The Lanczos equation on light-like hypersurfaces in a cosmologically viable class of kinetic gravity braiding theories

Bence Racskó, L. Gergely

Research output: Contribution to journalArticle


We discuss junction conditions across null hypersurfaces in a class of scalar-tensor gravity theories (i) with second-order dynamics, (ii) obeying the recent constraints imposed by gravitational wave propagation, and (iii) allowing for a cosmologically viable evolution. These requirements select kinetic gravity braiding models with linear kinetic term dependence and scalar field-dependent coupling to curvature. We explore a pseudo-orthonormal tetrad and its allowed gauge fixing with one null vector standing as the normal and the other being transversal to the hypersurface. We derive a generalization of the Lanczos equation in a 2 + 1 decomposed form, relating the energy density, current, and isotropic pressure of a distributional source to the jumps in the transverse curvature and transverse derivative of the scalar. Additionally, we discuss a scalar junction condition and its implications for the distributional source.

Original languageEnglish
Article number616
Issue number5
Publication statusPublished - May 1 2019



  • Junction conditions
  • Null hypersurfaces
  • Scalar-tensor gravity

ASJC Scopus subject areas

  • Computer Science (miscellaneous)
  • Chemistry (miscellaneous)
  • Mathematics(all)
  • Physics and Astronomy (miscellaneous)

Cite this