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V. A. Sadovnikova

Publications and source records attributed to V. A. Sadovnikova.

31 records · Page 2Linked to original sources
arXiv2005

Nucleon QCD sum rules with the radiative corrections

QCD sum rules for the nucleon are considered in complex q^2 plane with inclusion of the radiative corrections of the order alpha_s. It is shown that the radiative corrections affect mainly the residue lambda^2 of the nucleon pole. Their influence on the value of the nucleon mass is much smaller. Following the ideas of Ioffe and Zyablyuk we expand the analysis to complex values of q^2. This provides a more stable solution. Varying the weights of the contributions of different dimensions by changing the value of the angle in the complex plane we find the value of the six-quark condensate which insures the best consistency of the right hand sides and left hand sides of the sum rules. The corresponding value of the six-quark condensate appears to be only about 10% smaller then the one, provided by the factorization approximation. The value of the four-quark condensate also appears to be close to the one, corresponding to the factorization assumption. The role of the gluon condensate and its possible values are discussed.

hep-ph↗
arXiv2005

Analysis of zero-frequency solutions of the pion dispersion equation in nuclear matter

In this paper we consider instability of nuclear matter which takes place when the frequencies of the collective excitations turn to zero. We investigate collective excitations with pion quantum numbers J^π=0^-. We study the dependence of zero-frequency solutions of the pion dispersion equation on the value of the spin-isospin quasiparticle interaction G'. The solutions of the pion dispersion equation describe the different types of the excitations in the matter, ω_i(k). At the critical density ρ=ρ_c one of solutions of the definite type turns to zero: ω_{i0}(k_c)=0. When ρ>ρ_c, the excitations ω_{i0}(k) become amplified. It is shown that there is such a "transitional" value of G'=G'_{tr} that for G' G'_{tr} they pertain to the type ω_c. The solutions of the type ω_{sd} correspond to instability to small density fluctuations of the nuclear matter at G'\le -1. On the other hand, ω_c is responsible for the "pion condensation" at G'\approx 2. For the stable nuclear matter the branches of solutions ω_{sd}(k) and ω_c(k) are located on the unphysical sheets of the complex plane of frequency.

nucl-th↗
arXiv2004

Nucleon QCD sum rules in nuclear matter including four-quark condensates

We calculate the nucleon parameters in nuclear matter using the QCD sum rules approach in Fermi gas approximation. Terms up to 1/q^2 in the operator product expansion (OPE) are taken into account. The higher moments of the nucleon structure functions are included. The complete set of the nucleon expectation values of the four-quark operators is employed. Earlier the lack of information on these values has been the main obstacle for the further development of the approach. We show that the four-quark condensates provide the corrections of the order 20% to the results obtained in the leading orders of the OPE. This is consistent with the assumption about the convergence of the OPE. The nucleon vector self-energy Σ_v and the nucleon effective mass m^* are expressed in terms of the in-medium values of QCD condensates. The numerical results for these parameters at the saturation value of the density agree with those obtained by the methods of nuclear physics.

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arXiv2004

QCD Sum Rules Description of Nucleons in Asymmetric Nuclear Matter

We calculate the nucleon parameters in isospin asymmetric nuclear matter using the QCD sum rules. The nucleon self-energies are expressed in terms of the in-medium values of QCD condensates. The simple approximate expressions for the self-energies are obtained in terms of these condensates. Relation between successive inclusion of the condensates and the meson-exchange picture of the nucleon interaction with medium is analyzed. The values of the self-energies and of the symmetry energy agree with those obtained by the methods of nuclear physics.

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arXiv2003

Expectation values of four-quark operators in the nucleon

We calculate expectation values of QCD operators consisting of the products of the four operators of the light quarks corresponding to the scalar, pseudoscalar, vector, pseudovector (axial) and tensor Lorentz structures in the nucleon. All combinations of the light flavors are considered. For the evaluation we use elements of the Perturbative Chiral Quark Model (PCQM), approximating the contribution of the valence quarks by the contribution of the PCQM constituent quarks. The contribution of the sea quarks is treated by averaging over the QCD pions with the distribution of the pion field being determined by the PCQM. For quarks with the same flavor the expectation values are dominated by the contribution of the sea-quarks. In the scalar case the contribution of the sea quarks is dominated by the "disconnected terms" were one of the pairs of the quark operators acts on the vacuum while the other one acts on the quarks of the pion. The role of the interference terms with one of the quark pairs acting on the sea quarks and another one acting on the valence quarks increases for quarks with different flavors. The result for the scalar condensate is compared to the one obtained earlier in the framework of the Nambu -Jona-Lasinio model.

hep-ph↗
arXiv2002

Expectation values of four-quark operators in pions

The values of four-quark operators averaged over pions are expressed through those averaged over vacuum. The specific values are obtained in the framework of the factorization assumption. For the condensates of the light quarks of the same flavour \bar qΓq\bar qΓq the scalar condensate is shown to be an order of magnitude larger than the other ones. The condensates containing the strange quarks \bar q q\bar s s appear to be only about twice smaller than those of the light quarks. The degeneracy of the ground state in the Nambu--Jona--Lasinio model is shown explicitly.

hep-ph↗
arXiv2002

On the relation between the long-wave instability and the pion condensation in nuclear matter

The solutions to the zero-sound frequency equation and pion dispersion equation are considered for the different values of the parameters of the effective particle-hole interaction. The branches of solutions, responsible for the long-wave instability [Pomeranchuk] of the nuclear matter ω_P(k) are presented for the both equations. It is shown that in the pion dispersion equation the solutions ω_P(k) result in the instability not only for values of the spin-isospin constant g'\leq -1/2, violating stability criteria, but for all g' < g'_p (|g'_p|\ll 1 and g'_p < 0). At g' > g'_p the branches ω_P(k) turn into the solutions responsible for pion condensation.

nucl-th↗
arXiv2001

QCD condensates and hadron parameters in nuclear matter: self-consistent treatment, sum rules and all that

We review various approaches to the calculation of QCD condensates and of the nucleon characteristics in nuclear matter. We show the importance of their self-consistent treatment. The first steps in such treatment appeared to be very instructive. It is shown that the alleged pion condensation anyway can not take place earlier than the restoration of the chiral symmetry. We demonstrate how the finite density QCD sum rules for nucleons work and advocate their possible role in providing an additional bridge between the condensate and hadron physics.

nucl-th↗
arXiv2000

Solutions of the pion dispersion equation in the medium: new aspects

In symmetrical nuclear matter the solutions of pion dispersion equation are investigated in the complex plane of the pion frequency ω. There are three well-known branches of solutions on the physical sheet : sound, pion and isobar, at the matter density less than the critical one ρ<ρ_c. At ρ>ρ_c the fourth branch appears on the physical sheet. For this branch the condition ω^2_c\leq0 (in general case Reω^2_c\leq0) takes place. This points out the instability of the ground state which is possibly related to the pion condensation.

nucl-th↗
arXiv1999

Low- and intermediate-energy nucleon-nucleon interactions and the analysis of deuteron photodisintegration within the dispersion relation technique

The nucleon-nucleon interaction in the region of the nucleon kinetic energy up to 1000 MeV is analysed together with the reaction $γd \to pn$ in the photon energy range $E_γ=0-400$ MeV. Nine nucleon-nucleon $s$-channel partial amplitudes are reconstructed in the dispersion relation $N/D$ method: $^1S_0$, $^3S_1-^3D_1$, $^3P_0$, $^1P_1$, $^3P_1$, $^3P_2$, $^1D_2$, $^3D_2$ and $^3F_3$. Correspondingly, the dispersive representation of partial amplitudes $NΔ\to pn$, $NN^* \to pn$ and $NNπ\to pn$ is given. Basing on that, we have performed parameter-free calculation of the amplitude $γd \to pn$, taking into account: $(i)$ pole diagram, $(ii)$ nucleon-nucleon final-state rescattering $γd \to pn \to pn$, and $(iii)$ inelastic final-state rescatterings $γd \to NΔ(1232) \to pn$, $γd \to NN^*(1400) \to pn$ and $γd \to NNπ\to pn$. The $γd \to pn$ partial amplitudes for nine above-mentioned channels are found. It is shown that the process $γd \to pn \to pn$ is significant for the waves $^1S_0$, $^3P_0$, $^3P_1$, at $E_γ =50 -100$ MeV, while $γd \to NΔ\to pn$ for the waves $^3P_2$, $^1D_2$,$^3F_3$ dominates at $E_γ > 300$ MeV. Meson exchange current contributions into the deuteron disintegration are estimated: they are significant at $E_γ=100-400$ MeV.

nucl-th↗
arXiv1998

Self-consistent treatment of the quark condensate and hadrons in nuclear matter

We calculate the contribution of pions to the $\bar qq$-expectation value $κ(ρ)= $ in symmetric nuclear matter. We employ exact pion propagator renormalized by nucleon-hole and isobar-hole excitations. Conventional straightforward calculation leads to the "pion condensation" at unrealistically small values of densities, causing even earlier restoration of chiral symmetry. This requires a self-consistent approach, consisting in using the models, which include direct dependence of in-medium mass values on $κ(ρ)$, e.g. the Nambu-Jona-Lasinio-model. We show, that in the self-consistent approach the $ρ$-dependence of the condensate is described by a smooth curve. The "pion condensate " point is removed to much higher values of density. The chiral restoration does not take place at least while $ρ<2.8ρ_0$ with $ρ_0$ being the saturation value. Validity of our approach is limited by possible accumulation of heavier baryons (delta isobars) in the ground state of nuclear matter. For the value of effective nucleon mass at the saturation density we found $m^*(ρ_0)=0.6m$, consistent with nowadays results of other authors.

hep-ph↗
arXiv1995

Contribution of the NN inelasticity into photodisintegration of the deuteron

The technique of dispersion integration over the mass of composite particle is used to describe the reaction of the deuteron photodisintegration. The influence of the final state interaction (FSI) on the total cross section, calculated with and without inelasticity is investigated. Numerical results depend on the choice of the vertex function for the isobar photoproduction.

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