40,231 research outputs found

### Structure and decay of the pygmy dipole resonance in 26Ne

The low-lying spectra of $^{24,25,26}{\rm Ne}$ and the structure of the pygmy
dipole resonance (PDR) in $^{26}{\rm Ne}$ have been theoretically studied by
the antisymmetrized molecular dynamics (AMD) and its extended version called
shifted-basis AMD. The calculated energy and strength of the PDR reasonably
agree with the observation, and the analysis of the wave function shows that
the PDR is dominated by neutron excitation coupled to the quadrupole excited
core nucleus $^{25}{\rm Ne}$, which explains the observed unexpected decay of
PDR to the excited states of $^{25}{\rm Ne}$. The large isoscalar component of
PDR is also shown and the enhancement of the core excitation in neutron-rich Ne
isotopes is conjectured

### The intruder feature of 31Mg and the coexistence of many particle and many hole states

The low-lying level structure of $^{31}{\rm Mg}$ has been investigated by the
antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM)
with the Gogny D1S force. It is shown that the N=20 magic number is broken and
the ground state has the pure neutron $2p3h$ configuration. The coexistence of
many particle and many hole states at very low excitation energy is discussed

### Structure and decay pattern of linear-chain state in 14C

The linear-chain states of $^{14}$C are theoretically investigated by using
the antisymmetrized molecular dynamics. The calculated excitation energies and
the $\alpha$ 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 $\alpha$ decay pattern. It is shown that the linear-chain states
decay to the excited states of daughter nucleus $^{10}{\rm Be}$ 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

### Regularity of the minimiser of one-dimensional interaction energies

We consider both the minimisation of a class of nonlocal interaction energies
over non-negative measures with unit mass and a class of singular integral
equations of the first kind of Fredholm type. Our setting covers applications
to dislocation pile-ups, contact problems, fracture mechanics and random matrix
theory. Our main result shows that both the minimisation problems and the
related singular integral equations have the same unique solution, which
provides new regularity results on the minimiser of the energy and new
positivity results on the solutions to singular integral equations.Comment: 46 page

### Anisotropic Electronic Structure of the Kondo Semiconductor CeFe2Al10 Studied by Optical Conductivity

We report temperature-dependent polarized optical conductivity
[$\sigma(\omega)$] spectra of CeFe$_2$Al$_{10}$, which is a reference material
for CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$ with an anomalous magnetic
transition at 28 K. The $\sigma(\omega)$ spectrum along the b-axis differs
greatly from that in the $ac$-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 $4f$ states, namely $c$-$f$
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
CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$.Comment: 5 pages, 4 figure

### $A$-cation control of magnetoelectric quadrupole order in $A$(TiO)Cu$_4$(PO$_4$)$_4$ ($A$ = Ba, Sr, and Pb)

Ferroic magnetic quadrupole order exhibiting macroscopic magnetoelectric
activity is discovered in the novel compound $A$(TiO)Cu$_4$(PO$_4$)$_4$ with
$A$ = Pb, which is in contrast with antiferroic quadrupole order observed in
the isostructural compounds with $A$ = Ba and Sr. Unlike the famous lone-pair
stereochemical activity which often triggers ferroelectricity as in PbTiO$_3$,
the Pb$^{2+}$ cation in Pb(TiO)Cu$_4$(PO$_4$)$_4$ 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 $A$-O bond
covalency and a stability of the ferroic quadrupole order.Comment: 7 pages, 4 figure

### 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.

### Stochastic delocalization of finite populations

Heterogeneities in environmental conditions often induce corresponding
heterogeneities in the distribution of species. In the extreme case of a
localized patch of increased growth rates, reproducing populations can become
strongly concentrated at the patch despite the entropic tendency for population
to distribute evenly. Several deterministic mathematical models have been used
to characterize the conditions under which localized states can form, and how
they break down due to convective driving forces. Here, we study the
delocalization of a finite population in the presence of number fluctuations.
We find that any finite population delocalizes on sufficiently long time
scales. Depending on parameters, however, populations may remain localized for
a very long time. The typical waiting time to delocalization increases
exponentially with both population size and distance to the critical wind speed
of the deterministic approximation. We augment these simulation results by a
mathematical analysis that treats the reproduction and migration of individuals
as branching random walks subject to global constraints. For a particular
constraint, different from a fixed population size constraint, this model
yields a solvable first moment equation. We find that this solvable model
approximates very well the fixed population size model for large populations,
but starts to deviate as population sizes are small. The analytical approach
allows us to map out a phase diagram of the order parameter as a function of
the two driving parameters, inverse population size and wind speed. Our results
may be used to extend the analysis of delocalization transitions to different
settings, such as the viral quasi-species scenario

- …