Dilatonic ghost condensate as dark energy

Abstract

We explore a dark energy model with a ghost scalar field in the context of the runaway dilaton scenario in low-energy effective string theory. We address the problem of vacuum stability by implementing higher-order derivative terms and show that a cosmologically viable model of "phantomized" dark energy can be constructed without violating the stability of quantum fluctuations. We also analytically derive the condition under which cosmological scaling solutions exist starting from a general Lagrangian including the phantom type scalar field. We apply this method to the case where the dilaton is coupled to non-relativistic dark matter and find that the system tends to become quantum mechanically unstable when a constant coupling is always present. Nevertheless, it is possible to obtain a viable cosmological solution in which the energy density of the dilaton eventually approaches the present value of dark energy provided that the coupling rapidly grows during the transition to the scalar field dominated era.

Dynamics of cosmological scalar fields

“…This includes the canonical choice if one considers f (B) = B − 1. In [37,38] it has been shown that, within general relativity, the most general Lagrangian leading to cosmological scaling solutions with an exponential potential can be written as 2 (29). In addition the dimensionless variables (12) turn out to be of great advantage if a scalar field Lagrangian is assumed as in (29).…”

“…2 In [37,38] this Lagrangian was writtes as L φ = X f (B), however a simple redefinition of the function f can bring this in the form (29).…”

Arbitrary scalar-field and quintessence cosmological models

“…Contrary to the cosmological constant, the quintessence equation of state changes dynamically with time [6]. In fact, a plethora of exotic fluids have been proposed to explain the accelerated expansion of the Universe, which include amongst many others k-essence models, in which the late-time can be driven by the kinetic energy of the scalar field [7][8][9][10][11]; coupled models where dark energy interacts with dark matter [12][13][14][15][16][17][18][19][20][21][22]; and unified models of dark matter and dark energy [23][24][25].…”

Dilatonic topological defects in3+1dimensions and their embeddings

“…In the limit of infinite values of these parameters, the dynamics of the scalar fields freeze and the dynamics of the action (2) reduces to the Einstein-Maxwell action dynamics. The scalar fields φ and ψ emerge naturally in the context of string theory as dilatons [10,11].…”