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In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Five-Loop Running of the QCD Coupling Constant.

P A Baikov1, K G Chetyrkin2, J H Kühn2

  • 1Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University 1(2), Leninskie Gory, Moscow 119991, Russian Federation.

Physical Review Letters
|March 11, 2017
PubMed
Summary
This summary is machine-generated.

We calculated a new five-loop term for the strong coupling constant (αs) in Quantum Chromodynamics (QCD). This improves precision for αs at the Z-boson scale and refines predictions for the Higgs boson

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Area of Science:

  • High-energy physics
  • Quantum Chromodynamics (QCD)
  • Particle physics

Background:

  • The strong coupling constant (αs) describes the strength of interactions between quarks and gluons.
  • Precise determination of αs is crucial for testing the Standard Model and searching for new physics.
  • Higher-order calculations in perturbation theory are necessary to reduce theoretical uncertainties.

Purpose of the Study:

  • To analytically compute the five-loop term in the beta function for QCD.
  • To reduce the theoretical uncertainty in the value of αs at the Z-boson scale.
  • To provide improved predictions for Higgs boson couplings and decay rates.

Main Methods:

  • Analytical computation of Feynman diagrams.
  • Renormalization group techniques.
  • Perturbation theory expansion to five loops.

Main Results:

  • The five-loop term in the QCD beta function has been analytically calculated.
  • This calculation reduces the theory uncertainty in αs extracted from τ-lepton decays.
  • New, improved predictions for Higgs boson effective couplings to gluons and its decay rate to quark-antiquark pairs were obtained.

Conclusions:

  • The five-loop calculation represents a significant advancement in the precision of QCD predictions.
  • The improved determination of αs and Higgs boson properties will enhance the sensitivity of future experimental searches.
  • This work contributes to a more precise understanding of fundamental particle interactions within the Standard Model.