arXiv subjects
Publications and source records attributed to R. Lazauskas.
We describe 19B in terms of a 17B-n-n three-body system, where the two-body subsystems 17B-n and n-n are unbound (virtual) states close to the unitary limit. The energy of 19B ground state is well reproduced and two low-lying resonances are predicted. Their eventual link with the Efimov physics is discussed. This model can be extended to describe the recently discovered resonant states in 20,21B.
Background: Several previous studies provided contradicting results for the four-neutron system, some claiming the existence of a 0+ near-threshold resonance, others denying presence of any observable resonant states. Purpose: Since most of the studies employed enhanced two-neutron interactions to follow the evolution of an artificially bound state into a continuum one, we examine several enhancement schemes that produce a bound dineutron as well. Methods: We study the four-neutron system by solving exact four-particle equations. By varying the interaction enhancement factor we calculate two-dineutron scattering phase shifts and cross sections. Results: When the same enhancement factor is used in all partial waves, a bound tetraneutron emerges together with a strongly bound dineutron. Furthermore, such a 0+ tetraneutron evolves not into a resonance but into a virtual state. Weak enhancement of S waves together with strongly enhanced higher waves is needed for the emergence of the resonant state. Anyhow the resonant behavior disappears well before reaching the physical interaction strength. Conclusions: The interaction enhancement scheme using the same factor for all waves, employed in several previous works, is misleading for the search of 0+ resonance as only a virtual state can emerge. Evolution of a bound tetraneutron into a resonance via an intermediate virtual state is possible with strong enhancement of higher two-neutron waves.
The quantum Monte Carlo study [S. Gandolfi, H.-W. Hammer, P. Klos, J. E. Lynn, and A. Schwenk, Phys. Rev. Lett. {\bf 118}, 232501 (2017), arXiv:1612.01502] of few-neutron resonant states provided results incompatible with rigorous few-body calculations. In this Comment we point out serious shortcomings in the work by Gandolfi et al, leading to misinterpretation of unbound few-body systems.
By solving the 5-body Faddeev-Yakubovsky equations in configuration space with realistic nuclear Hamiltonians we have studied the resonant states of $^5$H isotope. Two different methods, allowing to bypass the exponentially diverging boundary conditions, have been employed providing consistent results. The existence of $^5$H broad J$^π$=1/2$^+$,3/2$^+$,5/2$^+$ states as S-matrix poles has been confirmed and compared with the, also calculated, resonant states in $^4$H isotope. We have established that the positions of these resonances only mildly depend on the nuclear interaction model.
The three-body scattering problem in Coulombic systems is widespread, however yet unresolved problem by the mathematically rigorous methods. In this work this long term challenge has been undertaken by combining distorted waves and Faddeev-Merkuriev equation formalisms in conjunction with the complex scaling technique to overcome difficulties related with the boundary conditions. Unlike the common belief, it is demonstrated that the smooth complex scaling method can be applied to solve three-body Coulomb scattering problem in a wide energy region, including fully elastic domain and extending to the energies well beyond atom ionization threshold. Newly developed method is used to study electron scattering on ground states of Hydrogen and Positronium atoms as well as a $e^+$+H(n=1) $\rightleftarrows$ p+Ps(n=1) reaction. Where available, obtained results are compared with the experimental data and theoretical predictions, proving accuracy and efficiency of the newly developed method.
p-3H and n-3He scattering in the energy range above the n-3He but below the d-d thresholds is studied by solving the 4-nucleon problem with a realistic nucleon-nucleon interaction. Three different methods -- Alt, Grassberger and Sandhas, Hyperspherical Harmonics, and Faddeev-Yakubovsky -- have been employed and their results for both elastic and charge-exchange processes are compared. We observe a good agreement between the three different methods, thus the obtained results may serve as a benchmark. A comparison with the available experimental data is also reported and discussed.
We consider the theoretical possibility to generate a narrow resonance in the four neutron system as suggested by a recent experimental result. To that end, a phenomenological $T=3/2$ three neutron force is introduced, in addition to a realistic $NN$ interaction. We inquire what should be the strength of the $3n$ force in order to generate such a resonance. The reliability of the three-neutron force in the $T=3/2$ channel is exmined, by analyzing its consistency with the low-lying $T=1$ states of $^4$H, $^4$He and $^4$Li and the $^3{\rm H} + n$ scattering. The {\it ab initio} solution of the $4n$ Schrödinger equation is obtained using the complex scaling method with boundary conditions appropiate to the four-body resonances. We find that in order to generate narrow $4n$ resonant states a remarkably attractive $3N$ force in the $T=3/2$ channel is required.
The n-d elastic and breakup cross sections are computed by solving the three-body Faddeev equations for realistic and semi-realistic Nucleon-Nucleon potentials. These cross sections are inserted in the Monte Carlo simulation of the nuclear processes considered in the International Handbook of Evaluated Criticality Safety Benchmark Experiments (ICSBEP). The results obtained using thes ab initio n-d cross sections are compared with those provided by the most renown international libraries.
Solution of the scattering problem turns to be very difficult task both from the formal as well as from the computational point of view. If the last two decades have witnessed decisive progress in ab initio bound state calculations, rigorous solution of the scattering problem remains limited to A$\leq$4 case. Therefore there is a rising interest to apply bound-state-like methods to handle non-relativistic scattering problems. In this article the latest theoretical developments in this field are reviewed. Five fully rigorous methods will be discussed, which address the problem of nuclear collisions in full extent (including the break-up problem) at the same time avoiding treatment of the complicate boundary conditions or integral kernel singularities. These new developments allows to use modern bound-state techniques to advance significantly rigorous solution of the scattering problem.
In this lecture we aim to present a formalism based on Faddeev-like equations for describing nuclear three-cluster reactions that include elastic, transfer and breakup channels. Two different techniques based on momentum-space and configuration-space representations are explained in detail. An important new feature of these methods is the possibility to account for the repulsive Coulomb interaction between two of the three clusters in all channels. Comparison with previous calculations based on approximate methods used in nuclear reaction theory is also discussed.
The n-3H and p-3He elastic phase-shifts below the trinucleon disintegration thresholds are calculated by solving the 4-nucleon problem with three different realistic nucleon-nucleon interactions (the I-N3LO model by Entem and Machleidt, the Argonne v18 potential model, and a low-k model derived from the CD-Bonn potential). Three different methods -- Alt, Grassberger and Sandhas, Hyperspherical Harmonics, and Faddeev-Yakubovsky -- have been used and their respective results are compared. For both n-3H and p-3He we observe a rather good agreement between the three different theoretical methods. We also compare the theoretical predictions with the available experimental data, confirming the large underprediction of the p-3He analyzing power.
We develop a series of resonant short-range two-boson potentials reproducing the same two-body low-energy observables and apply them in three- and four-body calculations. We demonstrate that the universal behavior predicted by effective field theory may be strongly violated and analyze the conditions for this phenomenon.
In the future several Spallation Source facilities will be available worldwide. Spallation Sources produce large amount of neutrinos from decay-at-rest muons and thus can be well adapted to accommodate state-of-the-art neutrino experiments. In this paper low energy neutrino scattering experiments that can be performed at such facilities are reviewed. Estimation of expected event rates are given for several nuclei, electrons and protons at a detector located close to the source. A neutrino program at Spallation Sources comprises neutrino-nucleus cross section measurements relevant for neutrino and core-collapse supernova physics, electroweak tests and lepton-flavor violation searches.
We discuss the cross section formula both for massless and massive neutrinos on stable and radioactive nuclei. The latter could be of interest for the detection of cosmological neutrinos whose observation is one of the main challenges of modern cosmology. We analyze the signal to background ratio as a function of the ratio of the neutrino mass over the detector resolution and show that an energy resolution less than 0.5 eV would be required for sub-eV neutrino masses, independently of the gravitational neutrino clustering. Finally we mention the non-resonant character of neutrino capture on radioactive nuclei.
We discuss a scenario to extract up to 150 MeV neutrinos at a standard beta-beam facility using one and two detectors off-axis. In particular we show that the high-energy component of the neutrino fluxes can be subtracted through a specific combination of the response of two off-axis detectors. A systematic analysis of the neutrino fluxes using different detector geometries is presented, as well as a comparison with the expected fluxes at a low-energy beta-beam facility. The presented option could offer an alternative way to perform low-energy neutrino experiments.
We explore the possibility of performing nuclear structure studies using low energy neutrino beams. In particular, low energy beta-beams and conventional sources (muon decay-at-rest) are considered. We present results on the total charged-current as well as flux-averaged cross sections associated to electron (anti)-neutrino scattering on oxygen, iron, molybdenum and lead, as typical examples. It is shown that by using neutrinos from low energy beta-beams, information on forbidden states, in particular the spin-dipole, could be extracted.
Faddeev-Yakubovski equations are solved numerically for 4He tetramer and trimer states using realistic helium-helium interaction models. We describe the properties of ground and excited states, and we discuss with a special emphasis the 4He-4He3 low energy scattering.
We discuss the possibility of testing the weak currents and, in particular, the weak magnetism term through the measurement of the electron anti-neutrinos capture by protons at a low energy beta-beam facility. We analyze the sensitivity using both the total number of events and the angular distribution of the positrons emitted in a water Cerenkov detector. We show that the weak magnetism form factor might be determined with better than several percent accuracy using the angular distribution. This offers a new way of testing the Conserved Vector Current hypothesis.