arXiv subjects

V. I. Kukulin

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

At least 19 recordsLinked to original sources

arXiv2022

Dibaryon resonances and short-range $NN$ interaction

The dibaryon concept for the nuclear force is presented, assuming that the main attraction between the nucleons at medium distances is determined by the $s$-channel exchange of an intermediate six-quark (dibaryon) state. To construct the respective $NN$ interaction model, a microscopic six-quark description of the $NN$ system is used, in which symmetry aspects play a special role. It is shown that the $NN$ interaction in all important partial waves can be described properly by a superposition of the long-range $t$-channel one-pion exchange and the $s$-channel exchange by an intermediate dibaryon. The developed model gives a good description of both elastic phase shifts and inelasticities of $NN$ scattering in all $S$, $P$, $D$ and $F$ partial waves at energies from zero to 600 - 800 MeV and even higher.The parameters of the intermediate six-quark states corresponding to the best fit of $NN$ scattering data are found to be consistent with the parameters of the known dibaryon resonances in those $NN$ partial configurations where their existence has been experimentally confirmed. Predictions for new dibaryon states are given as well.

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arXiv2021

Isospin symmetry breaking in double-pion production in the region of ${d^*(2380)}$ and the scalar $σ$ meson

The first attempt is made to provide a quantitative theoretical interpretation of the WASA-at-COSY experimental data on the basic double-pion production reactions $pn \to d π^0π^0$ and $pn \to d π^+π^-$ in the energy region $T_p =1$ - $1.3$ GeV [P. Adlarson et al., Phys. Lett. B 721, 229 (2013)]. The data are analyzed within a model based on production and decay of an intermediate $I(J^P)=0(3^+)$ dibaryon resonance $\mathcal{D}_{03}$ (denoted also as $d^*(2380)$). The observed decrease of the near-threshold enhancement (the so-called ABC effect) in the reaction $pn \to d π^+π^-$ in comparison to that in the reaction $pn \to d π^0π^0$ is explained (at least partially) to be due to isospin symmetry violation in the two-pion decay of an intermediate near-threshold scalar $σ$ meson emitted from the $\mathcal{D}_{03}$ dibaryon resonance under conditions of the partial chiral symmetry restoration.

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arXiv2020

$P$-wave dibaryon resonances in $pp$ elastic scattering and near-threshold pion production

It is demonstrated within the dibaryon-induced model for $NN$ interaction that $pp$ scattering in $P$ waves is governed mainly by the production of the intermediate dibaryon resonances. Two dibaryon resonances with a mass of about 2200 MeV discovered recently by the ANKE-COSY Collaboration are shown to determine both elastic $pp$ phase shifts and inelasticities in the $^3P_0$ and $^3P_2$-$^3F_2$ channels from zero energy up to $T_p=0.7$-$0.9$ GeV. It is also demonstrated clearly that the $^3P_0$ dibaryon plays a decisive role in near-threshold neutral pion production in $pp$ collisions which is poorly understood to date. The missing dibaryon contribution is found to be the very possible reason for the failure of traditional approaches to explain near-threshold $π^0$ production.

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arXiv2020

Properties of dibaryons in nuclear medium

Properties of six-quark dibaryons in nuclear medium are considered by example of $A=6$ nuclei within the three-cluster $α+2N$ model. Dibaryon production in nuclei leads to the appearance of a three-body force between the dibaryon and nuclear core. This non-conventional scalar force is shown to provide an additional attractive contribution to the three-body binding energy. This three-body contribution improves noticeably agreement between theoretical results and experimental data for the majority of observables. The most serious difference between the traditional $NN$-force models and the dibaryon-induced model is found for the nucleon momentum distribution, the latter model providing a strong enrichment of the high-momentum components both for $^6$Li and $^6$He cases.

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arXiv2020

Nature of $\bm{S}$-wave $\bm{NN}$ interaction and dibaryon production at nucleonic resonance thresholds

Phase shifts and inelasticity parameters for $NN$ scattering in the partial-wave channels ${}^3S_1$--${}^3D_1$ and ${}^1S_0$ at energies $T_{\rm lab}$ from zero to about 1 GeV are described within a unified $NN$ potential model assuming the formation of isoscalar and isovector dibaryon resonances near the $NN^*(1440)$ threshold. Evidence for these near-threshold resonances is actually found in the recent WASA experiments on single- and double-pion production in $NN$ collisions. There, the excitation of the Roper resonance $N^*(1440)$ exhibits a structure in the energy dependence of the total cross section, which corresponds to the formation of dibaryon states with $I(J^π)=0(1^+)$ and $1(0^+)$ at the $NN^*(1440)$ threshold. These two $S$-wave dibaryon resonances may provide a new insight into the nature of the strong $NN$ interaction at low and intermediate energies.

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arXiv2019

Theoretical Study of Spin Observables in $pd$ Elastic Scattering at Energies $T_p = 800-1000$ MeV

Various spin observables (analyzing powers and spin-correlation parameters) in $pd$ elastic scattering at $T_p = 800-1000$ MeV are analyzed within the framework of the refined Glauber model. The theoretical model uses as input spin-dependent $NN$ amplitudes obtained from the most recent partial-wave analysis and also takes into account the deuteron $D$ wave and charge-exchange effects. Predictions of the refined Glauber model are compared with the existing experimental data. Reasonable agreement between the theoretical calculations and experimental data at low momentum transfers $|t| \lesssim 0.2$ (GeV/$c)^2$ is found for all observables considered. Moderate discrepancies found in this region are shown to be likely due to uncertainties in the input $NN$ amplitudes. Qualitative agreement at higher momentum transfers is also found for most observables except the tensor ones with mixed $x$ and $z$ polarization components. Possible reasons for observed deviations of the model calculations from the data at $|t| > 0.2$ (GeV/$c)^2$ are discussed.

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arXiv2019

To the nature of nuclear force

It has been shown for the first time that $NN$ interaction, at least in some partial waves, can be quantitatively described by the superposition of a long-range one-pion exchange and a short-range mechanism based on the complex pole in the $NN$ potential corresponding to the dibaryon resonance in this partial wave. For the partial waves $^3P_2$, $^1D_2$, $^3F_3$ and $^1S_0$ the parameters of the complex poles that give the best description of the elastic and inelastic phase shifts of $NN$ scattering are very close to the empirical parameters of the corresponding isovector dibaryon resonances detected experimentally. Based on the results obtained, a general conclusion is made about the nature of nuclear force at medium and small internucleon distances.

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arXiv2019

$^7$Be and $^{22}$Na radionuclides for a new therapy of cancer

The $^{10}$B isotope has been almost exclusively used in the neutron-capture radiation therapy (NCT) of cancer for decades. We have identified two other nuclides suitable for the radiotherapy, which have ca.10 times larger cross section of absorption for neutrons and emit heavy charged particles. This would provide several key advantages for potential NCT, such as the possibility to use either a lower nuclide concentration in the target tissues, or a lower neutron irradiation flux. By detecting the characteristic $γ$ radiation from the spontaneous decay of the radionuclides, one can image and control their accumulation. These advantages could be critical for the revival of the NCT as a safer, more efficient and more widely used cancer therapy.

physics.med-ph↗

arXiv2019

Single pole dominance in short- and intermediate-range $NN$ interaction

It is demonstrated that both elastic and inelastic $NN$ scattering at laboratory energies up to 600--800 MeV, at least in some partial waves characterized by a large inelasticity, can be described by a superposition of the conventional long-range one-pion exchange and a specific short-range interaction induced by the $s$-channel dibaryon exchange. For the $^3P_2$, $^1D_2$ and $^3F_3$ partial waves, the pole parameters giving the best fit of the real and imaginary parts of the $NN$ phase shifts are consistent with the parameters of the respective isovector dibaryon resonances found experimentally. In the $^1S_0$ channel, the suggested interaction gives two poles of the $S$-matrix -- the well-known singlet deuteron and an excited dibaryon. On the basis of the results presented, a conclusion is made about the nature of $NN$ interaction and its strong channel dependence.

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arXiv2018

Experimental and theoretical study of deuteron-proton elastic scattering for proton kinetic energies between $T_p = 882.2\;\textrm{MeV}$ and $T_p = 918.3\;\textrm{MeV}$

New precise unpolarised differential cross sections of deuteron-proton elastic scattering have been measured at 16 different deuteron beam momenta between $p_d = 3120.17\;\textrm{MeV}/c$ and $p_d =3204.16\;\textrm{MeV}/c$ at the COoler SYnchrotron COSY of the Forschungszentrum Jülich. The data, which were taken using the magnetic spectrometer ANKE, cover the equivalent range in proton kinetic energies from $T_p = 882.2\;\textrm{MeV}$ to $T_p = 918.3\;\textrm{MeV}$. The experimental results are analysed theoretically using the Glauber diffraction model with accurate nucleon-nucleon input. The theoretical cross section at $T_p = 900\;\textrm{MeV}$ agrees very well with the experimental one at low momentum transfers $|t| <0.2\;(\textrm{GeV}/c)^2$.

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arXiv2017

In-medium bound states and pairing gap

The propagator of two nucleons in infinite nuclear matter is evaluated by a diagonalization of the $pphh$ RPA Hamiltonian. This effective Hamiltonian is non-Hermitian and, for specific density domains and partial waves, yields pairs of complex conjugated eigenvalues representing in-medium bound states of two nucleons. The occurrence of these complex poles in the two-particle Greens function is tightly related to the well known BCS pairing approach. It is demonstrated that these complex eigenvalues and the corresponding bound state wavefunctions contain all information about the BCS gap function. This is illustrated by calculations for $^1S_0$ and $^3PF_2$ pairing gaps in neutron matter which essentially coincide with the corresponding gap functions extracted from conventional solutions of the gap equation. Differences between the bound states in the conventional BCS approach and the $pphh$ RPA are arising in the case of $^3SD_1$ channel in symmetric nuclear matter at low densities. These differences are discussed in the context of transition from BEC for quasi-deuterons to the formation of BCS pairing.

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arXiv2017

New estimation for neutron-neutron scattering length: charge symmetry and charge independence breaking revisited

Recent experimental results for neutron-neutron scattering length are reanalyzed from the point of view of three-nucleon force contribution. We found that the limiting value of $a_{nn}=- 15.8\pm 0.5$~fm must be free of any implicit three-body force contribution. We have also shown that the difference between the above experimental value of $a_{nn}$ and the well established value of neutron-proton scattering length $a_{np}$ can be explained by differences in the one-pion exchange potentials.

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arXiv2016

Refined Glauber model versus Faddeev calculations and experimental data for $pd$ spin observables

Spin-dependent observables in intermediate-energy $pd$ elastic scattering within the framework of the refined Glauber model are considered. The improvements include an account of all ten $pp$ and $pn$ helicity amplitudes at respective energies constructed on the basis of modern phase-shift analysis, accurate deuteron wave functions taken from the modern $NN$ force model and account of charge-exchange effects. Predictions of the refined diffraction model for the differential cross section and analyzing powers are compared with exact three-body Faddeev calculations and the recent experimental data. An amazingly good agreement between the results of both theoretical approaches as well as between the refined Glauber model and experiment in a wide angular range not only for differential cross section but also for vector and tensor analyzing powers has been found in the first time. Possible reasons for this agreement are discussed.

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arXiv2016

Manifestation of the $P$-wave diproton resonance in single-pion production in $pp$ collisions

It is demonstrated that many important features of single-pion production in $pp$ collisions at intermediate energies ($T_p \simeq 400$-$800$ MeV) can naturally be explained by supposing excitation of intermediate diproton resonances in $pp$ channels ${}^1D_2$, ${}^3F_3$ and ${}^3P_2$, in addition to conventional mechanisms involving an intermediate $Δ$-isobar. We predict for the first time the crucial role of the ${}^3P_2$ diproton resonance, found in recent experiments on the single-pion production reaction $pp \to pp({}^1S_0) π^0$, in reproducing the proper behavior of spin-correlation parameters in the reaction $pp \to d π^+$ which were poorly described by conventional meson-exchange models to date. The possible quark structure of the $P$-wave diproton resonances is also discussed.

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arXiv2016

Discrete Wave-Packet Representation in Nuclear Matter Calculations

The Lippmann-Schwinger equation for the nucleon-nucleon $t$-matrix as well as the corresponding Bethe-Goldstone equation to determine the Brueckner reaction matrix in nuclear matter are reformulated in terms of the resolvents for the total two-nucleon Hamiltonians defined in free space and in medium correspondingly. This allows to find solutions at many energies simultaneously by using the respective Hamiltonian matrix diagonalization in the stationary wave packet basis. Among other important advantages, this approach simplifies greatly the whole computation procedures both for coupled-channel $t$-matrix and the Brueckner reaction matrix. Therefore this principally novel scheme is expected to be especially useful for self-consistent nuclear matter calculations because it allows to accelerate in a high degree single-particle potential iterations. Furthermore the method provides direct access to the properties of possible two-nucleon bound states in the nuclear medium. The comparison between reaction matrices found via the numerical solution of the Bethe-Goldstone integral equation and the straightforward Hamiltonian diagonalization shows a high accuracy of the method suggested. The proposed fully discrete approach opens a new way to an accurate treatment of two- and three-particle correlations in nuclear matter on the basis of three-particle Bethe-Faddeev equation by an effective Hamiltonian diagonalization procedure.

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arXiv2016

Hidden dibaryons in one- and two-pion production in NN collisions

Processes of one- and two-pion production in $NN$ collisions are considered in connection with excitation of intermediate dibaryon resonances. In particular, relative contributions of the conventional meson-exchange and dibaryon excitation mechanisms in the reaction $pp \to d π^+$ are investigated in detail. Inclusion of the intermediate isovector dibaryon resonances is shown to essentially improve the description of experimental data for this reaction, provided the soft meson-baryon form factors consistent with $πN$ elastic scattering are used. Manifestation of the intermediate isoscalar and isovector dibaryons in the two-pion production processes is also studied. The role of the isovector dibaryon resonances in the reaction $pp \to pp ππ$ is discussed for the first time. An explanation of the observed strong differences between two-pion production cross sections in $pn$ and $pp$ collisions based in part on the analysis of dibaryon structure is suggested.

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arXiv2015

Fast GPU-based calculations in few-body quantum scattering

A principally novel approach towards solving the few-particle (many-dimensional) quantum scattering problems is described. The approach is based on a complete discretization of few-particle continuum and usage of massively parallel computations of integral kernels for scattering equations by means of GPU. The discretization for continuous spectrum of a few-particle Hamiltonian is realized with a projection of all scattering operators and wave functions onto the stationary wave-packet basis. Such projection procedure leads to a replacement of singular multidimensional integral equations with linear matrix ones having finite matrix elements. Different aspects of the employment of a multithread GPU computing for fast calculation of the matrix kernel of the equation are studied in detail. As a result, the fully realistic three-body scattering problem above the break-up threshold is solved on an ordinary desktop PC with GPU for a rather small computational time.

physics.comp-ph↗

arXiv2015

Wave-packet continuum discretization for quantum scattering

A general approach to a solution of few- and many-body scattering problems based on a continuum-discretization procedure is described in detail. The complete discretization of continuous spectrum is realized using stationary wave packets which are the normalized states constructed from exact non-normalized continuum states. Projecting the wave functions and all scattering operators like $t$-matrix, resolvent, etc. on such a wave-packet basis results in a formulation of quantum scattering problem entirely in terms of discrete elements and linear equations with regular matrices. It is demonstrated that there is a close relation between the above stationary wave packets and pseudostates which are employed often to approximate the scattering states with a finite $L_2$ basis. Such a fully discrete treatment of complicated few- and many-body scattering problems leads to significant simplification of their practical solution. Also we get finite-dimensional approximations for complicated operators like effective interactions between composite particles constructed via the Feshbach-type projection formalism. As illustrations to this general approach we consider several important particular problems including multichannel scattering and scattering in the three-nucleon system within the Faddeev framework.

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