TY - JOUR

T1 - Cuscuta-Galileon cosmology

T2 - Dynamics, gravitational constants, and the Hubble constant

AU - Maeda, Keiichi

AU - Panpanich, Sirachak

N1 - Funding Information:
K. M. would like to thank Antonio De Felice, Shinji Mukohyama, and Masroor C. Pookkillath for useful comments and fruitful discussions. K. M. also acknowledges the Yukawa Institute for Theoretical Physics at Kyoto University, where most of the present work was completed during the Visitors Program of FY2021. This work as supported in part by JSPS KAKENHI Grants No. JP17H06359 and No. JP19K03857 and by a Waseda University Grant for Special Research Project (No. 2021C-569).
Publisher Copyright:
© 2022 American Physical Society.

PY - 2022/5/15

Y1 - 2022/5/15

N2 - We discuss cosmology based on a Cuscuta-Galileon gravity theory, which preserves just two degrees of freedom. Although there exist no additional degrees of freedom, introduction of a potential of a scalar field changes the dynamics. The scalar field is completely determined by matter fields. Giving an exponential potential as an example, we discuss the cosmological dynamics. The gravitational "constant"GF appeared in the effective Friedmann equation becomes time dependent. We also present how to construct a potential when we know the evolution of the Hubble parameter. When we assume the ΛCDM cosmology for the background evolution, we find the potential form. We then analyze the density perturbations, which equation is characterized only by a change of the gravitational "constant"Geff, which also becomes time dependent. From the observational constraints such as the constraint from the big-bang nucleosynthesis and the constraint on time-variation of gravitational constant, we restrict the parameters in our models. The time dependence of the gravitational constant in the effective Friedmann equation, we may have a chance to explain the Hubble tension problem.

AB - We discuss cosmology based on a Cuscuta-Galileon gravity theory, which preserves just two degrees of freedom. Although there exist no additional degrees of freedom, introduction of a potential of a scalar field changes the dynamics. The scalar field is completely determined by matter fields. Giving an exponential potential as an example, we discuss the cosmological dynamics. The gravitational "constant"GF appeared in the effective Friedmann equation becomes time dependent. We also present how to construct a potential when we know the evolution of the Hubble parameter. When we assume the ΛCDM cosmology for the background evolution, we find the potential form. We then analyze the density perturbations, which equation is characterized only by a change of the gravitational "constant"Geff, which also becomes time dependent. From the observational constraints such as the constraint from the big-bang nucleosynthesis and the constraint on time-variation of gravitational constant, we restrict the parameters in our models. The time dependence of the gravitational constant in the effective Friedmann equation, we may have a chance to explain the Hubble tension problem.

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U2 - 10.1103/PhysRevD.105.104022

DO - 10.1103/PhysRevD.105.104022

M3 - Article

AN - SCOPUS:85130154291

VL - 105

JO - Physical Review D

JF - Physical Review D

SN - 2470-0010

IS - 10

M1 - 104022

ER -