Second order phase transition in two dimensional sine-Gordon field theory—Lattice model

Two dimensional sine-Gordon (SG) field theory on a lattice is studied using the single-site basis variational method of Drell and others. The nature of the phase transition associated with the spontaneous symmetry breakdown in a SG field system is clarified to be of second order. A generalisation is offered for a SG-type field theory in two dimensions with a potential of the from [cos ⁿ (√λ/m)ϕ−1].     

Reaction e + e ? → π + π ? π + π ? at energies of √ s ≤ 1 GeV

The e ⁺ e ⁻ → π ⁺ π ⁻ π ⁺ π ⁻ cross section is calculated for energies of 0.65 ≤ √s ≤ 1 GeV in the framework of the generalized hidden local symmetry model. The calculations are compared with the data of CMD-2 and BaBaR. It is shown that the inclusion of heavy isovector resonances ρ(1450) and ρ(1700) is necessary for reconciling calculations with the data. It is found that, at √s ≈ 1 GeV, the contributions of the above resonances are much larger, by a factor of 30, than the ρ(770) one, and amount to a considerable fraction ∼0.3–0.6 of the latter at √s ∼ m _ρ. The text was submitted by the authors in English.     

Stretched Exponential Fixation in Stochastic Ising Models at Zero Temperature

We study a class of continuous time Markov processes, which describes ± 1 spin flip dynamics on the hypercubic latticeℤ ^d , d≥ 2, with initial spin configurations chosen according to the Bernoulli product measure with density p of spins + 1. During the evolution the spin at each site flips at rate c= 0, or 0 < α≤ 1, or 1, depending on whether, respectively, a majority of spins of nearest neighbors to this site exists and agrees with the value of the spin at the given site, or does not exist (there is a tie), or exists and disagrees with the value of the spin at the given site. These dynamics correspond to various stochastic Ising models at 0 temperature, for the Hamiltonian with uniform ferromagnetic interaction between nearest neighbors. In case α= 1, the dynamics is also a threshold voter model. We show that if p is sufficiently close to 1, then the system fixates in the sense that for almost every realization of the initial configuration and dynamical evolution, each site flips only finitely many times, reaching eventually the state + 1. Moreover, we show that in this case the probability q(t) that a given spin is in state − 1 at time t satisfies the bound: for arbitrary ɛ > 0, q(t) ≤ exp(−t ^{(1/ d ) −ɛ}), for large t. In d= 2 we obtain the complementary bound: for arbitrary ɛ > 0, q(t) ≥ exp(−t ^{(1/2) +ɛ}), for large t. Received: 12 July 2001 / Accepted: 1 February 2002     

ESR and ENDOR investigations of the degenerate electron exchange reactions of various viologens in solution. Solvent dynamical effects

The temperature dependences of the rates of the degenerate electron transfer of various viologens (1,1′-di(hydrocarbyl)-4,4′-bipyridinium salts) are measured in seven different solvents by means of electron spin resonance (ESR) line broadening. Rates vary between 1.7·10⁸ and 1.1·10⁹ M⁻¹s⁻¹ at room temperature and clearly show a solvent dynamical effect, which is inferred from the dependence of the rate constants on the longitudinal relaxation time of the solvent. Activation energies ranging from 5.3 to 24.4 kJ mol⁻¹ are found. For the first time, hyperfine coupling constants are reported for the radical cations of the hydroxyethyl viologen and the amino viologen based on both continuous-wave ESR and electron-nuclear double resonance spectroscopy. Furthermore, the temperature and the solvent dependence of the hyperfine coupling constants of the methyl viologen radical cation are reported.     

Experimental study of the reaction e + e − → K S K L in the energy range √S = 1.04−1.38 GeV

We present a measurement of the e ⁺ e ⁻ → K _S K _L cross section in the energy range √s = 1.04−1.38 GeV. For an energy of √s ≥ 1.2 GeV the cross section exceeds vector meson dominance model predictions with only ρ(770), ω(783), and ϕ(1020) mesons taken into account. The measured cross section agrees well with previous measurements. Published in Russian in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 130, No. 5, pp. 831–839. This article was translated by the authors.     

Nonsecular contribution to the decay of spin-echo signals of quadrupolar nuclei in magnetically ordered materials

We analyze the influence of fluctuations of the nonsecular part of the spin Hamiltonian on the decay of ordinary and multiquantum signals of the two-pulse spin echo in a quadrupole spin system with an inhomogeneously broadened spectral line. Expressions are obtained for the rate of decay of an echo in the case of selective excitation of a signal from quadrupole nuclei with arbitrary spin. These expressions are then used to analyze the experimentally observed ordinary and multiquantum echo signals from quadrupole nuclei with spin I=3/2 (⁵³Cr, ⁶³Cu, and ⁶⁵Cu) in ferromagnetic chromium chalcogenide spinels. Zh. éksp. Teor. Fiz. 116, 204–216 (July 1999)     

The influence of the skin effect on gamma detected pulsed NMRON signals

The influence of the skin effect on single and triple (spin echo) gamma detected pulsed NMRON signals is calculated using a density matrix approach within a pure Zeeman manifold. For single pulse NMRON the turn angle dependences of the signals for uniform and exponential profiles of the resonant nuclei are presented for a typical inhomogeneous broadening applicable to intermediate mass impurities in ferromagnetic hosts. For triple pulse NMRON the baseline and principal spin echo amplitudes for equal resonant rf pulses are presented for the same inhomogeneous broadening. It is found that the skin effect leads to the form of pulsed NMRON signals that are in accord with experiment.     

A tunable laser at λ=3.39 μm with line width of 7 Hz used in investigating a hyperfine structure of theF 2 (2) line of methane

A laser spectrometer is described which was used in exploring resonance shapes of about 1000 Hz width in methane in the region of low absorption of about 10⁻⁶ cm⁻¹. We report on first measurements of relative intensities of hyperfine components of theF ₂ ⁽²⁾ line in methane, on direct observations of line splitting due to a recoil effect and of a non-linear dependence of collisional broadening of resonances in the transit region, and on observation of an anomalous Zeeman effect in hyperfine components in a longitudinal magnetic field. The results of this work were summarized by one of the authors (V.C.) at the 2nd Symposium on Frequency Standards and Metrology (Boulder, Colo., USA, July 1976) and at lectures in the School Enrico Fermi (Varenna, Italy, July 1976).     

N.M.R. dipolar echoes in solids containing spin-1/2 pairs

The proton echo responses to resonant 90°-τ-β_90° (XY) and 90-τ-β_0° (XX) pulse sequences in powdered crystalline hydrates are reported. The echo produced by the XY sequence consists of two components: one is proportional to sin² β and the other to sin² β cos² β; the former component decays much faster than the latter on increasing the pulse spacing τ. In contrast, the XX sequence produces a single component echo of the form - sin² β cosβ. The maximum echo amplitudes for the sequences 90°-τ-90°_90° and 90°-τ-54°44′_0° exhibit a gaussian dependence on τ² over at least 95 per cent of their decays. The decay constant for the 90-τ-90°_90° echo corresponds to M ₂(inter) = 5/6 M ₂ ^vv(inter), where M ₂ ^vv(inter) is the interpair second moment calculated by the van Vleck procedure. These observations can be explained in terms of a simple model consisting of a planar arrangement of two spin-1/2 pairs provided the interpair dipolar hamiltonian is truncated so that [?^o _a(intra) + ?^{o, t} _d(inter), ?_z] = 0 and [?^o _a(intra), ?^{o, t} _d(inter)] = 0.

The model predicts the echo behaviour only if the spin-1 character of the eigenfunctions of ?^o _d(intra) + ?_z is preserved in the presence of the interpair interactions. It is shown that the XX echo and the sin² β cos² β components of the XY sequence originate solely in the interpair interactions and contain no contributions from the intrapair interactions. The decay of the maximum echo amplitude with increasing τ is caused by the incomplete refocusing of the interpair interactions by the XX and XY sequences; the correct decay is only determined provided the interpair dipolar hamiltonian is correctly truncated. The model also accounts for the proton echo behaviour in solid hydrogen reported by Metzger and Gaines.

Interestingly, the N.M.R. behaviour observed for these spin-1/2 pair systems is largely determined by the eigenfunctions of the spin Hamiltonian with M_z = 0.     

Multiquantum triple-pulse spin-echo signals from quadrupole nuclei in magnetically ordered substances

We analyze theoretically the formation of NMR pulse responses from a quadrupole spin system in which the inhomogeneous broadening of a spectral line is due to both magnetic and electric quadrupole interactions. We derive formulas for the moments of formation of multiquantum echo signals in the case of three exciting pulses. For the first time we detected in experiments multiquantum spin-echo signals from copper nuclei in ferromagnetic copper sulfochromite in the cases of double-pulse and triple-pulse excitations. We find that there is good agreement between the calculated and experimentally observed moments of echo signal formation. Zh. éksp. Teor. Fiz. 115, 2106–2112 (June 1999)     

Buffer-gas pressure broadening for the 2ν3 band of methane measured with continuous-wave cavity ring-down spectroscopy

Buffer-gas pressure broadening for the P(1), Q(1), R(0) and R(1) transitions in the 2ν ₃ band of CH₄ was investigated in the 1660 nm region. The pressure broadening coefficients, γ(gas), were determined for a variety of buffer gases: N₂, O₂, He, Ne, Ar, Kr and Xe. The γ values generally increased with increasing polarizability of the buffer gases. γ(air) are 0.056(2) for P(1), 0.056(1) for R(0), 0.061(1) for R(1) and 0.059(1) for Q(1) in units of cm⁻¹ atm⁻¹ where numbers in parentheses are one standard deviation in units of the last digits quoted. The temperature dependent parameter (broadening exponent) for air is 0.84(7) for P(1) within the temperature range 233–298 K.     

Beta-gamma-gamma directional correlation in103Rh

β-γ-γ directional correlation studies for the cascades (i)β-rays ofE _max=0.12 MeV,γ-rays of 557 keV andγ-rays of 53 keV and (ii)β-rays ofE _max=0.21 MeV,γ-rays of 444 keV andγ-rays of 53 keV have been made. The triple correlation functionsW(θ) were obtained to beW(θ)=1+(−0.153±0.031)P ₂(cosθ)+(0.004±0.035)P ₄(cosθ) forβ-rays ofE _max 0.12 MeV→557→53 keV cascade andW(θ)=1+(0.163±0.042)P ₂(cosθ)+(−0.035±0.058)P ₄(cosθ) forβ rays ofE _max=0.21 MeV→444 keV→53 keV cascade. Spins and parities of the 650, 537 and 93 keV levels of¹⁰³Rh are deduced by triple angular correlation and the internal conversion coefficient studies. Multipolarities of the transitions are also determined.     

Identification of a forbidden ammonia transition: Confirmation by pressure broadening measurements

Summary Pressure broadening measurements confirm the identification of the forbidden ammonia transitionss ⁻³(4, 3) at 887.780 cm⁻¹, Moreover, its pressure shift together with those of submillimeter transitions adds new confidence on the validity of the shift additivity.

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Riassunto Misure di allargamento per pressione confermano l'identificazione della riga proibita dell'ammoniacass ⁻³ P(4,3) a 887.780 cm⁻¹. Inoltre il suo spostamento per pressione insieme agli spostamenti di transizioni submillimetriche dimostra ancora una volta la validitá dell'additività negli spostamenti.

     

Gamma detected NMRON spin echo profiles for equal turn angle pulses-zero skin effect

The theoretical profiles for both principal (τ₂=τ₁) and harmonic (τ₂=1/2τ₁, 2τ₁) spin echoes in gamma detected triple pulse NMRON experiments are systematically calculated for a wide range of the parameter for inhomogeneous broadening using analytic expressions derived from physical ensemble rotation considerations, specific to a pure Zeeman Hamiltonian. In the absence of skin effects, and assuming equal turn angle pulses, these calculations provide the optimum turn angle conditions for maximum spin echo amplitude.     

Laser-based measurements of line strength, self- and pressure-broadening coefficients of the H35Cl R(3) absorption line in the first overtone region for pressures up to 1 MPa

A high-resolution spectrometer based on a vertical-cavity surface-emitting laser (VCSEL) was developed and used to determine the line strength S(T ₀)=12.53(11)×10⁻²¹ cm⁻¹/(molec cm⁻²) and the self-broadening coefficient g⁰_HCl=0.021787(61)\gamma^{0}_{\mathrm{HCl}}=0.021787(61)  cm⁻¹/atm of the R(3) absorption line in the first rovibrational overtone (2←0) band of H³⁵Cl. Furthermore, the first laser-based high-pressure study on the pressure broadening of HCl by He, N₂ and O₂(g⁰_N2=0.07292(5)\mathrm{O}_{2}(\gamma^{0}_{\mathrm{N}_{2}}=0.07292(5)  cm⁻¹/atm, g⁰_He=0.02113(1)\gamma^{0}_{\mathrm{He}}=0.02113(1)  cm⁻¹/atm, g⁰_O2=0.03978(6)\gamma^{0}_{\mathrm{O}_{2}}=0.03978(6)  cm⁻¹/atm) is presented covering pressures of up to 1 MPa. The results are compared to previously available low-pressure data.     

Particle flow calorimetry at the international linear collider

One of the most important requirements for a detector at the ILC is good jet energy resolution. It is widely believed that the particle flow approach to calorimetry is the key to achieving the goal of 0.3/√E(GeV). This paper describes the current performance of the PandoraPFA particle flow algorithm. For 45 GeV jets in the Tesla TDR detector concept, the ILC jet energy resolution goal is reached. At higher energies the jet energy resolution becomes worse and can be described by the empirical expression: σ _E /E ≈ 0.265/√E(GeV) + 1.2 × 10⁻⁴ E(GeV).      

A μSR Study of Er Spin Dynamics in (Y1−x Er x )Ni2B2C Superconductors

Zero field μSR has been used to probe rare earth spin dynamics in the magnetic superconductors, Y_1−x Er _x Ni₂B₂C. The muon spin relaxation function is stretched exponential, exp (−(λt)^β), in form, as usually found for spin glass systems above the glass temperature. However, the Y_1−x Er _x Ni₂B₂C compounds show no evidence of coexisting superconducting and static spin glass ground states even at concentrations below the critical value (x=0.6) for long range antiferromagnetic order. The temperature dependence of both the muon spin relaxation rate λ and the exponent β suggests that Er spin dynamics change significantly at the superconducting transition temperature. This revised version was published online in September 2006 with corrections to the Cover Date.     

Spin correlations and magnetonuclear cross-correlation in Sm(Sr)-Mn-O perovskites in the low-temperature phase

The results of measurements of spin correlations and magnetonuclear cross-correlations (MNCCs) in the system ¹⁵⁴Sm_1−x Sr_xMnO₃ with the perovskite structure (x=0.25,0.4) in the low-temperature phase in magnetic fields 0<H<1 kOe are presented. These are the first measurements performed by the small-angle polarized-neutron scattering method (SAPNS). It is shown that ferromagnetic correlations with a scale of 180–250 Å and MNCCs characterizing the intercoupling of the magnetic and lattice subsystems on this scale exist in the system. It is found that in the low-temperature phase the system exhibits spin-glass properties. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 323–328 (25 February 1999)     

Effect of lattice relaxation on spin density of nitrogen-vacancy centers in diamond and oscillator strength calculations

Using a generalized Hubbard Hamiltonian, many-electron wavefunctions of negatively charged (NV⁻) and neutral nitrogen-vacancy (NV⁰) centers in diamond were calculated. We report the effect of symmetric relaxation of surrounding atoms on the spin density, calculated from the many electron wavefunctions in the ground and excited states. We evaluated the error, that, arises in estimation of spin density when lattice relaxation effect is neglected in Electron Paramagnetic Resonance experiment and showed that the ground state spin density distribution is accessible in outward relaxations. The computed oscillator strengths give a higher efficiency for the 1.945 eV photoluminescence (PL) line of NV⁻ with respect to 2.156 eV PL line of NV⁰ which agrees well with experiment. This result is explained based on the largest the ground state spin among available values for the NV⁻ with respect to NV⁰. The transition probability between degenerate ground and excited states slightly depends on the S _z value. Finally, we report on the electronic configurations which contribute to the ground and excited states and discuss the population variation of electronic configurations with relaxation.