Effective Ru moment in RuSr2Eu2−xCexCu2O10 from high-temperature magnetic susceptibility

We have made high-temperature (250 K<T<800 K) DC susceptibility measurements in the compounds RuSr₂Eu_2−xCe_xCu₂O₁₀ for x=0.6,0.8, and 1.0 in order to determine the Ru effective magnetic moment. After carefully subtracting all contributions to the magnetic susceptibility except that of the Ru ions, we have been able to fit the Ru susceptibility with a law χ_Ru=χ₀+C_Ru/(T−Θ_Ru). We have found that the Ru effective moment falls between the values expected for Ru⁵⁺ in spin states and . We have also found a dependence of μ_eff(Ru) and Θ_Ru with the Ce content x.     

Rigorous pion-pion scattering lengths from threshold πN → ππN data

A new evaluation of the universal ππ scattering length relation is used to extract the ππ s-wave scattering lengths from threshold pion production data. Previous work has shown that the chiral perturbation series relating threshold pion production to ππ scattering lengths appears to converge well only for the isospin-2 case, giving a₂ = −0.031 ± 0.007m_π⁻¹. A model-independent and data-insensitive universal curve then implies a₀ = 0.235 ± 0.03m_π⁻¹ for the isospin-0 scattering length.     

Double inflation and the low CMB quadrupole

Recent released WMAP data show a low value of quadrupole in the CMB temperature fluctuations, which confirms the early observations by COBE. In this Letter we consider a model of two inflatons with different masses, , m₁>m₂ and study its effects on CMB of suppressing the primordial power spectrum P(k) at small k. Inflation is driven in this model firstly by the heavier inflaton φ₁, then the lighter field φ₂. But there is no interruption in between. We numerically calculate the scalar and tensor power spectra with mode by mode integrations, then fit the model to WMAP temperature correlations TT and the TE temperature-polarization spectra. Our results show that with m₁10¹⁴ GeV and m₂10¹³ GeV, this model solves the problems of flatness, etc. and the CMB quadrupole predicted can be much lower than the standard power-law ΛCDM model.     

Low-temperature phase and magnetic interactions in FCC Fe-Cr-Ni alloys

The low-temperature (5 K < T < 300 K) magnetic properties of a set of nine isostructural fcc Fe-Cr-Ni (Fe ≈ 68 at %, Cr ≈ 20 at%, Ni ≈ 9 at%) alloys were studied by SQUID magnetometry, neutron diffraction and ultrasonic techniques. Type-1 antiferromagnetic (AF) ordering was observed below the Néel temperature, T_N. The dc susceptibility, χ(T), did not exhibit a simple Curie-Weiss dependence. Above T_N, atemperature independent component χ₀ was observed, i.e., χ(T) = χ₀ + C / (itT + θ. T_N was systematically influenced by the lattice parameter, a, decreasing from (47.9 ± 0.5) K to (35.0 ± 0.5) K as a increased by only 0.25%. The average magnetic moment of ≈ 0.6μ_B obtained from neutron scattering was lower than the ≈ 1 μ_B obtained from the SQUID data. Mean field estimates of antiferromagnetic nearest-neighbors exchange interaction (J₁) and ferromagnetic second-nearest-neighbors interaction (J₂) indicate that |J₂/J₁|≈ 1.5. We believe that this is evidence of the RKKY interaction, and self-consistently argue that only the external d electrons are responsible for the localized average moment. This may mean that s-d hybridization of the external electrons is weak in these alloys.     

Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f0(980), a0(980) scalar mesons

We use a non-perturbative approach which combines coupled channel Lippmann-Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f₀ and a₀ resonances. The ππ → ππ, phase shifts and inelasticities in the T = 0 scalar channel are well reproduced as well as the π⁰η and mass distributions in the T = 1 channel. Furthermore, the total and partial strong decay widths of the f₀ and a₀ resonances are properly reproduced. The results seem to indicate that chiral symmetry constraints at low energy and unitarity in coupled channels is the basic information contained in the meson-meson interaction below GeV.     

Low-energy expansion of meson form factors

We calculate the corrections to various low-energy theorems concerning the behaviour of the pseudoscalar meson form factors near t=0. In particular we discuss (i) the Ademollo-Gatto theorem, (ii) Sirlin's relation between the K_l3 form factor ƒ₊^Kπ(t) and the electromagnetic form factors, (iii) the Callan-Treiman relation, and (iv) the Dashen-Weinstein relation, which connects the slope λ₀ of ƒ₀^Kπ(t) with the ratio F_K/F_π. Furthermore, we point out a remarkable isospin breaking effect which is clearly visible in the experimental rates of the decays K⁺→π⁰e⁺ν, K⁰→π⁻e⁺ν.     

Low-temperature AC conductivity of Bi2Sr2CaCu2O8+δ

We report measurements of anamolously large dissipative conductivities, σ₁, in Bi₂Sr₂CaCu₂O_8+δ at low temperatures. We have measured the complex conductivity of Bi₂Sr₂CaCu₂O_8+δ thin films at 100–600 GHz as a function of doping from the underdoped to the overdoped state. At low temperatures there exists a residual σ₁ which scales with the T=0 superfluid density as the doping is varied. This residual σ₁ is larger than the possible contribution to σ₁ from a thermal population of quasiparticles (QP) at the d-wave gap nodes.     

Normal skin effect in the polycrystals

The surface impedance γ and the penetration depth δ of the electromagnetic field was calculated for a polycrystalline conductor under the conditions of the normal skin effect. The polycrystal is composed from the single-phase slightly anisotropic single-crystalline grains of arbitrary symmetry. Corrections (γ-γ₀)/γ₀ and (δ-δ₀)/δ₀ due to the polycrystallinity are functions of the parameter ζ=δ₀/a, where γ₀ and δ₀ are the impedance and the penetration depth of the isotropic conductor with the conductivity σ₀=Sp σ_ik/3, σ_ik is the separate grain conductivity tensor, and a is the mean size of a grain.

The effective conductivity of a polycrystal can be obtained either from the impedance γ (σ_ef^(γ)) or from the penetration depth δ (σ_ef^(δ)) It was found that σ_ef^(γ)≠σ_ef^(δ) The corrections (σ-σ_ef^((γ))/σ₀ and (σ₀-σ_ef^(δ))/σ₀ depend on the frequency of the incident wave.

The obtained results are also applicable in the infrared spectrum region. It was shown that, just as for the isotropic conductor, there is the total reflection of the electromagnetic wave from the polycrystal surface.

It was necessary to examine the oblique incidence of an electromagnetic wave onto the surface of an isotropic metal for the substantiation of the set of the boundary conditions used.     

1-forms over the moduli space of irreducible connections defined by the spectrum of Dirac operators

Let (P) be the moduli space of irreducible connections of a G-principal bundle P over a closed Riemannian spin manifold M. Let D_A be the Dirac operator of M coupled to a connection A of P and f a smooth function on M. We consider a smooth variation A(u) of A with tangent vector ω and denote T_ω:= (D_A(u)−f) (u=0. The coefficients of the asymptotic expansion of trace (T_ω · e^-t(D_A−f)2) near t=0 define 1-forms a^(k)_f, K=0, 1, 2, … on (P). In this paper we calculate aa⁽⁰⁾_f, a⁽¹⁾_f, a⁽²⁾_f and study some of their properties. For instance using the 1-form a⁽²⁾_f for suitable functions f we obtain a foliation of codimension 5 of the space of G-instantons of S⁴.     

Observations of ω0/2 harmonic emission from 0.35μm laser-irradiated plasmas

Observations of ω₀/2 harmonic emission from both spherical and plane targets irradiated by 0.35 μm, 800 ps laser pulses have been obtained with simultaneous high spectral and temporal resolutions of 16 Å and 20 ps respectively. The ω₀/2 harmonic emission spectrum is interpreted as providing a direct measurement of the frequency of the ω₀/2 plasma waves and hence can be used to estimate the electron temperature.     

Noncritical vectorial phase matchings in nonlinear optics of crystals and infrared up-conversion

The exact analytic expressions for the vectorial group phase matching (PM) conditions have been obtained for sum and difference frequency generation processes ω₃ = ω₁ ± ω₂ (ω₃= ω₂ − ω₁) in nonlinear anisotropy crystals, which ensure a wide-band conversion of signals (ω₂) and images. The tangential PM conditions for all possible interaction types in the negative and positive uniaxial crystals have been studied. Scanning of the frequency of vectorial group PM has been studied by examples of LiNbO₃, LiIO, and HgGa₂S₄ crystals when changing the pump direction or pump frequency ω₁. The possibility of tuning the wide-band operation all over the transparency region of the LiIO₃, crystal has been shown. The double noncriticality conditions of PM in frequency cd; and acceptance angle have been studied and the possibility of their realization in a near and middle infrared region (IR) has been shown. A generalization of consideration to the other types of noncritical PMs (including multiples ones), has been made, including at an angle 90° between the propagation directions of waves with frequencies ω₁ (1) and ω₂ (2). The method of definition of the spectral bandwidths and acceptance angles of critical and noncritical PM taking into account the concordant change in the propagation angles of waves 1 and 2 has been proposed.     

Measurement of L X-ray production cross sections and Li subshell fluorescence yields

L_i (i=1, 2 and 3) X-ray production cross sections have been measured for 14 elements in the atomic number range 55≤Z≤81 at 15.73 keV. The values of L_i subshell fluorescence yields (ω₁, ω₂ and ω₃) have been determined using the presently measured X-ray production cross sections and the theoretical L_i subshell photoionization cross sections values, Coster–Kronig transition probabilities and radiative emission rates. The measured X-ray production (XRP) cross-sections and fluorescence yield values were compared with the theoretical and semi empirical values, respectively.     

Magnetic and microstructural investigations of melt-spun Fe(NdPr)B

The magnetic behavior of rapidly solidified FePrB was investigated in the composition range Fe_77+χPr₁₅B_8−χ (0 ≤ χ ≤ 4). Furthermore, the magnetic and microstructural properties of Fe(NdPr)B were analyzed in the range Fe₇₈(Nd_χPr_1−χ)₁₅B₇ (0 ≤ χ ≤ 1). The temperature dependence of the critical field was analyzed with a modified form of Brown's expression for the nucleation field. From this analysis the values for the microstructural parameters, _K and N_eff, were determined which describe the deteriorating effects of the non-ideal microstructure on the coercivity.     

Frequency and temperature dependence of a.c. conductivity of vitreous silver phosphate electrolytes

The a.c. conductivity behaviour in the 20–300 K temperature range has been investigated for (Ag₂S)_x(AgPO₃)_1−x and (Ag₂SO₄)_x(AgPO₃)_1−x glasses at various salt contents (x). The temperature dependence at selected frequencies in the radioand micro-wave region displays several relaxational contributions which are indistinct in the frequency domain. The low temperature experimental data are discussed and a proposed ‘new universality’ has been examined.     

Supersymmetric contributions to direct CP violation in K→ππγ decays

We analyze the supersymmetric contributions to direct–CP–violating observables in K→ππγ decays induced by gluino–mediated magnetic–penguin operators. We find that ε′_+−γ and the differential width asymmetry of K^±→π^±π⁰γ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where ε′/ε is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in |ΔS|=1 transitions, complementary to ε′/ε and rare decays.     

Stable heavy pentaquark states

If the Θ⁺(1540) is interpreted as a bound state of a quark and two (ud) diquarks in a relative P-wave, then it is very likely that there exist pentaquark states with a heavy antiquark, or , and two “light” diquarks in a relative S-wave which are stable against strong decays. We make a mass estimate for exotic states of this type and discuss their weak decays. Isospin relations are constructed which test their flavor quantum numbers.     

Measurement of electro-optic coefficients of low-symmetry crystal YbCa4O(Bo3)3

In this paper, we report on all the electro-optic coefficients of the low-symmetry crystal YbCa₄O(BO₃)₃ measured by the interferometric method. The new sample orientations, which have not been reported so far, have been used for measuring the skew electro-optic coefficients γ₅₁, γ₅₃, γ₄₂ and γ₆₂ independently. The results obtained are γ₁₁=0.6, γ₂₁=0.4, γ₃₁=0.3, γ₁₃=0.3, γ₂₃=0.2, γ₃₃=2.2, γ₅₁=0.9, γ₅₃=4.1, γ₄₂=0.8 and γ₆₂=0.4×10⁻¹² m/V.     

Electrical transport and superconductivity in the Al2O3-Bi2Sr1.8Ca1.2Cu2Oy and MgO-Bi2Sr1.8Ca1.2Cu2Oy composites

We have measured the resistivities of Al₂O₃-Bi₂Sr_1.8Ca_1.2Cu₂O_y and MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y composites with the nominal Bi₂Sr_1.8Ca_1.2Cu₂O_y volume fraction, ₂₂₁₂, ranging from 0.15 to 1.00. For the Al₂O₃-Bi₂Sr_1.8Ca_1.2Cu ₂O_y composites, we find for the samples with ₂₂₁₂≥0.6 that the superconducting transition temperature, T_c, is not disturbed by the addition of Al₂O₃. For ₂₂₁₂<0.3, no zero-resistivity state is observed. For the MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y composites, T_c is barely disturbed for the samples with ρ₂₂₁₂≥0.7. No superconducting state is observed for the samples with ρ₂₂₁₂<0.35. The variation of (300 K) with ρ₂₂₁₂ indicates a three-dimensional percolating Bi-Sr-Ca-Cu-O matrix occurring at ρ₂₂₁₂≈0.19 and ≈0.15 in Al₂O₃-Bi₂Sr_1.8Ca_1.2 Cu₂O_y and MgO-Bi₂Sr_1.8Ca_1.2Cu₂O_y, respectively. Both resistivity and magnetization measurements suggest that the reactions of Bi₂Sr_1.8Ca_1.2Cu₂O_y with MgO are weaker than with Al₂O₃.     

Measurement of electro-optic coefficients of low symmetry crystal GdCa4O(BO3)3

In this paper, we report all of the electro-optic coefficients of the low symmetry crystal GdCa₄O(BO₃)₃ measured by the interferometric method. The new sample orientations, which have not been reported so far, have been used for measuring the skew electro-optic coefficients γ₅₁, γ₅₃, γ₄₂ and γ₆₂ independently. The results obtained are γ₁₁=0.4, γ₂₁=0.5, γ₃₁=0.6, γ₁₃=0.1, γ₂₃=0.4, γ₃₃=2.0, γ₅₁=0.7, γ₅₃=1.5, γ₄₂=0.5, γ₆₂=0.8×10⁻¹²m/V.