Ravi K. Sheth

Ravi K. Sheth
Standing Faculty

Professor and Graduate Chair


Research Areas: Cosmology, Galaxy Formation, Stochastic processes



I was a Marshall Scholar at Cambridge where I got my PhD in 1994. I then spent time at UCBerkeley (1994-1996), the Max-Planck Institut fuer Astrophysik in Garching (1996-1999), and Fermilab (1999-2001) before becoming an Assistant Professor at the University of Pittsburgh (2002-2004).  I moved to Penn in 2005, where I became an Associate Professor in 2007 and a full Professor in 2009. I spend my summers at the International Centre for Theoretical Physics in Trieste, and serve as a member of the Science Advisory Board of the Kaufman Foundation and the Scientific Council of the East Africa Institute for Fundamental Research.


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.

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. I have also used physically motivated models to illustrate the ubiquity of what are now called scale-dependent bias, tidal bias and velocity bias.

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.  From 2004 to 2006 I extended the approach to predict how the morphology (sheets, filaments, voids) rather than simply the density, of large scale structure evolves.  I have since studied 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.  

In 1996 I solved an old combinatorial problem on the partitions of integers which turns out to have interesting connections to coagulation and branching processes.  In 1998 I showed how to extend the approach to model the counts in cells distribution in the nonlinear density field.  In 2002, I developed a new method for estimating the evolution of the optical depth in the Lyman-alpha forest. In 2005, I showed how to use Mark Correlations to quantify and model environmental trends in the galaxy distribution.  In 2007 my collaborators and I showed that local black hole samples are a biased subset of all galaxies, a study that has seen renewed interest since 2016.  Between 2007-2009 I 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. In 2013, I showed how to unify the Excursion Set and Peaks Theory descriptions of the Cosmic Web, and provided the first quantitative predictions for the effects of tides on the large scale structure of biased tracers, sometimes called nonlocal or tidal bias.  In 2020, I extended these methods to estimate the abundance of Primordial Black Holes.  In 2016 my collaborators and I described a new standard ruler for cosmological measurements.  In 2018 I showed that self-consistently accounting for stellar population gradients yields good agreement between dynamical (Jeans equation) and stellar population based estimates of the stellar masses in galaxies. 

Courses Taught

At Penn:

Non-science majors:  Survey of the Universe; Life in the Universe; The Big Bang and Beyond 
Science majors: Mechanics and Waves; Electromagnetism
Graduate:  Mechanics, Dynamics and Chaos; Introduction to Cosmology


 Lecturer          Observational probes of cosmology, EAIFR, Kigali (August 2019)
 Lecturer          Large scale structure, ICTP, Trieste (June 2018)
 GIAN Lectures     Nonlinear structure formation, JMI, Delhi (April 2018)
 Lecturer          Structure formation in cosmology, IPM, Tehran (August 2017)
 Lecturer           Nonlinear structure formation, ON, Rio de Janiero (August 2016)
 Lecturer           Dark matter structures, IFT, Sao Paolo (July 2016)
 Lecturer           Statistical methods in astronomy, University of Padova (May 2016)
 Lecturer           Formation of cosmic structures & IUCAA, Pune (February 2016)
 Lecturer           Structure formation, Bogota, Columbia (November 2015)
 Lecturer           Large scale structure, SAIFR, Sao Paolo (December 2014)
 Lecturer           Dark matter structures, ISAPP, Belgirate (July 2014)
 Lecturer           Statistical methods in astronomy, University of Padova (May 2014)
 Lecturer           Statistical approaches in cosmology, IHP, Paris (November 2013)
 Lecturer           Galaxy surveys, TIFR, India (December 2012)
 Lecturer           Structure formation, STIAS, South Africa (Jan 2012)
 Visiting Lecturer  Nonlinear clustering, HRI, India (February 2009)
 Lecturer           XIII BSCG, Rio de Janiero, Brazil (July 2008)
 PIRE Lectures      Hierarchical structure formation, Santiago, Chile (March 2007)
 Lecturer           Galaxies and Cosmology, University of Padova (January 2007)
 NOVA Lectures    The halo model, The Netherlands (November 2006)

Selected Publications

A universal threshold for primordial black hole formation
A. Escriva, C. Germani, Ravi K. Sheth, 2020, Physical Review D, 101, 044022 (5 pages)

M*/L gradients driven by IMF variation: Large impact on dynamical stellar mass estimates
M. Bernardi, Ravi K. Sheth, et al., 2018, Monthly Notices of the Royal Astronomical Society, 477, 2560-2571

Beating non-linearities: Improving the Baryon Acoustic Oscillations with the linear point
S. Anselmi, G. D. Starkman & Ravi K. Sheth, 2016, Monthly Notices of the Royal Astronomical Society, 455, 2474-2483

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

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

On estimating luminosity and redshift distributions in photometric redshift surveys
Ravi K. Sheth,  2007, Monthly Notices of the Royal Astronomical Society, 378, 709-715

The halo model description of mark correlations
Ravi K. Sheth,  2005, Monthly Notices of the Royal Astronomical Society, 364, 796-806

On the environmental dependence of halo formation
Ravi K. Sheth & G. Tormen, 2004, Monthly Notices of the Royal Astronomical Society, 350, 1385-1390

A hierarchy of voids:  Much ado about nothing
Ravi K. Sheth & R. van de Weygaert, 2004, Monthly Notices of the Royal Astronomical Society, 350, 517-538

The Halo Model of Large Scale Structure
Asantha Cooray & Ravi K. Sheth, 2002, Physics Reports, 372, 1-129.

Ellipsoidal collapse and an improved model for the number and spatial distribution of dark matter haloes
Ravi K. Sheth, H. J. Mo & G. Tormen, 2001, Monthly Notices of the Royal Astronomical Society, 323, 1-12

Large scale bias and the peak background split
Ravi K. Sheth & G. Tormen, 1999, Monthly Notices of the Royal Astronomical Society, 308, 119-126

An excursion set model for the distribution of dark matter and dark matter halos
Ravi K. Sheth, 1998, Monthly Notices of the Royal Astronomical Society, 300, 1057-1070

Galton-Watson branching processes and the growth of gravitational clustering
Ravi K. Sheth, 1996, Monthly Notices of the Royal Astronomical Society, 281, 1277-1289


Scientific Council, East Africa Institute for Fundamental Research, Rwanda (2018-)
Vikram Sarabhai Chair, Indian Nat. Sci. Acad., India (2017-2018)
Associate Member, Simons CCA, New York (2016-)
Visiting Professor, JMI, Delhi, India (2016-2018)
Staff Associate, ICTP, Trieste, Italy (2015-2023)
Senior Associate, ICTS, Bangalore, India (2014--2016)
Visiting Professor, Institut Henri Poincare, France (November 2013)
Visiting Professor, LUTH - Meudon Observatory, France (June 2013)
Science Advisory Board, Kaufman Foundation, Pittsburgh (2012-)
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)