Bulletin of the American Physical Society
Four Corners Section 2022 Meeting
Volume 67, Number 14
Friday–Saturday, October 14–15, 2022; Albuquerque, New Mexico
Session B02: Gravitation / Cosmology I |
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Chair: Rouzbeh Allahverdi, UNM Room: UNM PAIS 1140 |
Friday, October 14, 2022 10:00AM - 10:24AM |
B02.00001: A Symmetry of Cosmological Observables: Looking at Hubble through the Mirror Invited Speaker: Francis-Yan Cyr-Racine
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Friday, October 14, 2022 10:24AM - 10:36AM |
B02.00002: The Characteristic Problem in Ideal GRMHD James Bleazard, Eric W Hirschmann, Matthew R Robinson, Justin C Tackett We consider the characteristic problem in ideal general relativistic magnetohydrodynamics. Combining the fluid and Maxwell equations, we have verified the characteristic equation their wave speeds. We provide corrections to a previous calculation of the eigenvector and its wave speeds. Having calculated all the left and right eigenvectors, we are now in a position to be able to explore the variety of motions within relativistic charged fluids. We consider on possible applications of the full characteristic decomposition in multi-messenger astronomy, high resolution shock capturing techniques and high energy astrophysical systems such as jet launching, and the modelling accretion disks around black holes. We discuss future work on applying strategies for constraint damping. This is to reduce errors in the numerical approach so that constraint violations are minimized. |
Friday, October 14, 2022 10:36AM - 10:48AM |
B02.00003: Constraint Damping in the Characteristic Problem of Ideal GRMHD Matthew R Robinson, Eric W Hirschmann, James Bleazard, Justin C Tackett We investigate the characteristic problem of ideal general relativistic magnetohydrodynamics (GRMHD). We build on previous work that uses conservation laws and Maxwell's equations in an arbitrary, dynamic spacetime to find the characteristic equation and wave speeds for modeling GRMHD numerically. Such simulated systems can accumulate errors from multiple sources as they evolve. This can eventually cause the solution to become non-physical. There are a number of approaches to constrain and even dynamically reduce this error. Here, we discuss extending earlier work on the characteristic problem in GRMHD by including constraint damping of the ∇ · Β = 0 (no magnetic monopoles) constraint. We also consider an approach by which we renormalize the left and right eigenvectors to handle degenerate cases. Taken together, these approaches to GRMHD systems will have bearing on simulations which incorporate high-resolution shock capturing techniques to model jet launching, accretion disks around black holes, and other high-energy astrophysical phenomenon like neutron star mergers. |
Friday, October 14, 2022 10:48AM - 11:00AM |
B02.00004: The Cosmological Constant and the Characteristic Development of Trapped Surfaces Paul N Demmie TThe cosmological constant is a model of dark energy that is one explanation for the accelerated expansion of the universe. The concept of a trapped surface provides a precise characterization of gravitational collapse that has proceeded beyond the point of no return, resulting in a black hole. Therefore, because of its importance, we examined spherically-symmetric spacetimes with a cosmological constant to determine its impact on the characteristic development of trapped surfaces. The principal result of this study is a relationship between the mass (m) and the cosmological constant (Λ) that is a necessary and sufficient condition for trapped surfaces to develop to the future of a branch of a perfect null hypersurface. For the cosmological constant obtained from the Planck-satellite data, there is a maximum mass for a black hole. We determined the value for the cosmological constant for a Planck-mass black hole and showed that it is 120 orders of magnitude larger than the cosmological constant obtained from the Planck-satellite data. Finally, we argue that that our universe is too massive to be closed and spatially bounded given the value of the cosmological constant obtained from these data. |
Friday, October 14, 2022 11:00AM - 11:12AM |
B02.00005: Probing Dark Matter with Strong Gravitational Lensing Anisotropies Birendra Dhanasingham, Francis-Yan Cyr-Racine, Annika Peter, Andrew Benson, Daniel Gilman Strong gravitational lensing provides a promising way to look for clues to the elusive particle nature of dark matter. Indeed, subtle perturbations to lensed images can reveal the dark-matter distribution on sub-galactic scales. In addition to the subhalos of the main lens, a significant contribution to these perturbations comes from dark matter halos along the line-of-sight between the observer and the source. Handling these multiplane lensing effects is computationally expensive. Here we introduce a new approach called "effective multiplane gravitational lensing" to study the collective effect of line-of-sight halos and main-lens dark matter substructure on extended lensed arcs. In this approach, the lens mapping between the source and image planes can be fully characterized by two "effective" lensing potentials encompassing the complete structure of the deflection field, and the line-of-sight halos and main-lens substructure contribute differently to each potential. Using this approach, we point out that line-of-sight halos between the observer and the source imprint a previously unstudied quadrupolar signature in the two-point correlation function of the effective convergence field. Our approach based on this anisotropic signal has the potential to statistically distinguish the line-of-sight halo contribution to lensing perturbations from that of main-lens subhalos in a strongly lensed system, hence significantly improving the constraint on dark matter from strong gravitational lensing. |
Friday, October 14, 2022 11:12AM - 11:24AM |
B02.00006: A Classification of Spacetime Symmetries Compatible with a Generic Lagrangian Guillermo Frausto, Charles G Torre Symmetry reduction is an important tool for simplifying physical problems. But in some cases, symmetry reducing the Lagrangian may lead to incorrect equations. When this issue occurs, a symmetry is said to violate the principle of symmetric criticality (PSC). It's known that for PSC to hold in a local field theory, two conditions must be true (the Palais and Lie conditions), but for most spacetime symmetries, the validity of PSC has not been established. In this project, we provide a classification of spacetime symmetries based upon the validity of PSC for gravitational field theory. Using the DifferentialGeometry package in Maple, we tested both PSC conditions against a database listing all 92 possible spacetime symmetries. We found that over half of all spacetime symmetries violate PSC, with most obstructions coming from the boundary term of the first variational formula. The conditions used here are from a Lagrangian built locally from a metric field, but in the future, a similar analysis could be done for a Lagrangian built from additional fields. This classification will allow researchers to avoid pitfalls when using symmetry reduction in exotic gravitational problems. |
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