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N. N. Achasov

Publications and source records attributed to N. N. Achasov.

At least 73 records · Page 4Linked to original sources
arXiv2010

Nature of the a_0(980) Meson in the Light of Photon-Photon Collisions

New high-statistics Belle data on the reaction γγ\toπ^0ηare analyzed to clarify the two-photon production mechanisms and the nature of the a_0(980) meson. The obtained solution for the amplitude γγ\toπ^0ηis consistent with the chiral theory expectation for the πηscattering length, with the strong coupling of the a_0(980) to the πη, K\bar K, and πη' channels, and with a key role of the rescattering mechanisms a_0(980)\to(K\bar K+ π^0η+π^0η')\toγγin the a_0(980)\toγγdecay. Such a picture argues in favor of the q^2\bar q^2 nature of the a_0(980) meson and is in agreement with the properties of its partners, the σ_0(600) and f_0(980) mesons, in particular, with those that manifest themselves in γγ\toππ. An important role of the vector meson exchanges in the formation of the nonresonant background in γγ\toπ^0ηis also revealed. The preliminary information on the reaction π^0η\toπ^0ηis obtained.

hep-ph↗
arXiv2010

Light Scalar Mesons as Manifestation of Spontaneously Broken Chiral Symmetry

Attention is paid to the production mechanisms of light scalars that reveal their nature. We reveal the chiral shielding of the σ(600) meson. We show that the kaon loop mechanism of the ϕradiative decays, ratified by experiment, points to the four-quark nature of light scalars. We show also that the light scalars are produced in the two photon collisions via four-quark transitions in contrast to the classic P wave tensor q\bar q mesons that are produced via two-quark transitions $γγ\to q\bar q$. The history of spontaneous breaking of symmetry in quantum physics is discussed in Appendix.

hep-ph↗
arXiv2009

Nature of light scalars through photon-photon collisions

The surprising thing is that arising almost 50 years ago from the linear sigma model (LSM) with spontaneously broken chiral symmetry, the light scalar meson problem has become central in the nonperturbative quantum chromodynamics (QCD) for it has been made clear that LSM could be the low energy realization of QCD. First we review briefly signs of four-quark nature of light scalars. Then we show that the light scalars are produced in the two photon collisions via four-quark transitions in contrast to the classic $P$ wave tensor $q\bar q$ mesons that are produced via two-quark transitions $γγ\to q\bar q$. Thus we get new evidence of the four-quark nature of these states.

hep-ph↗
arXiv2008

Light Scalars in Field Theory

Outline: 1. Introduction, 2. Confinement, chiral dynamics and light scalar mesons, 3. Chiral shielding of σ(600), chiral constraints, σ(600), f_0(980) and their mixing in ππ\toππ, ππ\to K\bar K, and ϕ\toγ\pi0\pi0, 4. The ϕmeson radiative decays on light scalar resonances. 5. Why a0(980) and f0(980) are not the K\bar K molecules. 6. Light scalars in γγcollisions. Evidence for four-quark components of light scalars is given. The priority of Quantum Field Theory in revealing the light scalar mystery is emphasized.

hep-ph↗
arXiv2008

Lightest Scalar Resonances and the Dynamics of the γγ\toππReactions

The high-statistics Belle data on the γγ\toπ^+π^- and γγ\toπ^0π^0 reactions have been jointly analyzed. The main dynamical mechanisms of these reactions for energies below 1.5 GeV have been revealed. It has been shown that the direct coupling constants of the σ(600) and f_0(980) resonances with a γγpair are small and that the σ(600)\toγγand f_0(980)\toγγdecays are four-quark transitions due primarily to π^+π^- and K^+K^- loop mechanisms, respectively. The role of the chiral shielding of the σ(600) resonance is emphasized. The widths of the f_0(980)\toγγand σ(600)\toγγdecays averaged over the resonance mass distributions, as well as the width of the f_2(1270)\toγγdecay, are estimated as (Γ_{f_0\toγγ})_{ππ}\approx 0.19 keV, (Γ_{σ\toγγ})_{ππ}\approx 0.45 keV, and Γ_{f_2\toγγ}(m^2_{f_2})\approx 3.8$ keV.

hep-ph↗
arXiv2008

Reaction e^+e^-\toπ^+π^-π^+π^- at energies \sqrt{s}\leq 1 GeV

The cross section of reaction e^+e^-\toπ^+π^-π^+π^- is calculated for energies 0.65\leq \sqrt{s}\leq1 GeV in the framework of the generalized hidden local symmetry model. The calculations are compared with the data of CMD-2 and BaBaR. It is shown that the inclusion of heavy isovector resonances ρ(1450) and ρ(1700) is necessary for reconciling calculations with the data. It is found that at \sqrt{s}\approx1 GeV the contributions of above resonances are much larger, by the factor of 30, than the ρ(770) one, and are amount to a considerable fraction \sim0.3-0.6 of the latter at \sqrt{s}\sim m_ρ.

hep-ph↗
arXiv2008

Hidden local symmetry and the reaction e^+e^-\toπ^+π^-π^+π^- at energies \sqrt{s}\leq 1 GeV

Based on the generalized hidden local symmetry as the chiral model of pseudoscalar, vector, and axial vector mesons, the excitation curve of the reaction e^+e^-\toπ^+π^-π^+π^- is calculated for energies in the interval 0.65\leq \sqrt{s}\leq1 GeV. The theoretical predictions are compared to available data of CMD-2 and BaBaR. It is shown that the inclusion of heavy isovector resonances ρ(1450) and ρ(1700) is necessary for reconciling calculations with the data. It is found that at \sqrt{s}\approx1 GeV the contributions of the above resonances are much larger, by the factor of 30, than the ρ(770) one, and are amount to a considerable fraction \sim0.3-0.6 of the latter at \sqrt{s}\sim m_ρ.

hep-ph↗
arXiv2008

Theory of Scalars

Outline: 1. Introduction, 2. Confinement, chiral dynamics and light scalar mesons, 3. Chiral shielding of the σ(600), chiral constraints (the CGL band), the σ(600) and the f0(980) in ππ->ππ, ππ->KKbar, ϕ->γ\pi0\pi0, 4. The ϕmeson radiative decays on light scalar resonances, 5. Light scalars in γγcollisions. Evidence for four-quark components of light scalars is given. The priority of Quantum Field Theory in revealing the light scalar mystery is emphasized.

hep-ph↗
arXiv2008

Lightest scalar and tensor resonances in $γγ\toππ$ after the Belle experiment

New high statistics Belle data on the $γγ\toπ^+π^-$ reaction cross section measured in the range of pion-pair invariant masses $\sqrt{s}$ between 0.8 GeV and 1.5 GeV are analyzed to clarify the current situation around the $σ(600)$, $f_0(980)$, and $f_2(1270)$ resonances in $γγ$ collisions. The present analysis shows that the direct coupling constants of the $σ(600)$ and $f_0(980)$ resonances to $γγ$ are small, and the $σ(600)\toγγ$ and $f_0(980)\toγγ$ decays are four-quark transitions caused by the $π^+π^-$ and $K^+K^-$ loop mechanisms, respectively. The chiral shielding of the $σ(600)$ resonance takes place in the reactions $γγ\toππ$ as well as in $ππ$ scattering. Some results of a simultaneous description of the $γγ\toπ^+π^-$ and $γγ\toπ^0π^0$ Belle data are also presented. In particular, the following tentative estimate of the $f_2(1270)\toγγ$ decay width is obtained: $Γ_{f_2\toγγ}(m^2_{f_2})\approx 3.68$ keV.

hep-ph↗
arXiv2007

Once more about the K\bar K molecule approach to the light scalars

We show that the recent paper \cite{kalash}, claiming that the radiative decays ϕ\to a_0(980)γand ϕ\to f_0(980)γshould be of the same order of magnitude regardless of whether the a_0(980) and f_0(980) are compact four-quark states or extended K\bar K molecule states, is misleading.

hep-ph↗
arXiv2007

Once more about gauge invariance in ϕ\toγ\pi0\pi0

It is argued that the realization of gauge invariance condition as a consequent of cancellation between the ϕ\toγf0\toγ\pi0\pi0 resonance contribution and a ϕ\toγ\pi0\pi0 background one, suggested in Ref. [1], is misleading.

hep-ph↗
arXiv2007

Lightest scalar in the SU_L(2)*SU_R(2) linear σmodel

We consider the lightest scalar meson in the frame of the $SU_L(2)\times SU_R(2)$ linear $σ$ model, keeping in mind that this model could be the low energy realization of the two-flavour QCD. We show that the $σ$ field is described by its four-quark component at least in the $σ$ resonance energy (virtuality) region and the $σ\toγγ$ decay is the four quark transition. We emphasize that residues of the $σ$ pole in the $ππ\toππ$ and $γγ\toππ$ amplitudes do not give an idea about the $σ$ meson nature, and the progress in studying the $σ$ meson production mechanisms in different processes could essentially further us in understanding its nature.

hep-ph↗
arXiv2006

Properties of the light scalar mesons face experimental data

The following topics are considered. 1) Confinement, chiral dynamics, and light scalar mesons. 2) Chiral shielding of the σ(600) 3)The ϕmeson radiative decays about nature of light scalar resonances. 4) The J/ψdecays about nature of light scalar resonances. 5) The a0(980)\toγγand f0(980)\toγγdecays about nature of light scalar resonances. 6) New round in γγ\toπ^+π^-, the Belle data. 7) The a0(980)-f0(980) mixing: theory and experiment. Arguments in favor of the four-quark model of the a0(980) and f0(980) mesons are given.

hep-ph↗
arXiv2006

Replay to hep-ph/0606266

The ϕ\toγππamplitude is found from the e+e-\toγππamplitude suggested in Ref. hep-ph/0606266. It is shown that the found amplitude differs essentially from that studied in Refs. hep-ph/0606266 and [3]. It is noticed that the suggestion of the author of Ref. hep-ph/0606266 about the phase of the ϕ\toγππamplitude is misleading.

hep-ph↗
arXiv2006

Light Scalar Mesons from Phi to Psi

The following topics are considered. 1) Confinement, chiral dynamics, and light scalar mesons. 2) Chiral shielding of the $σ(600)$. 3) The $ϕ$ meson radiative decays about nature of light scalar resonances. 4) The $J/ψ$ decays about nature of light scalar resonances. 5) The $a_0(980)\toγγ$ and $f_0(980)\toγγ$ decays about nature of light scalar resonances. 6) New round in $γγ\toπ^+π^-$, the Belle data. Arguments in favor of the four-quark model of the $a_0(980)$ and $f_0(980)$ mesons are given.

hep-ph↗
arXiv2006

Multipion decays of omega(782) and phi(1020)

Using the chiral model of pseudoscalar, vector, and axial vector mesons based on the hidden local symmetry added with the terms induced by the Wess-Zumino anomaly, the results of calculations of the branching fractions of the decays omega(782) and phi(1020) mesons to the 2pi+ 2pi- pi0, pi+ pi -3pi0 multipion states are presented.

hep-ph↗