Bulletin of the American Physical Society
APS April Meeting 2013
Volume 58, Number 4
Saturday–Tuesday, April 13–16, 2013; Denver, Colorado
Session B8: Cosmology & Early Universe |
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Sponsoring Units: DAP Chair: Andrew Zentner, University of Pittsburgh Room: Governor's Square 10 |
Saturday, April 13, 2013 10:45AM - 10:57AM |
B8.00001: A Novel Investigation into a Multiple Big Bang Scenario William Duhe, Tirtibhar Biswas A unique way of realizing inflation has been proposed recently in the context of cyclic cosmology where the universe grows by a constant factor in each cycle. This leads to an overall exponential growth over many cycles. In a given cycle such a growth is possible if, for instance, ``heavy particles'' can decay into radiation (photons) leading to an increase in entropy. However, to sustain this mechanism over successive cycles, it is crucial to reproduce the heavy particles back through quantum scattering processes and re-establish thermal equilibrium between all the species. We attempt to prove the viability of a ``multiple bang'' scenario to produce known cosmological data as well as use it to predict fluctuations in the upcoming higher resolution plank telescope data. This paradigm opens doors for new investigations into the principles surrounding the content and origin of the universe. [Preview Abstract] |
Saturday, April 13, 2013 10:57AM - 11:09AM |
B8.00002: Cosmology and Structure Formation with Scalar Field Dark Matter Tanja Rindler-Daller, Bohua Li, Paul R. Shapiro The exploration of the nature of the cosmological dark matter is an ongoing hot topic in modern cosmology and particle physics. Suggested candidates include ultra-light particles which are described by a real or complex scalar field. Previous literature has revealed the richness of this candidate in terms of its power to explain astrophysical and cosmological observations, from the background cosmological evolution to galactic rotation curves. However, a lot of research remains to be done to find out which parts of the parameter space of this kind of dark matter is able to explain observations on all scales consistently. In this talk, we will present our current and ongoing work on the study of complex scalar field dark matter (SFDM). We find that this SFDM underwent three distinctive states in the early Universe, a scalar-field dominated, a radiation-dominated and a matter-dominated phase. The timing and longevity of each phase places important first constraints on the parameters of the model. For this SFDM model, we revisit classical problems of structure formation theory, like the tophat collapse, the problem of virial shocks, and the cosmological infall problem for an isolated halo, in order to find viable model parameters which match the constraints from cosmology. [Preview Abstract] |
Saturday, April 13, 2013 11:09AM - 11:21AM |
B8.00003: Examining the Diffeomorphism Field as an Inflaton Candidate Christopher Doran, Vincent Rodgers, Wade Bloomquist, Kory Stiffler We revisit the diffeomorphism field (or $D_{\mu\nu}$) Lagrangian interacting with the Friedman-Robertson-Walker-LeMaitre metric, as derived by Rodgers and Yasuda (2006). This Lagrangian suggested a natural origin of both the inflaton, as the trace component of $D_{\mu\nu}$, and dark matter fields as the remaining traceless rank-two tensor. We follow up on the previous calculations that demonstrated several e-foldings of cosmic inflation and dark-energy-like behavior. A $D_{\mu\nu}$ solution as a source of inflation is interesting for several reasons. It has a non-canonical kinetic Lagrangian with four derivatives in the highest-order term and its structure is fairly unique among k-inflation theories. Also, its full interacting formulation shows it to interact with a point particle in a manner that is similar to $R_{\mu\nu}$. We numerically integrate the classical field equations in order to find a region of parameter space where the resulting cosmological data make sense, including a more realistic number of e-foldings. With this we hope to illuminate the post-inflation, radiation-era interaction of $D_{\mu\nu}$ with a radiation field like the CMB, in order to see what observational effects there would be. [Preview Abstract] |
Saturday, April 13, 2013 11:21AM - 11:33AM |
B8.00004: Dark Energy or Modified Gravity? An Effective Field Theory Approach Jolyon Bloomfield, Eanna Flanagan, Minjoon Park, Scott Watson We take an Effective Field Theory (EFT) approach to unifying existing proposals for the origin of cosmic acceleration and its connection to cosmological observations. Building on earlier work where EFT methods were used with observations to constrain the background evolution, we extend this program to the level of the EFT of the cosmological perturbations, following the example from the EFT of Inflation. Within this framework, we construct the general theory around an assumed background and identify the parameters of interest for constraining dark energy and modified gravity models with observations. [Preview Abstract] |
Saturday, April 13, 2013 11:33AM - 11:45AM |
B8.00005: Generation of Coherent Structures After Cosmic Inflation Marcelo Gleiser The transition from inflation to power-law expansion is a rich nonlinear nonequilibrium physical process. For this reason, much is still unknown about this epoch in early universe physics, which has been dubbed the ``new big bang" by many colleagues. Here I describe results from the past few years of research, some of which in collaboration with Noah Graham and Nik Stamatopoulos, where we explored the generation on extended structures at the end of inflation known as oscillons. In particular, in hybrid inflation models we solve the coupled Einstein-Klein-Gordon equations to find that as the field responsible for inflating the universe rolls down to oscillate about its minimum, it triggers the formation of long-lived two-field oscillons, which can contribute up to 20\% of the total energy density of the universe. We show that these oscillons emerge for a wide range of parameters consistent with WMAP 7-year data. These objects contain total energy of about $25\times10^{20}$ GeV, localized in a region of approximate radius $6\times 10^{-26}$ cm. We argue that these structures could have played a key role during the reheating of the universe, influencing the reheating temperature. We also explore the notion that these objects will appear in most symmetry-breaking phase transitions. [Preview Abstract] |
Saturday, April 13, 2013 11:45AM - 11:57AM |
B8.00006: ABSTRACT WITHDRAWN |
Saturday, April 13, 2013 11:57AM - 12:09PM |
B8.00007: Implications of the Cosmological Constant for Spherically Symmetric Mass Distributions Omair Zubairi, Fridolin Weber In recent years, scientists have made the discovery that the expansion rate of the Universe is increasing rather than decreasing. This acceleration leads to an additional term in Albert Einstein's field equations which describe general relativity and is known as the cosmological constant. This work explores the aftermath of a non-vanishing cosmological constant for relativistic spherically symmetric mass distributions, which are susceptible to change against Einstein's field equations. We introduce a stellar structure equation known as the Tolman-Oppenhiemer-Volkoff (TOV) equation modified for a cosmological constant, which is derived from Einstein's modified field equations. We solve this modified TOV equation for these spherically symmetric mass distributions and obtain stellar properties such as mass and radius and investigate changes that may occur depending on the value of the cosmological constant. [Preview Abstract] |
Saturday, April 13, 2013 12:09PM - 12:21PM |
B8.00008: Massive Free-Streaming Neutrinos and Rise of $N_\nu$ at Recombination J. Birrell, C. Yang, P. Chen, J. Rafelski We present the Einstein-Vlasov solution for the momentum distribution of the relic free-streaming neutrinos. We show that it is possible to explain a rise in the effective number of neutrinos ($N_\nu$) from those present at the end of big bang nucleosynthesis (BBN) $N_\nu(T_{BBN})=3.046$ (theoretical) or $N_\nu(T_{ BBN})=3.71^{+0.47}_{-0.45}$ (measured) towards $N_\nu(T_{r})=4.34^{+.086}_{-0.88}$ (measured) at the time of electron-ion recombination (r). The effect is due to the ambient temperature, $T_r=0.253$ eV, being near to the neutrino mass. If a thermal equilibrium distribution is inadvertently used, one instead expects a decrease in $N_\nu$ between BBN and recombination. We present explicit values for $m_\nu$ needed to account for the observed increase in $N_\nu$. The smaller the number of dominant mass neutrinos and the larger the change in $N_\nu$ needed between BBN and recombination, the larger is the value of $m_\nu$ we find. If no new mechanism is discovered to increase the theoretical value $N_\nu(T_{BBN})=3.046$ then the relic neutrinos are predicted to have $0.528\le \sum m_{\nu_i} \le 2.26$ eV and will contribute between $5\%$ and $22\%$ of the matter inventory in the Universe. [Preview Abstract] |
Saturday, April 13, 2013 12:21PM - 12:33PM |
B8.00009: Challenging the status quo with weak gravitational lensing Ali Vanderveld Weak gravitational lensing, wherein the images of distant galaxies are distorted by matter in the foreground, can be a powerful cosmological probe if we have good statistics and systematics control. The former will be made possible by forthcoming large-area surveys, such as with the Euclid satellite. The latter, however, is still a work in progress despite the improvements from going to space. To that end, I will show how we can use weak lensing to robustly test the cosmological ``standard model'' by using state-of-the-art expansion history data to make timely predictions for these anticipated future observations. Using this methodology I will show how various theoretical and observational uncertainties impact our ability to possibly falsify the standard model with Euclid weak lensing data, thereby exploring the effects of dynamical dark energy, warm dark matter, baryonic physics, and additional neutrino species. [Preview Abstract] |
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