Fermions, scalars and Randall-Sundrum gravity on domain-wall branes.pdfVIP

a r X i v : 0 7 0 5 .1 3 9 1 v 4 [ h e p - p h ] 2 5 S e p 2 0 0 7 Fermions, scalars and Randall-Sundrum gravity on domain-wall branes Rhys Davies? and Damien P. George? School of Physics, Research Centre for High Energy Physics, The University of Melbourne, Victoria 3010, Australia (Dated: February 1, 2008) Abstract We analyse the general features of localisation of fermions and scalars in smoothed field- theoretical versions of the type 2 Randall- Sundrum braneworld model. A scalar field domain-wall forms the brane, inducing warped gravity, and we study the mass spectra of the matter fields in the dimensionally reduced theory. We demonstrate explicitly that both scalar and fermion fields exhibit a continuum of properly normalisable modes starting at zero mass. If discrete bound modes are present in the gravity-free case, these become resonances in the continuum, while off-resonant modes are highly suppressed on the brane. We describe briefly how another scalar field can be used to break a symmetry on the domain-wall while leaving it unbroken far from the wall, as has already been done in the flat space case. Finally we present numerical calculations for a toy model which demonstrates the decoupling of continuum modes at low energies, so the theory becomes four dimensional. PACS numbers: 04.50.+h, 11.27.+d ?Electronic address: daviesr@physics.unimelb.edu.au ?Electronic address: d.george@physics.unimelb.edu.au 1 I. INTRODUCTION Over the last decade there has been a lot of research into the possibility that our observ- able 3 + 1-dimensional universe resides on a defect in a higher-dimensional bulk spacetime. If this is the case, we should be able to construct a model which explains why physics at low energies is insensitive to the extra dimensions. It has been known for some time that bulk fermions coupled to a scalar field domain-wall have a spectrum containing a zero mode which is localised to the wall [1]. In the case of a 4 + 1-dimensional bulk, this zer