Abstract

Teleparallel gravity offers a new avenue in which to construct gravitational models beyond general relativity. While teleparallel gravity can be framed in a way to be dynamically equivalent to general relativity, its modifications are mostly not equivalent to the traditional route to modified gravity. f(T, B) gravity is one such gravitational theory where the second and fourth order contributions to the field equations are decoupled. In this work, we explore the all important cosmological perturbations of this new framework of gravity. We derive the gravitational propagation equation, its vector perturbation stability conditions, and its scalar perturbations. Together with the matter perturbations, we derive the effective gravitational constant in this framework, and find an interesting branching behaviour that depends on the particular gravitational models being probed. We close with a discussion on the relation of these results with other gravitational theories.

Highlights

  • CDM cosmological model is supported by an abundance of evidence in describing the evolution of the Universe at all cosmological scales [7,8] when matter beyond the standard model of particle physics is included

  • Even though great efforts have been directed at this part of the theory, internal problems persist with the concept of a cosmological constant [15], and direct evidence for dark matter particles remains elusive [16]

  • Teleparallel Gravity (TG) offers a novel approach to gravitation where curvature is replaced by teleparallel torsion giving a new framework in which to produce gravitational models. f (T, B) gravity is a interesting expression of TG in which the second and fourth order contributions to the Ricci scalar are separated

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Summary

Introduction

The CDM model was realised as a confrontation with Hubble expansion data but the so-called H0 tension calls this feature into question, where the observational discrepancy between model independent measurements in the late Universe [17,18] are in a meaning disagreement with the predicted value from the early Universe [19,20]. This tension has only grown in recent years [19,21]. Saying that the problem still appears to be open with measurements from the tip of the red giant branch (TRGB, Carnegie-Chicago Hubble Program) pointing to a lower H0 tension, the issue may be resolved by novel future observations such as measurements using gravitational wave astronomy standard candles [22,23] which may

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Modified teleparallel theories of gravity
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Tensor perturbations
Scalar perturbations
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Branch
Conclusion and discussion
Scalar and pseudo scalar perturbations
Branch C
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