2D BAO vs. 3D BAO: Solving the Hubble Tension with Bimetric Cosmology

Ordinary 3D Baryon Acoustic Oscillations (BAO) data are model-dependent, requiring the assumption of a cosmological model to calculate comoving distances during data reduction. Throughout the present-day literature, the assumed model is <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">Λ</mi></semantics></math></inline-formula>CDM. However, it has been pointed out in several recent works that this assumption can be inadequate when analyzing alternative cosmologies, potentially biasing the Hubble constant (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>H</mi><mn>0</mn></msub></semantics></math></inline-formula>) low, thus contributing to the Hubble tension. To address this issue, 3D BAO data can be replaced with 2D BAO data, which are only weakly model-dependent. The impact of using 2D BAO data, in combination with alternative cosmological models beyond <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">Λ</mi></semantics></math></inline-formula>CDM, has been explored for several phenomenological models, showing a promising reduction in the Hubble tension. In this work, we accommodate these models in the theoretically robust framework of bimetric gravity. This is a modified theory of gravity that exhibits a transition from a (possibly) negative cosmological constant in the early universe to a positive one in the late universe. By combining 2D BAO data with cosmic microwave background and type Ia supernovae data, we find that the inverse distance ladder in this theory yields a Hubble constant of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mrow><mo>(</mo><mn>71.0</mn><mspace width="3.33333pt"></mspace><mo>±</mo><mspace width="3.33333pt"></mspace><mn>0.9</mn><mo>)</mo></mrow><mspace width="0.166667em"></mspace><mi>km</mi><mo>/</mo><mi mathvariant="normal">s</mi><mo>/</mo><mi>Mpc</mi></mrow></semantics></math></inline-formula>, consistent with the SH0ES local distance ladder measurement of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mrow><mo>(</mo><mn>73.0</mn><mspace width="3.33333pt"></mspace><mo>±</mo><mspace width="3.33333pt"></mspace><mn>1.0</mn><mo>)</mo></mrow><mspace width="0.166667em"></mspace><mi>km</mi><mo>/</mo><mi mathvariant="normal">s</mi><mo>/</mo><mi>Mpc</mi></mrow></semantics></math></inline-formula>. Replacing 2D BAO with 3D BAO results in <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><mrow><mo>(</mo><mn>68.6</mn><mspace width="3.33333pt"></mspace><mo>±</mo><mspace width="3.33333pt"></mspace><mn>0.5</mn><mo>)</mo></mrow><mspace width="0.166667em"></mspace><mi>km</mi><mo>/</mo><mi mathvariant="normal">s</mi><mo>/</mo><mi>Mpc</mi></mrow></semantics></math></inline-formula> from the inverse distance ladder. We conclude that the choice of BAO data significantly impacts the Hubble tension, with ordinary 3D BAO data exacerbating the tension, while 2D BAO data provide results consistent with the local distance ladder.