TY - JOUR

T1 - Weak gravity on a ΛcDM background

AU - GANNOUJI, RADOUANE

AU - Perivolaropoulos, Leandros

AU - Polarski, David

AU - Skara, Foteini

N1 - Funding Information:
This research is co-financed by Greece and the European Union (European Social Fund) through the Operational Programme “Human Resources Development, Education and Lifelong Learning 2014–2020” in the context of the project “Scalar Fields in Curved Spacetimes: Soliton Solutions, Observational Results and Gravitational Waves” (Project No. MIS 5047648). This article has also benefited from the COST Action CA15117 (CANTATA - Cosmology and Astrophysics Network for Theoretical Advances and Training Actions) supported by the European Cooperation in Science and Technology. R. G. is supported by Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT) Project No. 1171384.
Publisher Copyright:
© 2021 American Physical Society.
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/3/11

Y1 - 2021/3/11

N2 - We consider Horndeski modified gravity models obeying stability, velocity of gravitational waves cT equals c and quasistatic approximation on subhorizon scales. We assume further a Lambda cold dark matter background expansion and a monotonic evolution on the cosmic background of the α functions as αi=αi0as where i=M, B, a is the scale factor and αi0 (αM0,αB0), s are arbitrary parameters. We show that the growth and lensing reduced (dimensionless) gravitational couplings μGgrowth/G, ςGlensing/G exhibit the following generic properties today: ς0<1 for all viable parameters, μ0<1 (weak gravity today) is favored for small s while μ0>1 is favored for large s. We establish also the relation μ≥ς at all times. Taking into account the fσ8 and EG data we constrain the parameter s to satisfy s≲2. Hence these data select essentially the weak gravity regime today (μ0<1) when s<2, while μ0>1 subsists only marginally for s≈2. At least the interval 0.5≲s≲2 would be ruled out in the absence of screening. We consider further the growth index γ(z) and identify the (αM0,αB0,s) parameter region that corresponds to specific signs of the differences γ0-γ0ΛCDM, and γ1-γ1ΛCDM, where γ0γ|z=0 and γ1dγdz|z=0. In this way important information is gained on the past evolution of μ. We obtain in particular the signature γ0>γ0ΛCDM for s<2 in the selected weak gravity region.

AB - We consider Horndeski modified gravity models obeying stability, velocity of gravitational waves cT equals c and quasistatic approximation on subhorizon scales. We assume further a Lambda cold dark matter background expansion and a monotonic evolution on the cosmic background of the α functions as αi=αi0as where i=M, B, a is the scale factor and αi0 (αM0,αB0), s are arbitrary parameters. We show that the growth and lensing reduced (dimensionless) gravitational couplings μGgrowth/G, ςGlensing/G exhibit the following generic properties today: ς0<1 for all viable parameters, μ0<1 (weak gravity today) is favored for small s while μ0>1 is favored for large s. We establish also the relation μ≥ς at all times. Taking into account the fσ8 and EG data we constrain the parameter s to satisfy s≲2. Hence these data select essentially the weak gravity regime today (μ0<1) when s<2, while μ0>1 subsists only marginally for s≈2. At least the interval 0.5≲s≲2 would be ruled out in the absence of screening. We consider further the growth index γ(z) and identify the (αM0,αB0,s) parameter region that corresponds to specific signs of the differences γ0-γ0ΛCDM, and γ1-γ1ΛCDM, where γ0γ|z=0 and γ1dγdz|z=0. In this way important information is gained on the past evolution of μ. We obtain in particular the signature γ0>γ0ΛCDM for s<2 in the selected weak gravity region.

UR - http://www.scopus.com/inward/record.url?scp=85103082405&partnerID=8YFLogxK

U2 - 10.1103/PhysRevD.103.063509

DO - 10.1103/PhysRevD.103.063509

M3 - Article

AN - SCOPUS:85103082405

VL - 103

JO - Physical Review D

JF - Physical Review D

SN - 2470-0010

IS - 6

M1 - 063509

ER -