3,916 research outputs found

    Hard thermal loops in static background fields

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    We discuss the high temperature behavior of retarded thermal loops in static external fields. We employ an analytic continuation of the imaginary time formalism and use a spectral representation of the thermal amplitudes. We show that, to all orders, the leading contributions of static hard thermal loops can be directly obtained by evaluating them at zero external energies and momenta.Comment: 5 pages, to be published in The European Physical Journal

    Resummation of infrared divergences in the free-energy of spin-two fields

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    We derive a closed form expression for the sum of all the infrared divergent contributions to the free-energy of a gas of gravitons. An important ingredient of our calculation is the use of a gauge fixing procedure such that the graviton propagator becomes both traceless and transverse. This has been shown to be possible, in a previous work, using a general gauge fixing procedure, in the context of the lowest order expansion of the Einstein-Hilbert action, describing non-interacting spin two fields. In order to encompass the problems involving thermal loops, such as the resummation of the free-energy, in the present work, we have extended this procedure to the situations when the interactions are taken into account.Comment: 12 pages, 25 figure

    High temperature limit in static backgrounds

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    We prove that the hard thermal loop contribution to static thermal amplitudes can be obtained by setting all the external four-momenta to zero before performing the Matsubara sums and loop integrals. At the one-loop order we do an iterative procedure for all the 1PI one-loop diagrams and at the two-loop order we consider the self-energy. Our approach is sufficiently general to the extent that it includes theories with any kind of interaction vertices, such as gravity in the weak field approximation, for dd space-time dimensions. This result is valid whenever the external fields are all bosonic.Comment: 15 pages, 11 figures. To be published in Physical Review

    Thermal Effective Lagrangian of Static Gravitational Fields

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    We compute the effective Lagrangian of static gravitational fields interacting with thermal fields. Our approach employs the usual imaginary time formalism as well as the equivalence between the static and space-time independent external gravitational fields. This allows to obtain a closed form expression for the thermal effective Lagrangian in dd space-time dimensions.Comment: Accepted for publication in the Physical Review

    A longitudinal comparison of capital structure between young for-profit social and commercial enterprises

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    This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordWe develop a new perspective on capital structure differences between for-profit social and commercial enterprises by combining imprinting and social entrepreneurship theory. Using a longitudinal matched sample, we find that for-profit social enterprises have 40% to 13% lower leverage and up to four times greater leverage stability over time than commercial enterprises. Our results suggest that these differences in capital structure derive from the process of prosocial organizing, which goes beyond the primary focus on financial preferences. Thus, for-profit social enterprises—and similar hybrid organizations, such as B corporations—may require theories adjusted to their context

    Magnetization plateau in a two-dimensional multiple-spin exchange model

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    We study a multiple-spin exchange model on a triangular lattice, which is a possible model for low-density solid 3He films. Due to strong competitions between ferromagnetic three-spin exchange and antiferromagnetic four-spin one, the ground states are highly degenerate in the classical limit. At least 2^{L/2}-fold degeneracy exists on the L*L triangular lattice except for the SO(3) symmetry. In the magnetization process, we found a plateau at m/m_{sat}=1/2, in which the ground state is "uuud state" (a collinear state with four sublattices). The 1/2-plateau appears due to the strong four-spin exchange interaction. This plateau survives against both quantum and thermal fluctuations. Under a magnetic field which realizes the "uuud" ordered state, a phase transition occurs at a finite temperature. We predict that low-density solid 3He thin films may show the 1/2-plateau in the magnetization process. Experimental observation of the plateau will verify strength of the four-spin exchange. It is also discussed that this magnetization plateau can be understood as an insulating-conducting transition in a particle picture.Comment: 10 pages, RevTeX, 12 figures, added a reference and corrected typos, to be published in Phys.Rev.B (01 APR 99

    Possible chiral phase transition in two-dimensional solid 3^3He

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    We study a spin system with two- and four-spin exchange interactions on the triangular lattice, which is a possible model for the nuclear magnetism of solid 3^3He layers. It is found that a novel spin structure with scalar chiral order appears if the four-spin interaction is dominant. Ground-state properties are studied using the spin-wave approximation. A phase transition concerning the scalar chirality occurs at a finite temperature, even though the dimensionality of the system is two and the interaction has isotropic spin symmetry. Critical properties of this transition are studied with Monte Carlo simulations in the classical limit.Comment: 4 pages, Revtex, 4 figures, to appear in Phys.Rev.Let
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