2025/11/07 by Peter K. S. Dunsby, Dunsby, Peter K. S., Maria-Alexia Caldis +3 · 1 voice
Physics and Astronomy · #Cosmology and Gravitation Theories #Noncommutative and Quantum Gravity Theories #Advanced Differential Geometry Research
paper · doi:10.1007/s10714-026-03568-5
openalex publication_date 2026/06/01 · openalex created_date 2026/06/04 · openalex updated_date 2026/07/29
Abstract We present a fully covariant and gauge–invariant analysis of linear cosmological perturbations in Energy-Momentum Squared Gravity. Working within the 1 + 3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mspace/> <mml:mo>+</mml:mo> <mml:mspace/> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> formalism, we derive the exact propagation equations for scalar, vector, and tensor modes on FLRW backgrounds, in the case of radiation and dust. Two representative subclasses are examined in detail, in which non-linearity enters through \mathcal O(η ρ 2) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>O</mml:mi> <mml:mo>(</mml:mo> <mml:mi>η</mml:mi> <mml:msup> <mml:mi>ρ</mml:mi> <mml:mn>2</mml:mn> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> corrections or modifications in the equation-of-state parameter and the sound speed. For scalar perturbations, the density contrast can be enhanced or reduced relative to General Relativity, depending on the coupling parameter and the wavelength regime. A similar behavior occurs for vector modes, allowing for a non-trivial vorticity at early times. Tensor modes, described by the magnetic part of the Weyl tensor and the shear tensor propagate as damped waves with slowly varying effective masses. All sectors reduce continuously to their GR limits as η → 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>η</mml:mi> <mml:mspace/> <mml:mo>→</mml:mo> <mml:mspace/> <mml:mn>0</mml:mn> </mml:mrow> </mml:math> . The framework isolates robust signatures—early-time scalar tilts, tensor damping shifts, and altered vorticity decay—that can be confronted with CMB and large-scale-structure observations to constrain these theories of gravity.