Oscillating scalar fields in extended quintessence

Abstract

We study a rapidly-oscillating scalar field with potential V (φ) = k|φ| n nonminally coupled to the Ricci scalar R via a term of the form (1 − 8πG 0 ξφ 2 )R in the action. In the weak coupling limit, we calculate the effect of the nonminimal coupling on the time-averaged equation of state parameter γ = (p + ρ)/ρ. The change in γ is always negative for n ≥ 2 and always positive for n < 0.71 (which includes the case where the oscillating scalar field could serve as dark energy), while it can be either positive or negative for intermediate values of n. Constraints on the timevariation of G force this change to be infinitesimally small at the present time whenever the scalar field dominates the expansion, but constraints in the early universe are not as stringent. The rapid oscillation induced in G also produces an additional contribution to the Friedman equation that behaves like an effective energy density with a stiff equation of state, but we show that, under reasonable assumptions, this effective energy density is always smaller than the density of the scalar field itself.

Kinetic Sunyaev–Zel’dovich effect in rotating galaxy clusters from MUSIC simulations

“…For instance, a very recent example is the work by Adam et al (2017), where they report the first high-significance detection of the kSZ towards two cluster substructures in MACS J0717.5+3745 (with 3.4 and 5.1σsignificance, respectively), from measurements at 260 GHz with an effective angular resolution of 22 arcseconds. Also, cluster motions have been detected with high significance in a statistical fashion, by estimating the pairwise momentum between couples of galaxy clusters using CMB data (Hand et al 2012;Planck Collaboration et al 2016;Li et al 2018). It is worth to stress that, to quantify cluster velocities from single-cluster measurements, it is necessary to use complementary data from X-ray observations, since the kSZ alone is not sufficient to disentangle the contribution to the total signal coming from both the electron density -that can be inferred from measurements of the X-ray luminosity -and the velocity.…”

Cosmic acceleration in screening hybrid quintessence model

“…Equipped with these equations, we perform our model as follows: Initially, we assume that the scalar fields are settled down in the stable minimum of the potential (11), i.e. φ = 0, ψ = 0.…”

“…Astrophysical data indicate that the expansion of the Universe is accelerating [1,2]. The origin of this positive acceleration which has begun from the matter dominated era is still unclear but may be caused by a scalar field, whose pressure is negative, called quintessence [3][4][5][6][7][8][9][10][11][12][13][14].…”

“…At the end let us note that the gravitational effects of the nonminimal coupling to the curvature in a general hybrid model have also been carried out in the context of the parameterized post-Newtonian approximation (PPN)in [47]. There was shown that in the lowest order approximation, V (φ, ψ) = 0 and V ,φ (φ, ψ) = V ,ψ (φ, ψ) = 0 hold, which for the potential (11) gives : φ = ψ = 0. This implies that the non minimal coupling does not affect the parameterized post-Newtonian parameters in gravitational test [47] which is consistent with the screening effect used in our article.…”

Quasinormal modes of scalar field coupled to Einstein's tensor in the non-commutative geometry inspired black hole

“…However, in Galileon theories, in order for the scalar field to have a non-trivial profile and to be finite on the horizon, these solutions must comply with strict constraints. This model is usually used to describe inflation [36][37][38][39][40][41][42] and late acceleration [30,[43][44][45][46][47][48][49][50][51][52][53]. NMDC acts as a friction term in early inflationary cosmology [24,30,36,54,55],…”