Understanding the Tensor Product of Two One-Forms in Differential Geometry

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SUMMARY

The tensor product of two one-forms, denoted as \(\alpha\) and \(\beta\) in the context of differential geometry, is correctly defined as \((\alpha \otimes \beta)(\mathbf{v}, \mathbf{w}) = \alpha(\mathbf{v})\beta(\mathbf{w})\), where \(\alpha, \beta \in V^{\ast}\) and \(\mathbf{v}, \mathbf{w} \in V\). When expressed in a coordinate basis, this translates to \((dx^{\mu} \otimes dx^{\nu})(\mathbf{v}, \mathbf{w}) = V^{\mu}W^{\nu}\). The representation of one-forms in terms of the coordinate basis \(\{dx^{\mu}\}\) confirms that \((\alpha \otimes \beta)(\mathbf{v}, \mathbf{w}) = \alpha_{\mu}\beta_{\nu}V^{\mu}W^{\nu}\) is indeed accurate.

PREREQUISITES
  • Understanding of one-forms in differential geometry
  • Familiarity with tensor products and their properties
  • Knowledge of coordinate bases and their representations
  • Basic concepts of vector spaces and dual spaces
NEXT STEPS
  • Study the properties of tensor products in differential geometry
  • Learn about the dual space and its significance in vector calculus
  • Explore applications of one-forms in physics, particularly in general relativity
  • Investigate the role of coordinate transformations in tensor calculus
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Students and professionals in mathematics, particularly those focusing on differential geometry, theoretical physicists, and anyone interested in the mathematical foundations of general relativity.

"Don't panic!"
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I'm relatively new to differential geometry and would like to check that this is the correct definition for the tensor product of (for simplicity) two one-forms \alpha,\;\beta\;\;\in V^{\ast}: (\alpha\otimes\beta)(\mathbf{v},\mathbf{w})=\alpha (\mathbf{v})\beta (\mathbf{w}) where \alpha\otimes\beta\;\;\in V^{\ast}\otimes V^{\ast} and \mathbf{v},\;\mathbf{w}\;\;\in V.
Given this, is it correct to write, (dx^{\mu}\otimes dx^{\nu})(\mathbf{v},\mathbf{w})=dx^{\mu}(\mathbf{v})dx^{\nu}(\mathbf{w})=V^{\mu}W^{\nu}
where we have expressed \mathbf{v}=V^{\mu}\partial_{\mu} and \mathbf{w}=W^{\nu}\partial_{\nu} in terms of a coordinate basis \lbrace\partial_{\mu}\rbrace for V, and \lbrace dx^{\mu}\otimes dx^{\nu}\rbrace is a coordinate basis for V^{\ast}\otimes V^{\ast} (with \lbrace dx^{\mu}\rbrace a basis for V^{\ast}). As such, if we express \alpha and \beta in terms of the coordinate basis \lbrace dx^{\mu}\rbrace as \alpha = \alpha_{\mu}dx^{\mu} and \beta = \beta_{\nu}dx^{\nu}, respectively, we have (\alpha\otimes\beta)(\mathbf{v},\mathbf{w})=\alpha (\mathbf{v})\beta (\mathbf{w})=\alpha_{\mu}\beta_{\nu}dx^{\mu}\otimes dx^{\nu}(\mathbf{v},\mathbf{w})=\alpha_{\mu}\beta_{\nu}V^{\mu}W^{\nu}.

Would this be correct at all?
 
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"Don't panic!" said:
Would this be correct at all?
Yes.
 
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Likes Ahmad Kishki
Excellent, thanks.
 

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