Current Research Interests

My research interests are mostly in cosmology, especially the study of the cosmic microwave background radiation.  Undergraduates from the University of Richmond work with me on most of the projects I’m involved with.  Here are some specific areas I’ve been working on.

I’m part of a group that’s building QUBIC, a new telescope for studies of the polarization of the cosmic microwave background radiation. QUBIC combines bolometric detectors with some ideas from interferometry to produce an instrument that will (we hope) combine extremely high sensitivity with excellent control of systematic errors.

My main interest is in examining the effects of various systematic errors on the proposed design. The US-based portion of the QUBIC team is currently working on a suite of simulation software to assess the effects of various systematic errors on interferometric telescopes in general. This work is computationally intensive. Fortunately, my colleague Jerry Gilfoyle and I were awarded an NSF Major Research Instrumentation grant enabling us to purchase a supercomputing cluster.

In some versions of the QUBIC design, it is necessary to apply a sequence of phase shifts to all of the various input horns in order to extract all of the useful information (the “visibilities”). Brent Follin, one of the research students in my group, figured out the optimal pattern of phase shifts. He presented this work as a poster at a national meeting of the American Astronomical Society, and then we published a paper on it.

Maps of CMB polarization look kind of like the vector fields you might see in a course on electricity and magnetism, although they’re really a different mathematical beast known as a “spin-2 field.”  One key step in analyzing a polarization map is decomposing it into two components called E and B.  I recently published an article  presenting an efficient way to do this numerically.  Figuring out improvements and extensions of this sort of technique would be a good student project for someone who’s interested. (For instance, I only implemented the method in the “flat-sky approximation,” but it should be possible to extend it to the full spherical sky.)

Other students in my research group are examining possible explanations for large-angle anomalies in the microwave background. These are unexpected patterns that have been noticed in maps of the microwave background: things are supposed to look random, but they don’t.  The significance of these anomalies has been hotly debated in the literature. We are carefully examining the viability of various proposed sources of the anomalies.  Austin Bourdon and I published a paper showing that a broad class of proposed explanations actually make one of the problems worse, not better.  More recently, Haoxuan (Jeff) Zheng and I published a paper using Bayesian techniques to examine the evidence for another batch of possible explanations. Current student Jocelyn Xue is working on using future observations of CMB polarization to test these models. She presented her results at a recent meeting of the American Astronomical Society, and we hope to submit a paper for publication soon.

One way to resolve the puzzle of these large-angle anomalies is to find other data sets that probe the same very large length scales.  I did some work on one possible way of doing this: detecting ultra-large-scale variations in the distribution of matter in the Universe by observing the scattering of microwave background radiation in distant galaxy clusters.

In addition to pure research articles, I also write expository articles from time to time.  David Hogg and I wrote about our opinion of the best way to understand the redshift caused by the expanding Universe, and I wrote a short piece explaining the relationship between evolution and the second law of thermodynamics.

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