Why can we freely disposal the renormalization conditions?

In summary: There is always some risk of going astray, but on the whole, the rewards for pursuing these methods are often considerable.
  • #1
ndung200790
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Please teach me this:
The parameters(mass,interaction constant) in classical Lagrangian can be freely changed in classical framwork,but how about in quantum framework?Then why we can freely arrange the renormalization conditions,because I think that we do not know whether the parameters can freely be changed in quantum framework.
Thank you very much in advanced.
 
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  • #2
And why we can put the condition: 1PI=0 at square(p)= -square(M)(spacelike momentum)(e.g in the renormalization of Phi4 theory)?
 
  • #3
In ordinary renormalization procedure,there are some relation with m(mass),that becomes singular at m=0.Then are there any wrong with this renormalization procedure or are there exist the redudancy configuration in case m=0,so in this case there is exist an infinity?
 
  • #4
At the moment,I see that the ''classical'' parameters relate with the quantum factors,so we can change the ''classical'' parameters,then the quantum factors are dependently changed.So that we can freely disposal the renormalization conditions.
 
  • #5
All the parameters in QFT are not given from theory but have to be fit to experiment. Sometimes relations between quantities are constraint by symmetry principles, particularly local gauge symmetry (Ward-Takahashi/Slavnov-Taylor identities). You find a rather detailed explanation concerning basic renormalization theory in my QFT manuscript:

http://theorie.physik.uni-giessen.de/~hees/publ/lect.pdf
 
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  • #6
ndung200790 said:
Please teach me this:
The parameters(mass,interaction constant) in classical Lagrangian can be freely changed in classical framework,but how about in quantum framework?Then why we can freely arrange the renormalization conditions,because I think that we do not know whether the parameters can freely be changed in quantum framework.
The parameters define (both in classical and in quantum mechanics a family of theories,
from which one is picked by the renormalization conditions to match a real system.
ndung200790 said:
Thank you very much in advanced.
Since you repeat the same incorrect phrase over and over again: It should read ''Thank you very much in advance.''
 
  • #7
Thanks very much for all your helpfull answers!My English still weak,I am Vietnamese.

By the way,it seem that the Ward-Takahashi identity is accepted at the begining.They accept the corresponding symmetry for the diagrams as a proposition.But why we are permited to do that?
 
  • #8
ndung200790 said:
By the way,it seem that the Ward-Takahashi identity is accepted at the beginning.They accept the corresponding symmetry for the diagrams as a proposition.But why we are permitted to do that?
It is _derived_ from the symmetry of the action.

Thus the only question is why we are permitted to use a symmetric action. The answer to that is because it proved to work!
 
  • #9
It seem that the symmetry of Lagrangian is not the same symmetry of correlation functions.Then the symmetry of Lagrangian is not the symmetry of corresponding diagrams.The symmetry of the Lagrangian is the same symmetry of correlation only happens when it also is the symmetry of the product of operators of fields at fix spacetime points.
 
  • #10
It seem that some UV cut-off violate Ward-Takahashi Identity,some make the dependence on m(mass) that become singularity at m=0.Then what is the best regulation(the cutting-off the UV divergence)?
 
  • #11
ndung200790 said:
It seem that some UV cut-off violate Ward-Takahashi Identity,some make the dependence on m(mass) that become singularity at m=0.Then what is the best regulation(the cutting-off the UV divergence)?

dimensional regularization seems to be the best for this.
 
  • #12
What is the error we meet when we use the ''not good'' regularity?How about the ''wrong'' when we use the ordinary renormalization, in this case, two types of counterterm ''entangle'' with each other(meaning the mass couterterm delta m and scale counterterm delta Z be subtracted at the same time).In the case there is a dependence on m(mass) and it becomes singularity at m=0(S-matrix=...log(.../square(m)))
 
  • #13
In Phi4 theory,at one loop pertubative,with dimension regularity,there is a singularity above(...log(.../square(m))).This problem is solved by renomalization group method.But how ''wrong'' is it with the ordinary renormalization procedure?
 
  • #14
ndung200790 said:
In Phi4 theory,at one loop pertubative,with dimension regularity,there is a singularity above(...log(.../square(m))).This problem is solved by renomalization group method.But how ''wrong'' is it with the ordinary renormalization procedure?

To find out how wrong something is, one must compute to higher orders or by different, more accurate methods, and compare. I don't know about this particular case.

Doing high accuracy computations in quantum field theory outside the well-trodden paths is always a mix of art and science!
 

1. Why is it necessary to use renormalization conditions in scientific calculations?

Renormalization conditions allow us to eliminate infinities and inconsistencies in certain calculations, particularly in quantum field theory. Without renormalization, many calculations would produce nonsensical results.

2. How do renormalization conditions affect the accuracy of scientific predictions?

Renormalization conditions do not affect the accuracy of predictions per se, but they do allow us to make meaningful predictions by eliminating mathematical inconsistencies. In fact, without renormalization, many predictions would be impossible to make.

3. Can different renormalization conditions produce different results?

Yes, different renormalization conditions can produce different results, but they should all lead to the same physical predictions. The choice of renormalization conditions is somewhat arbitrary, as long as they are consistent and lead to physically meaningful results.

4. How do scientists decide on the appropriate renormalization conditions to use?

The choice of renormalization conditions depends on the specific calculation being done and the theoretical framework being used. Scientists often use a combination of theoretical considerations and experimental data to determine the appropriate renormalization conditions for a given calculation.

5. Are there any limitations to using renormalization conditions?

While renormalization is a powerful tool in eliminating infinities and inconsistencies, it does have limitations. In some cases, renormalization may not work, leading to unresolved mathematical issues. Additionally, the choice of renormalization conditions can sometimes introduce ambiguity into calculations.

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