Axion model in extra dimensions with TeV scale gravity.pdfVIP

a r X i v : h e p - p h / 9 9 0 8 5 1 5 v 2 1 2 J a n 2 0 0 0 TU-572 Axion model in extra dimensions with TeV scale gravity Sanghyeon Chang, Shiro Tazawa and Masahiro Yamaguchi Department of Physics, Tohoku University, Sendai 980-8578, Japan Abstract A simple axion model is proposed in the scenario of large extra dimensions where gravity scale is as low as 1 TeV. To obtain an intermediate-scale decay constant of the axion, the axion is assumed to live in a sub-spacetime (brane) of the whole bulk. In this model there appear Kaluza-Klein modes of the axion which have stronger interaction than those of the graviton. The axion brane plays a role of absorber of the graviton Kaluza-Klein modes. Because of these reasons phenomenology and cosmology of the axion become highly non-trivial. We discuss various cosmological constraints as well as astrophysical ones and show that the model is viable for certain choices of the dimensionality of the axion brane. The structure of the model proposed here provides a viable realization of the fat brane idea to relax otherwise very severe cosmological constraints. Typeset using REVTEX 1 I. INTRODUCTION It has been suggested that the fundamental scale of nature can be as low as TeV, whereas the largeness of the effective Planck scale or the weakness of the gravity in a long distance can be explained by introducing large extra dimensions [1–4]. When there exist n of such extra dimensions, the relation between the gravitational constant 8πGN = 1/M 2 pl(4) in 4 dimensions and the fundamental scale Mpl(4+n) in (4 + n) dimensions is given M2pl(4) ～ VnMn+2pl(4+n), (1) where Vn is the volume of the extra dimensional space. For Mpl(4+n) ～ 1 TeV, the size of the extra dimensions rn is computed as rn ～ V 1/nn ～ 10 32 n ?6M ? 2 n ?1 TeV MeV ?1 ～ 10 32n ?17M? 2 n ?1 TeV cm, (2) where MTeV ≡ Mpl(4+n)/TeV. The case n = 1 is excluded because the gravitational law would change at macroscopic level, but the cases n ≥ 2 are allowed by gravity experim