103 research outputs found
Onset of -nuclear binding in a pionless EFT approach
and bound states are explored in stochastic
variational method (SVM) calculations within a pionless effective field theory
(EFT) approach at leading order. The theoretical input consists of regulated
and contact terms, and a regulated energy dependent contact
term derived from coupled-channel models of the nucleon
resonance plus a regulated contact term. A self consistency procedure
is applied to deal with the energy dependence of the subthreshold
input, resulting in a weak dependence of the calculated -nuclear binding
energies on the EFT regulator. It is found, in terms of the scattering
length , that the onset of binding \eta\,^3He requires a minimal
value of Re close to 1 fm, yielding then a few MeV binding
in \eta\,^4He. The onset of binding \eta\,^4He requires a lower value of
Re, but exceeding 0.7 fm.Comment: v4 consists of the published Physics Letters B version [31] plus
Erratum ([30], Appendix A here); main results and conclusions remain intac
Robustness of the nodal d-wave spectrum to strongly fluctuating competing order
We resolve an existing controversy between, on the one hand, convincing
evidence for the existence of competing order in underdoped cuprates, and, on
the other hand, spectroscopic data consistent with a seemingly homogeneous
d-wave superconductor in the very same compounds. Specifically, we show how
short-range fluctuations of the competing order essentially restore the nodal
d-wave spectrum from the qualitatively distinct folded dispersion resulting
from homogeneous coexisting phases. The signatures of the fluctuating competing
order can be found mainly in a splitting of the antinodal quasi-particles and,
depending of the strength of the competing order, also in small induced nodal
gaps as found in recent experiments on underdoped La{2-x}SrxCuO4.Comment: 5 pages, 4 figure
Efimov physics beyond three particles
Efimov physics originally refers to a system of three particles. Here we
review recent theoretical progress seeking for manifestations of Efimov physics
in systems composed of more than three particles. Clusters of more than three
bosons are tied to each Efimov trimer, but no independent Efimov physics exists
there beyond three bosons. The case of a few heavy fermions interacting with a
lighter atom is also considered, where the mass ratio of the constituent
particles plays a significant role. Following Efimov's study of the (2+1)
system, the (3+1) system was shown to have its own critical mass ratio to
become Efimovian. We show that the (4+1) system becomes Efimovian at a mass
ratio which is smaller than its sub-systems thresholds, giving a pure five-body
Efimov effect. The (5+1) and (6+1) systems are also discussed, and we show the
absence of 6- and 7-body Efimov physics there
Eta-mesic nuclei
In this contribution we report on theoretical studies of nuclear
quasi-bound states in few- and many-body systems performed recently by the
Jerusalem-Prague Collaboration [1-5]. Underlying energy-dependent
interactions are derived from coupled-channel models that incorporate the
resonance. The role of self-consistent treatment of the strong
energy dependence of subthreshold amplitudes is discussed. Quite large
downward energy shift together with rapid decrease of the amplitudes
below threshold result in relatively small binding energies and widths of the
calculated nuclear bound states. We argue that the subthreshold behavior
of scattering amplitudes is crucial to conclude whether nuclear
states exist, in which nuclei the meson could be bound and if the
corresponding widths are small enough to allow detection of these
nuclear states in experiment.Comment: 7 pages, 5 figures; presented at HADRON2017, Sept. 25-29, 2017,
Salamanca (Spain); prepared for Proceedings of Scienc
Few-body bound states of two-dimensional bosons
We study clusters of the type AB with in a
two-dimensional mixture of A and B bosons, with attractive AB and equally
repulsive AA and BB interactions. In order to check universal aspects of the
problem, we choose two very different models: dipolar bosons in a bilayer
geometry and particles interacting via separable Gaussian potentials. We find
that all the considered clusters are bound and that their energies are
universal functions of the scattering lengths and , for
sufficiently large attraction-to-repulsion ratios . When
decreases below , the dimer-dimer interaction
changes from attractive to repulsive and the population-balanced AABB and
AAABBB clusters break into AB dimers. Calculating the AAABBB hexamer energy
just below this threshold, we find an effective three-dimer repulsion which may
have important implications for the many-body problem, particularly for
observing liquid and supersolid states of dipolar dimers in the bilayer
geometry. The population-imbalanced ABB trimer, ABBB tetramer, and AABBB
pentamer remain bound beyond the dimer-dimer threshold. In the dipolar model,
they break up at where the atom-dimer interaction
switches to repulsion.Comment: 3 figure
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