4,215 research outputs found

    On the Logarithmic Asymptotics of the Sixth Painleve' Equation (Summer 2007)

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    We study the solutions of the sixth Painlev\'e equation with a logarithmic asymptotic behavior at a critical point. We compute the monodromy group associated to the solutions by the method of monodromy preserving deformations and we characterize the asymptotic behavior in terms of the monodromy itself.Comment: LaTeX with 8 figure

    Model building by coset space dimensional reduction in ten-dimensions with direct product gauge symmetry

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    We investigate ten-dimensional gauge theories whose extra six-dimensional space is a compact coset space, S/RS/R, and gauge group is a direct product of two Lie groups. We list up candidates of the gauge group and embeddings of RR into them. After dimensional reduction of the coset space,we find fermion and scalar representations of GGUT×U(1)G_{\mathrm{GUT}} \times U(1) with GGUT=SU(5),SO(10)G_{\mathrm{GUT}}=SU(5), SO(10) and E6E_6 which accomodate all of the standard model particles. We also discuss possibilities to generate distinct Yukawa couplings among the generations using representations with a different dimension for GGUT=SO(10)G_{\mathrm{GUT}}=SO(10) and E6E_6 models.Comment: 14 pages; added local report number, added refferenc

    Possible solution to the 7^7Li problem by the long lived stau

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    Modification of standard big-bang nucleosynthesis is considered in the minimal supersymmetric standard model to resolve the excessive theoretical prediction of the abundance of primordial lithium 7. We focus on the stau as a next-lightest superparticle, which is long lived due to its small mass difference with the lightest superparticle. It provides a number of additional decay processes of 7Li\mathrm{^{7}Li} and 7Be\mathrm{^{7}Be}. A particularly important process is the internal conversion in the stau-nucleus bound state, which destroys the 7Li\mathrm{^{7}Li} and 7Be\mathrm{^{7}Be} effectively. We show that the modification can lead to a prediction consistent with the observed abundance of 7Li\mathrm{^{7}Li}.Comment: 6 pages, 5 figure

    Movable algebraic singularities of second-order ordinary differential equations

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    Any nonlinear equation of the form y''=\sum_{n=0}^N a_n(z)y^n has a (generally branched) solution with leading order behaviour proportional to (z-z_0)^{-2/(N-1)} about a point z_0, where the coefficients a_n are analytic at z_0 and a_N(z_0)\ne 0. We consider the subclass of equations for which each possible leading order term of this form corresponds to a one-parameter family of solutions represented near z_0 by a Laurent series in fractional powers of z-z_0. For this class of equations we show that the only movable singularities that can be reached by analytic continuation along finite-length curves are of the algebraic type just described. This work generalizes previous results of S. Shimomura. The only other possible kind of movable singularity that might occur is an accumulation point of algebraic singularities that can be reached by analytic continuation along infinitely long paths ending at a finite point in the complex plane. This behaviour cannot occur for constant coefficient equations in the class considered. However, an example of R. A. Smith shows that such singularities do occur in solutions of a simple autonomous second-order differential equation outside the class we consider here

    Muonium as a shallow center in GaN

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    A paramagnetic muonium (Mu) state with an extremely small hyperfine parameter was observed for the first time in single-crystalline GaN below 25 K. It has a highly anisotropic hyperfine structure with axial symmetry along the [0001] direction, suggesting that it is located either at a nitrogen-antibonding or a bond-centered site oriented parallel to the c-axis. Its small ionization energy (=< 14 meV) and small hyperfine parameter (--10^{-4} times the vacuum value) indicate that muonium in one of its possible sites produces a shallow state, raising the possibility that the analogous hydrogen center could be a source of n-type conductivity in as-grown GaN.Comment: 4 figures, to be published in Phys. Rev. Letter

    Electronic structure of the muonium center as a shallow donor in ZnO

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    The electronic structure and the location of muonium centers (Mu) in single-crystalline ZnO were determined for the first time. Two species of Mu centers with extremely small hyperfine parameters have been observed below 40 K. Both Mu centers have an axial-symmetric hyperfine structure along with a [0001] axis, indicating that they are located at the AB_{O,//} and BC_{//} sites. It is inferred from their small ionization energy (~6 meV and 50 meV) and hyperfine parameters (~10^{-4} times the vacuum value) that these centers behave as shallow donors, strongly suggesting that hydrogen is one of the primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR

    Generalized Second Law of Black Hole Thermodynamics and Quantum Information Theory

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    We propose a quantum version of a gedanken experiment which supports the generalized second law of black hole thermodynamics. A quantum measurement of particles in the region outside of the event horizon decreases the entropy of the outside matter due to the entanglement of the inside and outside particle states. This decrease is compensated, however, by the increase in the detector entropy. If the detector is conditionally dropped into the black hole depending on the experimental outcome, the decrease of the matter entropy is more than compensated by the increase of the black hole entropy via the increase of the black hole mass which is ultimately attributed to the work done by the measurement.Comment: 5 pages, RevTex, submitted to PR
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