Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session Q10: Dark Matter and AstrophysicsLive
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Sponsoring Units: DAP Chair: Masha Baryakhtar, New York University Room: Roosevelt 5 |
Monday, April 20, 2020 10:45AM - 10:57AM Live |
Q10.00001: Applying Noether's Theorem to Matter in the Milky Way: Axisymmetry Tests with Gaia Data Release 2 Reveal External Perturbations and Non-Steady-State Effects Austin Hinkel, Susan Gardner, Brian Yanny Gaia Data Release 2 reveals the local structure of the Galaxy in unprecedented detail. In this talk, we show how axisymmetry tests of the Galaxy can be realized, and consider how these tests confront common assumptions in galactic dynamics. Namely, we apply Noether's theorem, vis-a-vis tests of axisymmetry, to probe the quality of the angular momentum about the axis normal to the Galactic plane as an integral of motion. The failure of this symmetry would speak to a Milky Way that is not isolated and/or not in steady-state. The axisymmetry-breaking pattern we have found reveals both effects, with a typical asymmetry of 0.5{\%}. We develop the selection of a data set suitable to such a study, avoiding regions with spiral arms and dust, and we evaluate the size of systematic effects with an estimated systematic asymmetry \textless 0.1{\%}. Finally, we present our recent results, highlighting how tests of axisymmetry can unearth various effects via their precise patterns of axisymmetry-breaking. For example, we note that a prolate form of the gravitational distortion of the Galaxy by the Magellanic Clouds, determined from Orphan stream fits by Erkal et al., 2019, is compatible with the axisymmetry-breaking we have discovered, suggesting a distortion of an emergent nature. [Preview Abstract] |
Monday, April 20, 2020 10:57AM - 11:09AM Live |
Q10.00002: Milky Way Satellite Census - Constraining Galaxy Formation and Dark Matter at the Smallest Scales Alex Drlica-Wagner Ultra-faint Milky Way satellite galaxies are the most ancient, most chemically pristine, and most dark-matter-dominated stellar systems ever observed. These extreme galaxies are critical to our understanding of galaxy formation and provide a unique opportunity to test the standard cold dark matter model of cosmology. Due to their low luminosity, the discovery of the faintest galaxies has only recently become possible thanks to the unprecedented sensitivity of digital sky surveys. I will describe a systematic search for ultra-faint satellite galaxies combining data from the Dark Energy Survey and the Pan-STARRS1 3pi Survey to cover $\sim$75\% of the high-Galactic-latitude sky. We apply the same search pipeline to a suite of simulated satellite galaxies to derive an observational selection function that describes the sensitivity and efficiency of our search. We then apply this selection function to cosmological zoom-in simulations to constrain the spatial anisotropy of the satellite population and a model of the galaxy--halo connection. Our analysis constrains the minimum mass of dark matter halos that host galaxies and the microphysics of dark matter (e.g., particle mass and interaction cross section). [Preview Abstract] |
Monday, April 20, 2020 11:09AM - 11:21AM Live |
Q10.00003: Implications of Triangular Features in the GAIA Sky Map for the Caustic Ring Model of the Milky Way Halo Yaqi Han, Sankha Charkrabarty, Pierre Sikivie, Anthony Gonzalez We interpret two triangular features in the GAIA map of the Milky Way as manifestations of the fifth caustic ring of dark matter in the Milky Way halo. The existence of a series of such rings was predicted by the Caustic Ring Model. The locations of the features imply that we on Earth are very close to the fifth caustic ring, much closer than thought on the basis of pre-GAIA observations. We are either just outside the tricusp structure associated with the 5th caustic ring, or inside. In the first case the dark matter density on Earth is dominated by a single cold flow, called the Big Flow. In the second case, there are two additional Big Flows, three altogether. We use the triangular features in the GAIA map and a matching feature in IRAS map to estimate the velocity vectors and densities of the Big Flows. [Preview Abstract] |
Monday, April 20, 2020 11:21AM - 11:33AM Live |
Q10.00004: The shapes of Milky-Way-mass galaxies with Self-Interacting Dark Matter Drona Vargya, Robyn Sanderson The cold dark matter plus dark energy ($\Lambda$CDM) cosmological model has been successful at reproducing the large-scale structure of the Universe. However, on length scales smaller than $\sim 1$ Mpc and halo masses smaller than $\sim 10^{11}$ M$_\odot$, this framework is challenged by observations that halos are less centrally dense than predicted. One way to reconcile these observations with theoretical predictions, without affecting the large-scale structure, is to consider self-interacting dark matter (SIDM) models. In order to incorporate the effects of both baryonic and SIDM interactions, we use the Feedback in Realistic Environments (FIRE-2) suite of Milky-Way-mass galaxies on a cosmological background and compare the shapes of the main dark matter halo predicted by SIDM simulations (at interaction cross-sections $\sigma/m$ of 1, 10, and 50 cm$^2$ g$^{-1}$) with CDM simulations using the same initial conditions. Even in the presence of baryonic feedback effects, we find that SIDM models produce potentially detectable differences in the inner structure of MW-mass galaxies. [Preview Abstract] |
Monday, April 20, 2020 11:33AM - 11:45AM Live |
Q10.00005: Gravitational searches for compact dark matter objects Charles Horowitz, Rudolf Widmer-Schnidreg Dark matter could be composed of compact dark objects (CDOs). These objects may interact very weakly with normal matter and could move freely {\it inside} astronomical bodies. We calculate the expected gravitational wave (GW) signal for a CDO merging with a galactic neutron star. We search data from the first advanced LIGO observing run for GWs from close CDO binaries orbiting inside the Sun. A CDO moving in the inner core of the Earth will have an orbital period near 55 min and produce a time dependent signal in a gravimeter. Data from superconducting gravimeters rule out such objects moving inside the Earth unless their mass $m_D$ and or orbital radius $a$ are very small so that $m_D\, a <1.2\times 10^{-13} M_E R_E$. Here $M_E$ and $R_E$ are the mass and radius of the Earth [1912.00940, Phys. Rev. Let. in press]. [Preview Abstract] |
Monday, April 20, 2020 11:45AM - 11:57AM Live |
Q10.00006: Sexaquark Dark Matter: Direct detection, astro and CMB constraints; exotic isotope predictions; self-interactions Xingchen Xu, Glennys Farrar In the Sexaquark Dark Matter scenario, DM is composed of six quarks (uuddss) and interacts with baryons by meson exchange. The observed DM-to-baryon density ratio is a consequence of QCD and is naturally preserved to late time (contrary to the conclusions of [arXiv:1809.06003]); SN1987a cooling is also not a problem. Unlike in the more commonplace weakly-coupled DM models, the SDM-baryon interaction is non-perturbative in much of the natural parameter space and therefore cannot be treated using Born approximation. The nuclear form factor and cross section scaling with atomic mass used in the literature are invalid and the SDM-baryon cross section exhibits resonant behavior. We re-evaluate the possible SDM parameter space, imposing constraints from XQC, CMB and dewar experiments; the most natural and interesting parameter region is allowed. If the interaction is attractive, S-nucleus bound states which appear as exotic isotopes can form. We examine the production of such isotopes in BBN as well as in Earth, and conclude that a ppb level abundance of exotic isotopes with mass-offset about 2 amu is natural but not inevitable in the Earth. We also explore the possibility of sexaquark as a realization of self-interacting dark matter and study its astrophysical consequences. [Preview Abstract] |
Monday, April 20, 2020 11:57AM - 12:09PM Live |
Q10.00007: New Experimental Constraints in a New Landscape for Composite Dark Matter Christopher Cappiello, Juan Collar, John Beacom Recently, it was shown that the scattering cross sections for pointlike dark matter with nuclei cannot be significantly larger than the geometric cross sections of these nuclei. This invalidates many claimed experimental constraints on strongly interacting dark matter, leaving a large window of high-cross section parameter space unprobed. The only way for dark matter to have a cross section in this parameter space is for it to be a composite particle, with a geometric size much larger than that of a nucleus. We use a liquid scintillator-based dark matter detector to set new constraints on heavy, composite dark matter, closing off much of the newly enlarged window in dark matter parameter space. [Preview Abstract] |
Monday, April 20, 2020 12:09PM - 12:21PM Not Participating |
Q10.00008: Assessing Mixed Sterile Neutrino Dark Matter Models Isabella Ianora, Anton Navazo, Chad Kishimoto Recent X-ray observations of galaxies and galaxy clusters suggest the existence of sterile neutrino dark matter with a mass of 7.1 keV. However, there is tension between calculated dark matter spectra and observations of small scale structure. In this talk, I will discuss a variety of mixed dark matter models, comprised of both cold dark matter and sterile neutrinos, whose inferred parameters are consistent with the X-ray observations.We assess the compatibility of these models in comparison to cosmological observables. [Preview Abstract] |
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