Sourced Gravitational Radiation in Parity-Violating Tetrad Gravity

Abstract

We study linear gravitational modes, sourced far-zone fields, and quadratic energy balance in a four-parameter tetrad theory of gravity. The theory contains three parity-even torsion invariants and a parity-odd coupling $v^μa_μ$, where $v_μ$ and $a_μ$ are the vector and axial torsion components. Linearizing around Minkowski spacetime and applying a scalar--vector--tensor decomposition, we find two tensor, two scalar, and four vector degrees of freedom in the generic nondegenerate parity-violating region. The tensor and scalar modes propagate at the speed of light, while the two vector branches have coupling-dependent propagation speeds. We derive their kinetic eigenvalues, characteristic speeds, and flux normalizations. An exact trace identity shows that the vector Hamiltonian is not positive definite in the generic branch, even when the kinetic eigenvalues are positive and the propagation speeds are real. We also derive the response to a general compact canonical source and obtain explicit source-to-amplitude relations for all eight linear polarizations. The field $V_μ=\partial^νB_{νμ}$ is used to illustrate intrinsic-spin multipoles. {We further prove that the quadratic Noether current equals the second-order Møller current for the chosen first-derivative tetrad Lagrangian and derive the corresponding mode-resolved energy and momentum fluxes.} The vector contribution remains a formal signed response because of the unbounded Hamiltonian. The stationary limit reproduces the results of Ref.~\cite{ShirafujiNashed1997}, and a representative parameter scan illustrates vector-mode splitting and kinetic degeneracy.