Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session B11: Early Universe and Dark Energy |
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Sponsoring Units: DAP Room: Sheraton Governor's Square 17 |
Saturday, April 13, 2019 10:45AM - 10:57AM |
B11.00001: The Evolution of Primordial Magnetic Fields due to Magnetohydrodynamic Turbulence, and their Cosmological Applications Sayan Mandal, Axel Brandenburg, Ruth Durrer, Tina Kahniashvili, Alberto Roper Pol, Alexander Tevzadze, Tanmay Vachaspati, Weichen Yin We study the generation of primordial magnetic fields (PMFs), with an emphasis on the observable signatures. We look at the following: (i) PMFs generated during inflation which have a scale-invariant spectrum. We see that this spectrum changes temporally at small scales and becomes a steeper weak-turbulence spectrum at progressively larger scales. We show numerically, this happens at the turbulent-diffusive scale which increases with the square root of time. We also show that the infrared cutoff scale of perturbations produced during inflation determines the observables signatures of these magnetic fields on the CMB. (ii) PMFs generated during the Electroweak Phase Transition (EWPT). We study the evolution of these fields from the time of generation till the epoch of recombination by magnetohydrodynamic (MHD) simulations. Various initial conditions, i.e., magnetically dominant or subdominant, different helicities, spectral shapes, etc., are studied and compared with bounds from Big Bang Nucleosynthesis (BBN) and TeV Blazar observations. The observable signatures of PMFs on primordial gravitational waves (PGWs) is also being studied. |
Saturday, April 13, 2019 10:57AM - 11:09AM |
B11.00002: The gamma-ray signature of an early matter-dominated era M Sten Delos, Adrienne L Erickcek, Tim Linden The thermal history of the Universe between inflation and Big Bang nucleosynthesis is unknown, but an early matter-dominated era (EMDE), driven by either an oscillating scalar field or a massive particle, is an unavoidable consequence of several early-Universe models. An EMDE enhances the growth of small-scale density fluctuations, causing most of the dark matter to be bound in sub-earth-mass microhalos at high redshift, long before the formation of galaxies. Dark matter annihilation within these unresolved microhalos generates a gamma-ray signal that broadly tracks the dark matter content, yielding a similar signature to that of decaying dark matter. However, in dense regions such as galactic centers, tidal stripping and other disruptive processes suppress the microhalo gamma-ray signal, resulting in a distinctive emission profile. We use N-body simulations to study microhalos subjected to tidal forces in order to determine the EMDE emission profile for dwarf spheroidal galaxies. We then analyze the gamma-ray emission from these galaxies to constrain the dark matter annihilation cross-section and microhalo properties, thereby probing the evolution of the early universe and the origins of dark matter. |
Saturday, April 13, 2019 11:09AM - 11:21AM |
B11.00003: Relativistic Electron Scattering and Big Bang Nucleosynthesis Atul S Kedia, Nishanth Sasankan, Grant James Mathews, Motohiko Kusakabe Big bang nucleosynthesis (BBN) is a valuable tool to constrain the physics of the early universe. An assumption for calculating abundances of nuclei due to BBN is that they obey Maxwell-Boltzmann(MB) statistics. This assumption is shown to be questionable and the modification to it is found. Firstly, we recognize that the nuclear distributions should be influenced by their surrounding particles. A nucleus interacts with e+ - e- lot more than other particles. e+ - e- are relativistic during BBN and hence obey modified Maxwell-Juttner(mMJ) distribution. Given these we build a Langevin model for Brownian motion of a heavy particle(nuclei) in a bath of light particles(e+ - e-). By imposing equipartition of energy we obtain a modified distribution for nuclei, altered only by a factor in temperature than MB distribution. Monte-Carlo simulations were built to simulate the thermalization process and the distribution obtained for nuclei corroborated Langevin model solution. When employed for BBN calculations, this distribution alters the light-element abundances, and worsens the discrepancies between BBN and observed primordial light-element abundances possibly suggesting the need for new physics. |
Saturday, April 13, 2019 11:21AM - 11:33AM |
B11.00004: Quantum Kinetics in the Early Universe Chad Kishimoto In the early universe, the evolution of neutrino states are complicated by both their coherent quantum evolution and their de-coherent kinetic evolution. The results of this quantum kinetic evolution are manifest in precision cosmological measurements, and may be important in the production of dark matter or other beyond standard model processes. This talk will focus on the quantum kinetic evolution of neutrino states in the early universe, where the quantum mechanical oscillation rate and scattering rate are both fast compared to the dynamical expansion rate. In this regime, we notice that the states quickly evolve to a point where the coherent and de-coherent effects balance, attaining a local quantum kinetic equilibrium that slowly evolves with the expanding universe. |
Saturday, April 13, 2019 11:33AM - 11:45AM |
B11.00005: Reheating in two-sector cosmology Peter Adshead, Pranjal Ralegankar, Jessie Shelton In this talk I describe scenarios where a hidden sector (HS) is directly populated by post-inflationary reheating along with the Standard Model (SM). Using numerical solutions of the appropriate Boltzmann equations describing perturbative reheating of the two sectors, I describe the role of quantum statistics and inflaton-mediated non-equilibrium energy transfer between the HS and SM in determining the temperature history. The resulting temperature ratio between the two sectors is a function of their couplings to the inflaton, and admits analytical approximations that allows the temperature ratios to be quickly estimated in a wide range of models. Additionally, I discuss how incorporating quantum statistics can lead to novel parametric behavior for radiation baths during perturbative reheating at temperatures large compared to the inflaton mass. |
Saturday, April 13, 2019 11:45AM - 11:57AM |
B11.00006: Observational and theoretical status of tachyon inflation in teleparallel gravity Yousef Izadi, Amin Rezaei Akbarieh The idea of inflation is of an essential importance in modern cosmology and solves the flatness, horizon and magnetic monopole problems. Recently, serious observational constraints have been applied on inflationary models which made some of them excluded. Many models have been extensively constructed to describe the inflationary epoch. One of the observationally consistent models is tachyon field coupled to gravity. In this talk, we will discuss a new inflationary model in which tachyonic field is used in teleparallel gravity. we will consider the case where there is no coupling between tachyonic field and the scalar torsion (f(φ) = 1 or any constant), and argue that for tachyonic field in open string theory and D-brane theory and also tachyonic potentials consistent with Noether's theorem, tachyonic field is a proper candidate for inflation. We will continue with talking about inflation of tachyons in the framework of f(T) and will consider the state in which f(φ) = 1 to show that one can find approximately n_{s}= 0.956 for the spectral index, and r = 0.0061 for tensor to the scalar ratio. The calculated r from tachyonic model agrees with the upper limited value obtained by Planck results. |
Saturday, April 13, 2019 11:57AM - 12:09PM |
B11.00007: Constraints on Dark Energy Potentials for Models with Neutrinos Coupled to Dark Energy Olga Avsajanishvili, Gennady Chitov, Yiwen Huang, Tina Kahniashvili, Sayan Mandal, Bijit Singha A connection is sought between dark energy and the origin of neutrino mass by considering the model of a quintessence scalar field Yukawa-coupled to a massless Dirac fermion field. This model is treated in the framework of finite temperature field theory to generate fermion mass that evolves with the dynamics of the quintessence field. The equation of state obtained in this framework is shown to be consistent with the cosmological evolution of the universe only in the context of specific quintessence potentials. Stricter constraints are found on the free parameters for the corresponding quintessence candidates for which this framework predicts a metastable phase, in accordance with the matter domination epoch, that slowly evolves towards a phase transition at a critical temperature at which the fermion and the scalar masses jump discontinuously to the doomsday vacuum state values. This framework is free from coincidence in scale and fine-tuning problem since the scale of the theory is determined by a single mass parameter of the quintessence potential. |
Saturday, April 13, 2019 12:09PM - 12:21PM |
B11.00008: Minimal Coupling Between Dark Matter and Dark Energy Kevin Ludwick Dark energy and dark matter are two of the |
Saturday, April 13, 2019 12:21PM - 12:33PM |
B11.00009: Comparison and detection of different models of dark energy Chen Xiao-Fan Comparison and detection of different models of dark energy are made. |
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