678 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
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
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
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
Updated dispersion-theoretical analysis of the nucleon electromagnetic form factors
In the light of the new data on the various neutron and proton
electromagnetic form factors taken in recent years, we update the
dispersion-theoretical analysis of the nucleon electromagnetic form factors
from the mid-nineties. The parametrization of the spectral functions includes
constraints from unitarity, perturbative QCD, and recent measurements of the
neutron charge radius. We obtain a good description of most modern form factor
data, with the exception of the Jefferson Lab data on G_E^p/G_M^p in the
four-momentum transfer range Q^2=3...6 GeV^2. For the magnetic radii of the
proton and the neutron we find r_M^p = 0.857 fm and r_M^n = 0.879 fm, which is
consistent with the recent determinations using continued fraction expansions.Comment: 5 pages, 3 ps figures, final version, exp. errors in Figs. 1 and 3
correcte
Universal Properties of the Four-Boson System in Two Dimensions
We consider the nonrelativistic four-boson system in two dimensions
interacting via a short-range attractive potential. For a weakly attractive
potential with one shallow two-body bound state with binding energy B_2, the
binding energies B_N of shallow N-body bound states are universal and thus do
not depend on the details of the interaction potential. We compute the
four-body binding energies in an effective quantum mechanics approach. There
are exactly two bound states: the ground state with B_4^(0)=197.3(1)B_2 and one
excited state with B_4^(1)=25.5(1)B_2. We compare our results to recent
predictions for N-body bound states with large N>>1.Comment: 7 pages, 1 ps figure, references and discussion added, final versio
Electromagnetic Structure of the Z_c(3900)
The observation of the exotic quarkonium state Z_c(3900) by the BESIII and
Belle collaborations supports the concept of hadronic molecules. Charmonium
states interpreted as such molecules would be bound states of heavy particles
with small binding energies. This motivates their description using an
effective theory with contact interactions. In particular, we focus on the
electromagnetic structure of the charged state Z_c(3900). Using first
experimental results concerning spin and parity, we interpret it as an S-wave
molecule and calculate the form factors as well as charge and magnetic radii up
to next-to-leading order. We also present first numerical estimations of some
of these observables at leading order.Comment: 5 pages, 4 figures, final version to appear in Phys. Lett.
Complete phase diagram for the integrable chain with alternating spins in the sectors with competing interactions
We investigate the anisotropic integrable spin chain consisting of spins
and by means of thermodynamic Bethe ansatz for the anisotropy
, where the analysis of the Takahashi conditions leads to a more
complicated string picture. We give the phase diagram with respect to the two
real coupling constants and , which contains a new region
where the ground state is formed by strings with infinite Fermi zones. In this
region the velocities of sound for the two physical excitations have been
calculated from the dressed energies. This leads to an additional line of
conformal invariance not known before.Comment: 13 pages, LaTeX, uses ioplppt.sty and epsfig.sty, figure 3 correcte
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