Adjoint representation admixture to weak nonleptonic decays in SU(4) and SU(8)

In order to remove some of the unsatisfactory features of the GIM model, we consider15-admixture in SU(4). ΔC=±ΔS decays remain unaffected. Lee-Sugawara sum-rule is obtained.15-admixture is extended then to63-admixture in SU(8). The most general Hamiltonian (H _w∼63⊕720⊕1232) in SU(8) is found to give Lee-Sugawara relation and Σ₊ ⁺=0 forS-wave decays of uncharmed baryons. Decay amplitude relations for ΔC=−1, ΔS=0 mode are obtained.     

Some consequences of neutral current systematics

Two kinds of general consequences of the ΔS=0 weak hadron neutral current independent of a gauge model are presented. Firstly are results which depend on the quark parton model. These involve bounds among neutrino inclusive cross-section and a bound onQ(Z, N) in terms of these inclusive cross-sections. Secondly are results which are independent of the quark-parton model and depend only on the SU(3) structure of the most general ΔS=0 neutral current. These tests of isopin and speciallyU-spin properties of the current are given forv+N→v+hadron+anything,v+N→v+baryon+meson ande ⁺ e ⁻→baryon+anti-baryon. In addition some conjectures are made with regard to the semi-inclusive neutrino-reactions using the quark parton model.     

Fractal simulation of the resistivity and capacitance of arsenic selenide

The temperature dependences of the ac resistivity R and ac capacitance C of arsenic selenide were measured more than four decades ago [V. I. Kruglov and L. P. Strakhov, in Problems of Solid State Electronics, Vol. 2 (Leningrad Univ., Leningrad, 1968)]. According to these measurements, the frequency dependences are R ∝ ω^{−0.80±0.01} and ΔC ∝ ω^{−0.120±0.006} (ω is the circular frequency and ΔC is measured from the temperature-independent value C ₀). According to fractal-geometry methods, R ∝ ω^1−3/h and ΔC ∝ ω^−2+3/h , where h is the walk dimension of the electric current in arsenic selenide. Comparison of the experimental and theoretical results indicates that the walk dimensions calculated from the frequency dependences of resistivity and capacitance are h _R = 1.67 ± 0.02 and h _C = 1.60 ± 0.08, which are in agreement with each other within the measurement errors. The fractal dimension of the distribution of conducting sections is D = 1/h = 0.6. Since D < 1, the conducting sections are spatially separated and form a Cantor set.     

Ferroelectric phase transition in LaBSiO5 crystals from results of thermal and dielectric measurements

The specific heat of the ceramic and the permittivity of a single-crystal sample of LaBSiO₅, a new ferroelectric in the stilwellite family, were measured in a temperature range which includes the phase transition point (T _C=140 °C). The excess entropy of the phase transition ΔS=1.05 J/mol · K and the Curie-Weiss constant C _C-W=3.2×10³ K were determined. The results indicate that the phase transition in this crystal is of a “mixed” nature and exhibits features of a displacement-type transition and an order-disorder transition. Fiz. Tverd. Tela (St. Petersburg) 40, 1310–1312 (July 1998)     

Coexistence curve and rectilinear diameter in the critical liquid system carbon disulphide+nitromethane

The phase boundary of the binary liquid system CS₂+CH₃NO₂ is studied over nearly six decades in reduced temperature 3×10⁻⁶<ε=(T _C−T)/T _C<2×10⁻¹ and over the composition range 8-98 mole % of CS₂. The critical parameters areT _C=335.13₂K andx _C=57.3₄ mole % of CS₂. A single critical exponentβ=0.315±0.004 fits the observations over the entire range with no indication ofβ increasing to the classical value of 1/2 far away fromT _C. The diameter of the coexistence curve shows a rectilinear behaviour only far away fromT _C. NearT _C, the deviation ΔX from the rectilinear law seems to fit a curve of the form ΔX=fε^7/8 exp (−gε ^h), the derivative of which has a singularity like that of specific heat. An ambiguity in the analysis of the data in terms of mole fractions and volume fractions is pointed out. It is also suggested that the curvature of the diameter may be much weaker in a liquid-gas system and hence might have escaped detection.     

Large magnetocaloric effect and magnetoresistance behavior in Gd4Co3

We report a large entropy change (ΔS) below 300 K, peaking near T _C = 220 K, due to isothermal change of magnetic field, for Gd₄Co₃, with a refrigeration capacity higher than that for, say, LaFe_11.4Si_1.6, ordering magnetically in the same temperature range. A noteworthy finding is that the isothermal magnetization is nonhysteretic — an important criterion for magnetic refrigeration without loss. ΔS behavior is also compared with that of magnetoresistance.     

Gravity-induced weak symmetry breaking and supergravity

We give here a review of the recent developments of grand unified theories based onN=1 supergravity. We start with a brief introduction of supersymmetry and supergravity multiplets, and then discuss the construction of an invariant Lagrangian. The phenomena of gravity-induced weak symmetry breaking via the super Higgs effect at the tree level, corresponding to the conventional SU(5) gauge group, are then considered. We then extend this idea to the larger group SO(10), showing two possible breaking chains given as (i) SO(10)×susy→SU(2) _L ×U(1) _R ×U(1) _B-L ×SU(3) _C (≡ G₂₁₁₃)×susy→U(1)_em×SU(3) _C (G _LE ) predicting a secondZ-boson having mass lower than 1 TeV, and (ii) SO(10)×susy→SU(2) _L ×SU(2) _R ×SU(4)→(≡G₂₂₄)×susy→ SU(2) _L ×U(1) _Y ×SU(3) _C (≡ G₂₁₃)×susy→U(1)_em×SU(3) _C . We also consider the radiative breaking of weak symmetry via renormalisation group effects, which predicts the top quark mass. Some experimental signatures of the supersymmetric particles are investigated and possible future outlook is discussed. Invited talk presented at the International Symposium on Theoretical Physics, Bangalore, November 1984.     

Influence of quantum fluctuations on the Néel temperature of a dilute two-dimensional anisotropic antiferromagnet

A quantum Monte Carlo procedure is used to calculate the energy, sublattice magnetization, Néel temperature, and the slopes of the S=[1/T _N(x=0)]dT _N(x)/dx curves as functions of the hole concentration and the exchange anisotropy Δ=1−J _x,y/J _z in the Heisenberg model with anisotropic negative interactions between nearest neighbors in a square lattice with dilution among the lattice sites. The slope diverges in the limit Δ→0: S∼ln(6.5/Δ). Fiz. Tverd. Tela (St. Petersburg) 39, 898–900 (May 1997)     

Entanglement entropy fluctuations in quantum Ising chains

The behavior of Ising chains with the spin-spin interaction value λ in a transverse magnetic field of constant intensity (h = 1) is considered. For a chain of infinite length, exact analytical formulas are obtained for the second central moment (dispersion) of the entropy operator Ŝ = -lnρ with reduced density matrix ρ, which corresponds to a semi-infinite part of the model chain occurring in the ground state. In the vicinity of a critical point λ_c = 1, the entanglement entropy fluctuation ΔS (defined as the square root of dispersion) diverges as ΔS ∼ [ln(1/|1 − λ|)]^1/2. For the known behavior of the entanglement entropy S, this divergence results in that the relative fluctuation δS = ΔS/S vanishes at the critical point, that is, a state with almost nonfluctuating entanglement is attained.     

Investigation of the characteristic energy losses of platinum (111)

With the help of a combined LEED- and Auger-investigation, the surface of a platinum (111) crystal was cleaned first. Then, the spectrum of the characteristic energy losses for both contaminated and cleaned surfaces is studied. On the cleaned surface the following losses were found: ΔE ₁=7.4 eV, ΔE ₂=13.5 eV, ΔE ₃=24.8 eV, ΔE ₄=31.8 eV, ΔE ₅=45.1 eV, ΔE ₆=54.1 eV, ΔE ₇=71.2 eV. The present results are compared with the measurement of other investigators. In particular, in good agreement with optical measurements we identify ΔE ₁ and ΔE ₂ as interband transitions, and ΔE ₃ and ΔE ₄ as surface and volume plasma loss, respectively.     

Bound-state versus collective-coordinate approaches in chiral soliton models and the width of the Θpentaquark

We thoroughly compare the bound-state and rigid-rotator approaches to three-flavored chiral solitons. We establish that these two approaches yield identical results for the baryon spectrum and kaon-nucleon S-matrix in the limit that the number of colors (N_C) tends to infinity. After proper subtraction of the background phase shift the bound-state approach indeed exhibits a clear resonance behavior in the strangeness S = + 1 channel. We present a first dynamical calculation of the widths of the Θ⁺ and Θ^* pentaquarks for finite N_C in a chiral soliton model.     

Quasi-particle model for lattice QCD: quark–gluon plasma in?heavy ion collisions

We propose a quasi-particle model to describe the lattice QCD equation of state for pure SU(3) gauge theory in its deconfined state, for T≥1.5T _c. The method involves mapping the interaction part of the equation of state to an effective fugacity of otherwise non-interacting quasi-gluons. We find that this mapping is exact. Using the quasi-gluon distribution function, we determine the energy density and the modified dispersion relation for the single particle energy, in which the trace anomaly is manifest. As an application, we first determine the Debye mass, and then the important transport parameters, viz., the shear viscosity, η, and the shear viscosity to entropy density ratio, h/S\eta/{\mathcal{S}}. We find that both η and h/S\eta/{\mathcal{S}} are sensitive to the interactions, and that the interactions significantly lower both η and h/S\eta/\mathcal{S}.     

Relaxation intensity in some polyacrylates

Empirical formula suggested by Kita and Koizumi for evaluation of relaxation intensity in a limited range of frequency around the relaxation frequency for the Cole-Cole type distribution has been tested for poly butyl acrylate (PBA), Poly butyl methacrylate (PBMA) and poly isobutyl methacrylate (PiBMA). The relaxation intensity Δε is expressed in terms ofε″ _M , the dielectric loss maxima andW, the frequency separation for half, two thirds or three quarters ofε″ _M , in the form Δε=ε″ _M /[(C ₁/W)+C ₂+C ₃ W], where the numerical constantsC ₁,C ₂,C ₃ are given for the respective type of relaxation.     

Some consequences of global horizontal symmetry

It is pointed out that the present SU(3) _c ×SU(2) _L ×U(1) gauge interactions with three families have a global horizontal symmetry (denoted hereby SU(3) _H ) which is broken only by the weak charged hadron currentJ _h. Also, with (u, c), (d, s), (v _e, {ie437-1}) and (e ⁻,μ ⁻) as doublets of SU(2) _H (subgroup of SU(3) _H ),J _h has simple transformation properties under this subgroup. Amplitude relations, using SU(2) _H symmetry, for hadronic leptonic and semileptonic decays are given.     

Baryon asymmetry at the weak phase transition in the presence of arbitrary CP violation

The interactions of fermions with the domain-wall bubbles produced during a first-order phase transition are considered. An exact solution of the Dirac equation’s fermion propagation is obtained for a wall profile incorporating a position-dependent CP-violating phase. The reflection coefficients through the wall are computed for particles and antiparticles. The asymmetry in the reflection coefficients is especially high (a resonance effect) when the energy and mass of the incident particles are E/m=Δθ/2, where Δθ is the phase variation across the wall width. We compute the chiral-charge flux through the wall surface and the corresponding baryon asymmetry of the Universe. It agrees in sign and magnitude with the observed baryonic excess ϱB/s ≈ 10^-10 for a larnge of parameters and CP violation. As a function of Δθ, the ratio ϱb/s reaches a maximum for large values of Δθ (m ≈ m _top). The text was submitted by the author in English.     

Weak nonleptonic decays of 3/2+ isobars in SU(3)

Weak transitions of decuplet isobars are expanded in terms of eigen-amplitudes of the direct channel in the framework of SU(3). Starting with the most general weak Hamiltonian and assuming intermediate states to be non-exotic, we obtain ΔI=1/2 rule for Ω⁻ decays. Invoking of the CP invariance forbids all thepv weak processesD(10)→D(10) +P(8). Decays of the charmed multiplets are also discussed in these dynamical considerations. We obtain triplet dominance of charm changing weak Hamiltonian for Ω*⁺⁺ ₃ decays.     

Magnetism,exchange and crystal field parameters in the orbitally unquenched Ising antiferromagnet FePS3

FePS₃ is a layered antiferromagnet (T _N=123 K) with a marked Ising anisotropy in magnetic properties. The anisotropy arises from the combined effect of the trigonal distortion from octahedral symmetry and spin-orbit coupling on the orbitally degenerate⁵ T _2g ground state of the Fe²⁺ ion. The anisotropic paramagnetic susceptibilities are interpreted in terms of the zero field Hamiltonian, ℋ=Σ_i [δ(L _iz ² −2)+|λ|L _i .S _i ]−Σ _ij J _ij S _i .S _j . The crystal field trigonal distortion parameter Δ, the spin-orbit coupling λ and the isotropic Heisenberg exchange,J _ij, were evaluated from an analysis of the high temperature paramagnetic susceptibility data using the Correlated Effective Field (CEF) theory for many-body magnetism developed by Lines. Good agreement with experiment were obtained for Δ/k=215.5 K; λ/k=166.5 K;J _nn k=27.7 K; andJ _nnn k=−2.3 K. Using these values of the crystal field and exchange parameters the CEF predicts aT _N=122 K for FePS₃, which is remarkably close to the observed value of theT _N. The accuracy of the CEF approximation was also ascertained by comparing the calculated susceptibilities in the CEF with the experimental susceptibility for the isotropic Heisenberg layered antiferromagnet MnPS₃, for which the high temperature series expansion susceptibility is available.     

First observation of optical radiation from fullerenes in the gas phase

Optical radiation of C₆₀ fullerenes in the gas phase was observed. The observed emission line λ=258 nm is identified with an electronic transition into the ground state h _g →h _u in C ₆₀. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 683–687 (10 May 1996)     

Heat capacity and magnetocaloric properties of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> manganites

The magnetocaloric effect and the heat capacity of La_{1 − x} K _x MnO₃ (x = 0.1, 0.15, 0.175) ceramic samples have been studied at temperatures in the range 77–350 K and in magnetic fields of up to 27 kOe. The technique for preparing the samples has been described. The heat capacity anomalies related to the ferromagnetic-paramagnetic magnetic phase transition have been revealed and interpreted. It has been demonstrated that the change in the magnetic entropy ΔS calculated from the data on the heat capacity C _p and direct measurements of the magnetocaloric effect ΔT reaches values that are of practical interest.     

Magnetic properties of nanoparticle La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> under applied hydrostatic pressure

Pressure effects on magnetic properties of two La_0.7Ca_0.3MnO₃ nanoparticle samples with different mean particle sizes were investigated. Both the samples were prepared by the glycine-nitrate method: sample S—as-prepared (10 nm), and sample S₉₀₀—subsequently annealed at 900 °C for 2 h (50 nm). Magnetization measurements revealed remarkable differences in magnetic properties with the applied pressure up to 0.75 GPa: (i) for S sample, both transition temperatures, para-to-ferromagnetic T _C = 120 K and spin-glass-like transition T _f = 102 K, decrease with the pressure with the respective pressure coefficients dT _C/dP = −2.9 K/GPa and dT _f/dP = −4.4 K/GPa; (ii) for S₉₀₀ sample, para-to-ferromagnetic transition temperature T _C = 261 K increases with pressure with the pressure coefficient dT _C/dP = 14.8 K/GPa. At the same time, saturation magnetization M _S recorded at 10 K decreases/increases with pressure for S/S₉₀₀ sample, respectively. Explanation of these unusual pressure effects on the magnetism of sample S is proposed within the scenario of the combined contributions of two types of disorders present in the system: surface disorder introduced by the particle shell, and structural disorder of the particle core caused by the prominent Jahn–Teller distortion. Both disorders tend to vanish with the annealing of the system (i.e., with the nanoparticle growth), and so the behavior of the sample S₉₀₀ is similar to that previously observed for the bulk counterpart.