Graduate Students

• Brown, Benjamin

Former Students

• Suman Bhattacharya

Associate Professor

Ph.D. 1994, University of Chicago

Research: Cosmology and Astrophysics

Arthur Kosowsky is an undergraduate advisor.

My research so far 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 of galaxies in the universe. 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 is building a custom-designed 6-meter microwave telescope with superconducting bolometric detectors to observe the microwave sky from the Atacama Desert in the Chilean Andes (see http://www.physics.princeton.edu/act/). ACT will produce microwave maps with arcminute angular resolution and micro-Kelvin temperature sensitivity, in three frequency bands. One result of these observations will be the detection of thousands 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 telescopes in Chile and also the new Southern African Large Telescope (see http://www.salt.ac.za).

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Selected Publications

• "Dark Energy Constraints from Galaxy Cluster Peculiar Velocities," S. Bhattacharya and A. Kosowsky, Phys. Rev. D 77, 083004 (2008)
• "Systematic Errors in Sunyaev-Zeldovich Surveys of Galaxy Cluster Velocities," S. Bhattacharya and A. Kosowsky, J. Cosm. Astropart. Phys. 08, 030 (2008)
• "Effects of Quasar Feedback on Galaxy Groups," S. Bhattacharya, T. Di Matteo, and A. Kosowsky, Mon. Not. Royal Ast. Soc. 389, 34 (2008)
• "Simulations of the Sunyaev-Zeldovich Effect from Quasars," S. Chatterjee, T. Di Matteo, A. Kosowsky, and I. Pelupessey, Mon. Not. Royal Ast. Soc., in press (2008)
• "Detectability of Gravitational Waves from Phase Transitions," T. Kahniashvili, A. Kosowsky, G. Gogoberidze, and Y. Maravin, Phys. Rev. D 78, 043003 (2008)
• "Constraints on Cosmological Parameters from Velocity Statistics of Galaxy Clusters," S. Bhattacharya and A. Kosowsky, Astrophys. J. Lett. 659, 83 (2007)
• "The Sunyaev-Zeldovich Effect from Quasar Feedback," S. Chatterjee and A. Kosowsky, Astrophys. J. Lett. 661, 113 (2007)
• "The Spectrum of Gravitational Radiation from Primordial Turbulence," G. Gogoberidze, T. Kahniashvili, and A. Kosowsky, Phys. Rev. D 76, 083002 (2007)
• "Milgrom Mass Models for Spiral Galaxies from Two-Dimensional Velocity Maps," E.I. Barnes, A. Kosowsky, and J. Sellwood, Astron. J. 133, 1698 (2007)