Change of energy under charge conjugation

In summary: Lepton number, baryon number and strangeness etc are related to charge. The others are not.Yes..I have read that..but what I wanted was an explanation for the statement that the energy does not change..Now can I say this..that out of lepton no,baryon no, charge etc..only charge couples with a field to give contribution to the hamiltonian..and through this thread, I have come to understand how flipping the charge does not change the energy..but am confused by the last line..Lepton number, baryon number and strangeness etc are related to charge. The others are not. These are related to charges because they
  • #1
krishna mohan
117
0
I was going through an article on antiparticles:
http://www.statemaster.com/encyclopedia/Antiparticles

The article mentions that energy is unchanged under charge conjugation among the CPT operations.
I do not understand this. Shouldn't a charged particle in an electric field have a change in energy under charge conjugation?
 
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  • #2
The electric field would also change under charge conjugation, and the energy would stay the same.
 
  • #3
Well..yes..that is fine..
so..you mean to say that when I apply charge conjugation operation, I should act it on everything in the system, including the source of the electric field?

But what about parity? Unless we have the special case where the electric field is invariant under parity, how can one say that the energy will be invariant under parity?
 
  • #4
The strength of the electric field won't change under parity, just its direction.
 
  • #5
Thanks...now I understand how energy is unchanged under charge conjugation when we consider electric charge...but charge conjugation here means flipping all the associated quantum numbers...how can we say that none of these changes will affect the energy??
 
  • #6
krishna mohan said:
Thanks...now I understand how energy is unchanged under charge conjugation when we consider electric charge...but charge conjugation here means flipping all the associated quantum numbers...how can we say that none of these changes will affect the energy??

Let's turn it around. Try and write down some operator that does change the energy.
 
  • #7
Do you mean to say that there are no operators that change energy?? Can that be proved??

What about, say, a scale change operator, which scales all distances in the system by a constant factor? Assuming that the electromagnetic interactions are between point charges, in which case it seems somewhat logical to assume that the charge will not be changed, we will have a change in the electromagnetic energy of the system.
 
  • #8
krishna mohan said:
What about, say, a scale change operator,

A second ago you were talking about the charge conjugation operator.
 
  • #9
krishna mohan said:
Thanks...now I understand how energy is unchanged under charge conjugation when we consider electric charge...but charge conjugation here means flipping all the associated quantum numbers...how can we say that none of these changes will affect the energy??

charge conjugation flips the charge quantum number, no other.

where did you learn to do charge conjugation? :P
 
  • #10
Vanadium 50 said:
Let's turn it around. Try and write down some operator that does change the energy.

Vanadium 50 said:
A second ago you were talking about the charge conjugation operator.

I have thought of this operator because I thought that is what you instructed me to do..or did I misinterpret your post?

I read about charge conjugation in Griffiths Elementary Particles: sec 4.7...
You can also find the definition at http://hyperphysics.phy-astr.gsu.edu/HBASE/Particles/cpt.html

The definition says you have to flip all the internal quantum numbers..
 
  • #11
krishna mohan said:
I have thought of this operator because I thought that is what you instructed me to do..or did I misinterpret your post?

I read about charge conjugation in Griffiths Elementary Particles: sec 4.7...
You can also find the definition at http://hyperphysics.phy-astr.gsu.edu/HBASE/Particles/cpt.html

The definition says you have to flip all the internal quantum numbers..

Read carefully:

In quantum mechanical systems, charge conjugation has some further implications. It also involves reversing all the internal quantum numbers like those for lepton number, baryon number and strangeness. It does not affect mass, energy, momentum or spin.

Lepton number, baryon number and strangeness etc are related to charge. The others are not.
 
  • #12
Yes..I have read that..but what I wanted was an explanation for the statement that the energy does not change..Now can I say this..that out of lepton no,baryon no, charge etc..only charge couples with a field to give contribution to the hamiltonian..and through this thread, I have come to understand how flipping the charge does not change the energy..but am confused by the last line..

What do you mean when you say lepton no etc are related to charge?
 
  • #13
postive electron lepton number is just a fancy way to say "negative electrical charged"
 
  • #14
Hmm..not really ..consider the neutrino..it has positive lepton no...an antineutrino has negative lepton no..but both of them are chargeless...
 
  • #15
Clarification: In the last post no stands for number..
 
  • #16
krishna mohan said:
Hmm..not really ..consider the neutrino..it has positive lepton no...an antineutrino has negative lepton no..but both of them are chargeless...

Well their lepton number is then related to another charge (like weak charge)
 

1. What is charge conjugation?

Charge conjugation is a mathematical operation that changes the sign of all the charges of a particle. It is also known as "C-symmetry" and is one of the fundamental symmetries in particle physics.

2. How does charge conjugation affect the energy of a system?

Under charge conjugation, the energy of a system remains unchanged. This is because the energy of a particle is not affected by changing the sign of its charge.

3. Can the energy of a system change under charge conjugation?

No, the energy of a system cannot change under charge conjugation. This is due to the fact that charge conjugation is a symmetry operation and does not alter the physical properties of a system.

4. How is charge conjugation related to other symmetries in particle physics?

Charge conjugation is related to other symmetries such as parity and time reversal. Together, these three symmetries form the "CPT" symmetry, which states that the laws of physics remain unchanged under simultaneous charge, parity, and time reversal transformations.

5. What are the practical applications of understanding the change of energy under charge conjugation?

Understanding the change of energy under charge conjugation is important in particle physics research, as it helps predict the behavior of particles and their interactions. It also has practical applications in technologies such as particle accelerators and medical imaging devices.

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