Sunday 3 December 2006

complex geometry - Is there a "simple commutation" relation between $D^{''}$ and $delta^{'}$, with $D^{''}$ the (0,1) part of the chern connection of a vector bundle and $delta^{'}$ the adjoint of the (1,0) part?

Yes, the relation is that they anti-commute.



Let's see this very briefly (you can find it in almost all books on Kähler geometry and Hodge theory).



We want to compute $[D''_E,delta'_E]$, where $[bullet,bullet]$ is the graded commutator and let me call $omega$ (instead of $g$) the Kähler form. Then one has that
$$
[Lambda_omega,D''_E]=-idelta'_E,
$$
so that
$$
[D''_E,delta'_E]=i[D''_E,[Lambda_omega,D''_E]],
$$
where $Lambda_omega=*^{-1}L_omega*$ is the formal adjoint of the operator of degree $(1,1)$ given by $L_omegabullet=omegawedgebullet$.



Now, the (graded) Jacobi identity gives
$$
-[D''_E,[Lambda_omega,D''_E]]+[D''_E,underbrace{[D''_E,Lambda_omega]}_{=-[Lambda_omega,D''_E]}]+[Lambda_omega,underbrace{[D''_E,D''_E]}_{=0}]=0,
$$
thus $-2[D''_E,[Lambda_omega,D''_E]]=0$ and
$$
D''_Edelta'_E+delta'_ED''_E=[D''_E,delta'_E]=0.
$$

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