Approaching Lambda without fine-tuning

Abstract

We address the fine-tuning problem of dark energy cosmologies which arises when the dark energy density needs to initially lie in a narrow range in order for its present value to be consistent with observations. As recently noticed, this problem becomes particularly severe in canonical Quintessence scenarios, when trying to reproduce the behavior of a cosmological constant, i.e. when the dark energy equation of state w_Q approaches -1: these models may be reconciled with a large basin of attraction only by requiring a rapid evolution of w_Q at low reshifts, which is in conflict with the most recent estimates from type Ia Supernovae discovered by Hubble Space Telescope. Next, we focus on scalar-tensor theories of gravity, discussing the implications of a coupling between the Quintessence scalar field and the Ricci scalar (``Extended Quintessence''). We show that, even if the equation of state today is very close to -1, by virtue of the scalar-tensor coupling the quintessence trajectories still possess the attractive feature which allows to reach the present level of cosmic acceleration starting by a set of initial conditions which covers tens of orders of magnitude; this effect, entirely of gravitational origin, represents a new important consequence of the possible coupling between dark energy and gravity.

References added; figures labels enlarged. To appear on PrD

References in corpus (4)

• Cosmology and the Fate of Dilatation Symmetry
• New dark energy constraints from supernovae, microwave background and galaxy clustering
• Non-linear perturbations in scalar-tensor cosmologies
• Tracking Quintessence Would Require Two Cosmic Coincidences

Cited by in corpus (31)

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• Cosmological observational constraints on the power law $f(Q)$ type modified gravity theory
• Reconstruction of the Dark Energy equation of state
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• Constraints on Scalar-Field Dark Energy from Galaxy Cluster Gas Mass Fraction versus Redshift
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• Scaling solutions in scalar-tensor cosmologies
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• New tracker models of dark energy
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• Breakdown of the initial value formulation of scalar-tensor gravity and its physical meaning
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• Perfect fluid solutions of Brans-Dicke and f(R)cosmology
• Light Thoughts on Dark Energy
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• Cosmological constraints on sterile neutrino Dark Matter production mechanisms