13,491 research outputs found

    Spectral Index in Curvaton Scenario

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    A red tilted primordial power spectrum is preferred by WMAP five-year data and a large positive local-type non-Gaussianity fNLf_{NL} might be observed as well. In this short note we find that a red tilted and large non-Gaussian primordial power spectrum cannot be naturally obtained in curvaton model, because fNLf_{NL} is related to the initial condition of inflation.Comment: 12 pages; refs adde

    Weak Gravity Conjecture with Large Extra Dimensions

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    In the presence of large extra dimensions, the fundamental Planck scale can be much lower than the apparent four-dimensional Planck scale. In this setup, the weak gravity conjecture implies a much more stringent constraint on the UV cutoff for the U(1) gauge theory in four dimensions. This new energy scale may be relevant to LHC.Comment: 8 pages; Refs added, version for publication in PL

    An analytic calculation of the growth index for f(R)f(R) dark energy model

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    We derive the analytic formula of the growth index for f(R)f(R) dark energy model where the effect on the growth of matter density perturbation δm\delta_m from modified gravity (MG) is encoded in the effective Newton coupling constant GeffG_{\rm eff} in MG (or equivalently gGeff/Gg\equiv {G_{\rm eff}/ G}). Based on the analytic formula, we propose that the parameter gg can be directly figured out by comparing the observed growth rate fgdlnδm/dlnaf_g\equiv d\ln\delta_m/d\ln a to the prediction of fgf_g in general relativity.Comment: 5 pages, 1 figure; refs added; minor revised, version accepted by EPJ