Dark energy from approximate U(1)de symmetry

The PLANCK observation strengthens the argument that the observed acceleration of the Universe is dominated by the invisible component of dark energy. We address how this extremely small DE density can be obtained in an ultraviolet complete theory. From two mass scales, the grand unification scale MG and the Higgs boson mass, we parametrize the scale of dark energy (DE). To naturally generate an extremely small DE term, we introduce an almost flat DE potential of a pseudo-Goldstone boson of an approximate global symmetry U(1)de originating from some discrete symmetries allowed in an ultraviolet complete theory, as e.g. obtained in string theory constructions. For the DE potential to be extremely shallow, the pseudo-Goldstone boson is required not to couple to the QCD anomaly. This fixes uniquely the nonrenormalizable term generating the potential suppressed by MG7 in supergravity models.