Dark matter production from cosmic necklaces

Cosmic strings have gained a great interest, since they are formed in a large class of brane inflationary models. The most interesting story is that cosmic strings in brane models are distinguished in future cosmological observations. If the strings in brane models are branes or superstrings that can move along compactified space, and also if there are degenerated vacua along the compactified space, kinks interpolate between degenerated vacua become ``beads'' on the strings. In this case, strings turn into necklaces. In the case that the compact manifold in not simply connected, a string loop that winds around a nontrivial circle is stable due to the topological reason. Since the existence of the (quasi-)degenerated vacua and the nontrivial circle is a common feature of the brane models, it is important to study cosmological constraints on the cosmic necklaces and the stable winding states. In this paper, we consider dark matter production from loops of the cosmic necklaces. Our result suggests that necklaces can put stringent bound on certain kinds of brane models.Comment: 27 pages, 5 figures, added many comments and 3 figures, accepted for publication in JCA

Q ball inflation

We show that inflation can occur in the core of a Q-ball.Comment: 11 pages, latex2e, no figure, references added, final version to appear in PR

Superconducting Gap Function in Antiferromagnetic Heavy-Fermion UPd_2Al_3 Probed by Angle Resolved Magnetothermal Transport Measurements

The superconducting gap structure of heavy fermion UPd_2Al_3, in which unconventional superconductivity coexists with antiferromagnetic (AF) order with atomic size local moments, was investigated by the thermal conductivity measurements in a magnetic field rotating in various directions relative to the crystal axes. The results provide strong evidence that the gap function \Delta(k) has a single line node orthogonal to the c-axis located at the AF Brillouin zone boundary, while \Delta(k) is isotropic within the basal plane. The determined nodal structure is compatible with the resonance peak in the dynamical susceptibility observed in neutron inelastic scattering experiments. Based on these results, we conclude that the superconducting pairing function of UPd_2Al_3 is most likely to be d-wave with a form \Delta(k)=\Delta_0 cos(k_zc)Comment: 10 pages, 9 figure

Formation of monopoles and domain walls after brane inflation

We study cosmological defect formation after brane inflation. The cosmological defects are corresponding to the branes that have less than three spacial dimensions in the uncompactified spacetime. Contrary to the previous arguments, production of monopoles and domain walls are not always negligible. Monopoles and domain walls are formed by the branes extended between mother branes.Comment: 27pages, 7 figures, many comments, footnotes and reviews are added, to appear in JHE

Constraint on the heavy sterile neutrino mixing angles in the SO(10) model with double see-saw mechanism

Constraints on the heavy sterile neutrino mixing angles are studied in the framework of a minimal supersymmetric ${\rm SO}(10)$ model with {\it double see-saw mechanism}. A new singlet matter in addition to the right-handed neutrinos is introduced to realize the double see-saw mechanism. The minimal ${\rm SO}(10)$ model gives an unambiguous Dirac neutrino mass matrix, which enables us to predict the masses and the mixing angles in the enlarged $9 \times 9$ neutrino mass matrix. Mixing angles between the light Majorana neutrinos and the heavy sterile neutrinos are shown to be within the LEP experimental bound on all ranges of the Majorana phases.Comment: 16 pages, 4 figures; the version to be published in Eur. Phys. J.

Line nodes in the superconducting gap function of noncentrosymmetric CePt_3Si

The superconducting gap structure of recently discovered heavy fermion CePt_3Si without spatial inversion symmetry was investigated by thermal transport measurements down to 40 mK. In zero field a residual T-linear term was clearly resolved as T-> 0, with a magnitude in good agreement with the value expected for a residual normal fluid with a nodal gap structure, together with a T^2-dependence at high temperatures. With an applied magnetic fields, the thermal conductivity grows rapidly, in dramatic contrast to fully gapped superconductors, and exhibits one-parameter scaling with T/sqrt{H}. These results place an important constraint on the order parameter symmetry, that is CePt_3Si is most likely to have line nodes.Comment: 5pages, 3figures, accpted for publication in Phys. Rev. Let

Theory of Metal-Insulator Transition in PrRu4P12 and PrFe4P12

All symmetry allowed couplings between the 4f^2-electron ground state doublet of trivalent praseodymium in PrRu4P12 and PrFe4P12 and displacements of the phosphorus, iron or ruthenium ions are considered. Two types of displacements can change the crystal lattice from body-centred cubic to simple orthorhombic or to simple cubic. The first type lowers the point group symmetry from tetrahedral to orthorhombic, while the second type leaves it unchanged, with corresponding space group reductions Im3 --> Pmmm and Im3 --> Pm3 respectively. In former case, the lower point-group symmetry splits the degeneracy of the 4f^2 doublet into states with opposite quadrupole moment, which then leads to anti-quadrupolar ordering, as in PrFe4P12. Either kind of displacement may conspire with nesting of the Fermi surface to cause the metal-insulator or partial metal-insulator transition observed in PrFe4P12 and PrRu4P12. We investigate this scenario using band-structure calculations, and it is found that displacements of the phosphorus ions in PrRu4P12 (with space group reduction Im3 --> Pm3) open a gap everywhere on the Fermi surface.Comment: 6 page

Evolution of curvature perturbation in generalized gravity theories

Using the cosmological perturbation theory in terms of the delta-N formalism, we find the simple formulation of the evolution of the curvature perturbation in generalized gravity theories. Compared with the standard gravity theory, a crucial difference appears in the end-boundary of the inflationary stage, which is due to the non-ideal form of the energy momentum tensor that depends explicitly on the curvature scalar. Recent study shows that ultraviolet-complete quantum theory of gravity may be approximated by using a generalized gravity action. Our paper may give an important step in understanding the evolution of the curvature perturbation during inflation, where the energy momentum tensor may not be given by the ideal form due to the corrections from the fundamental theory.Comment: 15pages, fixed references, accepted for publication in CQ