Friday, October 3
Location: LBNL 50-5026 – 12 p.m.
Speaker: Yin Li, Chicago
Title: “The power spectrum super-sample effect”
Abstract: The impact of density fluctuations with wavelengths larger than a survey must be considered when extracting cosmological information from power spectrum measurements. These modes change the power spectrum in the same way as a change in the cosmological background does. Using a handful of separate universe simulations, we accurately capture this effect in terms of response of the matter power spectrum to a single mode — the mean density fluctuation in the survey volume. The unknown amplitude of this mean density mode contributes to a (typically dominant) error in the matter power spectrum estimators. Alternatively, it can also be simply included in parameter estimation and forecasts by treating the mean density fluctuation as an additional cosmological parameter. Parameter degeneracies arise since the response of the power spectrum to the mean density mode and cosmological parameters share similar properties in changing the growth of structure and dilating the scale of features.
Tuesday, October 7
Location: UCB, Hearst Field Annex B-1 – 1:10 pm
Speaker: Benedikt Diemer, Chicago
Title: “The (non-)universality of halo density profiles”
Abstract: The density profiles of dark matter halos are an essential input for models of galaxy formation, as well as for the interpretation of numerous observations such as weak and strong lensing signals. The profiles are commonly thought to follow a simple, universal shape, and only depend on two parameters, mass and concentration. Using a large suite of cosmological simulations, I will show that the outer halo density profiles depend on an additional parameter, the mass accretion rate, and present an accurate new fitting formula that takes this dependence into account. I will further discuss the question of universality, and show that the definition of the halo boundary plays a crucial role. Similarly, halo concentrations are usually described as a universal function of mass and redshift. Instead, I will present a model in which concentration depends on an additional parameter: the local slope of the matter power spectrum. I will demonstrate that this model accurately (to better than 10-15%) describes simulated concentrations over a large range of redshifts, halo masses and cosmological parameters, and is in excellent agreement with the recent observations of the CLASH cluster survey.
For future BCCP talks, see this page.
BCCP Workshop: 5th annual Essential Cosmology for the Next Generation Meeting
BCCP and the Instituto Avanzado de Cosmologia Mexico held the 5th annual Essential Cosmology for the Next Generation meeting January 13-17, 2014, popularly known as Cosmology on the Beach. The conference blends a winter school of lecture courses by world-leading scholars with plenary talks on hot research topics. This year, topics included CMB polarization, gravitational wave cosmology, particle physics, tests of gravity, and statistical and experimental methods.
For slides from the BCCP/IAC meeting Essential Cosmology for the Next Generation 2014 workshop, click here. They are also available on the Presentations Page.
There are no open job opportunities at BCCP at this time. Please check back for future job postings.
A $2.1 million grant from the Gordon and Betty Moore Foundation to the University of California at Berkeley, through the Berkeley Center for Cosmological Physics (BCCP), will fund the development of revolutionary technologies for BigBOSS, a project now in the proposal stage designed to study dark energy with unprecedented precision. BigBOSS is based at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).
“BigBOSS is the next big thing in cosmology,” says Uroš Seljak, Director of the BCCP, who is a professor of physics and astronomy at UC Berkeley and a member of Berkeley Lab’s Physics Division. “It would map millions and millions of galaxies, allowing us to measure dark energy to high precision – and would yield other important scientific results as well, including determining neutrino mass and the number of neutrino families.”
Dark energy is the unknown something that appears to account for almost three-quarters of the mass-energy of the universe and is the cause of its accelerating expansion. The discovery of the accelerating universe, announced in 1998 by two teams, resulted in the 2011 Nobel Prize in Physics, divided between Berkeley Lab and UC Berkeley astrophysicist Saul Perlmutter, leader of the Supernova Cosmology Project, and Brian Schmidt and Adam Riess of the competing High‑z Supernova Search team.
“After we won the Nobel Prize, the question we all heard most was, ‘Now that you’ve discovered dark energy, what comes next?’” says Perlmutter, who is the Executive Director of the BCCP as well as principal investigator for the Moore Foundation’s BigBOSS grant. “The answer is pretty clear: we have to find out what dark energy is. There’s no end of theories. To know which are possible, what we need most is the kind of accurate observational evidence that only BigBOSS and other advanced experiments can give us.”
New data from the South Pole Telescope indicates that the birth of the first massive galaxies that lit up the early universe was an explosive event, happening faster and ending sooner than suspected.
Extremely bright, active galaxies formed and fully illuminated the universe by the time it was 750 million years old, or about 13 billion years ago, according to Oliver Zahn, a postdoctoral fellow at the Berkeley Center for Cosmological Physics (BCCP) at the University of California, Berkeley, who led the data analysis.