Let M be a manifold and ϕ a smooth function. I define a twisted Lie bracket:
[X,Y]ϕ=XϕY−YϕX=(Xϕ)Y−(Yϕ)X+ϕ[X,Y]
It is a vector field. If ϕ is inversible, we have:
[X,Y]ϕ=ϕ−1[ϕX,ϕY]
We have the Jacobi identities for the twisted Lie brackets.
Then, for a connection ∇, we can define a twisted curvature:
Rϕ(∇)(X,Y)=∇Xϕ∇Y−∇Yϕ∇X−∇[X,Y]ϕ=ϕR(X,Y)
We can also define a differential over the exterior forms:
dϕ(α)(X,Y)=Xϕα(Y)−Yϕα(X)−α([X,Y]ϕ)=ϕdα(X,Y)
Can we have a twisted De Rham cohomology?