StrongCPviolation and the neutron electric dipole moment reexamined

Abstract

Emission from high-dipole moment molecules such as HCN allows determination of the density in molecular clouds, and is often considered to trace the "dense" gas available for star formation. We assess the importance of electron excitation in various environments. The ratio of the rate coefficients for electrons and H 2 molecules, 10 5 for HCN, yields the requirements for electron excitation to be of practical importance if n(H 2) ≤ 10 5.5 cm −3 and X(e −) ≥ 10 −5 , where the numerical factors reflect critical values n c (H 2) and X * (e −). This indicates that in regions where a large fraction of carbon is ionized, X(e −) will be large enough to make electron excitation significant. The situation is in general similar for other "high density tracers", including HCO + , CN, and CS. But there are significant differences in the critical electron fractional abundance, X * (e −), defined by the value required for equal effect from collisions with H 2 and e −. Electron excitation is, for example, unimportant for CO and C +. Electron excitation may be responsible for the surprisingly large spatial extent of the emission from dense gas tracers in some molecular clouds (Pety et al. 2017; Kauffmann, Goldsmith et al. 2017). The enhanced estimates for HCN abundances and HCN/CO and HCN/HCO + ratios observed in the nuclear regions of luminous galaxies may be in part a result of electron excitation of high dipole moment tracers. The importance of electron excitation will depend on detailed models of the chemistry, which may well be non-steady state and non-static.

Neutron electric dipole moment in chiral quark-meson models

“…This has been discussed in some detail by Aoki and Hatsuda [9] and Cheng [12]. In particular the effects of strong C P violation should vanish if either the anomaly or any quark mass vanishes.…”

Full QCD calculation of neutron electric dipole moment with the external electric field method

“…If the CP invariance is preserved in the strong interaction in nature, QCD must be zero in QCD. Indeed a current experimental bound of the neutron electric dipole moment (NEDM) [1], d N < 6:3 Â 10 À13 e Á fm; (2) and the crude theoretical estimates [2][3][4], d N ¼ Oð10 À2 Þ QCD , gives the constraint that QCD & Oð10 À10 Þ. QCD must be very small or even zero. In the presence of the electroweak interaction, however, the above conclusion on QCD is modified.…”

Partial U(1)Arestoration and η enhancement in high-energy heavy-ion collisions

“…It is easy to check that Eq. (1) satisfies the anomalous Ward identity which is crucial for determining the form of U(1) A breaking [8]. In Eq.…”