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CMB Cosmology: A Special Section of Progress of Theoretical and Experimental Physics (PTEP)
Norisuke Sakai
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CMB Cosmology : A Special Section of Progress
of Theoretical and Experimental Physics (PTEP)


Progress of Theoretical and Experimental Physics (PTEP) publishes from time to time special sections comprising a number of review articles on hot topics. The June 2014 issue presents a special section entitled "CMB Cosmology". This special section is a collection of twelve articles on the theoretical and experimental studies of Our Universe by means of the cosmic microwave background (CMB), covering from basics to the forefront of research.


Systematic investigations of the cosmic microwave background (CMB) were initiated by the discovery of noise radio waves of the cosmic origin by A. A. Penzias and R.W. Wilson in 1965 and have a long history. In recent years, these investigations of CMB have revolutionized our understanding of the Universe, and the importance of CMB has increased dramatically. In particular, the observation by NASA's Cosmic Background Explorer (COBE) satellite in 1990's has given a precise measurement of energy spectrum and has discovered a temperature anisotropy of CMB. These discoveries have established the big bang universe model as a standard model. At the same time, it suggested the possibility for CMB studies to provide powerful means to explore the cosmological structure formation and the evolution of the universe.

A number of ground-based or balloon-borne experiments to study CMB have followed the lead of the COBE experiment. Among many experiments, NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite was planned as the successor of COBE satellite to study CMB and had brought the cosmological research with CMB to the next level. It had shown the flatness of our universe to high accuracy, and determined the spectrum of the primordial fluctuations of the Universe. Moreover it had provided accurate determinations of various cosmological parameters. These successes have opened up a possibility to explore the early universe before the Big Bang experimentally. ESA's Planck satellite and a host of ground-based experiments have been giving a continuing stimulus for this revolution initiated by the CMB discovery.

The completion of the WMAP project in 2012 and the release of Planck satellite data on the CMB temperature in 2013 have essentially completed the cosmological studies based on observations of CMB temperature anisotropy. Because of this fact, it is now the most appropriate time to review the achievements of CMB cosmology up until today, and to make clear what should be done by the next generation CMB experiments.

Of course the successes of WMAP have been brought about not only by experimentalists, but also by close cooperation with theorists. From the beginning, close interplay between theoretical and observational studies of CMB was indispensable in studying CMB to revolutionize cosmology. For this reason, both articles on experimental studies and on basic theoretical studies are represented in this special section on CMB cosmology.

WMAP is succeeded by Planck satellite and other high precision ground-based polarization measurements. They are producing new interesting data. However, WMAP is still playing an important role and the understanding of the basic concepts of WMAP and of the underlying theoretical studies is indispensable to understand and evaluate these new data properly. From this point of view, the special section contains twelve articles reviewing all essential points and latest developments of CMB cosmology from theoretical particle physics to astronomy.

The contents of the twelve articles are as follows. The principal investigator of the WMAP team, Charles L. Bennett and a principal member, Eiichiro Komatsu of the WMAP team give a detailed review of results of various CMB observations focusing on the WMAP experiment, and their implications to cosmology. Moreover, a compact and lucid review is made for data processing, noise and foreground separation methods, and estimation methods of cosmological parameters.

Reviews are also provided on theoretical investigations from the viewpoint of cosmological models and particle physics models. A review on basic aspects of CMB temperature anisotropy and cosmology is given by the leading theoretician of the field, Naoshi Sugiyama. Jun'ichi Yokoyama reviews the history of inflationary universe models and their verification through CMB experiments. Shinji Tsujikawa describes how to select various inflation models by means of CMB data. Tomo Takahashi gives a review of the significance and current experimental status of non-Gaussianity of CMB temperature fluctuations. Kazunori Nakayama reviews impacts of CMB observations on theoretical particle physics. Hiroyuki Tashiro describes information that can be derived from future high precision measurements of the CMB energy spectrum.

From the astronomy and astrophysics side, Toshiya Namikawa reviews the influence of gravitational lensing due to the cosmological matter distribution on the CMB temperature and polarization. Kiyotomo Ichiki describes emissions from Our Galaxy and other galaxies which can distort CMB observational data. Atsushi J. Nishizawa gives a review of the influence of time-dependent gravitational potential on CMB (the integrated Sachs-Wolfe effect) and its cosmological implications. Tetsu Kitayama describes the present and future of the cosmology and astrophysics using the effect of hot plasma in clusters of galaxies on CMB (the Sunyaev-Zeldovich effect). Lastly, Aravind Natarayan and Naoki Yoshida review the significance of CMB and future 21 cm line experiments for the investigation of the cosmological re-ionization history from the viewpoint of experts on star formation.

There has been no precedent of such a collection of review articles on the present and future of the CMB research from so many aspects and by so many experts actively involved in research of these fields. We anticipate that this special section should be extremely useful not only for experts, but also for those young researchers and graduate students, as well as researchers of related subject areas who wish to enter the research of this field.

Fig. 1: Experimental results from WMAP satellite.


  • "Introduction to temperature anisotropies of Cosmic Microwave Background radiation"
    Naoshi Sugiyama: Prog. Theor. Exp. Phys. (2014) 06B101. doi:10.1093/ptep/ptu073
  • "Results from the Wilkinson Microwave Anisotropy Probe"
    Eiichiro Komatsu and Charles L. Bennett (on behalf of the WMAP science team): Prog. Theor. Exp. Phys. (2014) 06B102. doi:10.1093/ptep/ptu083
  • "Inflation: 1980-201X"
    Jun'ichi Yokoyama: Prog. Theor. Exp. Phys. (2014) 06B103. doi:10.1093/ptep/ptu081
  • "Distinguishing between inflationary models from cosmic microwave background"
    Shinji Tsujikawa: Prog. Theor. Exp. Phys. (2014) 06B104. doi:10.1093/ptep/ptu047
  • "Primordial non-Gaussianity and the inflationary Universe"
    Tomo Takahashi: Prog. Theor. Exp. Phys. (2014) 06B105. doi:10.1093/ptep/ptu060
  • "Impacts of precision CMB measurements on particle physics"
    Kazunori Nakayama: Prog. Theor. Exp. Phys. (2014) 06B106. doi:10.1093/ptep/ptu079
  • "CMB spectral distortions and energy release in the early universe"
    Hiroyuki Tashiro: Prog. Theor. Exp. Phys. (2014) 06B107. doi:10.1093/ptep/ptu066
  • "Cosmology from weak lensing of CMB"
    Toshiya Namikawa: Prog. Theor. Exp. Phys. (2014) 06B108. doi:10.1093/ptep/ptu044
  • "CMB foreground: A concise review"
    Kiyotomo Ichiki: Prog. Theor. Exp. Phys. (2014) 06B109. doi:10.1093/ptep/ptu065
  • "The integrated Sachs-Wolfe effect and the Rees-Sciama effect"
    Atsushi J. Nishizawa: Prog. Theor. Exp. Phys. (2014) 06B110. doi:10.1093/ptep/ptu062
  • "Cosmological and astrophysical implications of the Sunyaev-Zel'dovich effect"
    Tetsu Kitayama: Prog. Theor. Exp. Phys. (2014) 06B111. doi:10.1093/ptep/ptu055
  • "The Dark Ages of the Universe and hydrogen reionization"
    Aravind Natarajan and Naoki Yoshida: Prog. Theor. Exp. Phys. (2014) 06B112. doi:10.1093/ptep/ptu067

Contact Information:

Hideo Kodama (Professor, Theory Center, Institute of Particle and Nuclear Physics, KEK)
Email: hideo.kodama@kek.jp
Eiichiro Komatsu (Director, Max Planck Institute for Astrophysics)
Email: komatsu@mpa-garching.mpg.de


Norisuke Sakai is the Editor-in-Chief of Progress of Theoretical and Experimental Physics, and a visiting professor at Research and Education Center for Natural Sciences, Keio University. After receiving a D.Sci from the University of Tokyo, he worked at Max-Planck Institute of Physics, Rutherford Laboratory, Tohoku University, Nordita, Fermilab, KEK, Tokyo Institute of Technology and Tokyo Woman's Christian University before joining Keio University in 2014. His research field is theoretical particle physics.

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