2,023 research outputs found
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 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
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 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-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 and 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
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