Differentiating the complex scalar field

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Discussion Overview

The discussion revolves around the differentiation of a complex scalar field within the context of scalar field theory, specifically focusing on the Lagrangian density of a free complex scalar field. Participants explore the implications of treating the scalar field as a complex function and the resulting equations of motion, while addressing the challenges in performing functional derivatives and the interpretation of partial derivatives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion regarding the differentiation of the complex scalar field, particularly how to correctly apply derivatives in the context of the Lagrangian density.
  • Another participant clarifies that the derivatives are with respect to the spacetime coordinates, not the field variables, suggesting that this might have been misunderstood.
  • A participant challenges the correctness of the factor of 2 obtained in the differentiation process, indicating that both factors of 2 presented in the calculations are incorrect.
  • Further elaboration on the Euler-Lagrange equations is provided, with one participant explaining how the mass term arises from the functional derivative of the Lagrangian density.
  • One participant suggests computing partial derivatives with respect to the real and imaginary components of the complex field to clarify the situation.
  • Another participant discusses the assumption of independence between the variables in the context of complex fields, questioning the validity of treating them as independent.
  • A later reply introduces a method for calculating derivatives using the real and imaginary parts of the complex field, leading to a clearer understanding of the differentiation process.
  • One participant reflects on their previous misunderstanding and acknowledges the contributions of others in clarifying the differentiation of the complex scalar field.
  • Another participant explains the factor of 2 in the relationship between the derivatives of the real and imaginary components of the complex field, attributing it to the definitions used in the differentiation process.

Areas of Agreement / Disagreement

Participants exhibit a mix of agreement and disagreement regarding the interpretation of differentiation in the context of complex fields. While some clarify and refine their understanding, others challenge the correctness of specific factors and assumptions, indicating that the discussion remains unresolved on certain points.

Contextual Notes

Participants express uncertainty regarding the assumptions made in the differentiation process, particularly in relation to the independence of variables and the application of the chain rule. The discussion highlights the complexity of handling functional derivatives in the context of complex scalar fields.

  • #61
Avodyne said:
I don't see the problem ... Is it because of the absolute-value signs?

Yes. The absolute value is not an analytic function. i.e., you can't expand it into a power series.
 

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