Evolution of linear cosmological perturbations and its observational implications in Galileon-type modified gravity

A scalar-tensor theory of gravity can be made not only to account for the current cosmic acceleration, but also to satisfy solar-system and laboratory constraints, by introducing a non-linear derivative interaction for the scalar field. Such an additional scalar degree of freedom is called "Galileon". The basic idea is inspired by the DGP braneworld, but one can construct a ghost-free model that admits a self-accelerating solution. We perform a fully relativistic analysis of linear perturbations in Galileon cosmology. Although the Galileon model can mimic the background evolution of standard $\Lambda$CDM cosmology, the behavior of perturbation is quite different. It is shown that there exists a super-horizon growing mode in the metric and Galileon perturbations at early times, suggesting that the background is unstable. A fine-tuning of the initial condition for the Galileon fluctuation is thus required in order to promote a desirable evolution of perturbations at early times. Assuming the safe initial condition, we then compute the late-time evolution of perturbations and discuss observational implications in Galileon cosmology. In particular, we find anticorrelations in the cross-correlation of the integrated Sachs-Wolfe effect and large scale structure, similar to the normal branch of the DGP model.Comment: 15 pages, 11 figures; v2: References added, typos correcte

Exotic Structure of Carbon Isotopes

We studied firstly the ground state properties of C-isotopes using a deformed Hartree-Fock (HF)+ BCS model with Skyrme interactions. Shallow deformation minima are found in several neutron$-$rich C-isotopes. It is shown also that the deformation minima appear in both the oblate and the prolate sides in $^{17}$C and $^{19}$C having almost the same binding energies. Secondly, we carried out shell model calculations to study electromagnetic moments and electric dipole transitions of the C-isotopes. We point out the clear configuration dependence of the quadrupole and magnetic moments in the odd C-isotopes, which will be useful to find out the deformations and the spin-parities of the ground states of these nuclei. We studied electric dipole states of C-isotopes focusing on the interplay between low energy Pigmy strength and giant dipole resonances. Reasonable agreement is obtained with available experimental data for the photoreaction cross sections both in the low energy region below $\hbar \omega$=14 MeV and in the high energy giant resonance region (14 MeV $<\hbar \omega \leq$30 MeV). The calculated transition strength below dipole giant resonance ($\hbar \omega \leq$14 MeV) in heavier C-isotopes than $^{15}$C is found to exhaust about $12\sim16$ of the classical Thomas-Reiche-Kuhn sum rule value and $50\sim80$ of the cluster sum rule value.Comment: 31 pages, 19 eps figure

Bose-Fermi mixed condensates of atomic gas with Boson-Fermion quasi-bound state

The phase structures of the boson-fermion (B and F) mixed condensates of atomic gas are discussed under the existence of boson-fermion composite fermions (quasi-bound states) BF from the equilibrium in B+F -> BF. Especially we discuss the competitions between the BF degenerate states and the Bose-Einstein condensates (BEC) in low-T. The criterion for the BEC realization is obtained from the algebraically-derived phase diagrams at T=0.Comment: 2 pages, 3 figure