Constraining the low-energy pion electromagnetic form factor with space-like and phase of time-like data

The Taylor coefficients c and d of the EM form factor of the pion are constrained using analyticity, knowledge of the phase of the form factor in the time-like region, 4m _π ²≤t≤t _in and its value at one space-like point, using as input the (g−2) of the muon. This is achieved using the technique of Lagrange multipliers, which gives a transparent expression for the corresponding bounds. We present a detailed study of the sensitivity of the bounds to the choice of time-like phase and errors present in the space-like data, taken from recent experiments. We find that our results constrain c stringently. We compare our results with those in the literature and find agreement with the chiral perturbation-theory results for c. We obtain when c is set to the chiral perturbation-theory values.     

Model independent bounds on the modulus of the pion form factor on the unitarity cut below the ωπ threshold

We study the structure of local baryon fields using the method of QCD sum rule. We only consider the single baryon fields and calculate their operator product expansions. We find that the octet baryon fields belonging to the chiral representations $[(\mathbf{3},\bar{\mathbf{3}}) \oplus(\bar{\mathbf{3}}, \mathbf{3})]$ and [(8,1)??(1,8)] and the decuplet baryon fields belonging to the chiral representations [(3,6)??(6,3)] lead to the baryon masses which are consistent with the experimental data of ground baryon masses. We also calculate their decay constants, check our normalizations for baryon fields in Chen et?al. (Phys. Rev.?D 81:054002, 2009) and find that they are well-defined.     

Measurement of the pion form factor for Mππ^2 between 0.1 and 0.85 GeV2 with the KLOE detector

The KLOE experiment at the φ-factory DAФPNE has measured the pion form factor in the range between 0.1 〈 Mππ^2 〈 0.85 GeV^2 using events taken at √s = 1 GeV with a photon emitted at large polar angles in the initial state. This measurement extends the Mππ^2 region covered by KLOE ISR measurements of the pion form factor down to the two pion production threshold. The value obtained in this measurement of the dipion contribution to the muon anomalous magnetic moment of △αμ^ππ= （478.5±2-0stat±4.8syst±2.9theo）·10^-10 further confirms the discrepancy between the Standard Model evaluation for αμ and the experimental value measured by the （g-2） collaboration at BNL.     

Measurement of the pion form factor for M_(ππ)～2 between 0.1 and 0.85 GeV~2 with the KLOE detector

The KLOE experiment at the φ-factory DAΦNE has measured the pion form factor in the range between 0.1M_(ππ)～2 0.85 GeV2 using events taken at s～(1/2)=1 GeV with a photon emitted at large polar angles in the initial state.This measurement extends the M_(ππ)～2 region covered by KLOE ISR measurements of the pion form factor down to the two pion production threshold.The value obtained in this measurement of the dipion contribution to the muon anomalous magnetic moment of aμππ =(478.5±2.0stat±4.8syst±2.9theo)·10-10 further confirms the discrepancy between the Standard Model evaluation for aμ and the experimental value measured by the(g-2) collaboration at BNL.     

Dependence of the form of a phase shifter’s phase–temporal characteristics on the parameters of ferrite spinels and the means of their fabrication

On the basis of experimental results, it is shown that the form of a phase shifter’s phase–temporal characteristics when working with waves of linear polarization in the 8 mm range can deviate substantially from linear and be unstable in the range of operating temperatures at the similar parameters of ferrites with critical saturation magnetic moments but certain differences in the manufacturing process.     

Experimental and theoretical investigations of the Knight shift of Pd and Ag in the alloy system Ag x Pd1−x

The Knight shift of Pd in Ag _x Pd_1–x has been determined for concentrationsx0.2. In full accordance with the expectations based on the behaviour of the magnetic susceptibility, it was found that the Knight shift of Pd is rapidly reduced in magnitude by adding Ag to Pd. To allow for a detailed interpretation of this finding, we have performed Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) band structure calculations for Ag _x Pd_1–x . These calculations clearly demonstrate that the decrease in spin susceptibility with increasingx is accompanied with a decrease in core polarization. In contrast to Pd, the negative Knight shift of Ag on the Pd-rich side of the system is caused by the valence band contribution, as it is demonstrated by our calculations. This is caused by an intersite effect in analogy to the transferred hyperfine field found for non-magnetic elements dissolved in a magnetic host.     

Critical behaviour in the commensurate-incommensurate phase transition of pure and γ-irradiated LiRbSO4 crystals

The effect of γ-irradiation on the incommensurate phase of LiRbSO₄ crystals has been studied by measuring the specific heat C_p . As a result of γ-irradiation, the values of C_p decreased and the transition temperature T_c shifted to lower values. The values of ΔH and ΔS decreased with increasing dose rate. The results are explained on the basis of an energy change due to induced lattice defects.     

Monte Carlo and cell model calculations for the solid—fluid phase behaviour of the triangle-well model

Monte Carlo simulations and cell model calculations are reported for the vapour-liquid and solid-liquid phase behaviour of the triangle-well model system. The behaviour is examined as a function of the range of the triangle-well attraction, from 1.05 to 2.5 times the diameter of the hard core of the potential. Cell model calculations indicate that the stable solid is almost always face-centred cubic (fcc), except for a small set of conditions where hexagonal close-packed (hcp) is favoured. This outcome differs markedly from a much earlier study performed for the square-well model potential, where a much richer phase diagram was observed, with significant regions of stability for hep and body-centred cubic (bcc) phases. Monte Carlo simulations indicate that the cell model calculations represent well the true phase behaviour for this model system. The differing behaviour between the triangle-well and square-well models indicates an important role for the flatness of the potential well in governing the stability of hcp and bcc phases relative to the fcc phase.     

Periodic and chaotic behaviour in a reduced form of the perturbed generalized Korteweg–de Vries and Kadomtsev–Petviashvili equations

The dynamical behaviour of a reduced form of the perturbed generalized Korteweg–de Vries and Kadomtsev–Petviashvili equations (extension of the Korteweg–de Vries equation to two space variables) are studied in this paper. Harmonic solutions of non-resonance and primary resonance are obtained using the perturbation method. Chaotic motion under harmonic excitations is studied using the Melnikov method.A wide range of solutions for the reduced perturbed generalized Korteweg–de Vries equations, in which non-linear phenomena appearing within transition from regular harmonic response (periodic solutions) to chaotic motion, are obtained using the time integration Runge–Kutta method. When chaos is found, it is detected by examining the phase plane, the Poincaré map, the sensitivity solution of the solution to initial conditions, and by calculating the largest Lyapunov exponent.     

Asymptotics of the cut discontinuity and large order behaviour from the instanton singularity: The case of lattice Schrödinger operators with exponential disorder

We discuss the relation between the singularity structure of the Borel transform, the asymptotics of the cut discontinuity and the large order behaviour of perturbation theory. In an explicit example — a tight binding model with exponential disorder — we show how to obtain the first instanton singularity from a cluster expansion in the Borel variable, and as an application we determine the exact decay of the density of states asE . The method opens some perspectives for similar problems arising from different models of Mathematical Physics.     

Determination of the neutron electric form factor in the D(e,e′n)p reaction and the influence of nuclear binding

The electric form factor of the neutron G _E,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q ²= 0.15 (GeV/c)² in a measurement of the recoil polarisation ratio P _x/P_z in the quasifree reaction D(e,e′n)p. At this Q ² the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively by a model of Arenh?vel et al.. After the corresponding corrections a value of G _E,n(0.15 (GeV/c)²) = 0.0481±0.0065_stat±0.0053_syst is obtained. Received: 12 April 1999     

Low-temperature phase behaviour of the binary system water–oxyethylated glycerol of polymerization degree n = 5 and intermolecular interactions in the system

In this paper, phase and glass transitions occurring in a binary system water–oxyethylated glycerol of polymerization degree n = 5 (OEG _{n =5}) are studied by differential scanning calorimetry (DSC) in the concentration range 0–100% (w/w) at temperatures lower than 273 K. The supplemented phase diagram of this system has been constructed for the first time. Concentration and temperature regions for the existence of a completely amorphous state and a heterogeneous crystalline/amorphous state have been determined. Processes of formation of crystalline and amorphous phases in the water–OEG _{n =5} system are studied by optical cryomicroscopy, both during cooling and subsequent heating. The cryomicroscopic data confirm the conclusions derived from the DSC data analysis. The number of strongly and weakly bound water molecules per OEG _{n =5} molecule has been calculated on the basis of the analysis of the supplemented phase diagram of the water–OEG _{n =5} system. The hydration number of an OEG _{n =5} molecule has been also determined by infrared spectroscopy.     

Study of the glassy magnetic behaviour and charge-ordering phase transitions in La0.75Ca0.25FeO3−δ perovskite

Abstract

In this work, La_0.75Ca_0.25FeO_3?δ perovskite sample was prepared by the coprecipitation method. The nanoparticle was found to crystallize in the orthorhombic (Pbnm) phase as confirmed by X-ray diffraction (XRD) and transmission electron microscopic (TEM). The oxygen non-stoichiometry (δ) and magnetic states of iron ions (three magnetic sextets and non-magnetic doublet) were investigated by Mössbauer spectroscopy at room temperature (RT). The shape of the magnetic hysteresis loop of the sample reveals the existence of a weak ferromagnetism at RT. The magnetization vs. temperature curves, measured in the 9 to 200 K range, showed that the sample exhibits two magnetic-phase transition temperatures at 29 K (T_g) and 120 K (T_CO). The magnetization isotherms, M (H), around these magnetic-phase transition temperatures for the sample are analyzed.