CP,T and/or CPT Violations in the K0-K0bar System --Implications of the KTeV,NA48 and CPLEAR Results

Possible violation of CP, T and/or CPT symmetries in the \ko-\kob system is studied from a phenomenological point of view. For this purpose, we first introduce parameters which represent violation of these symmetries in mixing parameters and decay amplitudes in a convenient and well-defined way and, treating these parameters as small, derive formulas which relate them to the experimentally measured quantities. We then perform numerical analyses, with the aid of the Bell-Steinberger relation, to derive constraints to these symmetry-violating parameters, firstly paying particular attention to the results reported by KTeV Collaboration and NA48 Collaboration, and then with the results reported by CPLEAR Collaboration as well taken into account. A case study, in which either CPT symmetry or T symmetry is assumed, is also carried out. It is demonstrated that CP and T symmetries are violated definitively at the level of 10^{-4} in $2\pi$ decays and presumably at the level of 10^{-3} in the \ko-\kob mixing, and that the Bell-Steinberger relation helps us to establish CP and T violations being definitively present in the \ko-\kob mixing and to test CPT symmetry to a level of 10^{-4} ~ 10^{-5}.Comment: 21 pages, 1 figure

The IMF of Extremely Metal-Poor Stars and the Probe into the Star-Formation Process of the Milky Way

We discuss the star formation history of the Galaxy, based on the observations of extremely metal-poor stars (EMP) in the Galactic halo, to gain an insight into the evolution and structure formation in the early universe. The initialmass function (IMF) of EMP stars is derived from the observed fraction of carbon-enhanced EXP (CEMP) stars among the EMP survivors, which are thought to originate from the evolution in the close binary systems with mass transfer. Relying upon the theory of the evolution of EMP stars and of their binary evolution, we find that stars of metallicity [Fe/H]<-2.5 were formed at typical mass of ~10M_sun. The top heavy IMF thus obtained is applied to study the early chemical evolution of the Galaxy. We construct the merging history of our Galaxy semi-analytically and derive the metallicity distribution function (MDF) of low-mass EMP stars that survive to date with taking into account the contribution of binary systems. It is shown that the resultant MDF can well reproduce the observed distribution of EMP survivors, and, in particular, that they almost all stem from a less-mass companion in binary systems. We also investigate how first stars affect the MDF of EMP stars.Comment: 5 pages, 4 figures, conference proceedings of First Star II

Noncoplanar spin canting in lightly-doped ferromagnetic Kondo lattice model on a triangular lattice

Effect of the coupling to mobile carriers on the 120$^\circ$ antiferromagnetic state is investigated in a ferromagnetic Kondo lattice model on a frustrated triangular lattice. Using a variational calculation for various spin orderings up to a four-site unit cell, we identify the ground-state phase diagram with focusing on the lightly-doped region. We find that an electron doping from the band bottom immediately destabilizes a 120$^\circ$ coplanar antiferromagnetic order and induces a noncoplanar three-sublattice ordering accompanied by an intervening phase separation. This noncoplanar phase has an umbrella-type spin configuration with a net magnetic moment and a finite spin scalar chirality. This spin-canting state emerges in competition between the antiferromagnetic superexchange interaction and the ferromagnetic double-exchange interaction under geometrical frustration. In contrast, a hole doping from the band top retains the 120$^\circ$-ordered state up to a finite doping concentration and does not lead to a noncolpanar ordering.Comment: 6 pages, 4 figures, accepted for publication in J. Phys.: Conf. Se

The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars

We describe the construction of a database of extremely metal-poor (EMP) stars in the Galactic halo whose elemental abundances have been determined. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the recent literature that report studies of EMP halo stars with [Fe/H] < -2.5. The compilation procedures for this database have been designed to assemble the data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria, and permits the user to explore relationships between the stored variables graphically. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering all of the relevant papers published by December 2007. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe/H] < -2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amount to ~30 % for [Fe/H] < -2.5. We find that known binaries exhibit different distributions of orbital period, according to whether they are giants or dwarfs, and also as a function of metallicity, although the total sample of such stars is still quite small.Comment: 24 pages, 10 figures, accepted by PASJ, final version. The SAGA database is available at http://saga.sci.hokudai.ac.j

Reply to Hagen & Sudarshan's Comment

We show that the argument in Phys Rev Lett 70 (1993) 1360 is correct and consistent, and that Hagen & Sudarshan's solution has inconsistency leading to non-vanishing commutators of $[P^1, P^2]$ and $[P^j, H]$ even in physical states. This proves that many of HS's statements in their Comment are based merely on incorrect guess, but not on careful algebra.Comment: one page, UMN-TH-1245/9

D-branes and Closed String Field Theory

We construct solitonic states in the OSp invariant string field theory, which are BRST invariant in the leading order of regularization parameter. One can show that these solitonic states describe D-branes and ghost D-branes, by calculating the scattering amplitudes.Comment: 8 pages, 2 figures, based on an invited talk presented at the international workshop "Progress of String Theory and Quantum Field Theory" (Osaka City University, December 7-10, 2007), to be published in the proceeding