Paniez Paykari

I am a cosmologist. I have been a post-doctoral researcher in the CosmoStat laboratory at CEA-Saclay since January 2010.
My primary field of research is the Cosmic Microwave Background (CMB). I work under the supervision of Dr Jean-Luc Starck . I was a Planck Associate Scientist until January 2014.

Contact info:

Tel: +33 1 69 08 99 27
Fax: +33 1 69 08 65 77
email: paniez.paykari AT cea DOT fr


Cosmic Microwave Background (CMB) Power Spectrum
Cosmic Microwave Background (CMB) is the light left over since the Big Bang. This left over radiation gives us clues about the phyiscs of the early universe, as well as the late universe through its journey from the last scattering surface (LSS) to us. The CMB radiation is very rich in terms of the number of parameters it can constrain and the quanity of the constraint. One way to estimate the cosmological parameters is by estimating the CMB power spectrum from a CMB anisotropy map measured by surveys such as WMAP and Planck . I have developed a technique, the TOUSI algorithm (see Softwares below), which estimates the theoretial power spectrum from a measured CMB power spectrum. This technique is based on the sparsity of the CMB power spectrum in the Discrete Cosine Transfrom (DCT) and Wavelet Transform (WT) dictionaries. For more information on these techniques please visit Jean-Luc Starck 's home page.

Primordial Power Spectrum Reconstruction
The primordial power spectrum describes the initial perturbations in the Universe which eventually grew into the large-scale structure we observe today, and thereby provides an indirect probe of inflation or other structure-formation mechanisms. This power spectrum can be reconstructed if we know the state of the universe today and its evolution since the Big Bang. One approach is to use the CMB power spectrum to reconstruct the primodial power spectrum. I investigate the optimal reconstruction method for this spectrum from CMB data, based on the sparsity of the CMB power spectrum and the primoridal power spectrum.

Sparse Sampling of the Sky
Observing the sky is expensive both in time and cost, raising questions regarding the optimal investment of this time and money. I investigate the criteria for selecting amongst observing strategies for constraining the galaxy power spectrum and the cosmological parameters. Depending on the parameters of interest, it may be more efficient to observe a larger, but sparsely sampled, area of sky instead of a smaller contiguous area. By making use of the principles of Bayesian Experimental Design, it is possible to investigate the advantages and disadvantages of the sparse sampling of the sky and discuss the circumstances in which a sparse survey is indeed the most efficient strategy.

Philosophy of Cosmology
Recently, I have become very interested in the philosophy of cosmology. I look forward to the day when it is defined as a new field in its own right, having its own problems and motivations. Observational cosmology is going through a golden age of discovery and has turned into a successful empirical discipline. However, a deeper understanding of the science of cosmology must involve deeper investigation into physics, philosophy, and cosmogony - a philosophy of cosmology. The questions I am currently interested in include:
1. The 'multi-universe' and 'bubble-universe' hypotheses and their testability.
2. The entropy of the universe and the arrow of time.
3. Natures of 'fundamental laws' and 'fundamental constants'.


  • Oct 2006 - Oct 2009: Imperial College London UK
    Supervisor: Prof. Andrew H. Jaffe
  • Sep 2002 - Jun 2006: University College London UK
    Astrophysics Msci (Overall result: 85%), Dean's list


Book Chapters:

  • P Paykari, J-L Starck, 2012 .
    "CMB Data Analysis" in Advances in Machine Learning and Data Mining for Astronomy
    Chapman and Hall, Eds.: M. Way, J. Scargle, K. Ali, A Srivastava.

Refereed Articles:

  • F. Lanusse, P. Paykari, J.-L. Starck, F. Sureau, J. Bobin, submitted to A&A
    PRISM: Recovery of the Primordial Power Spectrum from Planck Data
  • F. Sureau, J.-L. Starck, J. Bobin, P. Paykari, A. Rassat, A&A 566, A100 (2014)
    Sparse Point-Source Removal for Full-Sky CMB Experiments: Application to WMAP 9-year Data
  • A. Rassat, J.-L. Starck, P. Paykari, F. Sureau, J. Bobin, A&A (accepted) arXiv:1405.1844
    Planck CMB Anomalies: Astrophysical and Cosmological Foregrounds and the Curse of Masking
  • P. Paykari, F. Lanusse, J.-L. Starck, F. Sureau, J. Bobin, A&A 566, A77 (2014)
    PRISM: Sparse Recovery of the Primordial Power Spectrum
  • J. Bobin, F. Sureau, J.-L. Starck, A. Rassat, P. Paykari, A&A 563, A105 (2014)
    Joint Planck and WMAP CMB Map Reconstruction
  • P. Paykari, S. Pires, J. -L. Starck, A. H. Jaffe, arXiv:1306.3035
    Sparsely Sampling the Sky: Regular vs Random Sampling
  • Planck 2013 results. XV. CMB power spectra and likelihoodarXiv:1303.5075
  • Planck 2013 results. I. Overview of products and scientific results, arXiv:1303.5062
  • J. Bobin, F. Sureau, P. Paykari, A. Rassat, S. Basak, J. -L. Starck, A&A 553, L4 (2013)
    WMAP 9-year CMB estimation using sparsity
  • P. Paykari, A. H. Jaffe, MNRAS 433, 3523 (2013)
    Sparsely Sampling the Sky: A Bayesian Experimental Design Approach
  • P. Paykari, J-L. Starck, M. J. Fadili, A&A 541, A74 (2012)
    True CMB Power Spectrum Estimation
  • G. Nicholson, C. R. Contaldi, P. Paykari, JCAP01 (2010) 016
    Reconstruction of the Primordial Power Spectrum by Direct Inversion
  • P. Paykari, A. H. Jaffe, APJ 711, 1 (2010)
    Optimal Binning of the Primordial Power Spectrum

Conference Proceedings


  1. SCCC21 Conference - Portugal - Jun 2014
  2. ICG Portsmouth - Cosmology Seminars Series - Mar 2013
  3. Institu d'Astrophysique de Paris - ICAP Series - Feb 2013
  4. Imperial College London - CAPAC Cosmology Seminars Series - Nov 2012
  5. Oxford University - Cosmology Seminars Series - Nov 2012
  6. Cambridge University - Cosmology Seminars Series - Nov 2012 Invited
  7. SAp CEA Saclay - Post-doc Seminars Series - Nov 2012
  8. CITA Canada - Cosmology Seminars Series - Jun 2012 Invited
  9. ADA7 Conference - Corsica - May 2012
  10. PFNG Conference - India - Dec 2010
  11. UKCosmo - Cardiff University UK - 2009 Invited
  12. UKCosmo - Kings College London UK - 2008
  13. QueenMary University UK - 2008
  14. IPM Institute Iran - 2007


  • PRISM algorithm and results.