Simon Fraser University

Media Attention for Hojjati's Papers

Nov 4, 2013

Two papers by alumnus and current postdoc Alireza Hojjati are garnering significant media attention.

In the Physical Review Letters article New Constraints on the Early Expansion History of the Universe, Hojjati and co-authors Eric V. Linder and Johan Samsing analyzed the cosmic microwave background (CMB) radiation data from Planck satellite to examine the expansion of the universe as far back as a few hundred years after the Big Bang. "Our findings confirm the standard picture in cosmology; however, there are hints of the existence of some extra relativistic particles in the early universe. With the upcoming CMB polarization data, we can further explore the physics of that era," Hojjati says.

The work was first announced in the Berkeley news at:

The full journal reference is :
Alireza Hojjati, Eric V. Linder, Johan Samsing. New Constraints on the Early Expansion History of the Universe. Physical Review Letters, 2013; 111 (4) DOI: 10.1103/PhysRevLett.111.041301

A second article, profiled in Nature, is about a "Strong Lens Time Delay Challenge". Hojjati, who was involved in testing the simulated data for the challenge, summarizes the paper as follows: "The dynamics of dark energy can be studied by combining the standards distance probes in cosmology with novel and complementary measurements of the cosmological distances. Time delays between multiple images of the observed strong-lensed objects are shown to be a powerful probe of cosmology. The strong lensing group of the Large Synoptic Survey Telescope (LSST) have set up a ”Time Delay Challenge” at, an effort to assess the present capabilities of the community to measure accurately the time delays."

View the Nature profile at:

The full paper is available at::
Dobler, G. et al. Preprint at (2013).

Hojjati completed his PhD thesis, Observational tests of cosmic acceleration, under the supervision of Levon Pogosian in 2011. Following a postdoc at the Institute for the Early Universe in Seoul, South Korea, he returned to the department in September 2013 as a postdoc with Pogosian.