open_problems:strong_cp_puzzle
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open_problems:strong_cp_puzzle [2018/04/15 11:22] ida [Concrete] |
open_problems:strong_cp_puzzle [2018/05/05 12:59] jakobadmin |
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| - | ====== The Strong CP Puzzle ====== | + | ====== Strong CP Puzzle ====== |
| <tabbox Intuitive> | <tabbox Intuitive> | ||
| - | The strong CP puzzle is the observation that in the [[models:standard_model|standard model]] nothing forbids that [[models:qcd|strong interactions]] violate [[advanced_notions:cp_symmetry|CP symmetry]] but so far such a CP violation by strong interactions was never observed. | + | The strong CP puzzle is the observation that in the [[models:standard_model|standard model]] nothing forbids that [[models:standard_model:qcd|strong interactions]] violate [[advanced_notions:cp_symmetry|CP symmetry]] but so far such a CP violation by strong interactions was never observed. |
| The puzzle is regarded as a deep and interesting since upon closer inspection there are possibly two sources how strong interactions could violate CP symmetry. These two sources come from completely different sectors and thus its somewhat a mircale that they cancel exactly. | The puzzle is regarded as a deep and interesting since upon closer inspection there are possibly two sources how strong interactions could violate CP symmetry. These two sources come from completely different sectors and thus its somewhat a mircale that they cancel exactly. | ||
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| where | where | ||
| - | * $\theta_{\rm QCD}$ is the coefficient of the term $\alpha_s^2/ 8 \pi \, G\tilde G $ in the Lagrangian that we get when we consider [[models:qcd|QCD]] alone. | + | * $\theta_{\rm QCD}$ is the coefficient of the term $\alpha_s^2/ 8 \pi \, G\tilde G $ in the Lagrangian that we get when we consider [[models:standard_model:qcd|QCD]] alone. |
| * $\theta_{\rm F} = \arg \det M_u M_d$ is an additional contribution to the effective complete theta parameter $\theta$ that results when we consider QCD in the presence of fermions. The term enters since we have to diagonalize the mass matrices to switch to the mass basis and this diagonalization process necessarily involves a chiral rotation. | * $\theta_{\rm F} = \arg \det M_u M_d$ is an additional contribution to the effective complete theta parameter $\theta$ that results when we consider QCD in the presence of fermions. The term enters since we have to diagonalize the mass matrices to switch to the mass basis and this diagonalization process necessarily involves a chiral rotation. | ||
| * The experimental bound $\bar\theta<10^{-10}$ comes from the observation that the dipole moment of the neutron is tiny: $|d_n| \le 3.6 \times 10^{-26} e \, {\rm cm}$ ([[https://arxiv.org/abs/1509.04411|Source]]). | * The experimental bound $\bar\theta<10^{-10}$ comes from the observation that the dipole moment of the neutron is tiny: $|d_n| \le 3.6 \times 10^{-26} e \, {\rm cm}$ ([[https://arxiv.org/abs/1509.04411|Source]]). | ||
open_problems/strong_cp_puzzle.txt · Last modified: 2020/04/10 19:51 by 71.46.88.3
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