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Doctoral Thesis
DOI
10.11606/T.43.1981.tde-05072012-165016
Document
Author
Full name
Maria Teresa Climaco dos Santos Thomaz
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1981
Supervisor
Committee
Frenkel, Josif (President)
Abdalla, Elcio
Fleming, Henrique
Qualifik, Paul
Title in Portuguese
Um contra-exemplo ao teorema de Bloch-Nordsieck na cromodinâmica quântica
Keywords in Portuguese
cromodinâmica quântica
Teorema de Bloch-Nordsieck
Abstract in Portuguese
Usando teoria de perturbação, fizemos uma análise detalhada da divergência infravermelha em 4ª ordem do processo de aniquilação do par elétron-pósitron. Mostramos que o teorema de Bloch-Nordsieck garante o cancelamento destas divergências em QED. Em seguida, consideramos um processo em QCD com duas partículas coloridas no estado inicial, somando sobre as cores destas duas partículas. O processo escolhido foi o de aniquilação do par quark-anti-quark. O processo em 4ª ordem de perturbação e mostramos neste caso que o Teorema de Block-Nordsieck não se verifica. Este resultado é consequência do fato desta teoria ter um caráter não-abeliano. O não-cancelamento das divergências infravermelhas significa que a natureza do estado ligado é fundamental para o uso consistente da teoria de perturbação na QCD.
Title in English
A counter-example to the Bloch-Nordsieck theorem in quantum chromodynamics.
Keywords in English
Bloch-Nordsieck theorem
Quantum chromodynamics
Abstract in English
Using pertubation theory, we made a detailed analysis of the infrared divergencies to the 4th order for the phocess of annihilation of the pair electron-positron. We showed that the Bloch-Nordsieck theorem guarantees the cancellation of these divergencies in QED. Then we considered a process in QED involving two coloured particles in the initial state, summing over the colours of these particles. The process chosen was the annihilation of the pair quark-anti-quark. We calculated the process to the 4ª order in perturbation theory, and showed that in this case the Bloch-Nordsieck theorem in not verified. This result is a consequence of the fact that this theory has a non-abelian caracter. The non-cancellation of the infrared divergencies signifies that the nature of the bound-state is fundamental for the consistent use of perturbation theory in QCD.
 
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38090Thomaz.pdf (31.00 Mbytes)
Publishing Date
2012-07-05
 
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