12,118 research outputs found

    Localization-delocalization transition in one-dimensional electron systems with long-range correlated disorder

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    We investigate localization properties of electron eigenstates in one-dimensional (1d) systems with long-range correlated diagonal disorder. Numerical studies on the localization length ξ\xi of eigenstates demonstrate the existence of the localization-delocalization transition in 1d systems and elucidate non-trivial behavior of ξ\xi as a function of the disorder strength. The critical exponent ν\nu for localization length is extracted for various values of parameters characterizing the disorder, revealing that every ν\nu disobeys the Harris criterion ν>2/d\nu > 2/d.Comment: 6 pages, 6 figuers, to be published in Phys. Rev.

    Molecular Hydrogen Emission from Protoplanetary Disks

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    We have modeled self-consistently the density and temperature profiles of gas and dust in protoplanetary disks, taking into account irradiation from a central star. Making use of this physical structure, we have calculated the level populations of molecular hydrogen and the line emission from the disks. As a result, we can reproduce the observed strong line spectra of molecular hydrogen from protoplanetary disks, both in the ultraviolet (UV) and the near-infrared, but only if the central star has a strong UV excess radiation.Comment: 19 pages, accepted for publication in Astronomy and Astrophysic

    Dimension-six Proton Decays in the Modified Missing Doublet SU(5) Model

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    Dimension-five operators for nucleon decays are suppressed in the modified missing doublet (MMD) model in the supersymmetric SU(5) grand unification. We show that nonrenormalizable interactions decrease the unification scale in the MMD model which increases the nucleon decay rate of dimension-six operators by a significant amount. We find that the theoretical lower bound on the proton life time \tau(p \to \e^+ \pi^0) is within the observable range at SuperKamiokande.Comment: 9 pages, Latex, 1 Postscript figure

    Bulk U(1) Messenger

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    We propose a new U(1) gauge interaction in the bulk in higher dimensional spacetime, which transmits supersymmetry-breaking effects on the hidden brane to the observable our brane. We find that rather small gauge coupling constant of U(1)_{bulk}, αbulk5×104\alpha_{bulk} \simeq 5 \times 10^{-4}, is required for a successful phenomenology. This result implies the compactification length LL of the extra dimension to be L12×1015GeVL^{-1} \simeq 2 \times 10^{15}GeV for (4+1)-dimensional spacetime. This large compactification length LL is a crucial ingredient to suppress unwanted flavor-changing neutral currents and hence our proposal is very consistent with the Randall-Sundrum brane-world scenario.Comment: 9 pages, Late

    Shape-phase transitions in odd-mass γ\gamma-soft nuclei with mass A130A\approx 130

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    Quantum phase transitions between competing equilibrium shapes of nuclei with an odd number of nucleons are explored using a microscopic framework of nuclear energy density functionals and a particle-boson core coupling model. The boson Hamiltonian for the even-even core nucleus, as well as the spherical single-particle energies and occupation probabilities of unpaired nucleons, are completely determined by a constrained self-consistent mean-field calculation for a specific choice of the energy density functional and pairing interaction. Only the strength parameters of the particle-core coupling have to be adjusted to reproduce a few empirical low-energy spectroscopic properties of the corresponding odd-mass system. The model is applied to the odd-A Ba, Xe, La and Cs isotopes with mass A130A\approx 130, for which the corresponding even-even Ba and Xe nuclei present a typical case of γ\gamma-soft nuclear potential. The theoretical results reproduce the experimental low-energy excitation spectra and electromagnetic properties, and confirm that a phase transition between nearly spherical and γ\gamma-soft nuclear shapes occurs also in the odd-A systems.Comment: 13 pages, 15 figures, 9 table

    Signatures of shape phase transitions in odd-mass nuclei

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    Quantum phase transitions between competing ground-state shapes of atomic nuclei with an odd number of protons or neutrons are investigated in a microscopic framework based on nuclear energy density functional theory and the particle-plus-boson-core coupling scheme. The boson-core Hamiltonian, as well as the single-particle energies and occupation probabilities of the unpaired nucleon, are completely determined by constrained self-consistent mean-field calculations for a specific choice of the energy density functional and paring interaction, and only the strength parameters of the particle-core coupling are adjusted to reproduce selected spectroscopic properties of the odd-mass system. We apply this method to odd-A Eu and Sm isotopes with neutron number N90N \approx 90, and explore the influence of the single unpaired fermion on the occurrence of a shape phase transition. Collective wave functions of low-energy states are used to compute quantities that can be related to quantum order parameters: deformations, excitation energies, E2 transition rates and separation energies, and their evolution with the control parameter (neutron number) is analysed.Comment: 15 pages, 13 figures; Accepted for publication in Phys. Rev.

    Surface density of states of s+-wave Cooper pairs in a two-band model

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    We calculate surface density of state (SDOS) of s+-wave Cooper pair in two-band superconductor model, where gap functions have different signs between two bands. We find that Andreev bound state appears at surface due to the sign change in the gap function in the interband quasiparticle scattering. However, we do not obtain the zero-energy peak of SDOS in contrast to the d-wave case. The tunneling spectroscopy of s+-wave is much more complex as compared to the d-wave case realized in high-Tc cuprates.Comment: 7 pages, 10 figure

    A Gauge Mediation Model of Dynamical Supersymmetry Breaking without Color Instability

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    We construct a gauge mediation model of dynamical supersymmetry breaking (DSB) based on a vector-like gauge theory, in which there is a unique color-preserving true vacuum. The DSB scale Λ/4π\Lambda/4\pi turns out to be as high as Λ/4π1089GeV\Lambda/4\pi \simeq 10^{8-9} GeV, since the transmission of the DSB effects to the standard model sector is completed through much higher loops. This model is perfectly natural and phenomenologically consistent. We also stress that the dangerous D-term problem for the messenger U(1)_m is automatically solved by a charge conjugation symmetry in the vector-like gauge theory.Comment: 11 pages, Late
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