47,006 research outputs found

    Conserved cosmological structures in the one-loop superstring effective action

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    A generic form of low-energy effective action of superstring theories with one-loop quantum correction is well known. Based on this action we derive the complete perturbation equations and general analytic solutions in the cosmological spacetime. Using the solutions we identify conserved quantities characterizing the perturbations: the amplitude of gravitational wave and the perturbed three-space curvature in the uniform-field gauge both in the large-scale limit, and the angular-momentum of rotational perturbation are conserved independently of changing gravity sector. Implications for calculating perturbation spectra generated in the inflation era based on the string action are presented.Comment: 5 pages, no figure, To appear in Phys. Rev.

    Quantum fluctuations of Cosmological Perturbations in Generalized Gravity

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    Recently, we presented a unified way of analysing classical cosmological perturbation in generalized gravity theories. In this paper, we derive the perturbation spectrums generated from quantum fluctuations again in unified forms. We consider a situation where an accelerated expansion phase of the early universe is realized in a particular generic phase of the generalized gravity. We take the perturbative semiclassical approximation which treats the perturbed parts of the metric and matter fields as quantum mechanical operators. Our generic results include the conventional power-law and exponential inflations in Einstein's gravity as special cases.Comment: 5 pages, revtex, no figure

    Unified Analysis of Cosmological Perturbations in Generalized Gravity

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    In a class of generalized Einstein's gravity theories we derive the equations and general asymptotic solutions describing the evolution of the perturbed universe in unified forms. Our gravity theory considers general couplings between the scalar field and the scalar curvature in the Lagrangian, thus includes broad classes of generalized gravity theories resulting from recent attempts for the unification. We analyze both the scalar-type mode and the gravitational wave in analogous ways. For both modes the large scale evolutions are characterized by the same conserved quantities which are valid in the Einstein's gravity. This unified and simple treatment is possible due to our proper choice of the gauges, or equivalently gauge invariant combinations.Comment: 4 pages, revtex, no figure

    A conserved variable in the perturbed hydrodynamic world model

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    We introduce a scalar-type perturbation variable Φ\Phi which is conserved in the large-scale limit considering general sign of three-space curvature (KK), the cosmological constant (Λ\Lambda), and time varying equation of state. In a pressureless medium Φ\Phi is {\it exactly conserved} in all scales.Comment: 4 pages, no figure, To appear in Phys. Rev.

    Base manifolds for fibrations of projective irreducible symplectic manifolds

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    Given a projective irreducible symplectic manifold MM of dimension 2n2n, a projective manifold XX and a surjective holomorphic map f:MXf:M \to X with connected fibers of positive dimension, we prove that XX is biholomorphic to the projective space of dimension nn. The proof is obtained by exploiting two geometric structures at general points of XX: the affine structure arising from the action variables of the Lagrangian fibration ff and the structure defined by the variety of minimal rational tangents on the Fano manifold XX

    Relativistic Hydrodynamic Cosmological Perturbations

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    Relativistic cosmological perturbation analyses can be made based on several different fundamental gauge conditions. In the pressureless limit the variables in certain gauge conditions show the correct Newtonian behaviors. Considering the general curvature (KK) and the cosmological constant (Λ\Lambda) in the background medium, the perturbed density in the comoving gauge, and the perturbed velocity and the perturbed potential in the zero-shear gauge show the same behavior as the Newtonian ones in general scales. In the first part, we elaborate these Newtonian correspondences. In the second part, using the identified gauge-invariant variables with correct Newtonian correspondences, we present the relativistic results with general pressures in the background and perturbation. We present the general super-sound-horizon scale solutions of the above mentioned variables valid for general KK, Λ\Lambda, and generally evolving equation of state. We show that, for vanishing KK, the super-sound-horizon scale evolution is characterised by a conserved variable which is the perturbed three-space curvature in the comoving gauge. We also present equations for the multi-component hydrodynamic situation and for the rotation and gravitational wave.Comment: 16 pages, no figure, To appear in Gen. Rel. Gra