Effective theory of brane world with small tension - art. no. 106003

The five dimensional theory compactified on S-1 with two "branes" (two doma in walls) embedded in it is constructed, based on the field-theoretic mecha nism to generate the "brane." Some light states localized in the "brane" ap pear in the theory. One is the Nambu-Goldstone boson, which corresponds to the breaking of the translational invariance in the transverse direction of the "brane." In addition, if the tension of the "brane" is smaller than th e fundamental scale of the original theory, it is found that there may exis t not only massless states but also some massive states lighter than the fu ndamental scale in the "brane." We analyze the four dimensional effective t heory by integrating out the freedom of the fifth dimension. We show that s ome effective couplings can be explicitly calculated. As one of our results , some effective couplings of the state localized in the "brane" to the hig her Kaluza-Klein modes in the bulk are found to be suppressed by the width of the "brane." The resultant suppression factor can be quantitatively diff erent from the one analyzed by Bando et al. using the Nambu-Goto action, wh ile they are qualitatively the same.