40,200 research outputs found

    Structure and decay of the pygmy dipole resonance in 26Ne

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    The low-lying spectra of 24,25,26Ne^{24,25,26}{\rm Ne} and the structure of the pygmy dipole resonance (PDR) in 26Ne^{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 25Ne^{25}{\rm Ne}, which explains the observed unexpected decay of PDR to the excited states of 25Ne^{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

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    The low-lying level structure of 31Mg^{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 2p3h2p3h 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

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

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    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

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    We report temperature-dependent polarized optical conductivity [σ(ω)\sigma(\omega)] spectra of CeFe2_2Al10_{10}, which is a reference material for CeRu2_2Al10_{10} and CeOs2_2Al10_{10} with an anomalous magnetic transition at 28 K. The σ(ω)\sigma(\omega) spectrum along the b-axis differs greatly from that in the acac-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 4f4f states, namely cc-ff 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 CeRu2_2Al10_{10} and CeOs2_2Al10_{10}.Comment: 5 pages, 4 figure

    AA-cation control of magnetoelectric quadrupole order in AA(TiO)Cu4_4(PO4_4)4_4 (AA = Ba, Sr, and Pb)

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    Ferroic magnetic quadrupole order exhibiting macroscopic magnetoelectric activity is discovered in the novel compound AA(TiO)Cu4_4(PO4_4)4_4 with AA = Pb, which is in contrast with antiferroic quadrupole order observed in the isostructural compounds with AA = Ba and Sr. Unlike the famous lone-pair stereochemical activity which often triggers ferroelectricity as in PbTiO3_3, the Pb2+^{2+} cation in Pb(TiO)Cu4_4(PO4_4)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 AA-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

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    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

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    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
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