Scale-dependent growth from a transition in dark energy dynamics

Abstract

We investigate the observational consequences of the quintessence field rolling to and oscillating near a minimum in its potential, if it happens close to the present epoch (z 0.2). We show that in a class of models, the oscillations lead to a rapid growth of the field fluctuations and the gravitational potential on subhorizon scales. The growth in the gravitational potential occurs on timescales H −1 . This effect is present even when the quintessence parameters are chosen to reproduce an expansion history consistent with observations. For linearized fluctuations, we find that although the gravitational potential power spectrum is enhanced in a scale-dependent manner, the shape of the dark matter/galaxy power spectrum is not significantly affected. We find that the best constraints on such a transition in the quintessence field is provided via the integrated Sachs-Wolfe effect in the CMB temperature power spectrum. Going beyond the linearized regime, the quintessence field can fragment into large, localized, longlived excitations (oscillons) with sizes comparable to galaxy clusters; this fragmentation could provide additional observational constraints. Two quoted signatures of modified gravity are a scale-dependent growth of the gravitational potential and a difference between the matter power spectrum inferred from measurements of lensing and galaxy clustering. Here, both effects are achieved by a minimally coupled scalar field in general relativity with a canonical kinetic term. In other words we show that, with some tuning of parameters, scale-dependent growth does not necessarily imply a violation of General Relativity. 1 mamin@mit.edu 2 zukin@mit.edu 3 edbert@mit.edu arXiv:1108.1793v2 [astro-ph.CO] 23 Aug 2012 * * When the Floquet exponents are zero, there exist another class of solutions δϕ k (t) ∝ tP 1 (t) and δϕ k (t) ∝ P 2 (t) where P 1,2 (t) are periodic functions.

End of inflation, oscillons, and matter-antimatter asymmetry

“…For a simple algorithm to calculate the exponents, in similar notation, see the Appendix of [48]. If the Floquet exponents have a real part, then we have exponentially growing solutions.…”

Dark energy fromα-attractors

“…That is, the potential slope becomes shallower, just as for hilltop potentials. We know these have negative mass squared terms near the maximum (also see [9][10][11] for other anharmonic instabilities), and we find this as well for the α-model. Specifically,…”

Shape of the inflaton potential and the efficiency of the universe heating

“…We did not look for a theoretical justification for the chosen form of the potential (2.9), bearing in mind the large freedom for possible forms of the scalar field potential at large mass/energy scale, but it is noteworthy that a similar type of the potential which is quadratic near the minimum and is flatter away from the minimum was studied in Refs. [24,25]. Such potentials were in turn derived in Refs.…”

“…The properties of the inflationary model, which might be realized with the inflaton potentials of the type (2.9) can be understood from the results of Refs. [24,25].…”

“…Quoting Ref. [25]: "This choice was motivated by monodromy and supergravity models of inflation [26][27][28][29][30] and a recent model of axion quintessence [31]". Figure 1 for the potential (2.9) has a shape which is quite close to that depicted in Fig.…”