27,933 research outputs found
Structure and decay pattern of linear-chain state in 14C
The linear-chain states of C are theoretically investigated by using
the antisymmetrized molecular dynamics. The calculated excitation energies and
the decay widths of the linear-chain states were compared with the
observed data reported by the recent experiments. The properties of the
positive-parity linear-chain states reasonably agree with the observation, that
convinces us of the linear-chain formation in the positive-parity states. On
the other hand, in the negative-parity states, it is found that the
linear-chain configuration is fragmented into many states and do not form a
single rotational band. As a further evidence of the linear-chain formation, we
focus on the decay pattern. It is shown that the linear-chain states
decay to the excited states of daughter nucleus as well as to
the ground state, while other cluster states dominantly decay into the ground
state. Hence, we regard that this characteristic decay pattern is a strong
signature of the linear-chain formation
Spontaneous Z2 Symmetry Breaking in the Orbifold Daughter of N=1 Super Yang-Mills Theory, Fractional Domain Walls and Vacuum Structure
We discuss the fate of the Z2 symmetry and the vacuum structure in an
SU(N)xSU(N) gauge theory with one bifundamental Dirac fermion. This theory can
be obtained from SU(2N) supersymmetric Yang--Mills (SYM) theory by virtue of Z2
orbifolding. We analyze dynamics of domain walls and argue that the Z2 symmetry
is spontaneously broken. Since unbroken Z2 is a necessary condition for
nonperturbative planar equivalence we conclude that the orbifold daughter is
nonperturbatively nonequivalent to its supersymmetric parent. En route, our
investigation reveals the existence of fractional domain walls, similar to
fractional D-branes of string theory on orbifolds. We conjecture on the fate of
these domain walls in the true solution of the Z2-broken orbifold theory. We
also comment on relation with nonsupersymmetric string theories and
closed-string tachyon condensation.Comment: 37 pages, 7 figures. v2: various significant changes; revisions
explained in the introduction. Final version to appear in Phys.Rev.
Anisotropic Electronic Structure of the Kondo Semiconductor CeFe2Al10 Studied by Optical Conductivity
We report temperature-dependent polarized optical conductivity
[] spectra of CeFeAl, which is a reference material
for CeRuAl and CeOsAl with an anomalous magnetic
transition at 28 K. The spectrum along the b-axis differs
greatly from that in the -plane, indicating that this material has an
anisotropic electronic structure. At low temperatures, in all axes, a shoulder
structure due to the optical transition across the hybridization gap between
the conduction band and the localized states, namely -
hybridization, appears at 55 meV. However, the gap opening temperature and the
temperature of appearance of the quasiparticle Drude weight are strongly
anisotropic indicating the anisotropic Kondo temperature. The strong
anisotropic nature in both electronic structure and Kondo temperature is
considered to be relevant the anomalous magnetic phase transition in
CeRuAl and CeOsAl.Comment: 5 pages, 4 figure
Real-time evolution method and its application to 3 cluster system
A new theoretical method is proposed to describe the ground and excited
cluster states of atomic nuclei. The method utilizes the equation-of-motion of
the Gaussian wave packets to generate the basis wave functions having various
cluster configurations. The generated basis wave functions are superposed to
diagonalize the Hamiltonian. In other words, this method uses the real time as
the generator coordinate. The application to the system as a
benchmark shows that the new method works efficiently and yields the result
consistent with or better than the other cluster models. Brief discussion on
the structure of the excited and states is also made
3alpha clustering in the excited states of 16C
The alpha cluster states of 16C are investigated by using the antisymmetrized
molecular dynamics. It is shown that two different types of alpha cluster
states exist: triangular and linear-chain states. The former has an approximate
isosceles triangular configuration of alpha particles surrounded by four
valence neutrons occupying sd-shell, while the latter has the linearly aligned
alpha particles with two sd-shell neutrons and two pf-shell neutrons. It is
found that the structure of the linear-chain state is qualitatively understood
in terms of the 3/2 pi- and 1/2 sigma- molecular orbit as predicted by
molecular-orbital model, but there exists non-negligible Be+alpha+2n
correlation. The band-head energies of the triangular and linear-chain
rotational bands are 8.0 and 15.5 MeV, and the latter is close to the He+Be
threshold energy. It is also shown that the linear-chain state becomes the
yrast sstate at J=10 with excitation energy 27.8 MeV owing to its very large
moment-of-inertia comparable with hyperdeformation.Comment: 7 pages, 5 figure
Antisymmetrized molecular dynamics studies for exotic clustering phenomena in neutron-rich nuclei
We present a review of recent works on clustering phenomena in unstable
nuclei studied by antisymmetrized molecular dynamics (AMD). The AMD studies in
these decades have uncovered novel types of clustering phenomena brought about
by the excess neutrons. Among them, this review focuses on the molecule-like
structure of unstable nuclei. One of the earliest discussions on the clustering
in unstable nuclei was made for neutron-rich Be and B isotopes. AMD
calculations predicted that the ground state clustering is enhanced or reduced
depending on the number of excess neutrons. Today, the experiments are
confirming this prediction as the change of the proton radii. Behind this
enhancement and reduction of the clustering, there are underlying shell effects
called molecular- and atomic-orbits. These orbits form covalent and ionic
bonding of the clusters analogous to the atomic molecules. It was found that
this "molecular-orbit picture" reasonably explains the low-lying spectra of Be
isotopes. The molecular-orbit picture is extended to other systems having
parity asymmetric cluster cores and to the three cluster systems. O and Ne
isotopes are the candidates of the former, while the linear chains in
C isotopes are the latter. For both subjects, many intensive studies are now in
progress. We also pay a special attention to the observables which are the
fingerprint of the clustering. In particular, we focus on the monopole and
dipole transitions which are recently regarded as good probe for the
clustering. We discuss how they have and will reveal the exotic clustering.Comment: 96 pages, 44 figure
Infrared spectroscopy under multi-extreme conditions: Direct observation of pseudo gap formation and collapse in CeSb
Infrared reflectivity measurements of CeSb under multi-extreme conditions
(low temperatures, high pressures and high magnetic fields) were performed. A
pseudo gap structure, which originates from the magnetic band folding effect,
responsible for the large enhancement in the electrical resistivity in the
single-layered antiferromagnetic structure (AF-1 phase) was found at a pressure
of 4 GPa and at temperatures of 35 - 50 K. The optical spectrum of the pseudo
gap changes to that of a metallic structure with increasing magnetic field
strength and increasing temperature. This change is the result of the magnetic
phase transition from the AF-1 phase to other phases as a function of the
magnetic field strength and temperature. This result is the first optical
observation of the formation and collapse of a pseudo gap under multi-extreme
conditions.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev.
-cation control of magnetoelectric quadrupole order in (TiO)Cu(PO) ( = Ba, Sr, and Pb)
Ferroic magnetic quadrupole order exhibiting macroscopic magnetoelectric
activity is discovered in the novel compound (TiO)Cu(PO) with
= Pb, which is in contrast with antiferroic quadrupole order observed in
the isostructural compounds with = Ba and Sr. Unlike the famous lone-pair
stereochemical activity which often triggers ferroelectricity as in PbTiO,
the Pb cation in Pb(TiO)Cu(PO) is stereochemically inactive
but dramatically alters specific magnetic interactions and consequently
switches the quadrupole order from antiferroic to ferroic. Our first-principles
calculations uncover a positive correlation between the degree of -O bond
covalency and a stability of the ferroic quadrupole order.Comment: 7 pages, 4 figure
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