NMR relaxation at low temperature in one dimensional antiferromagnets: Comparison between S = 12 and S = 52

The proton spin-lattice relaxation time T₁ has been measured at low temperatures in spin $\text{5}\text{2}$ (CH₃)₄NMnCl₃ (TMMC) and spin $\text{1}\text{2}$ CuCl₂2NC₅H₅ (CuPC). The two systems have very different temperature dependences which we attribute to the different spin values.     

Possible origin of S =12 ESR lines in alkali-TCNQ Salts

Solitons in spin Peierls systems are studied with emphasis on the contribution of solitions to the ESR spectra. It is pointed out that the ESR line ($\text{S =}\text{1}\text{2}$) observed in simple alkali-TCNQ salts can be due to solitons in spin Peierls state.     

Susceptibilities of the S = 12 XY model on the square lattice at T = 0

For the $\text{S =}\text{1}\text{2}\text{XY}$ model at T = 0 four susceptibilities have been calculated exactly on a sequence of finite square lattices and extrapolated to the infinite square lattice. For the ferromagnet χ_zz = 0 while χ_xx ～ N^2.9; for the antiferromagnet $\text{J}{}_{\mathrm{\chi xx}}\text{N(gμ}{}_{\mathrm{<mtext>B</mtext>}}\text{)}{}^2\text{= 0.025 ± 0.002}$ and $\text{J}{}_{\mathrm{\chi xx}}\text{N(gμ}{}_{\mathrm{<mtext>B</mtext>}}\text{)}{}^2\text{= 0.13 ± 0.03}$.     

Integral representation for the spin 12 Ising ferromagnet

A simpler derivation is given for a recently discovered integral representation for the spin $\text{1}\text{2}$ Ising ferromagnet.     

On the spectrum of singlet excitations of the S = 12 linear Heisenberg antiferromagnet

We note that available numerical data for the spectrum of small antiferromagnetic Heisenberg rings with nearest neighbour interaction, and $\text{S}\text{=}\text{1}\text{2}$ facilitate an extrapolation giving some idea of the form of the lower edge of the spectrum of singlet excitations for the infinite system. The result we obtain is radically different from the one given by Ovchinnikov in two respects: the singlet excitations are roughly equally distributed over the whole Brillouin zone, and the shape is better approximated by the formula valid for the triplet spectrum. A proof that there is a continuum of singlet excitations for every wave number is given.     

Quark-tadpole origin of the ΔI = 12 rule

In the context of a two-quark field picture of current quarks and renormalized constituent quarks, we show that an s-d current-quark tadpole generated by the weak Cabbibo-GIM current appears in the current-quark nonleptonic ΔY = 1 hamiltonian. Then we demonstrate that this $\text{ΔI =}\text{1}\text{2}$ operator in fact sets the observed scale of the K_s→ππ decays without recourse to any fitted parameters.     

Origin of 1ƒ noise

$\text{1}\text{?}$ noise dependence on temperature for both n- and p-type silicon has been measured. The formula for calculation of $\text{1}\text{?}$ noise is presented. The formula has been derived by presumption that only lattice scattering gives $\text{1}\text{?}$ noise. A good agreement between calculations and experimental results is found.     

The quark sea and the ΔI = 12 rule

The effect on nonleptonic processes of quark-antiquark pairs due to quantum chromodynamics is studied. Their presence improves agreement between theory and experiment for hyperon decays. In kaon decays a new $\text{ΔI =}\text{1}\text{2}$ contribution is found, but $\text{Δ =}\text{3}\text{2}$ effects are still large to to be in agreement.     

Comparison of pp and pp interactions at s = 53 GeV

Results are presented from the first p$\text{p}$ colliding beam runs at the CERN ISR, using the UA5 streamer chamber detector. p$\text{p}$ interactions at $\text{s}\text{= 53}\text{GeV}$ are compared with pp data taken in the same experiment. The results are in good agreement with extrapolations of low-energy p$\text{p}$ data.     

19F NMR in the S=12 antiferromagnets CuF2 and AgaF2

¹⁹F NMR has been observed in the antiferromagnetic phases of CuF₂ and AgF₂. These compounds, which are known to have very similar magnetic structures, have been shown to have similar magnetization curves and to have saturation sublattice magnetizations that scale approximately as their Neel temperatures.     

Phonon observations from 1ƒ noise measurements

From mobility fluctuation $\text{1}\text{?}$ noise parameter measurements five phononic energies corresponding to LO, TO vibrational modes as well as TA + S₂ or O, TO + TA, TO + O combined modes were identified. They stand for phonon replicas of non-radiative recombination processes. It is thus demonstrated that the carrier-phonon interaction is the source of $\text{1}\text{?}$ noise in semiconductors.     

Scattering of solitons with fermion number ±12

In a model of a Dirac field coupled to a sine-Gordon system, we have soliton solutions with half-integral fermion number. Scattering problems of such solitons are investigated. For soliton-soliton and soliton-antisoliton solutions, we find explicit solutions to the Dirac equations which are localized at the position of the (anti-)solitons. It is shown that the fermion number is generally transferred between the soliton and the (anti-)soliton in the scattering process.     

Spin-12 particles in the field of monopoles

The equations of motion of a $\text{spin}\text{-}\text{1}\text{2}$ particle in the field of a point-like (Abelian and non-Abelian) monopole are solved; helicity states and scattering solutions are constructed. The motion in an extended monopole and dyon source is discussed: charge-exchange scattering amplitudes are computed in the distorted-wave Born approximation. By the introduction of suitable spinors, the separation of variables is accomplished for any value of isospin. The non-existence of fermion zero modes in the field of an SU(2) monopole when $\text{T > 1, J >}\text{1}\text{2}$ is shown.     

The ΔI = 12 rule with heavy quarks and right-handed currents

The effect of strong interactions on a two-fermion operator is calculated in an asymptotically free theory, thereby completing the calculation of the logarithmic exponents for the operators contributing to non-leptonic amplitudes. The case of models with both left-and right-handed weak currents is discussed and the implications for the $\text{ΔI=}\text{1}\text{2}$ rule and other non-leptonic decays are deduced.     

Structures in pp → ππ

A Barrelet-zero analysis is presented of data on $\text{p}\text{p}\text{→ π π}$ in the momentum range 1 to 2 GeV/c. With π^?π⁺ data alone, the slope for ambiguity is very large, but the addition of π⁰π⁰ information enables the number of solutions to be reduced to just a few. Although the alternative solutions differ considerably, they significant common features, in particular, with plausible extra assumptions, all solutions appear to be dominated by resonances in all spin states from J = 1 to 5.     

Relativistic transport equation for spin 12 particles

For the model of positive energy Dirac particles with short range interaction a transport equation for the one- particle Wigner function is obtained. This transport equation is a generalization of the non-relativistic Walsmann- Snider equation for spin particles.     

The spin 12 gravitational anomalous magnetic moment

The gravitational anomalous magnetic moment of a spin $\text{1}\text{2}$ particle is calculated and compared with an earlier dimensional regularization result. The answers disagree although both agree the answer is finite. It is argued that this quantity is not uniquely determined by physical requirements. The methods used are shown to respect the gravitational and electromagnetic gauge invariances. In addition, a physical interpretation of the regularization method employed is offered.     

Excitation spectrum and T=0 dynamics of the one-dimensional planar spin-12 ferromagnet

The T=0 dynamics of the one-dimensional $\text{S}\text{=}\text{1}\text{2}$ ferromagnet with planar exchange anisotropy is studied by finite-chain calculations and a Green function approach. We demonstrate that the excitation spectrum relevant for appropriate low-T inelastic neutron scattering experiments is much more complex than predicted by linear spin-wave theory. It includes two continua and a set of discrete branches. Some of the low-lying excitations predicted by rigorous calculations, on the other hand, are shown to contribute no spectral weight to the T=0 dynamic structure factor S_zz(q,ω). We provide quantitative results for the spectral-weight distribution in S_zz(q,ω) at T=0 from bound states and continuum states, including a detailed analysis of the singularity in S_zz(q,ω) at the lower band edge. Further evidence is found for the prediction that some T=0 critical properties of the planar $\text{S}\text{=}\text{1}\text{2}$ ferro- and antiferromagnet are governed by exponents which depend continuously on the planar anisotropy.     

Weinberg-Salam model with two Higgs doublets and the ΔI = 12 rule

It is suggested that the modification in the Higgs sector of the Weinberg-Salam model which is required by CP violation, also provides an explanation for the $\text{ΔI =}\text{1}\text{2}$ enhancement in the non-leptonic decays of strange particles.