Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session H14: Cosmology I: Large-Scale Structure, Dark Matter, and Dark Energy |
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Sponsoring Units: DAP Chair: Cora Dvorkin, University of Chicago Room: Key 10 |
Sunday, April 12, 2015 8:30AM - 8:42AM |
H14.00001: How to disentangle the Cosmic Web? Sergei Shandarin, Mikhail Medvedev The Cosmic Web is a complicated highly-entangled geometrical object formed from remarkably simple -- Gaussian -- initial conditions. The full complexity of the Web can be fully appreciated in the six-dimensional phase space only, which study is, however, impractical due to numerous reasons. Instead, we suggest to use Lagrangian submanifold, i.e., the mapping $x = x(q)$, where $x$ and $q$ are three dimensional vectors representing Eulerian and Lagrangian coordinates. Being fully equivalent in dynamical sense to the phase space, it has the advantage of being a single valued and also metric space. In addition, we propose a new computational paradigm for the analysis of substructure of the Cosmic Web in cosmological cold dark matter (CDM) simulations. We introduce a new data-field -- the flip-flop field -- which carries wealth of information about the history and dynamics of the structure formation in the universe. The flip-flop (FF) field is an ordered data set in Lagrangian space representing the number of sign reversals of an elementary volume of each collisionless fluid element represented by a computational particle in a $N$-body simulation. This FF-field is effectively a multi-stream counter of each substructure element of the Cosmic Web. We demonstrate that the very rich subst [Preview Abstract] |
Sunday, April 12, 2015 8:42AM - 8:54AM |
H14.00002: Angular momentum - mass relation for dark matter haloes Shihong Liao, Dalong Cheng, Ming-chung Chu, Jiayu Tang We study the empirical relation between an astronomical object's angular momentum $J$ and mass $M$, $J=\beta M^\alpha$, the $J-M$ relation, using N-body simulations. In particular, we investigate the time evolution of the $J-M$ relation to study how the initial power spectrum and cosmological model affect this relation, and to test two popular models of its origin - mechanical equilibrium and tidal torque theory. We find that in the $\Lambda$CDM model, $\alpha$ starts with a value of 1.5 at high redshift $z$, increases monotonically, and finally reaches 5/3 near $z=0$, whereas $\beta$ evolves linearly with time in the beginning, reaches a maximum and decreases, and stabilizes finally. A three-regime scheme is proposed to understand this newly observed picture. We show that the tidal torque theory accounts for this time evolution behaviour in the linear regime, whereas $\alpha=5/3$ comes from the virial equilibrium of haloes. The $J-M$ relation in the linear regime contains the information of the power spectrum and cosmological model. The $J-M$ relations for haloes in different environments and with different merging histories are also investigated to study the effects of a halo's non-linear evolution. An updated and more complete understanding of this relation is thus obtained. [Preview Abstract] |
Sunday, April 12, 2015 8:54AM - 9:06AM |
H14.00003: Understanding the Large Scale Clustering of the Lyman-alpha Forest Agnieszka Cieplak, Anze Slosar, Nishikanta Khandai The Lyman-alpha forest has become a powerful probe of cosmological parameters by measuring large scale structure at intermediate redshift. With upcoming surveys increasing the scope of these measurements, understanding of the bias between the measured flux and the underlying matter power spectrum is becoming crucial to the percent level cosmological interpretation of these observations. We therefore employ cosmological hydrodynamic simulations to study the response of the Lyman-alpha forest clustering to large wavelength modes of the underlying matter large-scale structure and compare these to previous theoretical studies of this bias which used only N-body and hydro-PM simulations. We demonstrate this response by evolving smaller, curved universe cosmologies, representing the same universe with different overdense patches, and we use these to study the assumption of the analytical bias formula derived by Seljak (2012). A full theoretical understanding of this bias is important to fully understand the clustering of the Lyman-alpha forest and its cosmological implications. [Preview Abstract] |
Sunday, April 12, 2015 9:06AM - 9:18AM |
H14.00004: Bayesian semi-blind component separation for foreground removal in interferometric 21cm observations Le Zhang, Peter Tmbie, Benjamin Wandelt, Paul Sutter, Ata Karakci, Emory Bunn, Andrei Korotkov, Gregory Tucker We present a new Bayesian semi-blind approach which is an extension of Independent Component Analysis (ICA) from two-dimensional (2-D) CMB map to the three-dimensional (3-D) 21-cm cosmological signal. This technique provides a fully Bayesian inference of power spectra and maps. Only relying on the statistical independence of the components, this approach can jointly estimate the 3-D power spectrum of the 21-cm signal and, the 2-D angular power spectrum and the frequency dependence of each foreground component, without any prior assumptions about foregrounds. This approach has been tested intensively by applying it to mock data from an interferometric 21-cm intensity mapping observation. Based on the Expectation-Maximization (EM) algorithm, this blind approach provides much better performance in 21-cm power spectrum recovery over all the scales than the commonly used Principal Component Analysis (PCA). This technique could be straightforwardly applied to the epoch of reionization measurements. [Preview Abstract] |
Sunday, April 12, 2015 9:18AM - 9:30AM |
H14.00005: Measuring Dark Energy with CHIME Laura Newburgh The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new radio transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use the 21cm emission line of neutral hydrogen to map baryon acoustic oscillations between 400-800MHz across 3/4 of the sky. These measurements will yield sensitive constraints on the dark energy equation of state between redshifts 0.8 -- 2.5, a fascinating but poorly probed era corresponding to when dark energy began to impact the expansion history of the Universe. I will describe theCHIME instrument, the analysis challenges, the calibration requirements, and current status. [Preview Abstract] |
Sunday, April 12, 2015 9:30AM - 9:42AM |
H14.00006: Effects of Self Interacting Dark Matter on the Formation of Satellite Galaxies Aditya Dhumuntarao, Carl Gardner Based on the standard model of cosmology, dark matter accounts for 26\% of the matter in the universe and is essential for the formation and preservation of galaxies. The standard model, however, describes dark matter as collisionless, thus the dark matter particles interact with each other and other particles only through gravity and possibly the weak force. Self interacting dark matter is a hypothetical variation of dark matter consisting of particles with strong self-interactions and has been postulated to resolve a number of conflicts between observations and simulations on the galactic scale and smaller. Using computational models, we present a study of how a variant of SIDM influcences the formation of dwarf satellite galaxies. [Preview Abstract] |
Sunday, April 12, 2015 9:42AM - 9:54AM |
H14.00007: Dark Stars: Evolution and First Pulsation Results Tanja Rindler-Daller, Katherine Freese, Michael H. Montgomery, Donald E. Winget, Bill Paxton Among the first stars to form in the Universe may be ``dark stars,'' i.e. stars of primordial composition, but powered by the heating released in the process of dark matter (DM) particle self-annihilation, which also gives the correct relic density of DM today. It has been shown in the past that a DM-powered stellar phase is feasible, due to the high DM densities in the centers of primordial minihalos and the efficiency of DM annihilation. DM could thereby be responsible for an entirely new class of stellar objects, while possible detection of the latter would provide a smoking gun for DM. We have used the stellar evolution code MESA in order to improve upon previous stellar models, which were limited to polytropes. Our more accurate models confirm earlier results which found that dark stars can be very massive ($M > 10^5~ M_{\odot}$), bright, cool and puffy objects. Once these supermassive dark stars run out of DM fuel, they collapse and could be forming the seeds for the supermassive black holes which are observed in nearby and high-redshift galaxies. I will present our results on the evolution and properties of dark stars on their way of becoming supermassive, as well as new results on possible pulsations of dark stars and predicted observational signatures. [Preview Abstract] |
Sunday, April 12, 2015 9:54AM - 10:06AM |
H14.00008: Unified System of Mass, Energy, Space, and Time-MEST Dayong Cao Massenergy and spacetime build up a balance system of universe; massenergy equals negative spacetime. Like mass attract, opposite mass repel; like energy repel, opposite energy attract; like space attract, opposite space repel; like time repel, opposite time attract. The spacetime center of dark massenergy of dark hole system build up a balance system with the massenergy center of stellar matter. It explains of symmetry of CMB. According to observation of flat universe, cosmological constant of Einstein's equation is a negative Einstein's equation of structure of spacetime center which builds up a balance with Einstein's equation of the structure of massenergy center. According to Hubble's redshift equation, Hubble's redshift equals negative gravitational redshift which can be explained by negative Einstein's equation. The universe has 50\% of Dark hole system and 50\% of the stellar system which instead of 73\% of dark energy, 23\% of dark matter, and 4\% of stellar matter and so on because dark energy and dark matter can be explained by dark massenergy of dark hole. The paper also supposes the black hole of the center of galaxy equals the dark hole, and a dark hole builds up a balance system with sun. The quantum balance systemic equation: $E+E'{\psi}=mc^2+m'{\psi}c'^2=0, (c'^2=-\frac{({\partial}x)^2}{({\partial}t)^2})$. http://meeting.aps.org/link/BAPS.2015.MAR.Z23.14 http://meetings.aps.org/link/BAPS.2014.APR.Y9.1 http://meetings.aps.org/link/BAPS.2014.MAR.Y33.9 http://meetings.aps.org/link/BAPS.2010.DFD.QE.2 [Preview Abstract] |
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