BCCP talks

Tuesday, October 28
Location: UCB, Hearst Field Annex B-1, 1:10 p.m.
Speaker: Joseph Clampitt, Penn
Title: “Lensing Measurements of SDSS Voids and Filaments”Abstract: I will describe measurements of weak lensing mass profiles of voids from a volume-limited sample of SDSS Luminous Red Galaxies (LRGs). The stacked shear measurement has been performed on ~10,000 voids and subvoids with radii between 15-40 Mpc/h and redshifts between 0.16-0.37. The characteristic radial shear signal of voids is detected with a statistical significance that exceeds 13-sigma. The mass profile corresponds to a fractional underdensity of about -0.4 inside the void radius and a slow approach to the mean density indicating a partially compensated void structure. Time permitting, I will also describe a stacked weak lensing detection of filaments between close pairs of LRGs.

Friday, October 31
Location: LBNL, 50-5026, 12 p.m.
Speaker: Liang Dai, JHU
Title: “Conformal Fermi coordinates and the local universe formalism”Abstract: In an inhomogeneous Universe, the physical effect of long-wavelength perturbation on short distances should be such that short-wavelength perturbations effectively evolve in a modified homogeneous universe. We explicitly construct the so-called conformal Fermi normal coordinates (CFNC) through an expansion around the observer’s geodesic, which describe the local spacetime as a quasi-FRW metric and are valid at all times. The CFNC formalism demonstrates that the zeroth-order picture is that local expansion rate and spatial curvature are renormalized by long-wavelength perturbations, and the general condition for the spatial curvature to be a constant is derived. Beyond this “separate universe” picture, CFNC allows for systematic extraction of additional local effects from long-wavelength perturbations that cannot be attributed to a re-definition of the background FRW cosmology. The formalism can be useful in the studies of tracer bias, intrinsic alignment and gravitational-wave “fossil” effect.


For future BCCP talks, see this page.

BCCP Workshop in January 2014

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.

BigBOSS Gets a Kick-Start From the Gordon and Betty Moore Foundation December 4, 2012

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.”


Scientists Measure the Reionization of the Early Universe

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.