Hamiltonian Weak Gravitational Field - Learn Free Particle Theory

Click For Summary

Discussion Overview

The discussion revolves around the quantization of the gravitational field in a weak field regime, specifically focusing on the Hamiltonian formulation of the theory of free particles, referred to as gravitons. Participants explore the relationship between the Hamiltonian of this theory and that of the free electromagnetic field, as well as the relevant literature for further study.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that it is possible to quantize the gravitational field in a weak field regime, leading to a theory of free particles known as gravitons, similar to the electromagnetic field.
  • Another participant suggests several references, including Donoghue's lecture notes and DeWitt's work, while cautioning that older references may not align with the effective field theory perspective.
  • A participant questions whether the Hamiltonian operator for the gravitational theory is the same as that for the free electromagnetic field.
  • It is noted that the field operator in linearized gravity has spin 2, indicating that the Hamiltonians cannot be the same, and a suggestion is made to start with the Lagrangian to derive the Hamiltonian through a Legendre transformation.
  • One participant proposes that the Hamiltonian for the weak gravitational field should resemble that of the free Klein-Gordon field, acknowledging potential differences in constants but emphasizing a desire for a formal expression.
  • Another participant suggests using the Wheeler-DeWitt equation and linearization, or starting with the linearized Lagrangian while applying gauge constraints.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the Hamiltonians of the gravitational and electromagnetic fields, with no consensus reached on whether they are the same or different. The discussion remains unresolved regarding the exact form of the Hamiltonian in this context.

Contextual Notes

Participants highlight the importance of understanding the Lagrangian for covariant quantum field theory and the potential need for gauge conditions, indicating that the discussion may depend on specific assumptions and definitions related to the theory.

Andre' Quanta
Messages
32
Reaction score
0
In weak field regime i know that it is possible to quantize the gravitational field obtaining a quantum theory of free particles, called gravitons, which is very similar to the one for the electtromagnetic field.
Do you know some book in wiich i can study this theory?
In anycase what is the expression for the Hamiltonian of this theory in terms of creations and destructions operators?
 
Physics news on Phys.org
I'd suggest starting with Donoghue's lecture notes http://arxiv.org/abs/gr-qc/9512024. The first part of DeWitt's http://arxiv.org/abs/0711.2445, as well as the original papers by Feynman and DeWitt might be useful at some point too, but I think that the effective field theory point of view is important and those older references predate that whole perspective, so might not be the best pedagogy anymore.
 
  • Like
Likes   Reactions: Andre' Quanta
I was interested in the Hamiltonian operator for the theory, is it the same as the one of the free electromagnetic field?
 
Andre' Quanta said:
I was interested in the Hamiltonian operator for the theory, is it the same as the one of the free electromagnetic field?

The field operator in linearized gravity has spin 2 so it cannot be the same. I don't know off hand any place to find an explict expression for the Hamiltonian. It's best if you learn what the Lagrangian is, then you can see if it's easy to make a Legendre transformation to write a Hamiltonian. The Lagrangian is more useful for covariant QFT, though you might have some particular reason to study the Hamiltonian.
 
The weak gravitational field, the usual h mu nu, satisfies the simple D' Alemebert equation, so the lagrangian is the one of Klein-Gordon replacing the scalar field with the tensorial one in our theory: this will be valid also for the Hamiltonian so i would say the Hamiltonian that i am looking for is simply the same as the one used for the free Klein-Gordon field and the free electromagnetic field, am i wrong?
ps: there would be difference in some costant for the dimensionality, but we can neglect it, i am only looking for a formal expression
 
Maybe you want to use the Wheeler-DeWitt and linearize. Otherwise, you can start with the linearized Lagrangian and you'll have to apply constraints for the gauge conditions etc.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 33 ·
2
Replies
33
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 26 ·
Replies
26
Views
4K
  • · Replies 8 ·
Replies
8
Views
1K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K