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I apologize if this is a trivial question – GMT is not my area of expertise but I'm working my way through a proof that makes extensive use of GMT and I haven't been able to find an answer to my question in the usual books.

Suppose $(M^n, g)$ is a Riemannian manifold, for $j ≥ 0$ denote by $ℋ^j$ the induced $j$-dimensional Hausdorff measure. Let $T ∈ D_j(M)$ denote an (integer-multiplicity) rectifiable $j$-current in $(M, g)$, that is, for all compactly supported $j$-forms $ω ∈ D^j(M)$:

$$ T(ω) = ∫_A ⟨ ω, \vec{T} ⟩ \, θ \,dℋ^j \;\;, $$

where $A ⊂ M$ is a $j$-rectifiable set (i.e. up to an $ℋ^j$-nullset it is contained in a countable union of $j$-dimensional submanifolds of $M$), $\vec{T}: M → Λ^j(TM)$ is an $ℋ^j$-measurable section (a simple $j$-vector made of orthonormal vectors that orient the approximate tangent space $T_x A$ of $A$ at a.e. $x$) and $θ: A → ℕ$ is locally $ℋ^j$-integrable. (I'm following Leon Simon's definition here.)

Suppose I picked a different Riemannian metric $g'$ on $M$. Is $T$ then still a rectifiable current w.r.t. $(M, g')$ and the induced Hausdorff measure $ℋ'^j$? Heuristically speaking, when the metric changes, both $\vec{T}$ and $dℋ^j$ change and these changes should cancel out. At least for currents given by smooth submanifolds this is definitely the case. Is it true in general, though?

UPDATE: I'm increasingly sure that one can use a parametrization of $A$ by a countable family of Lipschitz functions (living on Borel sets in $\mathbb{R}^j$) together with the area formula to prove this. I'll be looking into this. In the meantime, in case anyone's got a reference or can give a definite answer to my question, I'd still very much appreciate it!

UPDATE 2: The proof indeed goes through by taking local parametrizations of the submanifolds containing the rectifiable set and then considering the pullback of the ambient metric under such parametrizations and using the area formula. I'll post a detailed proof as soon as I find the time.

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  • $\begingroup$ The way you define it, your class corresponds to the class of "locally integral currents" in Federer's book (see Section 4.1.24 for the definition in Euclidean space). This class is not affected by the change of a metric on a Riemmanian manifold because as metric spaces they are locally bi-Lipschitz equivalent (one can take the identity map). The class of integral currents (assuming they are allowed to have noncompact support) changes in general because a current may have finite mass with respect to one metric but not with respect to another. $\endgroup$
    – rozu
    Commented Feb 23, 2020 at 15:24
  • $\begingroup$ @rozu Thanks for your comment! However, I think you meant locally rectifiable currents, right? After all, I didn't say anything about the boundary. And yes, the mass (and its (un-)boundedness in case the current has non-compact support) can obviously change when the metric changes. Finally, thanks for pointing me at the bi-Lipschitz property – I'll look into that! $\endgroup$
    – Weekkola
    Commented Feb 24, 2020 at 19:46
  • $\begingroup$ Yes indeed, I meant locally rectifiable. $\endgroup$
    – rozu
    Commented Feb 24, 2020 at 21:13

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