Moments of nucleon structure functions at next-to-leading order in baryon chiral perturbation theory

Abstract

We obtain leading-and next-to-leading order predictions of chiral perturbation theory for several prominent moments of nucleon structure functions. These free-parameter free results turn out to be in overall agreement with the available empirical information on nearly all of the considered moments, in the region of low-momentum transfer (Q 2 < 0.3 GeV 2 ). Especially surprising is the situation for the spin polarizability δ LT , which thus far was not reproducible in chiral perturbation theory for proton and neutron simultaneously. This problem, known as the "δ LT puzzle," is not seen in the present calculation.

Precise determination of the deuteron spin structure at low to moderateQ2with CLAS and extraction of the neutron contribution

“…Again, we find good agreement between these two experiments using different effective neutron targets and with very different systematic uncertainties. We note that the neutron data are also well described by the two parametrizations [99,100], while they approach the GDH limit above (but marginally compatible with) the Chiral Perturbation calculations [38,101]. Figure 21 shows the forward spin polarizability for the bound neutron from our data, again compared to data from the 3 He experiment in Hall A [11].…”

“…17 shows our result for the forward spin polarizability γ 0 for the deuteron. We compare them again to the χPT calculations by Lensky et al [101] (upper yellow band) and by Bernard et al [38] (lower light blue band) as The open squares represent the result using only data and the solid black circles are data plus model results. The shaded area close to the x-axis is the total systematic uncertainty (blue for experimental only and black with extrapolation uncertainty included).…”

“…is an expansion up to third order with explicit inclusion of ∆(1232)3/2 + isobar degrees of freedom. The second, by Lensky et al [101] (wider dark green band), uses Baryon χPT including pion, nucleon and ∆(1232) degrees of freedom to calculate all moments in next-to-leading order (NLO). Both predictions are close to the GDH limit and show little sign of the observed deviation of the data towards less negative values as Q 2 increases; however, they agree with our lowest three points Q 2 < 0.08 GeV 2 within their statistical and systematic uncertainties.…”

Measurement of the Q2 Dependence of the Deuteron Spin Structure Function g1 and its Moments at Low Q2Adhikari1, Deur2, Fassi3 et al. 2018Phys. Rev. Lett.304320View full textAdd to dashboardCite

“…No data on δ p LT exist although some are anticipated soon [16]. This state of affairs triggered a refinement of the χPT calculations [25][26][27] and a very low Q 2 experimental program.…”

“…In the low and high Q 2 limits where Γ 1 can be related to global properties of the target, the sum rule tests our understanding of the nucleon spin structure. At intermediate Q 2 it has been used to test nonperturbative QCD calculations of Γ 1 such as the AdS/QCD approach [23], phenomenological models of the nucleon structure [24] and, at lower Q 2 , χPT calculations [25][26][27].…”