# Benjamin D. Wandelt

Adjunct Associate Professor

## Primary Research Area

- Astrophysics / Gravitation / Cosmology

## Biography

Professor Benjamin Wandelt received his Ph.D. in theoretical physics from the Imperial College, London. He worked as a postdoctoral fellow at the Theoretical Astrophysics Center in Copenhagen, Denmark from 1997 to 1999, and as a research associate at the Department of Physics, Princeton University, from 1999 to 2001. He joined the Department of Physics at the University of Illinois at Urbana-Champaign in August 2001.

A theoretical cosmologist, Professor Wandelt has studied a variety of problems in Cosmology. He is an internationally acclaimed expert in the analysis of cosmic microwave background (CMB) data, where he has invented innovative algorithms that make the analysis of huge new data sets tractable. Essentially all current efforts to observe the CMB anisotropy use his numerical and statistical methods for key stages in the theoretical interpretation of the data. By studying the properties of the CMB anisotropy one can learn about the physical processes that occurred in the very early Universe.

Recent projects of his included studying the bispectrum of the CMB anisotropy as measured by the space mission COBE/DMR in order to constrain the non-linearity of the perturbations created during inflation. Professor Wandelt has also participated in efforts to predict the properties of exotic forms of dark matter, designed to solve puzzles related to observations of the clustering properties of matter on galaxy scales.

Professor Wandelt is associated as a theorist with the ESA/NASA's Planck space mission to obtain the definitive maps of the cosmic microwave background anisotropies, and detailed all-sky observations of other components of the microwave sky. He co-leads Planck's harmonic analysis effort and is an associate of the theory and simulations team. Through Professor Wandelt's work, our department is one of only a few select US institutions to be involved in this major international endeavor in cosmology.

## Research Statement

Since its Nobel prize winning discovery in the late 1960s by Penzias and Wilson, the cosmic microwave background (CMB) radiation has become the cornerstone of cosmological astrophysics. This radiation was emitted when the Universe was only 380,000 years old. It therefore literally provides a snapshot of the early Universe when it was 36,000 times younger than it is now. Its main feature is its remarkably uniform brightness in all directions, on which small fluctuations are imprinted at the level of 1 part in 105 (the anisotropies). These anisotropies were first reliably detected at low resolution by the COBE satellite in the early 1990s, leading to a second set of Nobel Prizes, for George Smoot and John Mather in 2006. Since then, COBE's observations have been confirmed and vastly extended by a range of other instruments, most recently and prominently by the Wilkinson Microwave Anisotropy Probe (WMAP). This decade, the cosmic microwave background (CMB) observations by WMAP, the upcoming Planck satellite, several surveys mapping the three-dimensional distribution of galaxies to unprecedented depth, and other ambitious observational projects to probe the geometry and history of the Universe, will shape humankind's vision of the origin and evolution of the cosmos.

These observational projects bring with them new, fundamental challenges for theoretical cosmology at the interface between theory and observation. I am excited about the broad range of opportunities to tie together ideas from astrophysics and particle physics. At the same time new mathematical, statistical and computational methods are needed, both to sharpen up theoretical predictions and to enable us to bring the full weight of present and future data sets to bear on them.

My research goals within this context are:

- To develop new analysis techniques that allow the most accurate and instructive confrontation of current and future cosmological data sets with cosmological theory. These techniques lead to tests of the standard model of cosmology and to improved inferences about the global properties of the Universe (the cosmological parameters).
- To infer, in the most direct way possible, the initial conditions of the Universe— its properties at the highest energies during the first instants of time. This opens a cosmological window onto fundamental physics at the Planck scale or string scale, far beyond the reach of particle accelerators.
- To build a theoretical understanding of the fundamental puzzles posed by the nature of dark matter and dark energy, cosmic ingredients whose existence is strongly supported by observations of the large scale structure of the Universe as well as its accelerated expansion.
- To create new computational techniques that allow the accurate theoretical prediction of observationally accessible cosmological phenomena.
- To continue to play a leading rôle in the analysis and interpretation of the Planck data set.

## Research Honors

- Sofja Kovalevskaja Award of the German Ministry of Education and Research (declined), 2006
- Friedrich Wilhelm Bessel Research Award of the Alexander von Humboldt Foundation, 2006
- Center for Advanced Studies Fellow, 2004-2005

## Selected Articles in Journals

- K. M. Gorski, E. Hivon, A. J. Banday, B. D. Wandelt, F. K. Hansen, M. Reinecke, and M. Bartelmann. HEALPix: a framework for high-resolution discretization and fast analysis of data distributed on the sphere. Astrophys. J.
**622**, 759-771 (2005). - J. Mejia, I. O'Dwyer, and B. D. Wandelt. Galactic foreground contribution to the BEAST cosmic microwave background anisotropy maps. Astrophys. J. Suppl. Series
**158**, 109-117 (2005). - P. R. Meinhold, et al. A map of the cosmic microwave background from the BEAST experiment. Astrophys. J. Suppl. Series
**158**, 101-108 (2005). - C. Armitage and B. D. Wandelt. Deconvolution map-making for cosmic microwave background observations. Phys. Rev. D
**70**, 123007-1-7 (2004). - I. J. O'Dwyer, H. K. Eriksen, B. D. Wandelt, J. B. Jewell, D. L. Larson, K. M. Gorski, A. J. Banday, S. Levin, and P. B. Lilje. Bayesian power spectrum analysis of the first-year
*Wilkinson Microwave Anistropy Probe*data. Astrophys. J. Lett.**617**, L99-102 (2004).