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String-inspired cosmology: a late time transition from a scaling matter era to a dark energy universe caused by a Gauss–Bonnet coupling

Shinji Tsujikawa1 and M Sami2,3

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The Gauss–Bonnet (GB) curvature invariant coupled to a scalar field phi can lead to an exit from a scaling matter dominated epoch to a late time accelerated expansion, which is attractive for alleviating the coincidence problem of dark energy. We derive the condition for the existence of cosmological scaling solutions in the presence of the GB coupling for a general scalar field Lagrangian density p(phi,X), where X = −(1/2)(∇phi)2 is a kinetic term of the scalar field. The GB coupling and the Lagrangian density are restricted to being in the forms f(phipropto eλphi and p = Xg(Xeλphi), respectively, where λ is a constant and g is an arbitrary function. We also derive fixed points for such a scaling Lagrangian with a GB coupling f(phipropto eμphi and clarify the conditions under which the scaling matter era is followed by a de Sitter solution which can appear in the presence of the GB coupling. Among the scaling models proposed in the current literature, we find that the models which allow such a cosmological evolution are an ordinary scalar field with an exponential potential and a tachyon field with an inverse square potential, although the latter requires a coupling between dark energy and dark matter.


Keywords

cosmological applications of theories with extra dimensions

string theory and cosmology

 

E-print Number: hep-th/0608178

Cited: by |

Refers: to

PACS

98.80.Cq Particle-theory and field-theory models of the early Universe (including cosmic pancakes, cosmic strings, chaotic phenomena, inflationary universe, etc.)

95.36.+x Dark energy

95.35.+d Dark matter (stellar, interstellar, galactic, and cosmological)

Subjects

Gravitation and cosmology

Particle physics and field theory

Astrophysics and astroparticles

Dates

Issue 01 (January 2007)

Received 3 October 2006, accepted for publication 15 December 2006

Published 10 January 2007



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    Shinji Tsujikawa and M Sami JCAP01(2007)006

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