University of Pittsburgh
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Grad StudentsBenjamin Brown
My research has centered on cosmology and related issues of theoretical physics. I have done extensive work on the theory of the cosmic microwave background radiation and the ways in which it constrains our models of the universe. Current microwave observations, combined with optical observations of the large-scale galaxy distribution, cosmic abundances of light elements, and the supernova-1a Hubble diagram, combine to give tight constraints on the properties of the universe. The resulting "standard model" fits most observations well, but is troubling theoretically: our best guess says that only 5 percent of the universe's energy density is in the form of ordinary matter, 25 percent is made of as-yet undetected dark matter (which does not interact either via the strong or electromagnetic forces), and the remaining 70 percent is in an even stranger "dark energy", evenly distributed in space and having a negative effective pressure. Theorists have a number of good candidates for the dark matter particles, which are currently being pursued by many experimental groups, including the high energy experiment group at Pitt. Current ideas as to the nature of dark energy are all highly speculative.
I am interested in a variety of techniques to test our model of cosmology; these include further observations of the temperature and polarization fluctuations in the microwave background radiation, gravitational lensing, dynamics of galaxies and clusters of galaxies, and the large-scale distribution and velocities of galaxies and galaxy clusters. I am also interested in possible alternatives to the standard cosmological model, and observational tests which can distinguish particular alternatives from the standard cosmology. As an example, the "dark energy" may actually be telling us that the usual equations describing the expansion of the universe, based on general relativity, are not valid; in other words, we could be observing not the result of a mysterious form of energy density but rather the breakdown of our basic theory of gravitation.
On the observational side, I am a member of the Atacama Cosmology Telescope (ACT) project, which has built a custom-designed 6-meter microwave telescope with superconducting bolometric detectors to observe the microwave sky from the Atacama Desert in the Chilean Andes. ACT has produced microwave maps with arcminute angular resolution in three frequency bands. One result of these observations is the detection of dozens of galaxy clusters via their thermal distortion of the microwave radiation (the Sunyaev-Zeldovich effect), and another aspect of the project is optical follow-up observations of these newly detected galaxy clusters, using a variety of ground and space-based telescopes in several wave bands. Notable ACT achievements have included the first direct detection of gravitational lensing of the cosmic microwave background radiation, the first detection of seven acoustic peaks in the microwave background power spectrum, improved constraints on the parameters describing the standard cosmology, the first detection of galaxy cluster motions via their imprint on the microwave background radiation, and detection of one of the earliest and largest galaxy clusters. A new higher-sensitivity receiver with polarization capability, known as ACTPol, is being constructed and will begin operating on the telescope during 2013.
- “Detection of Galaxy Cluster Motions with the Kinematic Sunyaev-Zel'dovich Effect,” N. Hand et al. (58 authors including A. Kosowsky, primary author), Physical Review Letters 109, 041101 (2012).
- “The Atacama Cosmology Telescope: ACT-CL J0102-4215 `El Gordo,' A Massive Merging Cluster at Redshift 0.87,” F. Menanteau et al. (24 authors including A. Kosowsky), Astrophysical Journal 748, 7 (2012).
- “Detection of the Power Spectrum of Cosmic Microwave Background Lensing by the Atacama Cosmology Telescope,” S. Das et al. (41 authors including A. Kosowsky), Physical Review Letters 107, 021301 (2011).
- “The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz in the 2008 Survey,” T. Marriage et al. (69 authors including A. Kosowsky), Astrophysical Journal 737, 61 (2011).
- “The Atacama Cosmology Telescope: Cosmological Parameters from the 2008 Power Spectrum,” J. Dunkley et al. (67 authors including A. Kosowsky), Astrophysical Journal 739, 52 (2011).
- “The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectrum at 148 and 218 GHz from the 2008 Southern Survey,” S. Das et al. (67 authors including A. Kosowsky), Astrophys. J. 729, 62 (2011).
- “Galaxy Peculiar Velocities from Large-Scale Supernova Surveys as a Dark Energy Probe,” S. Bhattacharya, A. Kosowsky, J.A. Newman, and A. Zentner, Physical Review D 83, 043004 (2011).
- “Signature of Local Motion in the Microwave Sky,” A. Kosowsky and T. Kahniashvili, Physical Review Letters 106, 191301 (2011).
- “Dwarf Galaxies, MOND, and Relativistic Gravitation,” A. Kosowsky, Advances in Astronomy 2010, 357342 (2010).
- “A Future Probe of Gravity with Galaxy Cluster Velocities,” A. Kosowsky and S. Bhattacharya, Physical Review D 80, 062003 (2009).
- “Microwave Background Circular Polarization from Nonstandard Photon Couplings,” S.H.S. Alexander, J.R. Ochoa, and A. Kosowsky, Physical Review D 79, 063524 (2009).
- “Faraday Rotation Limits on a Primordial Magnetic Field from Wilkinson Microwave Anisotropy Probe Five-Year Data,” T. Kahniashvili, Y. Maravin, and A. Kosowsky, Physical Review D 80, 023009 (2009).
- "Dark Energy Constraints from Galaxy Cluster Peculiar Velocities," S. Bhattacharya and A. Kosowsky, Physical Review D 77, 083004 (2008).
- "Simulations of the Sunyaev-Zeldovich Effect from Quasars," S. Chatterjee, T. Di Matteo, A. Kosowsky, and I. Pelupessey, Monthly Notices of the Royal Astronomical Society 390, 535 (2008).
- "The Spectrum of Gravitational Radiation from Primordial Turbulence," G. Gogoberidze, T. Kahniashvili, and A. Kosowsky, Physical Review D 76, 083002 (2007).