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N. I. Kochelev

Publications and source records attributed to N. I. Kochelev.

At least 19 recordsLinked to original sources
arXiv2018

Corrections of two-photon interactions in the fine and hyperfine structure of the P-energy levels of muonic hydrogen

In the framework of the quasipotential method in quantum electrodynamics we calculate corrections to the nuclear structure proportional to $r_N^2$ from two-photon exchange amplitudes in the fine and hyperfine structure of P-states in muonic hydrogen, as well as the photon-photon interaction amplitudes, leading to the exchange of the axial vector meson. In constructing the quasipotential of the muon-nucleus interaction, we use the method of projection operators on states of two particles with a definite spin and total angular momentum. Analytical calculation of the matrix elements is performed and contributions to the fine and hyperfine structure of the $2P_{1/2}$ and $2P_{3/2}$ levels are obtained.

hep-ph↗
arXiv2018

The contribution of pseudoscalar and axial-vector mesons to hyperfine structure of muonic hydrogen

In the framework of the quasipotential method in quantum electrodynamics we calculate the contribution of light pseudoscalar (PS) and axial-vector (AV) mesons to the interaction operator of a muon and a proton in muonic hydrogen atom. The coupling of mesons with the muon is via two-photon intermediate state. The parametrization of the transition form factor of two photons into PS and AV mesons, based on the experimental data on the transition form factors and QCD asymptotics, is used. Numerical estimates of the contributions to the hyperfine structure of the spectrum of the S and P levels are presented. It is shown that such contribution to the hyperfine splitting in muonic hydrogen is rather important for a comparison with precise experimental data.

hep-ph↗
arXiv2017

The contribution of axial-vector mesons to hyperfine structure of muonic hydrogen

The contribution from the axial-vector meson exchange to the potential of the muon-proton interaction in muonic hydrogen induced by anomalous axial-vector meson coupling to two photon state is calculated. It is shown that such contribution to the hyperfine splitting in muonic hydrogen is large and important for a comparison with precise experimental data. In the light of our result, the proton radius "puzzle" is discussed.

hep-ph↗
arXiv2017

The contribution of pseudoscalar mesons to hyperfine structure of muonic hydrogen

In the framework of the quasipotential method in quantum electrodynamics we calculate the contribution of pseudoscalar mesons to the interaction operator of a muon and a proton in muonic hydrogen atom. The parametrization of the transition form factor of two photons into $π$, $η$ mesons, based on the experimental data on the transition form factors and QCD asymptotics is used. Numerical estimates of the contributions to the hyperfine structure of the spectrum of the S and P levels are presented.

hep-ph↗
arXiv2014

Anomalous nonperturbative quark-gluon chromomagnetic interaction and spin effects in high energy reactions

We disscuss a new nonperturbative mechanism for spin effects in high energy reactions with hadrons. This mechanism is based on the existence of a large anomalous quark chromomagnetic moment (AQCM) induced by the nontrivial topological structure of QCD vacuum. As an example, we estimate the contribution of this interaction to the single spin asymmetry (SSA) in the inclusive pion production in the proton-proton scattering. We show that SSA induced by AQCM is large and its value is in qualitative agreement with experimental data.

hep-ph↗
arXiv2013

QCD sum rule study on the $f_0(980)$ structure as a pure $K \bar{K}$ bound state

We perform a QCD sum rule analysis for the scalar $f_0(980)$ meson to investigate whether it can be described as a pure bound state of $K$ and $\bar{K}$ mesons. Based on the QCD sum rule with the operators of up to dimension 10 within the operator product expansion, we found that it is hard to treat the $f_0(980)$ as a simple $K\bar{K}$ bound state, which implies that the $f_0(980)$ scalar meson has more complicated structure being mixed states of various configurations.

hep-ph↗
arXiv2010

Gluonic components of the pion and the transition form factor $γ^*γ^*\toπ^0 $

We propose an effective lagrangian for the coupling of the neutral pion with gluons whose strength is determined by a low energy theorem. We calculate the contribution of the gluonic components arising from this interaction to the pion transition form factor $γ^*γ^*\toπ^0 $ using the instanton liquid model to describe the QCD vacuum. We find that this contribution is large and might explain the anomalous behavior of the form factor at large virtuality of one of the photons, a feature which was recently discovered by the BaBar Collaboration.

hep-ph↗
arXiv2009

Exclusive photoproduction of $f_1(1285)$ meson off proton in the JLab kinematics

Within the Regge approach, we calculated the exclusive $f_1(1285)$ meson photoproduction cross section at energy of few GeV. The calculation shows that the cross section is sizable, being in the range of 100 nb, and much larger than the the expected cross section of the $η(1295)$ meson photoproduction at the same energy. These two facts make possible to use this reaction to study the poor known properties of the $f_1(1285)$ meson in the JLab kinematics.

nucl-th↗
arXiv2009

Single Spin Asymmetries in High Energy Reactions and Nonperturbative QCD Effects

We discuss some experimental and theoretical results on single spin asymmetries (SSA) in high energy lepton-hadron and hadron-hadron reactions. In particular, recent results on meson SSA obtained by HERMES are considered in detail. We also discuss the SSA results obtained recently by COMPASS, as well as those from BRAHMS, PHENIX and STAR. Special attention is paid to a possible nonperturbative QCD mechanism that might be responsible for the observed meson SSA. This mechanism originates from the spin-flip quark-gluon chromomagnetic interaction induced by the complex topological structure of the QCD vacuum. We argue that in semi-inclusive deep-inelastic scattering a large SSA is expected not only for mesons but also for baryons due to strong nonperturbative final state interactions between $ud$-diquark and $u$-quark in the fragmenting proton.

hep-ph↗
arXiv2008

Instantons and Spin-Flavor effects in Hadron Physics

We discuss the role of instantons in the spectroscopy of ordinary and exotic hadrons as well as in high energy reactions. We argue that the instanton induced flavor- and spin-dependent quark-quark and quark-gluon interactions can explain many features of the hadron spectrum. The observed anomalous spin and flavor effects in various reactions with hadrons can also be understood within the instanton model for QCD vacuum.

hep-ph↗
arXiv2008

On the $ππ$ contribution to the QCD sum rules for the light tetraquark

We perform a QCD sum rule analysis for the $f_0$ light tetraquark taking into account the contribution arising from the two pion intermediate state. With the interpolating currents of the different chiral combinations of scalar and pseudoscalar diquarks, it is demonstrated that the interpolating current with maximum chirality has a large coupling to the two pion state, but the current with zero chirality interacts only weekly with this state. Taking into account the form factor in the $f_0$--two pion vertex, it is shown that the $f_0$--coupling to the two pion state leads to an increase of the lightest tetraquark mass by a value of about 100 MeV. The analysis of the resulting sum rule shows that the $σ(f_0(600))$--meson state might be treated as the four--quark bound state in the instanton field which has a rather strong coupling to the two pion state.

hep-ph↗
arXiv2006

Instanton contribution to the Sivers function

We study the Sivers function for valence u and d quarks in the proton within the instanton model for QCD vacuum, adopting the MIT bag model wave functions for quarks. Within approaches based on perturbative one-gluon final state interactions a non-zero value of the Sivers function is related to the presence of both S and P wave components in quark wave functions. We show that the instanton-induced chromomagnetic, nonperturbative interaction leads to very specific spin-spin correlations between the struck and spectator quarks, resulting in a non-trivial flavour dependence of the Sivers function. Comparison of the obtained Sivers functions with phenomenological parameterizations is discussed.

hep-ph↗
arXiv2006

Instanton interpolating current for $σ$--tetraquark

We perform a QCD sum rule analysis for the light scalar meson $σ$ ($f_0(600)$) with a tetraquark current related to the instanton picture for QCD vacuum. We demonstrate that instanton current, including equal weights of scalar and pseudoscalar diquark-antidiquarks, leads to a strong cancelation between the contributions of high dimension operators in the operator product expansion (OPE). Furthermore, in the case of this current direct instanton contributions do not spoil the sum rules. Our calculation, obtained from the OPE up to dimension 10 operators, gives the mass of $σ$--meson around 780MeV.

hep-ph↗
arXiv2005

A QCD sum rule analysis of the pentaquark

We perform a QCD sum rule calculation to determine the mass and the parity of the lowest lying pentaquark state. We include operators up to dimension $d=13$ in the OPE and the direct instanton contributions. We find evidence for a positive parity state. The contribution from operators of dimension $d>5$ is instrumental in determining the parity of the state and achieving the convergence of the sum rule.

hep-ph↗
arXiv2005

Triquark correlations and pentaquarks in a QCD sum rule approach

The role of quark correlations in the description of hadron dynamics in many domains of physics, from low energy dynamics to very hot(dense) systems, is being appreciated. Strong correlations of two quarks (diquark) have been widely investigated in this respect. Recently, we have proposed a dynamical scheme to describe the $Θ^+$ pentaquark in which also three quark correlations (triquark) were instrumental in producing a low mass exotic state. We perform a study, within the QCD sum rule approach including OPE and direct instanton contributions, of triquark correlations and obtain two quasi-bound light $ud\bar{s}$ color quark clusters of 800 MeV and 930 MeV respectively.

hep-ph↗
arXiv2005

Evidence for unusual events in high energy cosmic ray interactions

Anomalous events with a large transverse momenta $P_T$ were found for all secondary particles in an analysis of experimental data on cosmic ray interactions at $E_0 > 5\cdot 10^{13} eV$. In order to clarify the underlying mechanism of these events, the intermittency analysis of interactions with both large and usual transverse momentum was performed. It is shown that behavior of intermittency indices $ϕ(q)$ as a function of rank factorial momentum $q$ for such interactions is very peculiar. The indices show slight growth for the events with large transverse momenta for all secondary particles in contrast with the fast growth for events with normal average transverse momenta for final particles. The significant difference in the behavior of intermittency indices gives strong evidence on the existence of the new class of hadron interactions with large $P_T$ for all secondary particles in the event. A possible interpretation of these anomalous events as a manifistation of Color Glass Condensate in high energy hadron-hadron interactions is given.

astro-ph↗
arXiv2004

Effects of QCD Vacuum and Stability of H Dihyperon

Within the composite quark model taking into account the interaction of quarks in the bag with vacuum fields of QCD the masses of H (I=0,S=-2,J=0,1^C) and H* (I=0,S=-2,J=1,1^C) dihyperons are estimated: M_H=2.16 GeV, M_H*=2.34 GeV. It is shown that the leading effect giving a stable with respect to strong decays H dihyperon is the instanton interaction forming diquarks: q^2(J=0,C=3), q^2(J=0,C=6). With the approach developed the contribution of QCD hyperfine interaction is suppressed, and instanton induced three-particle forces in multiquark hadrons (q^3(J=1/2,C=8) - channel) are rather small.

hep-ph↗