2,424 research outputs found
Precision nucleon-nucleon potential at fifth order in the chiral expansion
We present a nucleon-nucleon potential at fifth order in chiral effective
field theory. We find a substantial improvement in the description of
nucleon-nucleon phase shifts as compared to the fourth-order results of Ref.
[E. Epelbaum, H. Krebs, U.-G. Mei{\ss}ner, arXiv:1412.0142 [nucl-th]]. This
provides clear evidence of the corresponding two-pion exchange contributions
with all low-energy constants being determined from pion-nucleon scattering.
The fifth-order corrections to nucleon-nucleon observables appear to be of a
natural size which confirms the good convergence of the chiral expansion for
nuclear forces. Furthermore, the obtained results provide strong support for
the novel way of quantifying the theoretical uncertainty due to the truncation
of the chiral expansion proposed in Ref. [E. Epelbaum, H. Krebs, U.-G.
Mei{\ss}ner, arXiv:1412.0142 [nucl-th]]. Our work opens up new perspectives for
precision ab initio calculations in few- and many-nucleon systems and is
especially relevant for ongoing efforts towards a quantitative understanding
the structure of the three-nucleon force in the framework of chiral effective
field theory.Comment: 5 pages, 4 figures, 3 table
Nuclear axial current operators to fourth order in chiral effective field theory
We present the complete derivation of the nuclear axial charge and current
operators as well as the pseudoscalar operators to fourth order in the chiral
expansion relative to the dominant one-body contribution using the method of
unitary transformation. We demonstrate that the unitary ambiguity in the
resulting operators can be eliminated by the requirement of renormalizability
and by matching of the pion-pole contributions to the nuclear forces. We give
expressions for the renormalized single-, two- and three-nucleon contributions
to the charge and current operators and pseudoscalar operators including the
relevant relativistic corrections. We also verify explicitly the validity of
the continuity equation.Comment: 72 pages, 21 figures, 3 table
Improved chiral nucleon-nucleon potential up to next-to-next-to-next-to-leading order
We present improved nucleon-nucleon potentials derived in chiral effective
field theory up to next-to-next-to-next-to-leading order. We argue that the
nonlocal momentum-space regulator employed in the two-nucleon potentials of
Refs. [E. Epelbaum, W. Gloeckle, U.-G. Mei{\ss}ner, Nucl. Phys. A747 (2005)
362], [D.R. Entem, R. Machleidt, Phys. Rev. C68 (2003) 041001] is not the most
efficient choice, in particular since it affects the long-range part of the
interaction. We are able to significantly reduce finite-cutoff artefacts by
using an appropriate regularization in coordinate space which maintains the
analytic structure of the amplitude. The new potentials do not require the
additional spectral function regularization employed in Ref. [E. Epelbaum, W.
Gloeckle, U.-G. Mei{\ss}ner, Nucl. Phys. A747 (2005) 362] to cut off the
short-range components of the two-pion exchange and make use of the low-energy
constants c_i and d_i determined from pion-nucleon scattering without any fine
tuning. We discuss in detail the construction of the new potentials and
convergence of the chiral expansion for two-nucleon observables. We also
introduce a new procedure for estimating the theoretical uncertainty from the
truncation of the chiral expansion that replaces previous reliance on cutoff
variation.Comment: 34 pages, 13 figures, 7 table
New insights into the spin structure of the nucleon
We analyze the low-energy spin structure of the nucleon in a covariant
effective field theory with explicit spin-3/2 degrees of freedom to third order
in the small scale expansion. Using the available data on the strong and
electromagnetic width of the Delta-resonance, we give parameter-free
predictions for various spin-polarizabilities and moments of spin structure
functions. We find an improved description of the nucleon spin structure at
finite photon virtualities for some observables and point out the necessity of
a fourth order calculation.Comment: 13 pages, 6 figure
Complex-mass renormalization in hadronic EFT: applicability at two-loop order
We discuss the application of the complex-mass scheme to multi-loop diagrams
in hadronic effective field theory by considering as an example a two-loop
self-energy diagram. We show that the renormalized two-loop diagram satisfies
the power counting.Comment: 8 pages, 2 figures, version accepted for publication in EPJ
Reconciling threshold and subthreshold expansions for pion-nucleon scattering
Heavy-baryon chiral perturbation theory (ChPT) at one loop fails in relating
the pion-nucleon amplitude in the physical region and for subthreshold
kinematics due to loop effects enhanced by large low-energy constants. Studying
the chiral convergence of threshold and subthreshold parameters up to fourth
order in the small-scale expansion, we address the question to what extent this
tension can be mitigated by including the as an explicit degree
of freedom and/or using a covariant formulation of baryon ChPT. We find that
the inclusion of the indeed reduces the low-energy constants to more
natural values and thereby improves consistency between threshold and
subthreshold kinematics. In addition, even in the -less theory the
resummation of corrections in the covariant scheme improves the results
markedly over the heavy-baryon formulation, in line with previous observations
in the single-baryon sector of ChPT that so far have evaded a profound
theoretical explanation.Comment: 10 pages, 4 tables, Mathematica notebook with the analytic
expressions for threshold and subthreshold parameters included as
supplementary material; journal versio
Improved analysis of neutral pion electroproduction off deuterium in chiral perturbation theory
Near threshold neutral pion electroproduction on the deuteron is studied in
the framework of heavy baryon chiral perturbation theory. We include the
next-to-leading order corrections to the three-body contributions. We find an
improved description of the total and differential cross section data measured
at MAMI. We also obtain more precise values for the threshold S-wave
multipoles. We discuss in detail the theoretical uncertainties of the
calculation.Comment: 14 pp, 11 figs, uses svjour.cl
- …