10,880 research outputs found

    A Note on Tachyon Moduli and Closed Strings

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    The collective behavior of the SL(2,R) covariant brane states of non-critical c=1 string theory found in a previous work, is studied in the Fermi liquid approximation. It is found that such states mimick the coset WZW model, whereas only by further restrictions one recovers the double-scaling limit which was purported to be equivalent to closed string models. Another limit is proposed, inspired by the tachyon condensation ideas, where the spectrum is the same of two-dimensional string theory. We close by noting some strange connections between vacuum states of the theory in their different interpretations.Comment: PDFLaTeX, 17 pages, 2 figures; Section 2 rewritten, several fixes throughout the text to improve clarit

    Formação e evolução do direito internacional : os ventos de mudança

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    Quasi-Topological Field Theories in Two Dimensions as Soluble Models

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    We study a class of lattice field theories in two dimensions that includes gauge theories. Given a two dimensional orientable surface of genus gg, the partition function ZZ is defined for a triangulation consisting of nn triangles of area ϵ\epsilon. The reason these models are called quasi-topological is that ZZ depends on gg, nn and ϵ\epsilon but not on the details of the triangulation. They are also soluble in the sense that the computation of their partition functions can be reduced to a soluble one dimensional problem. We show that the continuum limit is well defined if the model approaches a topological field theory in the zero area limit, i.e., ϵ0\epsilon \to 0 with finite nn. We also show that the universality classes of such quasi-topological lattice field theories can be easily classified. Yang-Mills and generalized Yang-Mills theories appear as particular examples of such continuum limits.Comment: 23 pages, 16 figures, uses psbox.te

    Dark-ages Reionization and Galaxy Formation Simulation -- XIX: Predictions of infrared excess and cosmic star formation rate density from UV observations

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    We present a new analysis of high-redshift UV observations using a semi-analytic galaxy formation model, and provide self-consistent predictions of the infrared excess (IRX) -- β\beta relations and cosmic star formation rate density. We combine the Charlot & Fall dust attenuation model with the Meraxes semi-analytic model, and explore three different parametrisations for the dust optical depths, linked to star formation rate, dust-to-gas ratio and gas column density respectively. A Bayesian approach is employed to statistically calibrate model free parameters including star formation efficiency, mass loading factor, dust optical depths and reddening slope directly against UV luminosity functions and colour-magnitude relations at z ~ 4-7. The best-fit models show excellent agreement with the observations. We calculate IRX using energy balance arguments, and find that the large intrinsic scatter in the IRX -β\beta plane is driven by the specific star formation rate. Additionally, the difference among the three dust models suggests a factor of two systematic uncertainty in the dust-corrected star formation rate when using the Meurer IRX - β\beta relation at z > 4.Comment: 15 pages, 10 figure. Accepted for publication in MNRA

    Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures

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    The occurrence of inhomogeneous spin-density distribution in multilayered ferromagnetic diluted magnetic semiconductor nanostructures leads to strong dependence of the spin-polarized transport properties on these systems. The spin-dependent mobility, conductivity and resistivity in (Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a function of temperature, scaled by the average magnetization of the diluted magnetic semiconductor layers. An increase of the resistivity near the transition temperature is obtained. We observed that the spin-polarized transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure
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