Spectra, vacua and the unitarity of Lovelock gravity in D-dimensional AdS spacetimes

We explicitly confirm the expectation that generic Lovelock gravity in D dimensions has a unitary massless spin-2 excitation around any one of its constant curvature vacua just like the cosmological Einstein gravity. The propagator of the theory reduces to that of Einstein's gravity, but scattering amplitudes must be computed with an effective Newton's constant which we provide. Tree-level unitarity imposes a single constraint on the parameters of the theory yielding a wide range of unitary region. As an example, we explicitly work out the details of the cubic Lovelock theory.Comment: 9 pages, 2 references adde

Green's Matrix for a Second Order Self-Adjoint Matrix Differential Operator

A systematic construction of the Green's matrix for a second order, self-adjoint matrix differential operator from the linearly independent solutions of the corresponding homogeneous differential equation set is carried out. We follow the general approach of extracting the Green's matrix from the Green's matrix of the corresponding first order system. This construction is required in the cases where the differential equation set cannot be turned to an algebraic equation set via transform techniques.Comment: 19 page

Kerr-Schild-Kundt metrics are universal

We define (non-Einsteinian) universal metrics as the metrics that solve the source-free covariant field equations of generic gravity theories. Here, extending the rather scarce family of universal metrics known in the literature, we show that the Kerr-Schild-Kundt class of metrics are universal. Besides being interesting on their own, these metrics can provide consistent backgrounds for quantum field theory at extremely high energies. © 2017 IOP Publishing Ltd

All unitary cubic curvature gravities in D dimensions

We construct all the unitary cubic curvature gravity theories built on the contractions of the Riemann tensor in D -dimensional (anti)-de Sitter spacetimes. Our construction is based on finding the equivalent quadratic action for the general cubic curvature theory and imposing ghost and tachyon freedom, which greatly simplifies the highly complicated problem of finding the propagator of cubic curvature theories in constant curvature backgrounds. To carry out the procedure we have also classified all the unitary quadratic models. We use our general results to study the recently found cubic curvature theories using different techniques and the string generated cubic curvature gravity model. We also study the scattering in critical gravity and give its cubic curvature extensions.Comment: 24 pages, 1 figure, v2: A subsection on cubic curvature extensions of critical gravity is added, v3: The part regarding critical gravity is revised. Version to appear in Class. Quant. Gra

Localization and Amount of Thyroid Remnant in Totally Thyroidectomized

Objective:To determine the frequency, localization and amount of thyroid remnant in extracapsular thyroidectomized patients.Methods:We postoperatively evaluated the thyroid bed of 38 totally thyroidectomized patients using thyroid scintigraphy, a thyroid uptake study and bilateral neck ultrasonography (US) to determine the extent of residual thyroid tissues.Results:In scintigraphic assessment, thyroid remnant was not seen in the thyroid bed in 13 cases, minimal thyroid remnant was detected in 15 cases, and visible uptake was seen in 10 cases. Ultrasonographic findings revealed the presence of remnant in 12 cases. However, US did not detect all remnant tissues diagnosed by TS.Conclusion:This study demonstrates that minimal thyroid remnant is left in the majority of cases, even after extracapsular total thyroidectomy, especially in the upper and middle zones