668 research outputs found
Three-nucleon force at large distances: Insights from chiral effective field theory and the large-N_c expansion
We confirm the claim of Ref. [D.R. Phillips, C. Schat, Phys. Rev. C88 (2013)
3, 034002] that 20 operators are sufficient to represent the most general local
isospin-invariant three-nucleon force and derive explicit relations between the
two sets of operators suggested in Refs. [D.R. Phillips, C. Schat, Phys. Rev.
C88 (2013) 3, 034002] and [H. Krebs, A.M. Gasparyan, E. Epelbaum, Phys.Rev. C87
(2013) 5, 054007]. We use the set of 20 operators to discuss the chiral
expansion of the long- and intermediate-range parts of the three-nucleon force
up to next-to-next-to-next-to-next-to-leading order in the standard formulation
without explicit Delta(1232) degrees of freedom. We also address implications
of the large-N_c expansion in QCD for the size of the various three-nucleon
force contributions.Comment: 15 pages, 6 figure
Lattice calculations for A=3,4,6,12 nuclei using chiral effective field theory
We present lattice calculations for the ground state energies of tritium,
helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our results were
previously summarized in a letter publication. This paper provides full details
of the calculations. We include isospin-breaking, Coulomb effects, and
interactions up to next-to-next-to-leading order in chiral effective field
theory.Comment: 38 pages, 11 figures, final publication versio
, and molecules
We investigate theoretically baryon systems made of three hadrons which
contain one nucleon and one D meson, and in addition another meson, or . The systems are studied using the Fixed Center Approximation
to the Faddeev equations. The study is made assuming scattering of a or a
on a cluster, which is known to generate the ,
or the scattering of a nucleon on the cluster, which has been shown
to generate a hidden charm resonance named X(3700). We also investigate the
configuration of scattering of on the cluster, which is known to
generate the . In all cases we find bound states, with the
system, of exotic nature, more bound than the .Comment: 9 figure
Lattice effective field theory calculations for A = 3,4,6,12 nuclei
We present lattice results for the ground state energies of tritium,
helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our analysis includes
isospin-breaking, Coulomb effects, and interactions up to
next-to-next-to-leading order in chiral effective field theory.Comment: 4 pages, 4 figures, published version to appear in Phys. Rev. Lett
Spin partners of the and revisited
We study the implications of the heavy-quark spin symmetry for the possible
spin partners of the exotic states and in the
spectrum of bottomonium. We formulate and solve numerically the coupled-channel
equations for the states that allow for a dynamical generation of these
states as hadronic molecules. The force includes short-range contact terms and
the one-pion exchange potential, both treated fully nonperturbatively. The
strength of the potential at leading order is fixed completely by the pole
positions of the states such that the mass and the most prominent
contributions to the width of the isovector heavy-quark spin partner states
with the quantum numbers () come out as predictions.
Since the accuracy of the present experimental data does not allow one to fix
the pole positions of the 's reliably enough, we also study the pole
trajectories of their spin partner states as functions of the binding
energies. It is shown that, once the heavy-quark spin symmetry is broken by
means of the physical and masses, especially the pion tensor force
has a significant impact on the location of the partner states clearly
demonstrating the need of a coupled-channel treatment of pion dynamics to
understand the spin multiplet pattern of hadronic molecules.Comment: 21 pages, 5 figures, 1 tabl
Ab initio calculation of the Hoyle state
The Hoyle state plays a crucial role in the hydrogen burning of stars heavier
than our sun and in the production of carbon and other elements necessary for
life. This excited state of the carbon-12 nucleus was postulated by Hoyle [1]
as a necessary ingredient for the fusion of three alpha particles to produce
carbon at stellar temperatures. Although the Hoyle state was seen
experimentally more than a half century ago [2,3], nuclear theorists have not
yet uncovered the nature of this state from first principles. In this letter we
report the first ab initio calculation of the low-lying states of carbon-12
using supercomputer lattice simulations and a theoretical framework known as
effective field theory. In addition to the ground state and excited spin-2
state, we find a resonance at -85(3) MeV with all of the properties of the
Hoyle state and in agreement with the experimentally observed energy. These
lattice simulations provide insight into the structure of this unique state and
new clues as to the amount of fine-tuning needed in nature for the production
of carbon in stars.Comment: 4 pp, 3 eps figs, version accepted for publication in Physical Review
Letter
Effective short-range interaction for spin-singlet P-wave nucleon-nucleon scattering
Distorted-wave methods are used to remove the effects of one- and two-pion
exchange up to order Q^3 from the empirical 1P1 phase shift. The one divergence
that arises can be renormalised using an order-Q^2 counterterm which is
provided by the (Weinberg) power counting appropriate to the effective field
theory for this channel. The residual interaction is used to estimate the scale
of the underlying physics.Comment: 4 pages, 3 figures (pdf
Spin partners from the line shapes of the and
In a recent paper Phys.Rev. D98, 074023 (2018), the most up-to-date
experimental data for all measured production and decay channels of the
bottomonium-like states and were analysed in a
field-theoretical coupled-channel approach which respects analyticity and
unitarity and incorporates both the pion exchange as well as a short-ranged
potential nonperturbatively. All parameters of the interaction were fixed
directly from data, and pole positions for both states were determined.
In this work we employ the same approach to predict in a parameter-free way the
pole positions and the line shapes in the elastic and inelastic channels of the
(still to be discovered) spin partners of the states. They are
conventionally referred to as 's with the quantum numbers
(). It is demonstrated that the results of our most
advanced pionful fit, which gives the best for the data
in the channels, are consistent with all states being
above-threshold resonances which manifest themselves as well pronounced hump
structures in the line shapes. On the contrary, in the pionless approach, all
's are virtual states which can be seen as enhanced threshold cusps in
the inelastic line shapes. Since the two above scenarios provide different
imprints on the observables, the role of the one-pion exchange in the
systems can be inferred from the once available
experimental data directly.Comment: 24 pages, 12 figure
Threshold neutral pion photoproduction off the tri-nucleon to O(q^4)
We calculate electromagnetic neutral pion production off tri-nucleon bound
states (3H, 3He) at threshold in chiral nuclear effective field theory to
fourth order in the standard heavy baryon counting. We show that the fourth
order two-nucleon corrections to the S-wave multipoles at threshold are very
small. This implies that a precise measurement of the S-wave cross section for
neutral pion production off 3He allows for a stringent test of the chiral
perturbation theory prediction for the S-wave electric multipole E_{0+}^{pi0
n}.Comment: 17 pages, 5 figures, title changed, final version to appear in EPJA.
arXiv admin note: substantial text overlap with arXiv:1103.340
Chiral dynamics in few-nucleon systems
We report on recent progress achieved in calculating various few-nucleon
low-energy observables from effective field theory. Our discussion includes
scattering and bound states in the 2N, 3N and 4N systems and isospin violating
effects in the 2N system. We also establish a link between the nucleon-nucleon
potential derived in chiral effective field theory and various modern
high-precision potentials.Comment: 12 pp, uses aipproc style files, 4 figures, contribution to the
conference on "Mesons and Light Nuclei", Prag, July 2001, to appear in the
proceeding
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