Nucleon and Pion Form Factors from $N_f=2+1$ Anisotropic Lattices

Scalar and tensor interactions were once competitors to the now well-established V − A structure of the Standard Model weak interactions. We revisit these interactions and survey constraints from low-energy probes (neutron, nuclear, and pion decays) as well as collider searches. Currently, the most stringent limit on scalar and tensor interactions arise from 0 + → 0 + nuclear decays and the radiative pion decay π → eνγ, respectively. For the future, we find that upcoming neutron beta decay and LHC measurements will compete in setting the most stringent bounds. For neutron beta decay, we demonstrate the importance of lattice computations of the neutronto-proton matrix elements to setting limits on these interactions, and provide the first lattice estimate of the scalar charge and a new average of existing results for the tensor charge. Data taken at the LHC is currently probing these interactions at the 10 −2 level (relative to the standard weak interactions), with the potential to reach the < ∼ 10 −3 level. We show that, with some theoretical assumptions, the discovery of a charged spin-0 resonance decaying to an electron and missing energy implies a lower limit on the strength of scalar interactions probed at low energy.

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“…In any case, one should include the excited states explicitly in the analysis of the matrix elements as demonstrated in Refs. [92,83].…”

Section: Nucleon Axial Charge G Amentioning

confidence: 99%

Probing novel scalar and tensor interactions from (ultra)cold neutrons to the LHC

et al. 2012

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“…Nucleon electromagnetic form factors have been calculated in the framework of lattice QCD (for a recent overview, see Refs. [61][62][63][64][65] and references therein). Several collaborations have reached pion masses down to 270 MeV.…”

Section: E Pion Mass Dependence Of the Form Factorsmentioning

confidence: 99%

Electromagnetic form factors of the nucleon in effective field theory

2012

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We calculate the electromagnetic form factors of the nucleon to third chiral order in manifestly Lorentz-invariant effective field theory. The ρ and ω mesons as well as the ∆(1232) resonance are included as explicit dynamical degrees of freedom. To obtain a self-consistent theory with respect to constraints we consider the proper relations among the couplings of the effective Lagrangian. For the purpose of generating a systematic power counting, the extended on-mass-shell renormalization scheme is applied in combination with the small-scale expansion. The results for the electric and magnetic Sachs form factors are analyzed in terms of experimental data and compared to previous findings in the framework of chiral perturbation theory. The pion-mass dependence of the form factors is briefly discussed.

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“…Responding to the phenomenological demand, several groups have recently determined g A [20][21][22][23][24][25][26][27][28][29], g T [30,31], g S and g T [32], g A and the induced pseudoscalar form factor [33][34][35][36], g A , g P and g * P [37,38] or g A , g S and g T [39,40] or the related form factors in lattice simulations. g V and gT are frequently determined in calculations of the electromagnetic form factors [28,33,35,38,39,[41][42][43][44][45][46][47], also see Refs.…”

Section: Introductionmentioning

confidence: 99%

Nucleon isovector couplings fromNf=2lattice QCD

et al. 2015

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We compute the axial, scalar, tensor and pseudoscalar isovector couplings of the nucleon as well as the induced tensor and pseudoscalar charges in lattice simulations with N f = 2 massdegenerate non-perturbatively improved Wilson-Sheikholeslami-Wohlert fermions. The simulations are carried out down to a pion mass of 150 MeV and linear spatial lattice extents of up to 4.6 fm at three different lattice spacings ranging from approximately 0.08 fm to 0.06 fm. Possible excited state contamination is carefully investigated and finite volume effects are studied. The couplings, determined at these lattice spacings, are extrapolated to the physical pion mass. In this limit we find agreement with experimental results, where these exist, with the exception of the magnetic moment. A proper continuum limit could not be performed, due to our limited range of lattice constants, but no significant lattice spacing dependence is detected. Upper limits on discretization effects are estimated and these dominate the error budget.

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Nucleon and Pion Form Factors from $N_f=2+1$ Anisotropic Lattices

Cited by 5 publications

References 17 publications

Probing novel scalar and tensor interactions from (ultra)cold neutrons to the LHC

Probing novel scalar and tensor interactions from (ultra)cold neutrons to the LHC

Electromagnetic form factors of the nucleon in effective field theory

Nucleon isovector couplings fromNf=2lattice QCD

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