Events Daily

Tuesday, November 13, 2018

Modjaz Group Mtg
Event Type: Modjaz Group Mtg
Time: 10:30 AM - 3:30 PM
Location: 726 Broadway, 901, Sm Conf

Early dark energy can resolve the Hubble tension
Tristan Smith, Swarthmore College
Event Type: Astro Seminar
Time: 2:00 PM - 3:15 PM
Location: 726 Broadway, 940, CCPP Seminar
Description: Early dark energy (EDE) that behaves like a cosmological constant at early times (redshifts > 3000) and then decays away like radiation or faster at later times can solve the Hubble tension. In these models, the sound horizon at decoupling is reduced resulting in a larger value of the Hubble parameter H0 inferred from the cosmic microwave background (CMB). We consider two physical models for this EDE, one involving an oscillating scalar field and another a slowly-rolling field. We perform a detailed calculation of the evolution of perturbations in these models. A Markov Chain Monte Carlo search of the parameter space for the EDE parameters, in conjunction with the standard cosmological parameters, identifies regions in which H0 inferred from Planck CMB data agrees with the SH0ES local measurement. In these cosmologies, current baryon acoustic oscillation and supernova data are described as successfully as in LCDM, while the fit to Planck data is slightly improved.

Nonlinear behavior of axions
Mark Hertzberg, Tufts University
Event Type: Special Seminar
Time: 3:30 PM - 5:00 PM
Location: 726 Broadway, 940, CCPP Seminar
Description: In this talk I begin by reviewing how dark matter axions can undergo Bose-Einstein condensation and why this is captured by classical field theory. I explain that such condensates are spatially localized clumps, as they are organized by gravitation and self-interactions, and they may populate the galaxy. I discuss both the ground state and finite angular momentum states. I then discuss the possibility of parametric resonance of these axion clumps into electromagnetic waves, which may leave an astrophysical signature. Also, I comment on using ultra-light axions to resolve the core-cusp problem at the center of galaxies.