A projective Dirac operator on $\mathbb{C}P^n$ and extended SUSY
We construct a universal spin$_c$ Dirac operator on $\mathbb{C}P^n$ built by projecting $su(n+1)$ left actions and prove its equivalence to the standard right action Dirac operator on $\mathbb{C}P^n$. The eigenvalue problem is solved and the spinor space constructed thereof, showing that the proposed Dirac operator is universal, changing only its domain for different spin$_c$ structures. Explicit expressions for the chirality and the eigenspinors are also found and consistency with the index theorem is established. Also, the extended $\mathcal{N} =2$ supersymmetry algebra is realised through the Dirac operator and its companion supercharge, and an expression for the superpotential of any spin$_c$ connection on $\mathbb{C}P^n$ is found and generalised to any spin coset manifold $G/H$ with $G,H$ compact, connected, and $G$ semisimple. The $R$-symmetry of this superalgebra is found to be equivalent to the $U(1)$ holonomy of the spin$_c$ connection.