{"id":68,"date":"2012-03-12T10:52:59","date_gmt":"2012-03-12T15:52:59","guid":{"rendered":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/?page_id=68"},"modified":"2012-03-12T15:29:57","modified_gmt":"2012-03-12T20:29:57","slug":"research","status":"publish","type":"page","link":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/research\/","title":{"rendered":"Research"},"content":{"rendered":"

Big Bang Nucleosynthesis<\/span><\/h3>\n

Big bang nucleosynthesis (BBN) is the production of light elements in the early universe.\u00a0 By comparing the predicted and observed element abundances (primarily deuterium and helium), we can determine the baryon density of the universe and constrain the evolution of the early universe.\u00a0 My first published paper (with Rocky Kolb) was an examination of the effect of massive neutrinos on BBN.\u00a0 With Jim Applegate and Craig Hogan, I published the first examination of the effects of a QCD phase transition on BBN.\u00a0 Recently, with Justin Menestrina (a Vanderbilt undergraduate), I studied the “dark radiation” produced by a particle decaying during the BBN epoch.<\/span><\/h4>\n

Large-scale Structure<\/span><\/h3>\n

Large-scale structure is the distribution of matter, including both galaxies and dark matter, on the largest scales in the universe.\u00a0 Ed Bertschinger and I examined the density field produced by the convolution of a fixed density field with a distribution of points.\u00a0 Although this work was originally inspired by the (now defunct) cosmic string model for large-scale structure, it later became the mathematical basis of the halo model, which models the distribution of galaxies embedded in halos of dark matter.\u00a0 David Weinberg and I examined galaxy bias, showing that, under fairly general assumptions, it is necessarily linear on large scales.\u00a0 With Qingqing Mao, Cameron McBride, and Andreas Berlind, I applied the copula formalism, commonly used in mathematical finance, to the description of primordial density fields.<\/span><\/h4>\n

Cosmic Microwave Background<\/span><\/h3>\n

The cosmic microwave background (CMB)\u00a0 is a nearly-uniform radiation field filling the universe — a relic of the big bang.\u00a0 It was long known that the fluctuations that gave rise to galaxies would also leave a tell-tale imprint on the CMB.\u00a0 This imprint was first observed by the COBE satellite, and later analyzed in detail by the WMAP satellite.\u00a0 Between these two experiments, Manoj Kaplinghat, Mike Turner, and I published the second examination of the effects of a time-varying fine structure constant on the CMB fluctuation spectrum — Steen Hannestad scooped us by one day!\u00a0 But this led to a collaboration with Steen, whom I have never met, on a variety of other projects.<\/span><\/h4>\n

Dark Matter and Particle Physics in the Early Universe<\/span><\/h3>\n

The late 1970s and early 1980s saw the application of particle physics to cosmology, with perhaps the most fundamental result being the idea that the dominant form of matter in the universe is an exotic relic particle.\u00a0 Mike Turner and I published a standard approximation for the abundance of a thermal dark-matter relic (see., e.g, the Kolb and Turner cosmology textbook).\u00a0 In a study of the thermodynamics of decaying particles in the early universe, we showed that such particles never “heat up” the universe, as had been previously believed.\u00a0 Instead, the universe simply cools more slowly.
\n<\/span><\/h4>\n

Dark Energy<\/span><\/h3>\n

Supernova observations in the late 1990s showed, rather surprisingly, that the expansion of the universe is speeding up instead of slowing down.\u00a0 The simplest explanation for this is a cosmological constant, but more exotic explanations, which go under the generic name of “dark energy”, have also been explored.\u00a0 Andrew Liddle and I did some of the early work on scalar field models for dark energy.\u00a0 More recently, in separate projects with Anjan Sen and Sourish Dutta, I examined simplifications to the scalar field equation of motion in the case where the background cosmological evolution is close to a cosmological constant.\u00a0 The equations can be solved analytically in this case, giving a rather general prediction for the evolution of the equation of state with redshift.\u00a0 Lawrence Krauss and I explored some of the implications of the accelerating universe for the distant future (see also our Scientific American article under “Popular Science”).\u00a0 Paul Frampton, Kevin Ludwick, and I examined models in which the future expansion is fast enough to destroy bound structures but not to produce a future singulary — a class of models we have dubbed the “little rip”.
\n<\/span><\/h4>\n","protected":false},"excerpt":{"rendered":"

Big Bang Nucleosynthesis Big bang nucleosynthesis (BBN) is the production of light elements in the early universe.\u00a0 By comparing the predicted and observed element abundances (primarily deuterium and helium), we can determine the baryon density of the universe and constrain the evolution of the early universe.\u00a0 My first published paper (with Rocky Kolb) was an…<\/p>\n","protected":false},"author":647,"featured_media":0,"parent":0,"menu_order":40,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"tags":[],"class_list":["post-68","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/pages\/68","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/users\/647"}],"replies":[{"embeddable":true,"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/comments?post=68"}],"version-history":[{"count":11,"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/pages\/68\/revisions"}],"predecessor-version":[{"id":70,"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/pages\/68\/revisions\/70"}],"wp:attachment":[{"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/media?parent=68"}],"wp:term":[{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/my.dev.vanderbilt.edu\/robertscherrer\/wp-json\/wp\/v2\/tags?post=68"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}