# QFT - particle annihilation

I need some advice. I have read that interacting fields can lead to quanta annihilation? How often does this happen, and can bound state quanta annihilate or is it just free quanta?

Thanks

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K^2
Quanta of what?

Quanta of what?

quanta of a fermion field. Can bound quanta of a fermion field be annihilated or is it just unbound quanta that can get annihilated.

how common is particle annihilation in quantum field theory

K^2
In QFT, the very propagation of particles is described with creation-annihilation events. So I'd say common. :) But that's a little different, since either number of particles doesn't change, or virtual particles are involved.

As far as particle-anti-particle annihilation, it actually tends to happen from bound state. Consider ep annihilation. It usually takes place via intermediate state of positronium, which will usually collapse to ground state first, and only then annihilate. That's what gives you the zero angular momentum condition on the emitted photons.

IM proberly not getting my point accross. The quanta that make up carbon are all in a bound state, can these quantum get annihilated, and if they do and it happens often, does this lead to atoms changing form?

mfb
Mentor
There are no "quanta that make up carbon".
Particles in a carbon atom interact with each other and their environment all the time, quantum field theory describes those interaction with creation and annihilation operators. This is a mathematical tool. It is not like a carbon atom would vanish somehow (unless you shoot antiparticles on it).

There are no "quanta that make up carbon".
Particles in a carbon atom interact with each other and their environment all the time, quantum field theory describes those interaction with creation and annihilation operators. This is a mathematical tool. It is not like a carbon atom would vanish somehow (unless you shoot antiparticles on it).

what does this mean? when the carbon atom interacts with itself and other atoms, parts of it/all of it are created and annihilated?

mfb
Mentor
I think you ran into some misconception about QFT here.
In QFT, particles are created and annihilated all the time - but they are not like billard balls, it is just a description of their interaction. The total number of real electrons and valence quarks (the quarks which define the type of nucleus -> proton vs. neutron) is constant.

I think you ran into some misconception about QFT here.
In QFT, particles are created and annihilated all the time - but they are not like billard balls, it is just a description of their interaction. The total number of real electrons and valence quarks (the quarks which define the type of nucleus -> proton vs. neutron) is constant.
what does that mean in terms of many particle systems? as they are made of particles, are the parts of these systems always being created and annihilated or is it just single particles that are annihilated? the ones not making up a carbon atom for example

A familiar example of bound state comes from quantum electrodynamics in which a hydrogen like thing called positronium which consists of electron and positron can go for a two photon annihilation.It contributes a big part in hyperfine splitting of it.The original method for treating such bound states were developed by karplus and klein.

mfb
Mentor
as they are made of particles
And all those particles behave like all other particles. This should answer your question.