https://doi.org/10.1140/epjc/s10052-025-15053-5
Regular Article - Theoretical Physics
Tilt in quadratic gravity II
1
Instituto de Matemática, Estatística e Física, Universidade Federal do Rio Grande, Caixa Postal 474, 96201-900, Rio Grande, Rio Grande do Sul, Brazil
2
Instituto de Física, Universidade de Brasília, Caixa Postal 04455, 70919-970, Brasília, Brazil
3
Department of Science and High Technology, University of Insubria, Via Valleggio 11, 22100, Como, Italy
a
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Received:
5
February
2025
Accepted:
9
November
2025
Published online:
20
November
2025
Abstract
We investigate a tilted fluid component on a Bianchi V geometry in the theories of General Relativity (GR) and Quadratic Gravity (QG). The main objective of this work is the study of how the properties of matter can modify the future evolution of the attractors and their consequences on the regions of initial conditions of the solutions. As is well known, QG contains the Ruzmaikina–Ruzmaikin (RR) solution. This solution describes the slow-roll regime of Starobinsky’s inflationary model, which is currently the best one due to the excellent agreement with Cosmic Microwave Background Radiation (CMBR) data. In QG, we found universes that can be attracted to the RR solution or recollapse toward the isotropic singularity attractor. If the Equation of State (EoS) parameter is ultra-radiative 
, the tilt variable increases both in RR and Milne for QG or GR, respectively. In both cases, the fluid expansion and acceleration diverge, while the vorticity initially increases and then decreases to zero.
© The Author(s) 2025
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