arXiv subjects

V. I. Kukulin

Publications and source records attributed to V. I. Kukulin.

At least 37 records · Page 2Linked to original sources

arXiv2014

New general approach in few-body scattering calculations: Solving discretized Faddeev equations on a graphics processing unit

Background: The numerical solution of few-body scattering problems with realistic interactions is a difficult problem that normally must be solved on powerful supercomputers, taking a lot of computer time. This strongly limits the possibility of accurate treatments for many important few-particle problems in different branches of quantum physics. Purpose: To develop a new general highly effective approach for the practical solution of few-body scattering equations that can be implemented on a graphics processing unit. Methods: The general approach is realized in three steps: (i) the reformulation of the scattering equations using a convenient analytical form for the channel resolvent operator; (ii) a complete few-body continuum discretization and projection of all operators and wave functions onto a $L_2$ basis constructed from stationary wave packets and (iii) the ultra-fast solution of the resulting matrix equations using graphics processor. Results: The whole approach is illustrated by a calculation of the neutron-deuteron elastic scattering cross section below and above the three-body breakup threshold with a realistic $NN$ potential which is performed on a standard PC using a graphics processor with an extremely short runtime. Conclusions: The general technique proposed in this paper opens a new way for a fast practical solution of quantum few-body scattering problems both in non-relativistic and relativistic formulations in hadronic, nuclear and atomic physics.

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arXiv2013

ABC effect as a signal of chiral symmetry restoration in hadronic collisions

A new nonconventional mechanism for the basic 2π-fusion reaction pn --> d+(ππ)_0 in the energy region T_p = 1.0-1.4 GeV is suggested. The mechanism is aimed at providing a consistent explanation for the comprehensive experimental studies of this reaction in exclusive setting done recently by the WASA-at-COSY Collaboration. The basic assumption of the model proposed is the production of the I(JP) = 0(3+) dibaryon resonance D03 in the pn collision. The interference of two decay channels of this resonance: D_03 --> d + σ --> d + (ππ)_0 and D_03 --> D_12 + π --> d + (ππ)_0 is shown to give a strong near-threshold enhancement in the ππ invariant mass spectrum, which is well known as the ABC effect. The σ-meson parameters found to reproduce the ABC enhancement are in a general agreement with models which predict the chiral symmetry restoration at high excitation energy and/or high density of matter, although they are essentially less than those accepted for the free σ meson. So, this result might be considered as an indication of partial chiral symmetry restoration in dense and excited quark matter.

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arXiv2012

Three-body breakup within the fully discretized Faddeev equations

A novel approach is developed to find the three-body breakup amplitudes and cross sections within the modified Faddeev equation framework. The method is based on the lattice-like discretization of the three-body continuum with a three-body stationary wave-packet basis in momentum space. The approach makes it possible to simplify drastically all the three- and few-body breakup calculations due to discrete wave-packet representations for the few-body continuum and simultaneous lattice representation for all the scattering operators entering the integral equation kernels. As a result, the few-body breakup can be treated as a particular case of multi-channel scattering in which part of the channels represents the true few-body continuum states. As an illustration for the novel approach, an accurate calculations for the three-body breakup process $n+d\to n+n+p$ with non-local and local $NN$ interactions are calculated. The results obtained reproduce nicely the benchmark calculation results using the traditional Faddeev scheme which requires much more tedious and time-consuming calculations.

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arXiv2012

Resonance structure in the γγ and $π^0π^0$ systems in dC interactions

Along with $π^0$ and η mesons, a resonance structure in the invariant mass spectrum of two photons at Mγγ = 360 \pm 7 \pm 9 MeV is observed in the reaction d + C \rightarrow γ + γ + X at momentum 2.75 GeV/c per nucleon. Estimates of its width and production cross section are Γ = 64 \pm 18 MeV and $σ_{γγ}$ = 98 \pm 24 μb, respectively. The collected statistics amount to 2339 \pm 340 events of 1.5 \cdot 10^6 triggered interactions of a total number ~ 10^12 of dC-interactions. The results on observation of the resonance in the invariant mass spectra of two $π^0$ mesons are presented: the data obtained in the d + C \rightarrow γ + γ reaction is confirmed by the d + C \rightarrow $π^0$ + $π^0$ reaction: $M_{π^0π^0}$ = 359.2 \pm 1.9 MeV, Γ = 48.9 \pm 4.9 MeV; the ratio of Br(R\rightarrowγγ) / Br(R\rightarrow$π^0π^0$) = (1.8 ÷ 3.7)\cdot10^-3.

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arXiv2008

Solving three-body scattering problem in the momentum lattice representation

A brief description of the novel approach towards solving few-body scattering problems in a finite-dimensional functional space of the $L_2$-type is presented. The method is based on the complete few-body continuum discretization in the basis of stationary wave packets. This basis, being transformed to the momentum representation, leads to the cell-lattice-like discretization of the momentum space. So the initial scattering problem can be formulated on the multi-dimensional momentum lattice which makes it possible to reduce the solution of any scattering problem above the breakup threshold (where the integral kernels include, in general, some complicated moving singularities) to convenient simple matrix equations which can be solved on the real energy axis. The phase shifts and inelasticity parameters for the three-body $nd$ elastic scattering with MT I-III $NN$ potential both below and above the three-body breakup threshold calculated with the proposed wave-packet technique are in a very good agreement with the previous accurate benchmark calculation results.

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arXiv2008

Experimental and theoretical evidences for an intermediate $σ$-dressed dibaryon in the NN interaction

Numerous theoretical and experimental arguments are presented in favor of the generation of intermediate $σ$-dressed dibaryon in $NN$ interaction at intermediate and short distances. We argue that this intermediate dibaryon can be responsible for the strong intermediate-range attraction and the short-range repulsion in the $NN$ interaction, and also for the short-range correlations in nuclei. The suggested mechanism for the $σ$-dressing of the dibaryon is identical to that which explains the Roper resonance structure, its dominant decay modes and its extraordinary low mass. A similar transformation mechanism from the glue to the scalar field was discovered in $J/Ψ$ decays. The new experimental data on 2$π$-production in the scalar-isoscalar channel produced in $pn$- and $pd$-collisions and in particular the very recent data on $γγ$ correlations in $p$C and $d$C scattering in the GeV region seems to corroborate the existence of the $σ$-dressed dibaryon in two- and three nucleon interactions.

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arXiv2008

Continuum discretization methods in a composite-particle scattering off a nucleus: the benchmark calculations

The direct comparison of two different continuum discretization methods towards the solution of a composite particle scattering off a nucleus is presented. The first approach -- the Continumm-Discretized Coupled Channel method -- is based on the differential equation formalism, while the second one -- the Wave-Packet Continuum Discretization method -- uses the integral equation formulation for the composite-particle scattering problem. As benchmark calculations we have chosen the deuteron off \nuc{58}{Ni} target scattering (as a realistic illustrative example) at three different incident energies: high, middle and low. Clear non-vanishing effects of closed inelastic channels at small and intermediate energies are established. The elastic cross sections found in both approaches are very close to each other for all three considered energies.

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arXiv2006

Isoscalar short-range current in the deuteron induced by an intermediate dibaryon

A new model for short-range isoscalar currents in the deuteron and in the NN system is developed; it is based on the generation of an intermediate dibaryon which is the basic ingredient for the medium- and short-range NN interaction which was proposed recently by the present authors.This new current model can very well describe the experimental data for the three basic deuteron observables of isoscalar magnetic type, viz. the magnetic moment, the circular polarization of the photon in the $np\to dγ$ process at thermal neutron energies and the structure function B up to Q$^2$=60 fm$^{-2}$.

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arXiv2005

Dibaryons as carriers of strong internucleon interactions and a basis for nuclear physics based on QCD

New concept of intermediate- and short-range nuclear force proposed by the authors a few years ago is discussed briefly. The general concept is based on an assumption on generation of the dressed dibaryon in intermediate state in $NN$ interaction. This new mechanism has been shown to lead not only to numerous new predictions in hadronic physics but also should be responsible for a large portion of nuclear binding energy and properties of nuclear wavefunctions at high momenta.

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arXiv2005

Description of intermediate- and short-range NN nuclear force within a covariant effective field theory

The present paper is aimed to developing an effective field theory in the GeV region to describe consistently both elastic and inelastic NN-scattering in a fully covariant way. In this development we employ our novel s-channel mechanism of NN-interaction at intermediate and short ranges assuming a formation of the six-quark bag dressed with basic meson fields such as $π$, $σ$, $ρ$ and $ω$ in the intermediate state. The peripheral part of the interaction is governed by t-channel one- and two-pion exchanges described fairly well by chiral perturbation theory. The $σ$-meson dressing should be especially important for the stabilization of the bag due to a high coupling constant of the $σ$-meson with the bag and also a strong interaction between the $σ$-field and space symmetric quark core $|s^6[6]>$. This stabilization of the intermediate dressed bag (which shifts the mass of the bag downward to NN threshold) will be crucially important for the description of $π$, $2π$, $ρ$ and $ω$-meson production in NN-collisions, and, in particular, for the correct description of $π^0$ production near threshold. So that, we expect that the results of the present work will lead to a deeper understanding the short- and intermediate-range nuclear forces and internucleon correlations in nuclei.

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arXiv2005

Dibaryon model for nuclear force and the properties of the $3N$ system

The dibaryon model for $NN$ interaction, which implies the formation of an intermediate six-quark bag dressed by a $σ$-field, is applied to the $3N$ system, where it results in a new three-body force of scalar nature between the six-quark bag and a third nucleon. A new multicomponent formalism is developed to describe three-body systems with nonstatic pairwise interactions and non-nucleonic degrees of freedom. Precise variational calculations of $3N$ bound states are carried out in the dressed-bag model including the new scalar three-body force. The unified coupling constants and form factors for $2N$ and $3N$ force operators are used in the present approach, in a sharp contrast to conventional meson-exchange models. It is shown that this three-body force gives at least half the $3N$ total binding energy, while the weight of non-nucleonic components in the $^3$H and $^3$He wavefunctions can exceed 10%. The new force model provides a very good description of $3N$ bound states with a reasonable magnitude of the $σNN$ coupling constant. A new Coulomb $3N$ force between the third nucleon and dibaryon is found to be very important for a correct description of the Coulomb energy and r.m.s. charge radius in $^3$He. In view of the new results for Coulomb displacement energy obtained here for A=3 nuclei, an explanation for the long-term Nolen--Schiffer paradox in nuclear physics is suggested. The role of the charge-symmetry-breaking effects in the nuclear force is discussed.

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arXiv2004

The properties of the three-nucleon system with the dressed-bag model for nn interaction. I: New scalar three-body force

A multi-component formalism is developed to describe three-body systems with nonstatic pairwise interactions and non-nucleonic degrees of freedom. The dressed-bag model for $NN$ interaction based on the formation of an intermediate six-quark bag dressed by a $σ$-field is applied to the $3N$ system, where it results in a new three-body force between the six-quark bag and a third nucleon. Concise variational calculations of $3N$ bound states are carried out in the dressed-bag model including the new three-body force. It is shown that this three-body force gives at least half the $3N$ total binding energy, while the weight of non-nucleonic components in the $^3$H and $^3$He wavefunctions can exceed 10%. The new force model provides a very good description of $3N$ bound states with a reasonable magnitude of the $σNN$ coupling constant. The model can serve as a natural bridge between dynamical description of few-nucleon systems and the very successful Walecka approach to heavy nuclei and nuclear matter.

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arXiv2004

The properties of the three-nucleon system with the dressed-bag model for $NN$ interaction. II: Coulomb and CSB effects

Coulomb and charge-symmetry breaking effects in the $^3$He ground state within the dressed dibaryon model developed recently for $2N$ and $3N$ forces are examined in detail. Particular attention has been paid to the Coulomb displacement energy $ΔE_C=E_B(^3{\rm H})- E_B(^3{\rm He})$ and rms charge radii of $^3$H and $^3$He. A new scalar $3N$ force between the third nucleon a$ dibaryon is found to be very important for a correct description of the Coulomb energy and rms charge radius in $^3$He. In view of the new results for $ΔE_C$ obtained here, the role of the effects of charge symmetry breaking in the nuclear force is discussed.

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arXiv2003

A six-quark dressed-bag description of np -> d γradiative capture

The radiative capture process $n p \to d γ$ is considered within the framework of a recently developed six-quark dressed-bag model for the nucleon-nucleon interaction. The calculations presented here include both the nucleon current and the meson-exchange current contributions. The latter uses short-range hadronic form factors for the pion exchange currents consistent with the soft cut-off parameter $Λ_{πNN}$ from the $NN$-potential. Contributions of the pion exchange current and $Δ$-isobar current to the total cross section still cannot explain the discrepancy between the theoretical and experimental cross sections. Possibilities for new types of meson exchange currents associated with chiral fields inside multi-quark dressed-bag states in nuclei are discussed.

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arXiv2002

A dressed bag model study of the final-state $NΔ$ interaction in photoproduction processes off the deuteron

The impact of the short-range $NΔ$ interaction on the pion photoproduction processes off the deuteron in the $Δ$-resonance region is studied in the framework of recently proposed dressed-bag model. A common dressing procedure for bare three- and six-quark states is used to describe both the pion decay widths of baryon resonances and the effective $NN$ (or $NΔ$) interaction at short ranges related to the inner dressed-bag states. It is shown that the effect of short-range $NΔ$ interaction for the forward-angle $π^\mathrm{o}$ photoproduction off the deuteron cannot be neglected. The prospects for further development of the model to describe the short-range $NN$ (or $NΔ$) correlations in the lightest nuclei are discussed.

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arXiv1999

An inversion procedure for coupled-channel scattering: determining the deuteron-nucleus tensor interaction

We present a practical $S$-matrix to potential inversion procedure for coupled-channel scattering. The inversion technique developed is applied to non-diagonal $S^J_{ll'}$ for spin one projectiles, yielding a tensor interaction $T_{\rm R}$, and is also applicable to spin-1/2 plus spin-1/2 scattering. The method is a generalization of the iterative-perturbative, IP, method. It is tested and evaluated and we investigate the degree of uniqueness of the potential, particularly for cases where there is insufficient information to define the potential uniquely. We examine the potentials which result when the $S$-matrix is generated from a $T_{\rm P}$ interaction. We also develop the generalisation, using established procedures, of IP $S$-matrix-to-potential inversion to direct observable-to-potential inversion. This `direct inversion' procedure is demonstrated to be an efficient method for finding a multi-component potential including a $T_{\rm R}$ interaction fitting multi-energy $σ$, ${\rm i}T_{11}$, $T_{20}$, $T_{21}$ and $T_{22}$ data for the scattering of spin-1 nuclei from spin-zero target. It is applicable to other channel spin 1 cases.

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arXiv1998

Spin 1 inversion: a Majorana tensor force for deuteron alpha scattering

We demonstrate, for the first time, successful S-matrix to potential inversion for spin one projectiles with non-diagonal $S^j_{ll'}$ yielding a $T_{\rm R}$ interaction. The method is a generalization of the iterative-perturbative, IP, method. We present a test case indicating the degree of uniqueness of the potential. The method is adapted, using established procedures, into direct observable to potential inversion, fitting $σ$, ${\rm i}T_{11}$, $T_{20}$, $T_{21}$ and $T_{22}$ for d + alpha scattering over a range of energies near 10 MeV. The $T_{\rm R}$ interaction which we find is very different from that proposed elsewhere, both real and imaginary parts being very different for odd and even parity channels.

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arXiv1998

Determination of Li-6 -- He-4 interaction from multi-energy scattering data

We present the first successful potential model description of Li-6 -- He-4 scattering. The differential cross-sections for three energies and the vector analyzing powers for two energies were fitted by a single potential with energy dependent imaginary components. An essential ingredient is a set of Majorana terms in each component. The potential was determined using a recently developed direct data-to-potential inversion method which is a generalisation of the IP S-matrix-to-potential inversion algorithm. We discuss the problems related to this phenomenological approach, and discuss the relationship of our results to existing and future theories.

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