Can Tetraneutron be a Narrow Resonance?

Abstract

The search for a resonant four-neutron system has been revived thanks to the recent experimental hints reported in Phys. Rev. Lett. 116, 052501 (2016) [1]. The existence of such a system would deeply impact our understanding of nuclear matter and requires a critical investigation. In this work, we study the existence of a four-neutron resonance in the quasi-stationary formalism using ab initio techniques with various two-body chiral interactions. We employ the No-Core Gamow Shell Model and the Density Matrix Renormalization Group method, both supplemented by the use of natural orbitals and a new identification technique for broad resonances. We demonstrate that while the energy of the four-neutron system may be compatible with the experimental value, its width must be larger than the reported upper limit, supporting the interpretation of the experimental observation as a reaction process too short to form a nucleus.

Ab initio no-core Gamow shell-model calculations of multineutron systems

“…The Hamiltonian matrix in the NCGSM is complex symmetric and bears complex eigenvalues. Coupling to the continuum is then present at basis level, and many-body correlations occur through configuration mixing [15,22,[25][26][27]. The widths of the eigenstates obtained in NCGSM take all particleemission channels into account, so that they are total decay widths.…”

“…There were numerous theoretical calculations taking into account inter-nucleon correlations and high-quality realistic nucleon-nucleon interactions in the frame of abinitio frameworks in recent years [8,9,[13][14][15][16][17][18][19]. The extrapolation of no-core shell model (NCSM) calculations utilizing the realistic two-body JISP16 interaction with a harmonic oscillator (HO) basis showed that tetraneutron is located near 0.8 MeV above threshold and that its width is about 1.4 MeV [13].…”

“…Calculations have also been done in the frame of no-core Gamow shell model (NCGSM), using the density matrix renormalization group (DMRG) method and natural orbitals (n.o.) [15]. It was speculated that the resonance width of tetraneutron is larger than 3.7 MeV, so that the formation of a nucleus therein is precluded.…”

“…It was speculated that the resonance width of tetraneutron is larger than 3.7 MeV, so that the formation of a nucleus therein is precluded. However, the calculations were incomplete, as they could be performed only in truncated model spaces or with unphysically overbinding interactions, so that no definite conclusion could be made [15].…”

Toward scalable many-body calculations for nuclear open quantum systems using the Gamow Shell Model

“…Techniques used in the construction of the Hamiltonian matrix are described in Sect. 3. The description of the JD eigensolver, implementation of a suitable preconditioner and use of angular momentum projection to ensure rotational invariance of the basis vectors are described in Sect.…”