Axions in Type IIA Superstring Theory and Dark Matter

Motivated by the M-theory compactification physics, we study a type IIA superstring quiver model with an open string axion field associated with the U(1)_{PQ} Peccei-Quinn global symmetry using D6-brane physics. This realization extends the symmetry of the SM-Like and contributes to the mediation of the electroweak symmetry breaking. The associated axion energy scales are approached in terms of D2 and D6-branes in type IIA compactifications on Calabi-Yau threeforlds. Using the fermion mass scales as well as string theory results, the allowed axion window is discussed in terms of intersecting D6-branes wrapping 3-cycles belonging to the middle cohomology of the type IIA internal space. The non-perturbative effect of the open string axion sector is dealt with using a D2-brane wrapping a 3-cycle producing (1+3)-dimensional stringy instantons. According to the known data, the vacuum expectation value of the axion and the mass scale of the involved scalar provide a probe of the stringy physics effect in the SM and a possible axionic dark matter candidate.