What is the relationship between creation and annihilation operators in k-space?

  • Context: Graduate 
  • Thread starter Thread starter Trave11er
  • Start date Start date
  • Tags Tags
    Creation Operator
Click For Summary

Discussion Overview

The discussion revolves around the relationship between creation and annihilation operators in k-space, particularly in the context of particle physics and spin waves. Participants explore whether an identity exists between these operators for particles with momentum k and -k, and how this relates to different types of particles.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether the identity a_k^\dagger = a_{-k} holds, suggesting that creating a particle with momentum k should be equivalent to destroying a particle with momentum -k.
  • Another participant introduces the concept of negative energy solutions in quantum electrodynamics (QED), stating that negative energy particles are interpreted as positrons, which complicates the relationship between creation and annihilation operators for charged particles.
  • A different viewpoint is presented, indicating that for uncharged particles, such as Majorana Fermions and bosons, there may be a valid relationship between the creation and annihilation operators for k and -k.
  • One participant mentions that the original question pertains to spin waves, which are bosonic excitations and not charged, suggesting that the proposed relationship in k-space should hold and could potentially be proven from definitions.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between creation and annihilation operators, particularly distinguishing between charged and uncharged particles. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

Participants reference specific particle types and their properties, indicating that the relationship may depend on the nature of the particles involved. The discussion also touches on the implications of negative energy states in QED, which may influence the validity of the proposed identity.

Trave11er
Messages
71
Reaction score
0
Hi,

Could anyone tell if there exists an identity a_k^\dagger = a_{-k} because intuitively there should be no difference between creating a particle with momentum k and destroying a particle with momentum -k.
If true is it possible to show that from the definition a_k = \frac{1}{√V}∫e^{ikx} a(x)?
 
Physics news on Phys.org
Hello Trave11er,

Given the value of p, there are two solutions for the energy, one possitive the other negative.

The vacuum state is defined as having all the negative eigenstates full (no particles with
negative energy) and all the possitive eigenstates empty (no particles). In QED negative energy particles are interpreted as particles with opposite charge traveling backwards in time (positrons), so the destruction of a hole (creation as a positron) is not the same that the creation of an electron.
 
Trave11er said:
intuitively there should be no difference between creating a particle with momentum k and destroying a particle with momentum -k.

That depends on the kind of particle. I think uncharged particles like Majorana Fermions and bosons can act as their own anti-particles. For charged particles, there is no such relation between creation and anihilation operators with k and -k respectively.
 
Thanks for the replies,

The original question actually arose in the context of spin waves which have bosonic excitations on chain of spins - they are not charged so to me it seems that the relation in k-space should hold and it should be possible to prove starting from definition.
 
Thanks for the replies,

The original question actually arose in the context of spin waves which have bosonic excitations on chain of spins - they are not charged so to me it seems that the relation in k-space should hold and it should be possible to prove starting from definition.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 0 ·
Replies
0
Views
2K
  • · Replies 0 ·
Replies
0
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 6 ·
Replies
6
Views
2K