Iwasawa N=8 attractors

Starting from the symplectic construction of the Lie algebra e due to Adams, we consider an Iwasawa parametrization of the coset ESU(8), which is the scalar manifold of N=8, d=4 supergravity. Our approach, and the manifest off-shell symmetry of the resulting symplectic frame, is determined by a noncompact Cartan subalgebra of the maximal subgroup SL(8,R) of E. In the absence of gauging, we utilize the explicit expression of the Lie algebra to study the origin of ESU(8) as scalar configuration of a 18-BPS extremal black hole attractor. In such a framework, we highlight the action of a U(1) symmetry spanning the dyonic 18-BPS attractors. Within a suitable supersymmetry truncation allowing for the embedding of the Reissner-Nördstrom black hole, this U(1) action is interpreted as nothing but the global R-symmetry of pureN=2 supergravity. Moreover, we find that the above mentioned U(1) symmetry is broken down to a discrete subgroup Z, implying that all 18-BPS Iwasawa attractors are nondyonic near the origin of the scalar manifold. We can trace this phenomenon back to the fact that the Cartan subalgebra of SL(8,R) used in our construction endows the symplectic frame with a manifest off-shell covariance which is smaller than SL(8,R) itself. Thus, the consistence of the Adams-Iwasawa symplectic basis with the action of the U(1) symmetry gives rise to the observed Z residual nondyonic symmetry. © 2010 American Institute of Physics.