Neutrino dispersion properties in an external magnetic field

The neutrino self-energy operator Σ(p) in a magnetic field is calculated for the case of high-energy neutrinos, this corresponding to the crossed field approximation. The probability of the neutrino decay ν → e ^? W ⁺ is found by using the imaginary part of the operator Σ(p). A simple analytic result is obtained in the parameter region that is the most interesting from the physical point of view and which was not considered earlier. The contribution of an external magnetic field to the neutrino magnetic moment is calculated. The result obtained here for this contribution corrects formulas available previously.     

Effect of Three Nucleon Forces in p − 3He Scattering

The effect of the inclusion of different models of three nucleon (3N) forces in p ? ³He elastic scattering at low energies is studied. Two models have been considered: one derived from effective field theory at next-to-next-to-leading order and one derived from a more phenomenological point of view—the so-called Illinois model. The four nucleon scattering observables are calculated using the Kohn variational principle and the hyperspherical harmonic technique and the results are compared with available experimental data. We have found that with the inclusion of both 3N force models the agreement with the experimental data is improved, in particular for the proton vector analyzing power A _y .     

Search for macroscopic CP violating forces using a neutron EDM spectrometer

The search for CP violating forces between nucleons in the so-called axion window of force ranges λ between 2 × 10^?5 m and 0.02 m is interesting because only little experimental information is available there. Axionlike particles would induce a pseudo-magnetic field for neutrons close to bulk matter. A laboratory search investigates neutron spin precession close to a heavy mirror using ultracold neutrons in a magnetic resonance spectrometer. From the absence of a shift of the magnetic resonance we established new constraints on the coupling strength of axion-like particles in terms of the product g _s g _p of scalar and pseudo-scalar dimensionless constants, as a function of the force range λ, g _s g _p λ² ≤ 2 × 10^?21 [cm²] (C.L.95%) for 10^?4 cm < λ < 1 cm. For 0.1 cm < λ < 1 cm previous limits are improved by 4 to 5 orders of magnitude.     

Relativistic Hartree-Bogoliubov description of the lithium isotopes

Here we report the development of the relativistic Hartree-Bogoliubov theory in coordinate space. Pairing correlations are taken into account by both density dependent force of zero range and finite range Gogny force. As a primary application the relativistic HB theory is used to describe the chain of Lithium isotopes reaching from ⁶Li to ¹¹Li. In contrast to earlier investigations within a relativistic mean field theory and a density dependent Hartree Fock theory, where the halo in ¹¹Li could only be reproduced by an artificial shift of the 1p _1/2 level close to the continuum limit, the halo is now reproduced in a self-consistent way without further modifications using the scattering of Cooper pairs to the 2s _1/2 level in the continuum. Excellent agreement with recent experimental data is observed.     

The harmonic force field of methanol

A 28-parameter harmonic force field for methanol is calculated from the matrix frequencies and frequency shifts of ten isotopic species of methanol determined by Barnes and Hallam; Mallinson and McKean; and Serrallach, Meyer, and Günthard. This present force field reproduces the observed harmonic frequencies and frequency shifts far better than either of the two most recent force fields. The presence of a 20 cm^?1 Fermi resonance shift on the lower A′ CH₃ stretching mode deduced in an earlier work is confirmed here.     

Formic acid anhydride: Matrix infrared spectra of five isotopic species,vibrational analysis,empirical and ab initio harmonic force field and thermodynamic functions

Argon matrix infrared spectra of formic acid anhydride (CHOOCHO, CDOOCHO, CDOOCDO, and CH¹⁸O¹⁸OCH¹⁸O) are presented. Assignments and normal coordinate analysis yield valence force constants (VFF I) reflecting a significant dependence on the conformation of the formyl groups. A similar dependence is borne out by force constants obtained from an ab initio SCF treatment. The quantum chemical force constants qualitatively confirm Badger's rule. It is shown that a second valence force field (VFF II) may be found which is in qualitative agreement with the quantum chemical force constants and also reproduces the observed frequencies just as well as VFF I. The stretching force constants appear to be enhanced for bonds which are trans to another bond.     

Classical Motion in Force Fields with Short Range Correlations

We study the long time motion of fast particles moving through time-dependent random force fields with correlations that decay rapidly in space, but not necessarily in time. The time dependence of the averaged kinetic energy 〈p ²(t)〉/2 and mean-squared displacement 〈q ²(t)〉 is shown to exhibit a large degree of universality; it depends only on whether the force is, or is not, a gradient vector field. When it is, 〈p ²(t)〉～t ^2/5 independently of the details of the potential and of the space dimension. The stochastically accelerated particle motion is then superballistic in one dimension, with 〈q ²(t)〉～t ^12/5, and ballistic in higher dimensions, with 〈q ²(t)〉～t ². These predictions are supported by numerical results in one and two dimensions. For force fields not obtained from a potential field, the power laws are different: 〈p ²(t)〉～t ^2/3 and 〈q ²(t)〉～t ^8/3 in all dimensions d≥1.     

A model of charge injection at metal-insulator contacts

A phenomenological model of charge carrier injection at metal-insulator contacts is proposed to quantify the injection property of such contacts, especially of non-Ohmic ones. The model contains two parameters: one is the injection current G at a given field, and the other is the field-dependence power p of the injection. It is shown that the values of G and p for a given contact can be determined from the results of step-voltage experiments. When applied to the data on Au-As₂Se₃ contact, it is found that the injection current is G≈10^?6 A cm^?2 at a field of 10⁵ V cm^?1, and the field dependence is approximately quadratic, p≈2. In addition, the field-dependence and the thickness-independence of the peak current can be explained.     

Magnetic-field oscillations of the critical current and the pinning force in PbTe/PbS semiconductor superlattices and YBa2Cu3O7–δ films

The magnetic-field dependences of the critical current I _c and the pinning force F _p in single-crystal semiconductor PbTe/PbS superlattices on KCl and YBa₂Cu₃O_7–δ films in magnetic fields oriented perpendicular to the plane of the samples or parallel to the current were investigated. Oscillations of I _c and F _p were observed for superlattices with a parallel orientation of the magnetic field and with two directions of the field for the YBa₂Cu₃O_7–δ film. A model was proposed for the vortex structures which correspond to extrema of the pinning force in superlattices. It was shown that the single points (extrema and points of inflection) of the field dependences of F _p for superlattices and a YBa₂Cu₃O_7–δ film appear for critical values of the magnetic field equal to H _cr = (p/q)H ₀, where p and q are integers, H ₀ = 838.37 Oe, and H ₀ = ch/π eR ₀ ² is determined by the length R ₀ = 88.607 nm, somewhat less than the reciprocal of the Rydberg constant R _∞ = me ⁴/π?³ c (R _∞ ^?1 = 91.127 nm). It was inferred on the basis of published data that the temperature and magnetic-field dependences of the properties of superlattices and HTSC materials follow general laws.     

The computed force constants and vibrational spectra of cubane

The geometry, complete harmonic force field, and dipole moment derivatives of cubane, C₈H₈, have been calculated at the Hartree-Fock level using a 4–21 Gaussian basis set. The infrared and Raman spectra of cubane and four deuterated derivatives were calculated and compared with previously observed spectra. A set of five scale factors for the calculated force constants was then derived by least-squares fitting of the fundamental vibrational frequencies calculated from the scaled force field to the frequencies obtained by direct experimental measurement. The resulting scaled quantum-mechanical (SQM) force field, containing 73 unique elements, is believed to give an accurate representation of the harmonic vibrational potential of cubane. In most cases, the spectral assignments previously made from purely empirical considerations were confirmed, but a few corrections are proposed. The only major alteration is for an A_2u mode revised to appear at 1030 cm^?1 in the undeuterated molecule. Coriolis constants and approximate infrared intensities are also calculated.     

Neutron inelastic scattering spectrum and valence force field for neopentane

The neutron inelastic scattering spectrum of neopentane has been measured between 10 and 2000 cm^?1. A partial reassignment of the normal modes of vibration is presented. A vibrational analysis based on the Snyder and Schachtschneider valence force field has been carried out using the frequencies of neopentane and neopentane-d₁₂. The calculated neutron spectrum, using our new force field, is found to be in good agreement with the observed neutron data.     

Methanol and deuterated species: Infrared data,valence force field,rotamers, and conformation

New infrared measurements of gaseous and matrix-isolated methanol and 7 deuterated species are presented and analyzed. A revised assignment for the species CH₃OH(D) and CD₃OH(D) is used to determine 15 significant parameters of a valence force field by a converged simultaneous least-squares adjustment to 44 observed fundamentals. The respective frequencies calculated for the rotamers of CH₂DOH(D) and CHD₂OH(D) turn out to be a valid prediction as they are used to assign 78 observed fundamentals of the species with partially deuterated methyl groups. The values of the 15 force constant parameters are refined by including all 122 observed fundamentals. The force field contains significant deviations from local C_3v symmetry of the methyl group. Such an asymmetry, in the CH-stretching diagonal part, produces a difference of about 10 cm^?1 in the zero point energy of symmetric and asymmetric rotamers of the species with partially deuterated methyl groups. Calculations based on equilibrium structures with and without methyl tilt yield better agreement with observed data in the nontilted case. A preliminary calculation of relative intensities reproduces the major effects of isotopic substitution and rotational isomerism. Experimental evidence for the staggered conformation is obtained from a comparison of observed data with calculated results based on staggered and eclipsed models.     

Observation of magnetic field dependent ultrasonic relaxation time in p-InSb

Ultrasonic attenuation and sound velocity measurements are presented for p-InSb (≈ 10¹⁴cm^?3) at low temperatures in high magnetic fields. A magnetic field dependent relaxation time is observed, which is interpreted as being due to a relaxation process via holes in the valence band.     

Enhanced flux pinning in pulsed laser deposited Y Ba2Cu3O7−δ : BaTiO3 nanocomposite thin films

The effect of incorporation of BaTiO₃(BTO) nanoparticles on the flux pinning properties of pulsed laser deposited YBCO:BTO thin films was studied. Substantial increase in the critical current density (J_C) and the pinning force density (F_p) of the nanocomposite thin films was observed. At 77 K, and zero applied magnetic field, the value of J_C for YBCO and YBCO:BTO (2%) thin films were 2.93 MA/cm² and 6.43 MA/cm², respectively. At the same temperature and an applied magnetic field of 4 T, the value of J_C increases from 3.6×10⁴ A/cm² for YBCO thin film to 2.7×10⁵ A/cm² for YBCO:BTO (2%) nanocomposite thin film. The study of temperature and field dependence of of YBCO and YBCO:BTO thin films indicates similar type of pinning. The lattice mismatch between YBCO and BTO seems to introduce more defects resulting in the improvement of flux pinning properties.     

Determination of the critical current density and the flux pinning force in single crystals YBa2Cu3O7-δ from the magnetization hysteresis cycles

In this study, the magnetization measurements have been performed on high-temperature superconductor's single crystals YBa₂Cu₃O_7-δ at large ranges of temperature T (15-85 K) and in magnetic fields up to 6T at different values of the angle θ between the applied magnetic field and c-axis. The critical current density Jc deduced from the magnetic hysteresis loops by the Bean formula for H parallel to the c-axis (θ=0°), our results have shown that the critical current density Jc was strongly dependent on the applied magnetic field. The pinning force Fp=Jc×μ₀H was determined from magnetization for H//c, however, a plot of the normalized pinning force density fp= Fp/Fpmax as a function of the reduced magnetic field h= H/Hirr at different temperatures have shown good scaling with the form fp ~h^p(1-h)^q, where p and q are scaling parameters. We also found that the point pinning is more dominant than surface pinning under high temperatures.     

Phenomenological model for describing pion-pair production on a proton by virtual photons in the energy region of nucleon-resonance excitation

A phenomenological model is developed for describing the production of π ⁺ π ^? pairs on a proton by virtual photons in the energy region of nucleon-resonance excitation.The cross sections are calculated for the channels γp → π ^?Δ⁺⁺, γp → π ⁺Δ⁰, and γp → ρp, which make a dominant contribution to pion-pair production, and the results are compared with available experimental data.The contributions of nucleon resonances to the cross section for the reaction γp → π ^?Δ⁺⁺ are predicted within the developed approach.     

Features of the Zeeman splitting of levels of the 1snp configurations of helium

The Zeeman splitting of the fine-structure levels of the 1s2p and 1s4p configurations of neutral helium in a magnetic field is calculated. The strengths of fields of intersection of magnetic sublevels are determined, and the field regions are found in which a constant energy gap between some sublevels is observed. The results are compared with the experimental data available in the literature.     

Übertragung von Polarisation bei sensibilisierenden Stößen angeregter Natriumatome

The transfer of magnetic polarization from state 3p ² p _1/2 to state 3p ² p _3/2 sensitizing collisions of sodium atoms with noble gas atoms has been observed. Sodium atoms were excited by absorption ofD ₁σ⁺-quanta. When buffer gas was added to the sodium vapour, unequal amounts ofD ₂σ⁺ andD ₂σ^? quanta could be detected in the fluorescent light. The difference of the amounts turned out to be proportional to the polarization transferred. The measurement of this difference as a function of the buffer gas pressure provided a method of determining the cross-sections of the polarization transfer. Values of the cross-sections are 22, 24, 26, 20, 23 Ų for the buffer gases He, Ne, Ar, Kr, Xe, respectively. A preliminary investigation shows that the sign of the polarization transferred is reversed when the vapour is exposed to a strong magnetic field acting along the incident light beam.     

Transition from the antiferromagnetic to a nonmagnetic state in FeBO3 under high pressure

A ⁵⁷FeBO₃ single crystal is studied by the nuclear forward scattering (NFS) method. The NFS time spectra from ⁵⁷Fe nuclei are recorded at room temperature under high pressures up to 50 GPa in a diamond anvil cell. In the pressure interval 0<p<44 GPa, the magnetic field H ^Fe at the ⁵⁷Fe nuclei is found to increase nonlinearly, reaching a maximum value of 48.1 T at p=44 GPa. As the pressure increases further and reaches the point p=46 GPa, the field H ^Fe abruptly drops to zero, indicating that a transition from the antiferromagnetic to a non-magnetic state occurs in the crystal. In the pressure interval 0<p<46 GPa, the magnetic moments of the iron ions lie in the (111) basal plane of the crystal. Several possible mechanisms of magnetic collapse are discussed.     

Parity violation in neutron scattering on lead isotopes

On the basis of an analysis of experimental data, it is shown that a subthreshold (negative) p-wave resonance can exist in the ²⁰⁴Pb isotope at E _p =?16 eV. The presence of this resonance may explain unexpectedly large values observed experimentally for the P-odd angle of the rotation of the spin of transversely polarized neutrons about their momentum that are scattered on a natural mixture of lead isotopes. No available data are at odds with the existence of the E _p =?16 eV subthreshold resonance in ²⁰⁴Pb.