Ravi Sheth

Cosmology, Galaxy Formation, Stochastic processes

My work on halo abundances and clustering forms the basis of methods which use clusters (e.g., X-ray luminosities, temperatures, the Sunyaev-Zeldovich effects, galaxy velocity dispersions) to study cosmology. Recently, I extended the approach to predict how the morphology (sheets, filaments, voids) rather than simply the density, of large scale structure evolves, and how these predictions are modified if the initial conditions were non-Gaussian, or if the force of gravity does not decrease as the inverse-square of separation.

I have played a leading role in the development of what is now the standard model of nonlinear clustering and biasing: the Halo Model. It is the currently the best language for interpreting measurements of weak lensing, the thermal and kinematic Sunyaev-Zeldovich effects, and how galaxy clustering depends on galaxy type, both in real and in redshift space. In 2004, I showed that dark matter halo formation is correlated with environment; I also discussed why, and pointed out that understanding this correlation is necessary if the Halo Model is to be used as a precision tool for cosmology. This correlation was sufficiently unexpected and the consequences
sufficiently important that a number of groups have since confirmed that the effect does indeed exist: the effect is now called Assembly Bias.

In 2002, I developed a new method for estimating the evolution of the optical depth in the Lyman-® forest. In 2005, I showed how to use Mark Correlations to quantify environmental trends in the galaxy distribution. More recently, I have developed methods for making unbiased estimates of the galaxy luminosity function and galaxy scaling relations from photometric redshift surveys. The methods can have broader impact, since they can be applied to studies where peculiar velocities are an important component of the observed redshift: these include using star counts to model the structure of our galaxy, and estimating the luminosity function of dwarf galaxies in our local (·50Mpc) neighborhood. And in 2012, I provided a simple formula for the first crossing distribution by walks with correlated steps which is accurate for a wide range of barrier shapes. I then showed how to extend it to treat n-dimensional walks – thus providing the first realistic fully analytic model of nonlocal bias. In the process, I showed how to unify the Excursion Set and Peaks Theory descriptions of the Cosmic Web.


1990 – 1994 Ph.D. in Astrophysics, Marshall Scholar, Institute of Astronomy and Jesus College, University of Cambridge
1986 – 1990 BSc (High Honors) in Physics, Dana S. McGill Scholar,  Haverford College
1983 – 1986 Four ‘IB’ HL certificates Kodaikanal International School, India

Research Interests: 

I develop physical models and statistical methods which allow the data from large scale galaxy and cluster surveys to constrain models of galaxy formation and cosmology.

Selected Publications: 

An accurate tool for the fast generation of dark matter halo catalogs P. Monaco, E. Sefusatti, S. Borgani, M. Crocce, P. Fosalba, Ravi K. Sheth & T. Theuns. 2013 Monthly Notices of the Royal Astronomical Society, revised

On the self-consistency of the excursion set approach I. Achitouv, Y. Rasera, Ravi K. Sheth & P.-S. Corasaniti. 2013 Physical Review Letters, submitted (arXiv:1212.1166)

Stochastic bias in multi-dimensional excursion set approaches E. Castorina & Ravi K. Sheth. 2013 Monthly Notices of the Royal Astronomical Society, revised (arXiv:1301.5128)

Peak-peak correlations in the cosmic background radiation from cosmic strings M. S. Movahed, B.Javanmardi & Ravi K. Sheth. 2013 Monthly Notices of the Royal Astronomical Society, revised (arXiv:1212.0964)

Systematic effects on the luminosity size relation: Dependence on model fitting and morphology M. Bernardi, A. Meert, V. Vikram, M. Huertas-Company, S. Mei, F. Shankar & Ravi K. Sheth. 2013 Monthly Notices of the Royal Astronomical Society, revised (arXiv:1211.6122)

Ellipsoidal halo finders and implications for models of triaxial halo formation G. Despali, G. Tormen & Ravi K. Sheth. 2013 Monthly Notices of the Royal Astronomical Society, in press (arXiv:1212.4157)

Excursion set peaks: A self-consistent model of dark halo abundances and clustering A. Paranjape, Ravi K. Sheth & V. Desjacques. 2013 Monthly Notices of the Royal Astronomical Society, in press (arXiv:1210.1483)

Nonlocal Lagrangian bias Ravi K. Sheth, K. C. Chan & R. Scoccimarro. 2013 Physical Review D, 87, 083002 (13 pages)

On the anisotropic density distribution on large scales P. Papai & Ravi K. Sheth. 2013 Monthly Notices of the Royal Astronomical Society, 429, 1133–1138

Measures of galaxy environment II - Rank ordered mark correlations R. Skibba, Ravi K. Sheth, et al. 2013 Monthly Notices of the Royal Astronomical Society, 429, 458–468

Scale dependent halo bias in the excursion set approach M. Musso, A. Paranjape, Ravi K. Sheth. 2012 Monthly Notices of the Royal Astronomical Society, 427, 3145–3158

Peaks theory and the excursion set approach A. Paranjape & Ravi K. Sheth. 2012 Monthly Notices of the Royal Astronomical Society, 426, 2789–2796

Lagrangian bias in the local bias model N. Frusciante & Ravi K. Sheth. 2012 Journal of Cosmology and Astroparticle Physics, 11, 016

Cosmic tides U.-L. Pen, Ravi K. Sheth, J. Harnois-Deraps, X. Chen, Z. Li. 2012 Physical Review D, submitted (arXiv:1202.5804)

Courses Taught: 

Courses Developed and Taught in Trieste:

Spring 2012 Cosmology ICTP Diploma

Spring 2012 Large Scale Structure SISSA PhD

Courses Developed and Taught at Penn:

Spring 2013 Survey of the Universe 125 non-science majors

Spring 2010 The Big Bang and Beyond 60 non-science majors

Fall 2009 The Big Bang and Beyond 25 freshman

Fall 2008 Survey of the Universe 60 non-science majors

Spring 2008 The Big Bang and Beyond 15 non-science majors

Fall 2007 The Big Bang and Beyond 13 non-science majors

Spring 2007 Life in the Universe 19 non-science majors

Fall 2006 The Big Bang and Beyond 115 non-science majors

Spring 2006 Life in the Universe 26 non-science majors

Fall 2005 Physics I: Mechanics and Waves 83 physics/engineering majors

Spring 2005 Mechanics, Dynamics and Chaos 4 graduate students

Courses Developed and Taught at Pitt:

Spring 2004 Stonehenge to Hubble 100 non-science majors

Fall 2003 Introduction to Astronomy 100 physics majors

Spring 2003 Galactic and Extra-galactic Astronomy 7 graduate students

Fall 2002 Introduction to Astronomy 100 physics majors

Spring 2002 Radiative Processes in Astrophysics 7 graduate students

Courses Developed and Taught Elsewhere:

Lecturer Galaxy surveys TIFR, India (December 2012)

Lecturer Structure formation STIAS, South Africa (Jan 2012)

Visiting Lecturer Nonlinear clustering HRI, India (February 2009)

Invited Lecturer XIII BSCG Rio de Janiero, Brazil (July 2008)

PIRE Lecturer Hierarchical structure formation Santiago, Chile (March 2007)

Invited Lecturer Galaxies and Cosmology University of Padova (January 2007)

NOVA Lecturer The halo model The Netherlands (November 2006)

Other Affiliations: 

Senior Visiting Scholar AIMS, Cape Town South Africa (2012–2015)

Visiting Professor LUTH - Meudon Observatory France (June 2012)

Visiting Professor GEPI - Meudon Observatory France (June 2011)

Visiting Scholar IPhT-CEA Saclay, France (June 2010)

Visiting Professor APC, Paris 7 Diderot Paris, France (June 2009)


CV (file):