Weak cosmic growth in coupled dark energy with a Lagrangian formulation

Ryotaro Kase, Shinji Tsujikawa

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

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 μμϕ. The coupling is described by an interacting Lagrangian f(X,Z), where f depends on X=−∂μϕ∂μϕ/2 and Z=uc μμϕ. 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.

Original languageEnglish
Article number135400
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Volume804
DOIs
Publication statusPublished - 2020 May 10
Externally publishedYes

ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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