9,748 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
Subleading contributions to the nuclear scalar isoscalar currents
We extend our recent analyses of the nuclear vector, axial-vector and
pseudoscalar currents and derive the leading one-loop corrections to the
two-nucleon scalar current operator in the framework of chiral effective field
theory using the method of unitary transformation. We also show that the scalar
current operators at zero momentum transfer are directly related to the quark
mass dependence of the nuclear forces.Comment: 14 pages, 6 figure
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
Near threshold neutral pion electroproduction on deuterium in chiral perturbation theory
Near threshold neutral pion electroproduction on the deuteron is studied in
the framework of baryon chiral perturbation theory at next-to-leading order in
the chiral expansion. We develop the multipole decomposition for pion
production off spin-1 particles appropriate for the threshold region. The
existing data at photon virtuality k^2 = -0.1 GeV^2 can be described
satisfactorily. Furthermore, the prediction for the S-wave multipole E_d at the
photon point is in good agreement with the data.Comment: 27 pp, 15 fig
On Matrix Product States for Periodic Boundary Conditions
The possibility of a matrix product representation for eigenstates with
energy and momentum zero of a general m-state quantum spin Hamiltonian with
nearest neighbour interaction and periodic boundary condition is considered.
The quadratic algebra used for this representation is generated by 2m operators
which fulfil m^2 quadratic relations and is endowed with a trace. It is shown
that {\em not} every eigenstate with energy and momentum zero can be written as
matrix product state. An explicit counter-example is given. This is in contrast
to the case of open boundary conditions where every zero energy eigenstate can
be written as a matrix product state using a Fock-like representation of the
same quadratic algebra.Comment: 7 pages, late
Ground state energy of dilute neutron matter at next-to-leading order in lattice chiral effective field theory
We present lattice calculations for the ground state energy of dilute neutron
matter at next-to-leading order in chiral effective field theory. This study
follows a series of recent papers on low-energy nuclear physics using chiral
effective field theory on the lattice. In this work we introduce an improved
spin- and isospin-projected leading-order action which allows for a
perturbative treatment of corrections at next-to-leading order and smaller
estimated errors. Using auxiliary fields and Euclidean-time projection Monte
Carlo, we compute the ground state of 8, 12, and 16 neutrons in a periodic
cube, covering a density range from 2% to 10% of normal nuclear density.Comment: 34 pages, 8 figures, journal version to appear in Eur. Phys. J.
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
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