TY - JOUR

T1 - Weak cosmic growth in coupled dark energy with a Lagrangian formulation

AU - Kase, Ryotaro

AU - Tsujikawa, Shinji

N1 - Funding Information:
We thank Edmund Copeland for useful correspondence about our previous paper [46] and for motivating us to study derivatively coupled DE and DM theories further. RK is supported by the Grant-in-Aid for Young Scientists B of the JSPS No. 17K14297 . ST is supported by the Grant-in-Aid for Scientific Research Fund of the JSPS No. 19K03854 and MEXT KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas “Cosmic Acceleration” (No. 15H05890 ).

PY - 2020/5/10

Y1 - 2020/5/10

N2 - We investigate a dark energy scenario in which a canonical scalar field ϕ is coupled to the four velocity uc μ of cold dark matter (CDM) through a derivative interaction uc μ∂μϕ. The coupling is described by an interacting Lagrangian f(X,Z), where f depends on X=−∂μϕ∂μϕ/2 and Z=uc μ∂μϕ. We derive stability conditions of linear scalar perturbations for the wavelength deep inside the Hubble radius and show that the effective CDM sound speed is close to 0 as in the standard uncoupled case, while the scalar-field propagation speed is affected by the interacting term f. Under a quasi-static approximation, we also obtain a general expression of the effective gravitational coupling felt by the CDM perturbation. We study the late-time cosmological dynamics for the coupling f∝X(2−m)/2Zm and show that the gravitational coupling weaker than the Newton constant can be naturally realized for m>0 on scales relevant to the growth of large-scale structures. This allows the possibility for alleviating the tension of σ8 between low- and high-redshift measurements.

AB - We investigate a dark energy scenario in which a canonical scalar field ϕ is coupled to the four velocity uc μ of cold dark matter (CDM) through a derivative interaction uc μ∂μϕ. The coupling is described by an interacting Lagrangian f(X,Z), where f depends on X=−∂μϕ∂μϕ/2 and Z=uc μ∂μϕ. We derive stability conditions of linear scalar perturbations for the wavelength deep inside the Hubble radius and show that the effective CDM sound speed is close to 0 as in the standard uncoupled case, while the scalar-field propagation speed is affected by the interacting term f. Under a quasi-static approximation, we also obtain a general expression of the effective gravitational coupling felt by the CDM perturbation. We study the late-time cosmological dynamics for the coupling f∝X(2−m)/2Zm and show that the gravitational coupling weaker than the Newton constant can be naturally realized for m>0 on scales relevant to the growth of large-scale structures. This allows the possibility for alleviating the tension of σ8 between low- and high-redshift measurements.

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U2 - 10.1016/j.physletb.2020.135400

DO - 10.1016/j.physletb.2020.135400

M3 - Article

AN - SCOPUS:85082738932

VL - 804

JO - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

JF - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

SN - 0370-2693

M1 - 135400

ER -