Internal geometry of hadron resonances

Motivated by previous work on high-energy quantum mechanics, a simple model is devised to study the internal geometry of hadron resonances. In this model we assume new basic canonical commutation relations between the (internal) coordinate and momentum operators of the hadronic quantum system. By systematically imposing Lie algebra commutation relations between these and other observables, we discuss the free and bound particle problems, identifying in each case the corresponding internal symmetries. For the bound particle problem, which models quark confinement, this symmetry turns out to be characterized by Dirac's two-oscillator representation of theO(3, 2) de Sitter group.     

Production of hadron resonances in heavy-ion collisions

The role of microscopic kinetics in the production of short-lived (broad) hadron resonances from subhadronic nuclear matter is considered. Anew approach to calculating the multiplicity of broad meson resonances is proposed. This approach takes explicitly into account the possibility that massive constituent quarks play a decisive role at the last stage of the expansion and cooling of matter produced in the central collisions of relativistic heavy nuclei. The resulting theoretical estimates are comparedwith available experimental data, and some quantitative and qualitative predictions are made.     

Three-body hadronic structure of low-lying 1/2+ Σ and Λ resonances⋆

We discuss the dynamical generation of some low-lying 1/2⁺ Σ 's and Λ 's in two-meson one-baryon systems. These systems have been constructed by adding a pion in the S -wave to the ˉN pair and its coupled channels, where the 1/2^- Λ(1405) -resonance gets dynamically generated. We solve Faddeev equations in the coupled-channel approach to calculate the T -matrix for these systems as a function of the total energy and the invariant mass of one of the meson-baryon pairs. This squared T -matrix shows peaks at the energies very close to the masses of the strangeness -1 , 1/2⁺ resonances listed in the particle data book.     

Magnetic properties of two-dimensional charged spin-1 Bose gases

Within the mean-field theory, we investigate the magnetic properties of a charged spin-1 Bose gas in two dimensions. In this system the diamagnetism competes with paramagnetism, where the Landé factor g   is introduced to describe the strength of the paramagnetic effect. The system presents a crossover from diamagnetism to paramagnetism with the increasing of the Landé factor. _gc$g_c$ denotes the critical value of the Landé factor. We get the same value of _gc$g_c$ both in the low temperature and strong magnetic field limit. Our results also show that in very weak magnetic field no condensation happens in the two-dimensional charged spin-1 Bose gas.     

Search for low-lying resonances in electron scattering by atomic hydrogen

Measurements of the transmission of an energy-selected electron beam through atomic hydrogen fail to indicate any resonance below 9·5-eV electron energy. The negative result contradicts recent suggestions by Rudkjøbing and by Van Rensbergenthat some diffuse interstellar absorption bands might be attributable to preionizing transitions in the hydrogen negative ion. A bulk of reliable theoretical data, however, justifies our finding.     

Effect of low-lying collective states on the structure of giant resonances

The influence of coupling of the usual particle-hole states to particle-hole states built on a collective state has been estimated. Numerical calculations are performed for Ni⁶⁰Zr⁹⁰ and²⁰⁸Pb.     

The paramagnetic properties of one-dimensional spin-1 single-ion anisotropic ferromagnet

One-dimensional single-ion anisotropic ferromagnet with spin-1 is investigated by means of Green's function treatment in this paper. The model Hamiltonian includes a Heisenberg ferromagnetic term, an external magnetic field, and a second-order single-ion anisotropy. The magnetic properties of the system are treated by the random phase approximation for the exchange interaction term and the Anderson-Callen approximation for the anisotropy term. Our paramagnetic results are in agreement with the other theoretical results.     

On biquadratic exchange interactions in spin-1 systems

It is showed rigorously that the spin-1 Ising-like Hamiltonian with biliniar and biquadratic exchange interactions and a Hamiltonian with uniaxial and biaxial quadrupolar pair interactions have exactly the same thermodynamic properties. Consequences of the theore, are discussed.     

In-medium modifications of hadron properties

The in-medium modifications of hadron properties are briefly discussed. We restrict the discussion to the lattice QCD calculations for the hadron masses, screening masses, decay constants and wave functions. We review the progress made so far and describe how to broaden its horizon.     

Influence of giant angular resonances on the electromagnetic characteristics of low-lying states

The two-rotor model0 with the Feshbach projection operator method is applied for investigating the properties of the positive parity low-lying collective states in the rare earth nuclei. The calculations of the energy spectra, E2-transition probability and magnetic properties of the states of β- and γ-bands are carried out for the isotopes ^{164, 166, 168}Er. The B(M1) values from 1⁺ states to the ground band are estimated.     

Magnetic properties of a mixed spin-1/2 and spin-3/2 transverse Ising model

A theoretical study of a mixed spin-1/2 and spin-3/2 Ising system with independent transverse fields is presented using an effective field method within the framework of a single-site cluster theory. In this approach the effective field equations are derived using a probability distribution method based on the use of generalized van der Waerden identities accounting exactly for the single-site kinematic relations. The effect of the transverse fields on the critical behaviour is studied. The thermal dependence of the longitudinal and transverse components of the magnetization and its higher moments is also studied.     

Electromagnetic transitions of low-lying nucleon resonances in point form relativistic quantum mechanics

Point form relativistic quantum mechanics is employed to calculate the electromagnetic transition amplitudes of low-lying nucleon resonances. The results obtained are compared with the non-relativistic approach and other model calculations. Differences among them are discussed.     

Tensor formulation of spin-1 and spin-2 fields

Spin projection operators which constitute a resolution of the identity in the space of second rank tensor wave functions are constructed. These projectors are then used to establish Lagrangian quantum field theories for free massive particles with spin-1 (two equivalent formulations) and spin-2.     

The magnetic properties of three-dimensional spin-1 easy-axis single-ion anisotropic antiferromagnets

The ordered and disordered phases of spin-1 Heisenberg and Ising antiferromagnets with easy-axis single-ion anisotropy on a three-dimensional lattice are studied. By using of the double-time Green’s function method within the Tyablikov decoupling for the exchange anisotropy and Callen’s approximation for the single-ion anisotropy, the Néel temperature, magnetization and susceptibility are investigated. Their relations with the temperature and anisotropic parameter are analyzed over the entire range of temperature. It is found that our results agree well with spin wave theory results at low temperature, agree with the high temperature series results at high temperature, and compare reasonably well with the linked-cluster series approach and ratio method results at intermediate temperature.     

Magnetic properties of charged spin-1 Bose gases with ferromagnetic coupling

The magnetic properties of a charged spin-1 Bose gas with ferromagnetic interactions are investigated within mean-field theory. It is shown that a competition between paramagnetism, diamagnetism and ferromagnetism exists in this system. It is shown that diamagnetism, being concerned with spontaneous magnetization, cannot exceed ferromagnetism in a very weak magnetic field. The critical value of reduced ferromagnetic coupling of the paramagnetic phase to ferromagnetic phase transition [Formula: see text] increases with increasing temperature. The Landé-factor g is introduced to describe the strength of the paramagnetic effect which comes from the spin degree of freedom. The magnetization density [Formula: see text] increases monotonically with g for fixed reduced ferromagnetic coupling [Formula: see text] as [Formula: see text]. In a weak magnetic field, ferromagnetism makes an immense contribution to the magnetization density. On the other hand, at a high magnetic field, the diamagnetism tends to saturate. Evidence for condensation can be seen in the magnetization density at a weak magnetic field.     

Thermodynamic properties of the mixed spin-1/2 and spin-1 Ising chain with both longitudinal and transverse single-ion anisotropies

The mixed spin-1/2 and spin-1 Ising chain with both longitudinal and transverse single-ion anisotropies is solved exactly by means of a mapping to the spin-1/2 Ising chains with alternating transverse fields and the Jordan-Wigner transformation. Within this scheme, the thermodynamic quantities of this model are rigorously determined by a recursion formula derived for the partition function based on the reduced spin-1/2 transverse Ising model. The corresponding thermodynamic properties are calculated and discussed.     

Exploring the entanglement of free spin-(1/2), spin-1 and spin-2 fields

In this study, we explore the entanglement of free spin-(1/2), spin-1, and spin-2 fields. We start with an example involving Majorana fields in 1+1 and 2+1 dimensions. Subsequently, we perform the Bogoliubov transformation and express the vacuum state with a particle pair state in the configuration space, which is used to calculate the entropy. This clearly demonstrates that the entanglement entropy originates from the particles across the boundary.Finally, we generalize this method to free spin-1 and spin-2 fields. These higher free massless spin fields have wellknown complications owing to gauge redundancy. We deal with the redundancy by gauge-fixing in the light-cone gauge. We show that this gauge provides a natural tensor product structure in the Hilbert space, while surrendering explicit Lorentz invariance. We also use the Bogoliubov transformation to calculate the entropy. The area law emerges naturally by this method.     

On the phase structure of spin-1 planar magnetic chains

The phase structure of a class of quantum spin-1 chains with axial symmetry is analyzed in the light of a pseudospin approach developed recently for the study of planar ferromagnets. The prominent feature of the resulting picture is that a transition to a Goldstone-like phase occurs at some critical coupling, in spite of the one-dimensional nature of the system which would prevent spontaneous breaking of the axial symmetry in the ordinary sense.