Narrow Results

We study a mathematically rigorous derivation of a quantum mechanical Hamiltonian in a general framework. We derive such a Hamiltonian by taking a scaling limit for a generalization of the Nelson model, which is an abstract interaction model between particles and a Bose field with some internal degrees of freedom. Applying it to a model for the field of the nuclear force with isospins, we obtain a Schrödinger Hamiltonian with a matrix-valued potential, the one pion exchange potential, describing an effective interaction between nucleons.

The pentaquark state of has been observed to decay with two decay modes: Θ⁺→nK⁺ and Θ⁺→pK⁰. The decay probability ratio of the two decay modes is studied with general symmetry consideration of isospin, spin and parity. We arrive at a result of the ratio , which is valid for the Θ⁺ state to be a pure isoscalar or isovector state, or an isoscalar and isovector mixing state, or an isotensor state with mixture of isoscalar and isovector components with coefficients α and β. The dependence on spin and parity of the pentaquark Θ⁺ state is found to be small due to small difference between the center-of-mass decay momenta k₁ and k₂ of the two decay modes. We also provide an analysis on the constraint of the isospin of Θ⁺ from the absence of a peak in the pK⁺ invariant mass distribution in the γp→pK⁺K^- process. Future experimental results about the decay probability ratio may provide information about the properties of the pentaquark Θ⁺ state.

The static properties of protons are useful for understanding the quark structure of the proton. In his work we have introduced the hypercentral constituent quark model and isospin dependent potentials. Here constituent quarks interact with each other via a potential in which we have taken into account the three-body force effect and the standard two-body potential contributions. According to our model the static properties of protons containing u and d quarks are better than the other models and closer to experimental results. The two key ingredients of this improvement are the effective quark–gluon hypercentral potentials, and hyperfine interaction and isospin dependence potential. Recently, Schrödinger equation has been solved by Giannini but we have solved the Dirac equation exact analytically and we have shown that a considerable improvement in the description of the static properties of proton is obtained with an isospin dependent potential and the complete interaction including spin and isospin terms reproduces the position of the quark.

Under the assumption of good isospin symmetry, T_z = ±3/2 → ±1/2 Gamow-Teller (GT) transitions in a mass A isobar are analogous, where T_z is the z component of isospin T defined by 1/2(N - Z). We studied the T_z = +3/2 → +1/2 GT transitions by using the ³⁷Cl(³He,t)³⁷Ar and ⁴¹K(³He,t)⁴¹Ca reactions at E_beam = 140 MeV/nucleon. The GT transition strengths in ³⁷Ar and ⁴¹Ca were obtained up to the excitation energy (E_x) of 14.2 MeV and 10.4 MeV with energy resolutions of 30 and 35 keV, respectively. The obtained GT strengths were compared with those of the T_z = -2/3 → -1/2 mirror transitions, measured by the β-decay of ³⁷Ca and ⁴¹Ti, respectively. It was found that the overall distributions of the mirror transitions were similar in both A = 37 and A = 41 systems. In A = 37 the differences seen at lower excitation energies are suggested to be the effect of the tensor interaction in the charge-exchange reaction. The differences seen at higher excitation energies are suggested to be the effect of the Coulomb interaction that can break the mirror symmetry of the strength distributions.

Comparative studies of hadron-induced interactions and heavy ion collisions have been performed at beam energies of 158 GeV/nucleon, corresponding to . They indicate that the heavy ion reaction is a mixture of various processes, including multiple nucleon collisions, isospin effects, and final state Coulomb interactions. The latter interactions result in surprising phenomena, like the presence of large and strongly varying structures in the shape of double-differential particle spectra. These phenomena depend on the initial conditions of the reaction and therefore can provide new information on the space and time evolution of the non-perturbative meson production process.

We review the properties of the parametric coupling model and analyze its results when considering neutron star observations and heavy-ion collision experiments, specially those concerning the isospin characteristics of symmetric and asymmetric nuclear matter. By the end of the analysis, we are able to constrain the free parameters to a very small range of acceptable values.

Symmetry energy coefficients of explicitly isospin asymmetric nuclear matter at variable densities (from 0.5ρ₀ up to 2ρ₀) are studied as generalized screening functions. An extended stability condition for asymmetric nuclear matter is proposed. We find the possibility of obtaining stable asymmetric nuclear matter even in some cases for which the symmetric nuclear matter limit is unstable. Skyrme-type forces are extensively used in analytical expressions of the symmetry energy coefficients derived as generalized screening functions in the four channels of the particle hole interaction producing alternative behaviors at different ρ and b (respectively, the density and the asymmetry coefficient). The spin and spin-isospin coefficients, with corrections to the usual Landau Migdal parameters, indicate the possibility of occurring instabilities with common features depending on the nuclear density and n–p asymmetry. Possible relevance for high energy heavy ions collisions and astrophysical objects is discussed.

Recent work unambiguously resolves the level of charge symmetry violation in moments of parton distributions using (2 + 1)-flavor lattice QCD. We introduce the methods used for that analysis by applying them to determine the strong contribution to the proton–neutron mass difference. We also summarize related work which reveals that the fraction of baryon spin which is carried by the quarks is in fact structure-dependent rather than universal across the baryon octet.

Band structure and electromagnetic transition properties of the low-lying states in the ${}^{22}$Ne nucleus were studied within the framework of interacting boson model (IBM) 3. The isospin excitation states, low-lying symmetry states, the main components of the eigen-state, isoscalar and isovector parts in the $E2$ and $M1$ transitions for low-lying states have been investigated. According to this study, the calculated results are in agreement with experimental data, and the nucleus ${}^{22}$Ne is in transition from $U(5)$ to $O(6)$.

Mixed-symmetry and isospin excited states are typical of the interacting boson model with isospin (IBM-3). With a view to look for such states, levels scheme of the IBM-3 dynamical symmetry is discussed. A systematic investigation in the proton and neutron degrees of freedom of the energy levels has been carried out. A sequence of isospin excitation bands has been identified. We have analyzed the wave functions and given the symmetrical labeling of the states. The transition probabilities between the isospin excitation states of model limits are analyzed in terms of isoscalar and isovector decompositions. The present calculations suggest that a combination of isospin excitation and mixed-symmetry states can provide substantial information on the structure of nuclear states. Calculations for ${}_{44}^{88}\mathrm{\text{Ru}}$ and ${}_{46}^{92}\mathrm{\text{Pd}}$ nuclei are presented and compared with the results of the shell model and available experimental data.

The eigensolutions of the collective Hamiltonian with different potentials suggested for description of the isovector pair correlations are obtained, analyzed and compared with the experimental energies. It is shown that the isovector pair correlations in nuclei around ${}^{56}$Ni can be described as anharmonic pairing vibrations. The results obtained indicate the presence of the $\alpha$-particle type correlations in these nuclei and the existence of the interaction different from isovector pairing which also influences on the isospin dependence of the energies.

The collective Hamiltonian including isovector pairing and $\alpha$-particle-type correlation degrees of freedom is constructed. The Hamiltonian is applied to description of the relative energies of the ground states of even–even nuclei around ${}^{56}$Ni. A satisfactory description of the experimental data is obtained. A significant improvement of the agreement with the experimental data compared to our previous calculations is explained by inclusion in the Hamiltonian of the dynamical variables describing $\alpha$-particle-type correlations.

We consider a scaling limit of the Hamiltonian of the generalized spin-boson (GSB) model which is an abstract quantum field theoretical model of particles interacting with a Bose field. Applying it to a Hamiltonian of the field of the nuclear force with isospin, we obtain an effective potential of the interaction between nucleons. Also, we discuss an application to a Hamiltonian of a lattice spin system interacting with a Bose field and obtain a spin–spin interaction in the vacuum of the Bose field. An interaction model between a Fermi field and a Bose field yields an interaction in the vacuum of the Bose field.

We discuss experimental probes of isospin-violating dark matter (IVDM), including direct and indirect detection strategies. We point out the important role which IVDM plays in understanding recent data regarding low-mass dark matter, and describe strategies for finding evidence of IVDM at current and upcoming experiments.

We report an experimental determination of the isospin of ${\mathrm{\Lambda }}_c/{\mathrm{\Sigma }}_c{\left(2765\right)}^{+}$ using 980 fb⁻¹ data in the e⁺e⁻ annihilation around $\sqrt{s}=10.6\text{GeV}$ collected by the Belle detector located at the KEKB collider. The isospin partners are searched for in the ${\mathrm{\Sigma }}_c{\left(2455\right)}^{++/0}{\pi }^0$ channels, and no evidence was obtained. Thus the isospin is determined to be zero, and the particle is established to be a Λ_c.

In this paper we present a study of the nucleon-pair approximation with the isospin symmetry. In this model the building blocks are collective nucleon-pairs with given spin and isospin. We exemplify our work by using the ⁹⁶Cd nucleus.

Recent work unambiguously resolves the level of charge symmetry violation in moments of parton distributions using (2+1)-flavor lattice QCD. We introduce the methods used for that analysis by applying them to determine the strong contribution to the proton–neutron mass difference. We also summarize related work which reveals that the fraction of baryon spin which is carried by the quarks is in fact structure-dependent rather than universal across the baryon octet.