Cosmology with Radion and Bulk Scalar Field in Two Branes Model
Abstract
We investigate cosmological evolutions of the bulk scalar field phi(t) and the radion d(t) in fivedimensional dilatonic two branes model. The bulk potential for the scalar field is taken as the exponential function V_{bulk}proptoexp (2(2)^{1/2}bphi), where b is the parameter of the theory. This model includes RandallSundrum model (with b = 0) and fivedimensional HoravaWitten theory (with b = 1). We consider matter on both branes and arbitrary potentials on the branes and in the bulk. These matter and potentials induce the cosmological expansion of the brane as well as the time evolution of the bulk scalar field and the radion. Starting with full fivedimensional equations, we derive fourdimensional effective equations which govern the lowenergy dynamics of brane worlds. A correspondent fivedimensional geometry is also obtained. The effective fourdimensional theory on a positive tension brane is described by biscalar tensor theory. If the radion is stabilized, the effective theory becomes BransDicke (BD) theory with BD parameter 1/2b^{2}. On the other hand, if the scalar field is stabilized, the effective theory becomes scalartensor theory with BD parameter 3/[2(3b^{2}+1)]varphi(t)/[1varphi(t)] where varphi is the BD field defined by radion d(t). If we do not introduce the stabilization mechanism for these moduli fields, the acceptable late time cosmology can be realized only if the dilaton coupling b is small (b^{2} < 1.6 × 10^{4}) and the negative tension brane is sufficiently away from the positive tension brane. We also construct several models for inflationary brane worlds driven by potentials on the brane and in the bulk.
 Publication:

Journal of High Energy Physics
 Pub Date:
 December 2002
 DOI:
 10.1088/11266708/2002/12/056
 arXiv:
 arXiv:hepth/0210029
 Bibcode:
 2002JHEP...12..056K
 Keywords:

 High Energy Physics  Theory;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 34pages, No figure, typos corrected and references added