory (ppBHPT) is typically used instead. For perturbations of Kerr, timedomain numerical solvers for the Teukolsky equation have traditionally been based on loworder finitedifference methods. In this talk I will discuss a spectrallyaccurate Discontinuous Galerkin method for the distributionallyforced Teukolsky equation. Importantly, the method maintains spectral accuracy even at the location of the delta function. I will present numerical results from the code, including the computation of Price tails and scalar field evolutions from a perturbing black hole in a circular orbit. 
Monday, April 11, 2022 4:33PM  4:45PM 
T16.00005: Particle motion under the conservative piece of the firstorder gravitational selfforce is Hamiltonian Francisco M Blanco, Eanna E Flanagan The two body problem in general relativity is of great theoretical and observational interest, and can be studied in the postNewtonian, postMinkowskian and small massratio approximations, as well as with effective onebody and fully numerical techniques. When gravitational wave dissipation is turned off, motion is expected to form a Hamiltonian dynamical system. This has been established to various orders in the postNewtonian and postMinkowskian approximations, but not yet in the small massratio regime beyond the leading order of geodesic motion. We show that the motion under the conservative (time even) piece of the firstorder selfforce is Hamiltonian in any stationary spacetime, and find an explicit expression for the Hamiltonian in terms of a Green's function. In Kerr, this result extends previous results of Fujita et. al. who derived a Hamiltonian description valid only for nonresonant orbits. As applications, we derive a simple necessary condition that the selfforce must satisfy for the motion to be integrable and clarify the domain of validity of the first law of binary black hole mechanics in the small massratio regime. 
Monday, April 11, 2022 4:45PM  4:57PM 
T16.00006: Precisely computing bound orbits of spinning bodies around black holes Lisa V Drummond, Scott A Hughes, Alexandra G Hanselman Very large massratio binary black hole systems are of interest as a clean limit of the twobody problem in general relativity, as well as for describing important lowfrequency gravitational wave (GW) sources. At lowest order, the smaller black hole follows a geodesic of the larger black hole's spacetime. Accurate models of large massratio systems include postgeodesic corrections which account for forces driving the small body away from the geodesic. Spincurvature forces, which arise due to the coupling of a test body's spin to the spacetime curvature, is an example of such an effect. In a previous talk, we outlined a frequencydomain method for precisely computing bound orbits of spinning test bodies experiencing spincurvature forces. In this talk, we show how to apply this approach to the fully generic case, in which orbits are inclined and eccentric and with the small body's spin arbitrarily oriented. An osculating geodesic integrator that includes both spincurvature forces and the backreaction due to GWs can be used to generate an adiabatic spinningbody inspiral. We present preliminary results combining the osculating element description with the tetrad formulation for Kerr parallel transport to build a framework for completely generic worldlines of spinning bodies. 
Monday, April 11, 2022 4:57PM  5:09PM 
T16.00007: Eccentric selfforced inspirals into a rotating black hole Philip A Lynch, Niels Warburton, Maarten van de Meent We develop the first model for extreme massratio inspirals (EMRIs) into a rotating massive black hole driven by the gravitational selfforce (GSF).Our model is based on an action angle formulation of the method of osculating geodesics for eccentric, equatorial motion in Kerr spacetime.The forcing terms are provided by an efficient spectral interpolation of the firstorder GSF in the outgoing radiation gauge. We apply a nearidentity (averaging) transformation to eliminate all dependence of the orbital phases from the equations of motion, while maintaining all secular effects of the firstorder GSF at postadiabatic order. As such, the model can be evolved without having to resolve all ~10^6 orbit cycles of an EMRI, yielding an inspiral that can be evaluated in less than a second for any massratio. In the case of a nonrotating black hole, we compare inspirals evolved using GSF data computed in the Lorenz and radiation gauges. We find that the two gauges produce differing inspirals with a deviation of comparable magnitude to the conservative GSF correction. This emphasizes the need for including the dissipative second order GSF to obtain gauge independent, postadiabatic waveforms. 
Monday, April 11, 2022 5:09PM  5:21PM 
T16.00008: Hyperboloidal method for frequencydomain selfforce calculations Benjamin J Leather, Rodrigo Panosso Macedo, Niels Warburton, Barry Wardell, Anil Zenginoglu Gravitational selfforce theory is the leading approach for modelling gravitational wave emission from small massratio compact binaries. This method perturbatively expands the metric of the binary in powers of the mass ratio. The source for the perturbations depends on the orbital configuration, calculational approach, and/or the order the perturbative expansion is carried too. These sources fall into three broad classes: distributional, extended and compact, and noncompact. The latter, in particular, is important for emerging secondorder in the mass ratio calculations. Traditional frequency domain approaches employ the variation of parameters method and compute the perturbation on constant time slices of the spacetime with numerical boundary conditions supplied at finite radius from series expansions of the asymptotic behaviour. This approach has been very successful but the boundary conditions calculations are tedious and the approach is not well suited to noncompact sources where homogeneous solutions must be computed at all radii. In this talk, I outline an alternative approach where the spacetime is foliated by horizonpenetrating hyperboloidal slices. Further compactifying the coordinates along these slices allows for simple treatment of the boundary conditions. We implement this approach with a multidomain spectral solver with analytic mesh refinement and present results for the scalarfield selfforce on circular orbits as an example problem. We find the method works efficiently for all three classes of sources encountered in selfforce calculations and has some distinct advantages over the traditional approach. 
Monday, April 11, 2022 5:21PM  5:33PM 
T16.00009: Gravitational waveforms for compact binaries from secondorder selfforce theory Barry Wardell, Adam Pound, Niels Warburton, Jeremy Miller, Leanne Durkan, Alexandre Le Tiec We produce gravitational waveforms for nonspinning compact binaries undergoing a quasicircular inspiral. Our approach is based on a twotimescale expansion of the Einstein equations in secondorder selfforce theory, which allows firstprinciples waveform production in milliseconds. Although the approach is designed for extreme mass ratios, our waveforms agree remarkably well with those from full numerical relativity, even for comparablemass systems. Our results will be invaluable in accurately modelling extrememassratio inspirals for the LISA mission and intermediatemassratio systems currently being observed by the LIGOVirgoKAGRA Collaboration. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2024 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700