Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session U5: Gravitational Waves and Dark MatterFocus
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Sponsoring Units: DAP Chair: Paul Shapiro, University of Texas Room: Virginia B |
Monday, January 30, 2017 3:30PM - 4:06PM |
U5.00001: The LIGO Discovery and Primordial Black Hole Dark Matter Invited Speaker: Ely Kovetz The LIGO observatory has recently reported several detections of gravitational waves from the coalescence of binary black holes. We consider the extraordinary possibility that the detected events involving heavier masses are mergers of primordial black holes making up the dark matter in the Universe. We will describe various ways of testing this proposition once more gravitational wave data is gathered, survey some of the existing constraints and present a novel probe of massive compact dark matter in the relevant mass range based on strong gravitational lensing of fast radio bursts. We will conclude with a summary of observational prospects to constrain the proposed scenario in the next decade. [Preview Abstract] |
Monday, January 30, 2017 4:06PM - 4:18PM |
U5.00002: Did LIGO Detect Dark Matter? Simeon Bird, Ilias Cholis, Julian Munoz, Yacine Ali-Haimoud, Marc Kamionkowski, Ely Kovetz, Alvise Raccanelli, Adam Riess There is a possibility that the recent LIGO detection of gravitational waves originated from the merger of two primordial black holes, making up the dark matter. Thirty solar mass black holes, as detected by LIGO, lie within an allowed mass window for primordial black hole dark matter. Interestingly, our best estimates of the number of observable mergers fall within the range implied by current LIGO data. I will explain these estimates and discuss the (considerable!) theoretical uncertainties. [Preview Abstract] |
Monday, January 30, 2017 4:18PM - 4:30PM |
U5.00003: Constraints on MACHO Dark Matter from Compact Stellar Systems in Ultra-Faint Dwarf Galaxies Timothy Brandt I show that a recently discovered star cluster near the center of the ultra-faint dwarf galaxy Eridanus II provides strong constraints on massive compact halo objects (MACHOs) of $>$5 $M_\odot$ as the main component of dark matter. MACHO dark matter will dynamically heat the cluster, driving it to larger sizes and higher velocity dispersions until it dissolves into its host galaxy. The stars in compact ultra-faint dwarf galaxies themselves will be subject to the same dynamical heating; the survival of at least ten such galaxies places independent limits on MACHO dark matter of masses $>$10 $M_\odot$. Both Eri II's cluster and the compact ultra-faint dwarfs are characterized by stellar masses of just a few thousand $M_\odot$ and half-light radii of 13 pc (for the cluster) and $\sim$30 pc (for the ultra-faint dwarfs). These systems close the $\sim$20$-$100 $M_\odot$ window of allowed MACHO dark matter and combine with existing constraints from microlensing, wide binaries, and disk kinematics to rule out dark matter composed entirely of MACHOs from $\sim$10$^{-7}$ $M_\odot$ up to arbitrarily high masses. [Preview Abstract] |
Monday, January 30, 2017 4:30PM - 4:42PM |
U5.00004: Effect of Primordial Black Holes on the Cosmic Microwave Background and Cosmological Parameter Estimates Massimo Ricotti, Jeremiah Ostriker, Katherine Mack We investigate the effect of nonevaporating primordial black holes (PBHs) on the ionization and thermal history of the universe. X-rays emitted by gas accretion onto PBHs modify the cosmic recombination history, producing measurable effects on the spectrum and anisotropies of the cosmic microwave background (CMB). Using the third-year WMAP data and COBE FIRAS data we improve existing upper limits on the abundance of PBHs with masses $>0.1$ M$_\odot$ by several orders of magnitude, thus ruling out PBHs in this mass range as a significant component of the dark matter. Fitting WMAP/Planck data with cosmological models that do not allow for nonstandard recombination histories, as produced by PBHs or other early energy sources, leads to underestimating the best-fit values of the amplitude of linear density fluctuations ($\sigma_8$) and the scalar spectral index ($n_s$). We find that a fraction $>0.1\%-1\%$ of the dark matter in $30$ M$_\odot$ PBHs produces CMB spectral distortions at a level detectable by FIRAS. Therefore, even allowing for possible modeling uncertainties, future missions measuring CMB spectral distortions will detect the imprint of dark matter if it’s composed of $\sim 30$ M$_\odot$ PBHs, as suggested to interpret recent LIGO results. [Preview Abstract] |
Monday, January 30, 2017 4:42PM - 4:54PM |
U5.00005: Pulsar timing can constrain primordial black hole dark matter in the LIGO mass window Katelin Schutz The recent discovery of gravitational waves from co-orbiting black holes has rekindled an interest in primordial black holes (PBHs) as a possible component of the dark matter (DM). In this paper, we show that existing proposals for probing DM substructure can also constrain the abundance of primordial black holes in the local Galactic halo. Specifically, pulsar timing arrays may already have sufficient data to constrain $1$-$1000\,M_\odot$ PBHs via the non-detection of their Shapiro time delay as the black holes move around the Galactic halo. We present the results of a simulation which suggests that existing data may already be capable of constraining the PBH density more stringently than other recently proposed methods for doing so. [Preview Abstract] |
Monday, January 30, 2017 4:54PM - 5:06PM |
U5.00006: Searching for the QCD Axion with Black Holes and Gravitational Waves Masha Baryakhtar The LIGO detection of gravitational waves has opened a new window on the universe. I will discuss how the process of superradiance, combined with gravitational wave measurements, makes black holes into nature's laboratories to search for new light bosons. When a bosonic particle's Compton wavelength is comparable to the horizon size of a black hole, superradiance of these bosons into bound "Bohr orbitals" extracts energy and angular momentum from the black hole. The occupation number of the levels grows exponentially and the black hole spins down. For efficient superradiance of stellar black holes, the particle must be ultralight, with mass below $10^{-10}$ eV; one candidate for such an ultralight boson is the QCD axion with decay constant above the GUT scale. Measurements of BH spins in X-ray binaries and in mergers at Advanced LIGO can exclude or provide evidence for an ultralight axion. Axions transitioning between levels of the gravitational "atom" and annihilating to gravitons may produce thousands of monochromatic gravitational wave signals, turning LIGO into a particle detector. [Preview Abstract] |
Monday, January 30, 2017 5:06PM - 5:18PM |
U5.00007: Complex scalar field dark matter and its impact on detectability of the stochastic gravitational wave background from inflation Tanja Rindler-Daller, Bohua Li, Paul Shapiro We consider an alternative dark matter candidate to WIMP-CDM, ultralight bosonic dark matter ($m\geq 10^{-22}$ eV) described by a complex scalar field (SFDM). In a $\Lambda$SFDM universe, SFDM starts relativistic, evolving from a maximal stiff equation of state to radiation-like, before becoming nonrelativistic at late times. The SFDM particle parameters, mass and selfinteraction coupling strength, are therefore constrained by cosmological observables, esp. $N_\rm{eff}$, the effective number of neutrino species during BBN, and the redshift of matter-radiation equality. Furthermore, since the energy density contributed by the stochastic gravitational wave background (SGWB) from inflation is amplified during the stiff phase, this makes possible the detection of this SGWB at high frequencies by current experiments, e.g. aLIGO/Virgo and eLISA. We show that, for SFDM particle parameters that satisfy those cosmological constraints, the amplified SGWB is detectable by aLIGO, for values of tensor-to-scalar ratio $r$ currently allowed by CMB polarization measurements, for a broad range of possible reheat temperatures. A nondetection by aLIGO O1 would provide a new kind of cosmological constraint on SFDM. Also, a wider range of parameters and reheat temperatures will be probed by aLIGO O5. [Preview Abstract] |
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