Alpha clustering in 4n nuclei from 4He to 40Ca

The α clustering in nuclei from ⁴He to ⁴⁰Ca has been presented on a systematic footing which depicts the similarities from nucleus to nucleus. Here, the isomorphic shell model has been employed, which is a hybrid between the conventional shell model and liquid drop model in conjunction with the nucleon finite size and which, in addition, uses no adjustable parameters. In the framework of the model an α-like particle is defined as four close-by nucleons (two neutrons and two protons) in relative angular momentum zero. Thus, up to ⁴⁰Ca nine such α-like particles and two deuterons are formed whose average positions are well specified in the model. Hence, each time an α-like particle is formed (following the aforementioned definition), this could have an average position only at one of the above nine available positions for such particles. Any 4n nucleus arranges its n α-like particles in the same way and any such arrangement corresponds to the ground state or to an excited state of this nucleus and serves as the band head of a rotational band. For ²⁰Ne nine such bands have been found, while for ¹²C and ²⁸Si two and five bands, respectively. The linear α-chain for ¹²C and persisting α-planar structures for heavier nuclei appear in a natural way in the framework of the model and are supported by many observables. The real novelty of this presentation is the fact that the axis of rotation and the number of rotating nucleons inside the same rotational band may change in such a way that the relevant moment of inertia increases monotonically in steps forming for each step a new branch of the band. Thus, several such bands have the same band head, a fact which closely resembles the phenomenon of superdeformation. This phenomenon here is the result of existence of several axes of symmetry and of several axes of rotation which, by changing the axis of rotation, permit the moment of inertia to increase up to the solid body limit.     

Quantal theory of Coulomb absorption in heavy-ion scattering

The component in the heavy-ion optical potential due to the Coulomb coupling to inelastic channels has been calculated using the on-energy-shell approximation for the intermediate-channel Green's functions. Closed expressions were derived for the Coulomb polarization potential representing coupling to all orders in the K = 0 rotational band. As a test of this general aproach for coupling to higher states, elastic-scattering calculations were performed with a truncated expression which included reorientation in the 2⁺ state and coupling to the 4⁺ state to all orders. Comparison with coupled-channels calculations indicate the increasing importance of off-shell effects with increasing coupling strength. An analytical estimate of offshell effects is presented. Limits on the range of validity of the optical-potential approach are determined.     

Strong coupling polaron theory and translational invariance

We develop a systematic, manifestly translation invariant, strong coupling theory for nonrelativistic Hamiltonians of the polaron type. As in earlier strong coupling theories, the position of the polarization well is a collective coordinate. The field is expanded in a set of basis functions centered about the well with three amplitudes deleted. A particle coordinate relative to the polarization center is introduced. The new coordinates are introduced using a point canonical transform leading to a Hermitian Hamiltonian, with properly normalized wavefunctions, and with a Jacobian that is evaluated in closed form. All subsequent approximations to the states are manifestly translation invariant. For the ground state the energy of the recoil terms to leading order depend on the coupling constant g as g^?4. The intrinsic part of the Hamiltonian determines the energy terms of order g⁴ and g⁰. An adiabatic canonical transformation is used to calculate all terms through order g^?4. The coefficients depend on the Green's function for the electron in a static potential well. We determine the first three terms in the inverse coupling constant expansion of the effective mass.     

A study of coupled-reaction channel effects in the36S +37Cl system,hybridization between single particle orbits

Elastic and inelastic scattering as well as transfer transitions involving a valence proton in thesd- andfp- shell orbits are studied in the interaction of³⁷Cl +³⁶S at E_CM=50 MeV. Experimental angular distributions of single particle states of³⁷Cl (elastic and inelastic transfer) are presented with a CRC analysis. In the CRC calculations the effects of inelastic and transfer couplings are studied using known spectroscopic information. In the CRC analysis six single particle bound states and the collective 2⁺ excitation of³⁶S are included in the coupling scheme. Higher order coupling effects are found to be important. A distinct effect, the mixing of single particle states (of different parity) due to direct and transfer interactions is observed to produce an enhancement of the transfer cross section to the low lying states. This feature is due to a change of the asymptotically defined single nucleon orbits via polarization in the field of the other nucleus, an effect which is analogous to hybridization, known from atomic physics.     

Electron-lattice interaction of Ag− and Cu− centers in alkali halides

Absorption, emission, and excitation spectra of Ag^? centers in KCl, RbCl, CsCl, and CsBr are measured at low temperatures. The positions of theA emission bands are slightly different afterC andA band excitation, respectively. This is believed to be due to the existence of two different types of minima in the adiabatic potential energy surface of the³ T _1u state. The symmetry of the energy minima in the¹ T _1u state is trigonal for KCl∶Ag^? and Cu^?, but tetragonal for CsBr∶Ag^?. This becomes evident from the polarization properties of the emission. The energy and temperature dependence of the polarization is discussed. Uniaxial stress causes polarized emission of Ag^? and Cu^? centers measured from LHeT to 100 K. This is due to a splitting and mixing of the relaxed excited states by the stress. The effects are used to calculate the coupling constants between thep electron and theE _g andT _2g lattice modes. They are compared with predictions from the point-charge model for different lattice structures. A new assignment of the absorption bands of KCl∶Cu^? to the excited states of Cu^? is established on measurements of emission spectra and lifetimes.     

Pairing factor and band structures in odd-A Pd nuclei

The band structures of the odd-A isotopes ¹⁰¹Pd, ¹⁰³Pd and ¹⁰⁵Pd are discussed in the framework of a core plus particle coupling model. The pairing factor (u_j² ? v_j²) contained in the effective coiupling strength is found to be responsible for the change of the $\text{5}\text{2}{}^{\mathrm{+}}\text{ΔJ = 2}$ band structure observed in ¹⁰¹Pd into a $\text{5}\text{2}{}^{\mathrm{+}}\text{ΔJ = 1}$ structure observed in the ^103,105Pd nuclei.     

The problem of the relation between double pomeron exchange in inclusive and exclusive experiments

The pionization region of the inclusive single-particle spectrum is accounted for by double pomeron exchange in the absorptive part of a six-point amplitude. In this paper a multiperipheral model for the six-point amplitude with double pomeron exchange is used for continuation by crossing and analyticity to the physical region of the exclusive two particle → four particle production process. The cross section for π^? p → π^?(π⁺π^?)p in the double-Regge region is then calculated and compared with the experimental analysis of Lipes, Zweig and Robertson which sets an upper bound to the strength of the double pomeron exchange coupling. This upper bound, coupled with the model for continuation to the inclusive cross section, is shown to give too small a magnitude for the double pomeron exchange in the pionization region. Further avenues for investigation are discussed.     

Cubic to tetragonal phase transition effects on the electronic structures of pure and iron doped barium titanate

Molecular orbital calculations relevant to TiO₆^8- and FeO₆^9- clusters are carried out in the O_h and C_4v symmetries in order to represent the electronic structures of pure and iron doped BaTiO₃ crystals in the cubic and tetragonal phases. The spontaneous polarization P_s is computed from the ground-state electronic distributions. The band gap anisotropy and the band edge polarization potentials are calculated and compared to experiment.     

Dielectric properties of glycine phosphite crystals in the model of a phase transition with inclusion of high-order invariants

Dielectric anomalies in the vicinity of the ferroelectric phase transition in nominally pure glycine phosphite (GPI) crystals and glycine phosphite crystals containing 2 mol % glycine phosphate (GP) are studied. It is revealed that the impurity-induced internal macroscopic polarization observed for GPI-GP crystals brings about smearing of the dielectric anomalies in directions both parallel and perpendicular to the axis of spontaneous polarization. The ferroelectric phase of the GPI and GPI-GP crystals is characterized by an unusual variation in the inverse permittivity in the Z direction perpendicular to the Y axis of spontaneous polarization. The temperature dependence of the inverse permittivity is described by a power expression (T _c ? T) ⁿ with an exponent n larger than unity. The experimental data are analyzed in terms of the proposed thermodynamic model with two order parameters, namely, the displacement parameter η and the order-disorder parameter P, which have different physical natures but the same symmetry and allow for coupling invariants of the ηP and η³ P types, as well as for the built-in polarization in the case of GPI-GP crystals. The experimental and theoretical dependences are in good agreement. The coefficients of bilinear and nonlinear coupling between the order parameters are determined. It is shown that the phase transition in the crystals occurs in the vicinity of the tricritical point and that the unusual behavior of the permittivity with a variation in the temperature is explained by the contribution from high-order invariants of coupling.     

Nucleon polarization and the nuclear charge operator

Effects of nucleon polarization on the nuclear charge operator have been evaluated in a constituent quark model. At momentum transfer q ≈ 4 fm^?1 monopole, dipole and quadrupole excitations are of equal importance. In a harmonic oscillator model for ³He all multipolarities give negative contributions, leading to an overall contribution comparable to the relativistic pair effect. The influence of realistic wave functions, coupling constants and off-shell form factors is discussed.     

TE/TM-mode pass polarizers and splitter based on an asymmetric twin waveguide and resonant coupling

A new passive TE/TM-mode polarization filter for an InP system based on an asymmetric twin waveguide and resonant coupling is investigated. Linear taper sections with different taper angles are introduced to couple between the two vertically separated waveguides. The underlying waveguide is designed to enable direct edge coupling from an optical fiber. At a wavelength of 1.55?μm power extinction ratios of 20 dB for the TE- and more than 10 dB for the TM-polarization are reported for devices shorter than 400?μm. An increased extinction ratio can be obtained by concatenating structures. Furthermore, we show this concept can be expanded to a polarization splitter.     

The coupling effect between ferroelectric and frustrated antiferromagnetic ordering in hexagonal ferroelectromagnet

Effects of the magnetoelectric coupling between the frustrated antiferromagnetic and ferroelectric ordering in hexagonal ferroelectromagnet are investigated by the soft-mode theory and molecular-field approximation. Applying the Heisenberg model for frustrated triangular antiferromagnets with exchange anisotropy and Diffour model for ferroelectric interaction, we discuss thermodynamic properties of the hexagonal ferroelectromagnetic system, including mean magnetization 〈s_i〉, polarization p, magnetization susceptibility χ_m, and polarization susceptibility χ_p, in a possible coupling form related to a combination of electric polarization and spin correlation. It is found that polarization induced by magnetic coupling leads to an anomaly in χ_p and a cusp in χ_m at low-temperature, which is consistent qualitatively with experimental results in hexagonal ferroelectromagnet YMnO₃.     

Faddeev-Born-Oppenheimer equations for molecular three-body systems: Adiabatic calculation of 9Be

The low-lying states of ⁹Be are calculated in the α-particle cluster model. The calculation is performed using a rotationally invariant molecular formulation of the three-body problem based on the Faddeev equations, which are solved for the α + n + α system in the adiabatic limit with the α-α interaction turned off. The resulting two-centre wave function is used to formulate an ansatz for the solution of the full hamiltonian of the system where all three particles interact. Unlike the traditional molecular approach, the ansatz we propose allows for the coupling between the movement of the light particle and the rotational motion of the heavy particles. This leads to a set of coupled ordinary differential equations for the three-body wave function that has good total angular momentum and parity. Although only one Born-Oppenheimer molecular energy curve is considered, all adiabatic corrections due to Coriolis coupling effects, mass polarization and derivatives of the two-centre wave function with respect to the separation distance between the α-particles are taken into account. Comparison with exact Faddeev results is presented for the ground-state energies of ⁹Be in a model problem where the α-α interaction is turned off. The validity of the molecular approach for small mass ratios between the heavy particle and the light particle is studied in a very general framework.     

Interrelationship between the polarization moments of different parity upon optical pumping of atoms under magnetic resonance conditions: II. Theory

The mutual coupling between the polarization moments with ranks of different parity is theoretically considered. The manifestation of this mutual coupling has been revealed previously in experiments on magnetic resonance of optically oriented cesium atoms. The two well-known types of the coupling between the polarization moments are considered: the field coupling of these moments that occur due to the breaking of the hyperfine coupling between the electronic and nuclear moments of the alkali atom by the magnetic field and the light coupling of the moments due to the absorption of the pumping light by polarized atoms. The experimentally observed similarity in the shape of resonance signals of alignment and orientation upon circularly polarized pumping can be explained by the fact that, for alkali atoms, the generation of alignment by light at the wavelength of the D ₁ line is of low efficiency. Therefore, alignment arises mainly from orientation by means of either the field or the light coupling of polarization moments. For metastable 2³ S ₁ ⁴He atoms, no influence of the orientation on the alignment was observed because, in these atoms, the field coupling between the polarization moments is absent and the light coupling is not displayed because the generation of alignment by the circularly polarized pumping light is more efficient than the creation of alignment from orientation by means of light coupling of polarization moments.     

Electromagnetic transition rates and vibrational modes in34S

States in³⁴S up to 6 MeV excitation energy, populated by the reaction³¹P(α, pγ), have been investigated by Doppler shift and line shape analysis andpγ andγγ angular correlation measurements. The strengths of electromagnetic transitions between even parity levels are compared with theoretical predictions of the weak coupling unified model and the many-particle shell model. The experimental evidence for a weak coupling of the single particle motion to vibrational modes is discussed.     

Influence of in-plane magnetic field on spin polarization in the presence of the oft-neglected k-Dresselhaus spin-orbit coupling

The influence of in-plane magnetic field on spin polarization in the presence of the oft-neglected k³-Dresselhaus spin-orbit coupling was investigated. The k³-Dresselhaus term can produce a limited spin polarization. The in-plane magnetic field plays a great role in the tunneling process. It can generate the perfect spin polarization of the electrons and the ideal transmission coefficient for spin up and down simultaneously. In energy scale, complete separation between spin up and down resonance was obtained by a relatively higher in-plane magnetic field while a comparatively lower in-plane magnetic field vanishes the spin separation. On the other hand, the spin relaxation can be suppressed by compensating the oft-neglected k³-Dresselhaus spin orbit coupling using a relatively lower in-plane magnetic field.     

Photonic dark matter portal and quantum physics

We study a model of dark matter in which the hidden sector interacts with standard model particles via a hidden photonic portal.We investigate the effects of this new interaction on the hydrogen atom,including the Stark,Zeeman and hyperfine effects.Using the accuracy of the measurement of energy,we obtain an upper bound for the coupling constant of the model as f≤10~(-12).We also calculate the contribution from the hidden photonic portal to the anomalous magnetic moment of the muon as α_μ≤ 2.2 × 10~(-23)(for the dark particle mass scale 100MeV),which provides an important probe of physics beyond the standard model.     

A novel “magnetic” field and its dual non-commutative phase space

In this Letter we have studied a new form of non-commutative (NC) phase space with an operatorial form of noncommutativity. A point particle in this space feels the effect of an interaction with an “internal  ” magnetic field, that is singular at a specific position θ⁻¹${\theta }^{\mathrm{-1}}$. By “internal” we mean that the effective magnetic fields depends essentially on the particle properties and modifies the symplectic structure. Here θ is the NC parameter and induces the coupling between the particle and the “internal” magnetic field. The magnetic moment of the particle is computed. Interaction with an external physical magnetic field reveals interesting features induced by the inherent fuzziness of the NC phase space: introduction of non-trivial structures into the charge and mass of the particle and possibility of the particle dynamics collapsing to a Hall type of motion. The dynamics is studied both from Lagrangian and symplectic (Hamiltonian) points of view. The canonical (Darboux) variables are also identified. We briefly comment, that the model presented here, can play interesting role in the context of (recently observed) real space Berry curvature in material systems.