Critical Examination of the "Field-Theoretical Approach" to the Neutron-Antineutron Oscillations in Nuclei

We demonstrate that so called "infrared divergences" which have been discussed in some publications during several years, do not appear within the correct treatment of analytical properties of the transition amplitudes, in particular, of the second order pole structure of the amplitudes describing the $n - \bar n$ transition in nuclei. Explicit calculation with the help of the Feynman diagram technique shows that the neutron-antineutron oscillations are strongly suppressed in the deuteron, as well as in heavier nuclei, in comparison with the oscillations in vacuum. General advantages and some difficulties of the field theoretical methods applied in nuclear theory are reminded for the particular example of the parity violating $np\to d\gamma$ capture amplitude.Comment: 15 pages, 4 figures; prepared for Eur.Phys.J.

Resonance states below pion-nucleon threshold and their consequences for nuclear systems

Regular sequences of narrow peaks have been observed in the missing mass spectra in the reactions pp --> p pi^+ X and pd --> ppX_1 below pion-production threshold. They are interpreted in the literature as manifestations of supernarrow light dibaryons, or nucleon resonances, or light pions forming resonance states with the nucleon in its ground state. We discuss how existence of such exotic states would affect properties of nuclear systems. We show that the neutron star structure is drastically changed in all three cases. We find that in the presence of dibaryons or nucleon resonances the maximal possible mass of a neutron star would be smaller than the observational limit. Presence of light pions does not contradict the observed neutron star masses. Light pions allow for the existence of extended nuclear objects of arbitrary size, bound by strong and electromagnetic forces.Comment: preprint ECT*-02-18, 6 pages, 3 figure

Search for NN-decoupled dibaryons using the process pp→γγXpp \to \gamma \gamma X below the pion production threshold

The energy spectrum for high energy $\gamma$-rays ($E_\gamma \geq 10$ MeV) from the process $pp \to \gamma \gamma X$ emitted at $90^0$ in the laboratory frame has been measured at an energy below the pion production threshold, namely, at 216 MeV. The resulting photon energy spectrum extracted from $\gamma-\gamma$ coincidence events consists of a narrow peak at a photon energy of about 24 MeV and a relatively broad peak in the energy range of (50 - 70) MeV. The statistical significances for the narrow and broad peaks are 5.3$\sigma$ and 3.5$\sigma$, respectively. This behavior of the photon energy spectrum is interpreted as a signature of the exotic dibaryon resonance $d^\star_1$ with a mass of about 1956 MeV which is assumed to be formed in the radiative process $pp \to \gamma d^\star_1$ followed by its electromagnetic decay via the $d^\star_1 \to pp \gamma$ mode. The experimental spectrum is compared with those obtained by means of Monte Carlo simulations.Comment: 14 pages, LaTex, 6 eps-figures, accepted for publication in Phys.Rev.

The Role of Color Neutrality in Nuclear Physics--Modifications of Nucleonic Wave Functions

The influence of the nuclear medium upon the internal structure of a composite nucleon is examined. The interaction with the medium is assumed to depend on the relative distances between the quarks in the nucleon consistent with the notion of color neutrality, and to be proportional to the nucleon density. In the resulting description the nucleon in matter is a superposition of the ground state (free nucleon) and radial excitations. The effects of the nuclear medium on the electromagnetic and weak nucleon form factors, and the nucleon structure function are computed using a light-front constituent quark model. Further experimental consequences are examined by considering the electromagnetic nuclear response functions. The effects of color neutrality supply small but significant corrections to predictions of observables.Comment: 37 pages, postscript figures available on request to [email protected]

Finkelstein-Rubinstein constraints for the Skyrme model with pion masses

The Skyrme model is a classical field theory modelling the strong interaction between atomic nuclei. It has to be quantized in order to compare it to nuclear physics. When the Skyrme model is semi-classically quantized it is important to take the Finkelstein-Rubinstein constraints into account. Recently, a simple formula has been derived to calculate the these constraints for Skyrmions which are well-approximated by rational maps. However, if a pion mass term is included in the model, Skyrmions of sufficiently large baryon number are no longer well-approximated by the rational map ansatz. This paper addresses the question how to calculate Finkelstein-Rubinstein constraints for Skyrme configurations which are only known numerically

Flavoured Multiskyrmions,

Static properties of multiskyrmions with baryon numbers up to 8 are calculated starting from recently given rational map ansaetze. The spectra of baryonic systems with strangeness, charm and bottom are estimated within a "rigid oscillator" version of the bound state soliton model. It is suggested that the recently observed negatively charged nuclear fragment can be considered as quantized strange multiskyrmion with baryon number 6 or 7 and large value of strangeness. In agreement with previous observation, it is argued that baryonic systems with charm or bottom quantum numbers have more chances to be bound with respect to strong interactions than strange baryonic systems.Comment: 7 pages, no figures. Submitted to JETP Letter

Skyrmions from SU(3) Harmonic Maps and Their Quantization

Static properties of SU(3) multiskyrmions with baryon numbers up to 6 are estimated. The calculations are based on the recently suggested generalization of the SU(2) rational map ansätze applied to the SU(3) model. Both SU(2) embedded skyrmions and genuine SU(3) solutions are considered and it is shown that although, at the classical level, the energy of the embeddings is lower, the quantum corrections can alter these conclusions. This correction to the energy of the lowest state, depending on the Wess–Zumino term, is presented in the most general case

Approximate Analytical Solutions of the Baby Skyrme Model.

In present paper we show that many properties of the baby skyrmions, which have been determined numerically, can be understood in terms of an analytic approximation. In particular, we show that this approximation captures properties of the multiskyrmion solutions (derived numerically) such as their stability towards decay into various channels, and that it is more accurate for the "new baby Skyrme model" which describes anisotropic physical systems in terms of multiskyrmion fields with axial symmetry. Some universal characteristics of configurations of this kind are demonstrated, which do not depend on their topological number.Comment: 12 pages, no figures; submitted to JET