Hyperspherical harmonic formalism for tetraquarks

We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. Our analysis shows that four-quark systems with non-exotic $2^{++}$ quantum numbers may be bound independently of the quark mass. $0^{+-}$ and $1^{+-}$ states become attractive only for larger quarks masses.Comment: 4 pages, to appear in the proceedings of 9th International Workshop on Meson Production, Properties and Interaction (Meson2006), Kracow (Poland), 9 - 13 June 200

Hyperspherical harmonic study of identical-flavor four-quark systems

We present an exact method based on a hyperspherical harmonic expansion to study systems made of quarks and antiquarks of the same flavor. Our formalism reproduces and improves the results obtained with variational approaches. This analysis shows that identical-flavor four-quark systems with non-exotic 2(++) quantum numbers may be bound independently of the quark mass. 0(+-) and 1(+-) states become attractive only for larger quarks masses

Theory of inter-edge superexchange in zigzag edge magnetism

A graphene nanoribbon with zigzag edges has a gapped magnetic ground state with an antiferromagnetic inter-edge superexchange interaction. We present a theory based on asymptotic properties of the Dirac-model ribbon wavefunction which predicts $W^{-2}$ and $W^{-1}$ ribbon-width dependencies for the superexchange interaction strength and the charge gap respectively. We find that, unlike the case of conventional atomic scale superexchange, opposite spin-orientations on opposite edges of the ribbon are favored by both kinetic and interaction energies.Comment: 4 pages 8 figure

On the Stability of Λ(1405)\Lambda(1405) Matter

A hypothesis of absolutely stable strange hadronic matter composed of $\Lambda(1405)$ baryons, here denoted $\Lambda^*$, is tested within many-body calculations performed using the Relativistic Mean-Field approach. In our calculations, we employed the $\Lambda^*\Lambda^*$ interaction compatible with the $\Lambda^*\Lambda^*$ binding energy $B_{\Lambda^*\Lambda^*}=40$~MeV given by the phenomenological energy-independent $\bar{K}N$ interaction model by Yamazaki and Akaishi (YA). We found that the binding energy per $\Lambda^*$, as well as the central density in $\Lambda^*$ many-body systems saturates for mass number $A\geq120$, leaving $\Lambda^*$ aggregates highly unstable against strong interaction decay. Moreover, we confronted the YA interaction model with kaonic atom data and found that it fails to reproduce the $K^-$ single-nucleon absorption fractions at rest from bubble chamber experiments.Comment: Proceedings of the HYP2018 conference, Norfolk/Portsmouth, USA, June 24 - 29, 2018, submitted to AIP Conference Proceeding

Eta-mesic nuclei

In this contribution we report on theoretical studies of $\eta$ nuclear quasi-bound states in few- and many-body systems performed recently by the Jerusalem-Prague Collaboration [1-5]. Underlying energy-dependent $\eta N$ interactions are derived from coupled-channel models that incorporate the $N^*(1535)$ resonance. The role of self-consistent treatment of the strong energy dependence of subthreshold $\eta N$ amplitudes is discussed. Quite large downward energy shift together with rapid decrease of the $\eta N$ amplitudes below threshold result in relatively small binding energies and widths of the calculated $\eta$ nuclear bound states. We argue that the subthreshold behavior of $\eta N$ scattering amplitudes is crucial to conclude whether $\eta$ nuclear states exist, in which nuclei the $\eta$ meson could be bound and if the corresponding widths are small enough to allow detection of these $\eta$ nuclear states in experiment.Comment: 7 pages, 5 figures; presented at HADRON2017, Sept. 25-29, 2017, Salamanca (Spain); prepared for Proceedings of Scienc

Neutrino Breakup of A=3 Nuclei in Supernovae

We extend the virial equation of state to include 3H and 3He nuclei, and predict significant mass-three fractions near the neutrinosphere in supernovae. While alpha particles are often more abundant, we demonstrate that energy transfer cross-sections for muon and tau neutrinos at low densities are dominated by breakup of the loosely-bound 3H and 3He nuclei. The virial coefficients involving A=3 nuclei are calculated directly from the corresponding nucleon-3H and nucleon-3He scattering phase shifts. For the neutral-current inelastic cross-sections and the energy transfer cross sections, we perform ab-initio calculations based on microscopic two- and three-nucleon interactions and meson-exchange currents.Comment: 6 pages, 2 figures, minor additions, to appear in Phys. Rev.

On the existence of exotic and non-exotic multiquark meson states

To obtain an exact solution of a four-body system containing two quarks and two antiquarks interacting through two-body terms is a cumbersome task that has been tackled with more or less success during the last decades. We present an exact method for the study of four-quark systems based on the hyperspherical harmonics formalism that allows us to solve it without resorting to further approximations, like for instance the existence of diquark components. We apply it to systems containing two heavy and two light quarks using different quark-quark potentials. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark correlations not taken into account by simple quark dynamical models.Comment: 3 pages. Contribution to the 20th European Conference on Few-Body Problems in Physics, Pisa, Italy. To be published in Few-Body system

Are there compact heavy four-quark bound states?

We present an exact method to study four-quark systems based on the hyperspherical harmonics formalism. We apply it to several physical systems of interest containing two heavy and two light quarks using different quark-quark potentials. Our conclusions mark the boundaries for the possible existence of compact, non-molecular, four-quark bound states. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark correlations not taken into account by simple quark dynamical modelsComment: 10 pages, 1 figure. Accepted for publication in Phys. Rev.