Butsuri

On March 21, 2013, the Planck collaboration has released the first 15.5-month data of temperature anisotropy of the cosmic microwave background, as well as the papers describing the cosmological interpretation. The most important discovery from the Planck data is that the amplitude of the primordial curvature perturbation on large scales is slightly larger than that on small scales. This is the first time that such a variation of the amplitudes of fluctuations on scales has been measured from the cosmic microwave background data alone with more than 5 standard deviations. This discovery provides the strongest ever evidence of the "cosmic inflation" paradigm.

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The cosmic microwave background is polarized, and the pattern formed by polarization directions in the sky can be decomposed into the so-called "E-mode" and "B-mode" patterns. Motion of plasmas falling into gravitational potential wells at the photon decoupling epoch generates E-mode polarization, whereas it cannot generate B-modes. There are two sources of B-mode polarization within the context of the standard cosmological model: one is the gravitational lensing effect converting E-modes to B-modes; and the other is the primordial gravitational waves generated during cosmic inflation. The E-mode polarization has been measured repeatedly over the past years, and we have witnessed a revolutionary growth in the quality and quantity of the B-mode measurements from the summer 2013 to the spring 2014. We review the current status of the polarization measurements and discuss future prospects.

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The Hartree-Fock-Bogoliubov (HFB) theory, an extended theory of the Bardeen-Cooper-Schrieffer theory, is rich in physical and mathematical structures. Nuclear physicists have struggled to find compact formulae to evaluate HFB transition matrix elements of many-body operators, which handle the pairing correlations. A recent breakthrough has brought us a new formula in terms of the Pfaffian. In the derivation, the Grassmann algebra and the Fermion coherent states were employed. These findings have opened up a new way to tackle the quantum many-body problems in the presence of the pairing.

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A large fraction of the baryons in the Universe, about 90%, have not been converted into stars, but instead reside in the hot, X-ray emitting, diffuse plasma which fills the space between galaxies. Until very recently, however, it was only possible to measure the properties of the brightest parts of this X-ray plasma. Thanks to the low background nature of the science instruments, Suzaku has opened up the possibility of exploring the clusters of galaxies out to the Virial radius for the first time. This has allowed us to study the ongoing largescale structure formation process by looking at how the gas that is constantly accretes onto clusters of galaxies from the surrounding cosmic web filaments comes into equilibrium with the rest of the intra-cluster medium. The mapping observations of the nearest and the brightest Perseus cluster of galaxies, being composed of 84 pointings in total in 8 different radial directions, revealed that the entropy distribution is flatter than that of theoretical prediction and the density at the cluster outskirt is larger than what is evaluated using the Sunyaev-Zel'dovich effect. These intriguing deviations can be explained if the accreting material is originally clumpy, and it retains the this inhomogeneity in density after it passes the shock front. The same mapping observations of the Perseus cluster have also allowed us to measure the metal content of the intracluster medium with exquisite accuracy out to the virial radius. The data revealed that the iron abundance is distributed very uniformly beyond the cluster core, not only as a function of radius but also as a function of azimuth. The fact that the metals are so well mixed, instead of following the distribution of the stars, implies that the metals must have been ejected from the galaxies into the intragalactic medium before the clusters formed and the entropy became stratified, preventing further mixing from taking place efficiently. The result suggests that the outflows driven by supernova explosions and by the supermassive black holes at the centers of massive galaxies were extremely powerful more than 10 billion years ago. This is new and important information that must be considered when modelling the evolution of galaxies in the early Universe. In addition, it leads to the important prediction that the metallicity in and around all massive clusters should be constant at about 0.3 of the solar value, which is the same value as measured in the Perseus cluster.

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