Neutron electric dipole moment using $N_f{=}2{+}1{+}1$ twisted mass fermions
| Autor: | Alexandrou, C., Athenodorou, A., Constantinou, M., Hadjiyiannakou, K., Jansen, K., Koutsou, G., Ottnad, K., Petschlies, M. |
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| Rok vydání: | 2015 |
| Předmět: | |
| Zdroj: | Phys. Rev. D 93, 074503 (2016) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevD.93.074503 |
| Popis: | We evaluate the neutron electric dipole moment $\vert \vec{d}_N\vert$ using lattice QCD techniques. The gauge configurations analyzed are produced by the European Twisted Mass Collaboration using $N_f{=}2{+}1{+}1$ twisted mass fermions at one value of the lattice spacing of $a \simeq 0.082 \ {\rm fm}$ and a light quark mass corresponding to $m_{\pi} \simeq 373 \ {\rm MeV}$. Our approach to extract the neutron electric dipole moment is based on the calculation of the $CP$-odd electromagnetic form factor $F_3(Q^2)$ for small values of the vacuum angle $\theta$ in the limit of zero Euclidean momentum transfer $Q^2$. The limit $Q^2 \to 0$ is realized either by adopting a parameterization of the momentum dependence of $F_3(Q^2)$ and performing a fit, or by employing new position space methods, which involve the elimination of the kinematical momentum factor in front of $F_3(Q^2)$. The computation in the presence of a $CP$-violating term requires the evaluation of the topological charge ${\cal Q}$. This is computed by applying the cooling technique and the gradient flow with three different actions, namely the Wilson, the Symanzik tree-level improved and the Iwasaki action. We demonstrate that cooling and gradient flow give equivalent results for the neutron electric dipole moment. Our analysis yields a value of $\vert \vec{d}_N\vert=0.045(6)(1)\ \bar{\theta} \ e \cdot {\rm fm}$ for the ensemble with $m_\pi=373$ MeV considered. Comment: Version accepted for publication in Phys. Rev. D.: 33 pages, 13 Figures |
| Databáze: | arXiv |
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