Elena Pierpaoli

Tenure Track Appointments

• Professor, University of Southern California, 01/2011 –
• Associate Professor, University of Southern California, 04/2007 – 12/2010
• Assistant Professor, University of Southern California, 06/2006 – 03/2007
• Research faculty, Caltech, 09/01/2004 – 05/31/2006
• Research Staff, Princeton University, 01/01/2002 – 09/01/2004
• CITA National Fellow, University of British Columbia, 11/15/1998 – 11/14/2001

Visiting and Temporary Appointments

• Visiting Associate, Caltech, 06/2006 –
• Non-resident Affiliate, JPL, 09/2004 –

Summary Statement of Research Interests

I am a theoretical cosmologist, specialized in model comparison with data. I mainly work on the cosmic microwave background and the large scale structure of the Universe.

Research Keywords

Cosmology, large scale structure, cosmic microwave background, dark matter, data analysis

Research Specialties

As a theoretical cosmologist, my main aim is to determine the content of the Universe, its evolution and characteristics now and at very early times. While these questions have been outstanding issues for Humankind for centuries, we are now in the position to address them is a quantitative way through the study of astrophysical objects outside our own Galaxy. Two major astrophysical observables can be invoked for this purpose: the Cosmic Microwave Background (CMB) radiation, otherwise known as the radiation that comes to us almost from the times of the Big Bang, and the distribution of galaxies beyond our own. The study of such anisotropies has tremendously advanced the knowledge of the field. Indeed, they convey very straightforward information on the global geometry of the Universe, the kind of matter and energy it contains and also the kind of processes that very early on have seeded the inhomogeneities which have then evolved into the observed bound structures around us (e.g. galaxies and clusters of galaxies). One of my research topics consists in testing possible theoretical scenarios of our Universe by comparing the predictions it would imply for these anisotropies with the actual observations. My group has been involved in the data analysis of the last CMB satellite (Planck) and it is now working with two other collaborations (the Simons Observatory and CMB-S4) to better map this primordial radiation and potentially shed light on the existence of primordial gravitational waves.
Apart from the CMB, I also extensively work on galaxy clusters. Clusters are the biggest gravitationally–bound objects in our Universe and are composed of dark matter, galaxies and free “gas” (free charged particles). Clusters are important for two reasons: first they are tracers of the underlying matter distribution, second they form for gravitational collapse (contrasting cosmic expansion) and merging events of smaller objects (like galaxies). Studying clusters we can therefore probe the nature of the dark energy (leading the current expansion), dark matter and the assembly of luminous matter.

Detailed Statement of Research Interests

As a theoretical cosmologist, my main aim is to determine the content of the Universe, its evolution and characteristics now and at very early times. While these questions have been outstanding issues for Humankind for centuries, we are now in the position to address them is a quantitative way through the study of astrophysical objects outside our own Galaxy. Two major astrophysical observables can be invoked for this purpose: the Cosmic Microwave Background (CMB) radiation, otherwise known as the radiation that comes to us almost from the times of the Big Bang, and the distribution of galaxies beyond our own. The study of such anisotropies has tremendously advanced the knowledge of the field. Indeed, they convey very straightforward information on the global geometry of the Universe, the kind of matter and energy it contains and also the kind of processes that very early on have seeded the inhomogeneities which have then evolved into the observed bound structures around us (e.g. galaxies and clusters of galaxies). The last generation CMB satellite (Planck) has flown and has collected precious data. Part of my group has been involved in the preparation and data analysis of this mission. While the satellite is no longer operative, the data collected are still being re-analyzed, also in conjunction with data from other surveys. The Simons Observatory (SO), a new CMB ground-based experiment covering a smaller area of the sky but with a higher spatial resolution, will come on line in the next few years, and will produce precious complementary information to what Planck produced. The USC cosmology group is involved in its preparation and will have access to the data analysis.  At the same time, we are contributing to plan the next generation of CMB experiments, called CMB-S4. 

One of my research topics consists in testing possible theoretical scenarios of our Universe by comparing the predictions it would imply for these anisotropies with the actual observations. The kind of questions the CMB can help to answer involve the amount on type of dark matter and dark energy, as well as characteristics of the initial fluctuations imprinted by the big bang. 

Planck provided an exquisite measurement of the CMB total intensity.

However, the CMB radiation also has another property, the polarization, which could yield an equivalent amount of information, and could actually be the smoking gun for particular phenomena. Polarization information could be crucial to characterize very early Universe phenomena like inflation through the study of the gravitational waves they generate. 

Planck observed the polarization quite well, but future missions like SO and CMB-S4 will be able to  extract all possible science. As the polarization signal is much weaker than the total intensity one, it is more difficult to detect and also its observation may be more easily contaminated by other astrophysical objects emitting in the same band. For this reason, I dedicated part of my attention to the issue of polarization data analysis with focus on component separation and its impact on parameter determination. We worked on the potentials of future surveys to recover the signal of these gravitational waves and disentangle inflationary models. 

Apart from the CMB, I also extensively work on galaxy clusters. Clusters are the biggest gravitationally–bound objects in our Universe and are composed of dark matter, galaxies and free “gas” (free charged particles). Clusters are important for two reasons: (i) they are tracers of the underlying matter distribution, (ii) they form for gravitational collapse (contrasting cosmic expansion) and merging events of smaller objects (like galaxies). By studying clusters we can therefore probe the nature of the dark energy (leading the current expansion), dark matter and the assembly of luminous matter. Moreover, as the gas in clusters underwent very little processing, it is considered a pristine sample of what was created in the early Universe during nucleosynthesis. Clusters are classically observed in the optical and X–ray band because of their galaxy and gas emission respectively. I dealt with clusters observed in both wavebands. Recently, my group lead the construction of a large optical cluster catalog from the Sloan Digital Sky Survey. We also characterized the population of the brightest galaxies in the clusters. By looking at the light emitted in different colors, it is possible to determine the age and characterize their formation. This information is important in understanding how matter in the Universe first assembled. Current and future  ground observations (like DESI, LSST) as well as space experiments (WFIRST, JWST and Euclid) will greatly contribute to advance our understanding of structure formation in clusters.

 A very novel way of studying clusters is through their interaction with the CMB. As the gas scatters the CMB radiation, clusters are also detectable in CMB experiments in the radio and infrared bands through the so–called Sunyaev-Zel’dovich (SZ) effect. The unique feature of this effect is that it does not depend on distance, allowing to detect clusters that are very far away.  Planck has  produced a full–sky map of the most massive clusters in the Universe, while experiments from the ground  (ACTPol, SPT, SO) are complementing this information with the detection of smaller clusters on a smaller area of the sky, by producing more resolved images of clusters. 

We are also currently working on high–resolution images of targeted, massive nearby clusters from recently acquired ground–based observations. We are combining radio and X–ray images to extract information on the precise mass profile of the cluster, with the ultimate goal of understanding how processes like mass accretion or central cooling on the cluster occur and affect the structure evolution, and study substructures to characterize the properties of dark matter.

 Finally, we are using the information on cluster’s velocities that can be inferred from the SZ signal in order to constrain bulk flows on the largest scales in our Universe, as well as peculiar motions of distant objects. 

We plan to use these observations for understanding fundamental physical principles, like how gravity works on large scales and what is the nature of dark energy and dark matter. 

• PHYS 190-Freshman Colloquium: “What’s new in Cosmology today”, 2010-2011
• TASI lectures: The Cosmic Microwave Background, 2009-2010

• Simons Foundation Fellow, 2019-2020
• G. and V. Cocconi Prize (European Physical Society – awarded to the Planck team), Fall 2019
• Gruber Cosmology Prize (awarded to the Planck team), Fall 2018
• NASA Group Achievement Award – Planck data analysis and development team, Fall 2013
• NASA Group Achievement Award – Planck Data Analysis and operations Team , Fall 2011
• NSF ADVANCE Fellow, 07/2004 – 06/2010

Committees

• Member, WiSE College committee and advisory Board, 2010-2011
• Member, Graduate Admissions, 09/2006 – 08/2010
• Member, Graduate and undergraduate curriculum, 2009-2010
• Member, Strategic University Planning, Spring 2010
• Member, Cosmology program, 03/2007 – 12/2009

Media, Alumni, and Community Relations

• USC Vision and Voices event “Einstein Cosmic Messangers”- organizer, 2010-2011
• 217th AAS Meeting: Press release on Planck early results, Spring 2011
• Invited guest at the USC College Program: “Junior Faculty Showcase”, 2007-2008
• Invited guest at the WISE Undergraduate Students Residence at USC, 2006-2007
• Invited guest at the USC College Doctoral Fellowship Program:”Inside the Academics Studio”, 2006-2007

Professional Memberships

• American Astronomical Society, 12/2010 –