Leaf of Leaf Foliation and Beltrami Parametrization in $d>2$ dimensional Gravity

TL;DR

This paper introduces a covariant Beltrami vielbein for higher-dimensional gravity, generalizing the 2D case, and explores its parametrization, gauge fixing, and potential to find new Ricci-flat solutions.

Contribution

It defines a covariant Beltrami vielbein in d>2 dimensions, extending the 2D framework, and relates it to the metric, spin connection, and Einstein action, with applications to solution classification.

Findings

Beltrami vielbein parametrization captures physical degrees of freedom.

Expresses Einstein action in terms of Beltrami fields.

Potential to identify new Ricci-flat solutions based on sub-foliation.

Abstract

This work shows the existence of a d>2 dimensional covariant "Beltrami vielbein" that generalizes the d=2 situation. Its definition relies on a sub-foliation \Sigma^{ADM}_{d-1}=\Sigma_{d-3}\times\Sigma_2 of the Arnowit--Deser--Misner leaves of d-dimensional Lorentzian manifolds {\cal M}_d. \Sigma_2 stands for the sub-foliating randomly varying Riemann surfaces in {\cal M}_d. The "Beltrami d -bein" associated to any given generic vielbein of {\cal M}_d is systematically determined by a covariant gauge fixing of the Lorentz~symmetry of the latter. It is parametrized by \frac{d(d+1)}2 independent fields belonging to different categories. Each one has a specific interpretation. The Weyl invariant field sector of the Beltrami d-bein selects the \frac{d(d-3)}{2} physical local degrees of freedom of d>2 dimensional gravity. The components of the Beltrami d-bein are in a one to one correspondence with those of the associated Beltrami d-dimensional metric. The Beltrami parametrization of the Spin connection and of the Einstein action delivers interesting expressions. Its use might easier the search of new Ricci flat solutions classified by the genus of the sub-manifold \Sigma_2. A gravitational "physical gauge" choice is introduced that takes advantage of the geometrical specificities of the Beltrami parametrization. Further restrictions simplify the expression of the Beltrami vielbein when {\cal M}_d has a given spatial holonomy. This point is exemplified in the case of d=8 Lorentzian spaces with G_2\subset SO(1,7) holonomy. The Lorentzian results presented in this paper can be extended to the Euclidean case.