Sigbjorn Hervik - Academia.edu (original) (raw)

Uploads

Papers by Sigbjorn Hervik

arXiv (Cornell University), Apr 6, 2015

arXiv (Cornell University), Jul 6, 2007

Classical and Quantum Gravity, Oct 6, 2009

Classical and Quantum Gravity, Jul 1, 2011

It is well known that certain pp-wave metrics, belonging to a more general class of Ricci-flat ty... more It is well known that certain pp-wave metrics, belonging to a more general class of Ricci-flat type N, τi = 0, Kundt spacetimes, are universal and thus they solve vacuum equations of all gravitational theories with Lagrangian constructed from the metric, the Riemann tensor and its derivatives of arbitrary order. In this paper, we show (in an arbitrary number of dimensions) that in fact all Ricciflat type N, τi = 0, Kundt spacetimes are universal and we also generalize this result in a number of ways by relaxing τi = 0, Λ = 0 and type N conditions. First, we show that a universal spacetime is necessarily a CSI spacetime, i.e. all curvature invariants constructed from the Riemann tensor and its derivatives are constant. Then we focus on type N where we arrive at a simple necessary and sufficient condition: a type N spacetime is universal if and only if it is an Einstein Kundt spacetime. Similar statement does not hold for type III Kundt spacetimes, however, we prove that a subclass of...

Journal of High Energy Physics, 2020

We prove that a generalized Schwarzschild-like ansatz can be consistently employed to construct d... more We prove that a generalized Schwarzschild-like ansatz can be consistently employed to construct d-dimensional static vacuum black hole solutions in any metric theory of gravity for which the Lagrangian is a scalar invariant constructed from the Riemann tensor and its covariant derivatives of arbitrary order. Namely, we show that, apart from containing two arbitrary functions a(r) and f (r) (essentially, the gtt and grr components), in any such theory the line-element may admit as a base space any isotropy-irreducible homogeneous space. Technically, this ensures that the field equations generically reduce to two ODEs for a(r) and f (r), and dramatically enlarges the space of black hole solutions and permitted horizon geometries for the considered theories. We then exemplify our results in concrete contexts by constructing solutions in particular theories such as Gauss-Bonnet, quadratic, F(R) and F(Lovelock) gravity, and certain conformal gravities.

Journal of Geometry and Physics, 2018

Classical and Quantum Gravity, 2018

Journal of High Energy Physics, 2017

Classical and Quantum Gravity, 2015

ISRN Geometry, 2011

A classical solution is called universal if the quantum correction is a multiple of the metric. T... more A classical solution is called universal if the quantum correction is a multiple of the metric. Therefore, universal solutions play an important role in the quantum theory. We show that in a spacetime which is universal all scalar curvature invariants are constant (i.e., the spacetime is CSI).