Nonlinear definition of the shadowy mode in higher-order scalar-tensor theories

Hamiltonian analysis of higher derivative scalar-tensor theories

We perform a Hamiltonian analysis of a large class of scalar-tensor Lagrangians which depend quadratically on the second derivatives of a scalar field. By resorting to a convenient choice of dynamical variables, we show that the Hamiltonian can be written in a very simple form, where the Hamiltonian and the momentum constraints are easily identified. In the case of degenerate Lagrangians, which...

Scintillation in scalar-tensor theories of gravity

We study the scintillation produced by time-varying gravitational fields within scalar-tensor theories of gravity. The problem is treated in the geometrical optics approximation for a very distant light source emitting quasi plane monochromatic electromagnetic waves. We obtain a general formula giving the time dependence of the photon flux received by a freely falling observer. In the weak-fiel...

Cold Black Holes in Scalar-tensor Theories

We study the possible existence of black holes in scalar-tensor theories of gravity in four dimensions. Their existence is verified for anomalous versions of these theories, with a negative kinetic term in the Lagrangian. The Hawking temperature TH of these holes is zero, while the horizon area is (in most cases) infinite. It is shown that an infinite value of TH can occur only at a curvature s...

Appendix: Tensor Decompositions via Two-Mode Higher-Order SVD (HOSVD)

Tensor Decompositions via Two-Mode Higher-Order SVD (HOSVD)

Tensor decompositions have rich applications in statistics and machine learning, and developing efficient, accurate algorithms for the problem has received much attention recently. Here, we present a new method built on Kruskal’s uniqueness theorem to decompose symmetric, nearly orthogonally decomposable tensors. Unlike the classical higher-order singular value decomposition which unfolds a ten...