Add the Hermetian conjugate to make Lagrangian real

In summary, adding the Hermetian conjugate to the Lagrangian is necessary for maintaining its reality and physical significance in describing the dynamics of a system. It accounts for the complex nature of certain physical quantities and does not change the form of the Lagrangian equations of motion, but ensures real and accurate solutions. While there are alternative methods, adding the Hermetian conjugate is often the simplest approach.
  • #1
Lapidus
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How does adding a h.c. term make a Lagrangian real? Like http://isites.harvard.edu/fs/docs/icb.topic521209.files/QFT-Schwartz.pdf on page 99 (11.51)?

thanks in advance
 
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  • #2
You add something with the same real part but with the negative imaginary part. The sum has an imaginary component of zero.

##z + \bar z## is always real (even if you replace z by more complex structures).
 
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FAQ: Add the Hermetian conjugate to make Lagrangian real

1. Why is it necessary to add the Hermetian conjugate to make the Lagrangian real?

Adding the Hermetian conjugate is necessary in order to ensure that the Lagrangian, which is a mathematical function used to describe the dynamics of a system, remains real and physically meaningful. This is important for making accurate predictions and calculations in physics.

2. What is the purpose of the Hermetian conjugate in the Lagrangian?

The Hermetian conjugate is added to the Lagrangian in order to account for the complex nature of certain physical quantities, such as quantum wavefunctions. By taking the complex conjugate of these quantities, the Lagrangian can accurately describe the system's dynamics in a real and consistent manner.

3. Can the Hermetian conjugate be added to any Lagrangian?

No, the Hermetian conjugate can only be added to Lagrangians for systems that involve complex quantities. If the system is purely real, then there is no need to add the Hermetian conjugate.

4. How does adding the Hermetian conjugate affect the Lagrangian equations of motion?

Adding the Hermetian conjugate does not change the form of the Lagrangian equations of motion, but it does ensure that these equations result in real and physically meaningful solutions. This allows for more accurate predictions and calculations in physics.

5. Are there any alternative methods to making the Lagrangian real?

Yes, there are alternative methods such as using a gauge symmetry, which involves introducing additional fields to the Lagrangian. However, adding the Hermetian conjugate is often the simplest and most straightforward way to ensure the Lagrangian remains real and consistent.

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