Technically natural cosmological constant from supersymmetric 6D brane backreaction
Abstract
We provide an explicit example of a higherdimensional model describing a nonsupersymmetric spectrum of 4D particles of mass M, whose 4D geometry  including loop effects  has a curvature that is of order R ∼ m_{KK}^{4}/M_{p}^{2} , where m_{KK} is the extradimensional KaluzaKlein scale and M_{p} is the 4D Planck constant. m_{KK} is stabilized and can in particular satisfy m_{KK} ≪ M . The system consists of a (5+1)dimensional model with a fluxstabilized supersymmetric bulk coupled to nonsupersymmetric matter localized on a (3+1)dimensional positivetension brane. We use recent techniques for calculating how extra dimensions respond to changes in brane properties to show (at the classical level) that the extradimensional volume adjusts to ensure that the lowenergy 4D geometry is exactly flat, independent of the value of the brane tensions. Its mechanism for doing so is the transfer of stabilizing flux between the bulk and the branes. The UV completion of the model can arise at scales much larger than M, allowing the calculation of quantum effects like the zeropoint energy of very massive particles in the vacuum. We find that branelocalized loops do not affect the 4D curvature at all, but bulk loops can. These can be estimated on general grounds and we show that supersymmetry dictates that they generate curvatures that are generically of order m_{KK}<XUP>4/M_{p}^{2} . For realistic applications this points to a world with two supersymmetric extra dimensions, with supersymmetry in the bulk broken at the subeV KK scale  as proposed in
 Publication:

Physics of the Dark Universe
 Pub Date:
 March 2013
 DOI:
 10.1016/j.dark.2012.10.001
 arXiv:
 arXiv:1108.0345
 Bibcode:
 2013PDU.....2....1B
 Keywords:

 High Energy Physics  Theory;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 23 pages + appendices and references