Isovector and isoscalar tensor charges of the nucleon from lattice QCD

Abstract

We present results for the isovector and flavor diagonal tensor charges g needed to probe novel tensor interactions at the TeV scale in neutron and nuclear β-decays and the contribution of the quark electric dipole moment (EDM) to the neutron EDM. The lattice QCD calculations were done using nine ensembles of gauge configurations generated by the MILC collaboration using the HISQ action with 2+1+1 dynamical flavors. These ensembles span three lattice spacings a ≈ 0.06, 0.09 and 0.12 fm and three quark masses corresponding to the pion masses Mπ ≈ 130, 220 and 310 MeV. Using estimates from these ensembles, we quantify all systematic uncertainties and perform a simultaneous extrapolation in the lattice spacing, volume and light quark masses for the connected contributions. The final estimates of the connected nucleon (proton) tensor charge for the isovector combination is g u−d T = 1.020(76) in the MS scheme at 2 GeV. The additional disconnected quark loop contributions needed for the flavor-diagonal matrix elements are calculated using a stochastic estimator employing the truncated solver method with the all-mode-averaging technique. We find that the size of the disconnected contribution is smaller than the statistical error in the connected contribution. This allows us to bound the disconnected contribution and include it as an additional uncertainty in the flavor-diagonal charges. After a continuum extrapolation, we find g

Isospin Breaking in the Nucleon Mass and the Sensitivity ofβDecays to New Physics

“…In turn, we discussed the consequences of this novel determination to the bounds set on nonstandard scalar interactions from β decays, finding the limit on ϵ S given in Eq. (15), which is much stronger than in previous analyses of β decays or than those currently obtained from the LHC.…”

“…The LHPC finds g S ¼ 1.08ð32Þ [16], whereas the PNDME Collaboration has recently published the result g S ¼ 0.66ð24Þ [15], which supersedes their original preliminary estimate g S ¼ 0.8ð4Þ [13].…”

“…The latter are needed to describe nuclear and neutron β decays if nonstandard (pseudo)scalar interactions are present [11][12][13][14], and they currently are subject to intensive research mainly through lattice QCD (LQCD) calculations [15,16]. These investigations are of crucial importance to assess the implications of precise β-decay measurements to constrain new physics.…”

Direct and indirect constraints on CP-violating Higgs-quark and Higgs-gluon interactions

“…Theoretically, by far the best understood operators are the quark EDMs whose contributions JHEP02(2016)011 to the nucleon EDMs have been recently calculated with lattice-QCD techniques [55,56], see table 4. The uncertainties on the up and down qEDM contributions are 10% − 15%, whereas the strange qEDM contribution is consistent with zero and thus highly uncertain.…”

Quark scalar, axial, and pseudoscalar charges in the Schwinger-Dyson formalism

“…By comparing the scalar density and the vector charge, it is possible to probe how relativistic the particles are. The isoscalar quark scalar density is known * yamanaka@ruby.scphys.kyoto-u.ac.jp as the pion-nucleon sigma term σ πN ≡ m q N |qq|N , and many phenomenological [1][2][3][4] and lattice QCD [5][6][7][8][9] analyses have been done. It is also a useful input in the direct search for dark matter [10], since it gives the strength of the interaction of the nucleon with the new particles beyond the standard model, such as the neutralino in supersymmetric models [11].…”