Inclusive ω photoproduction from nuclei and ω in the nuclear medium

With the aim of extracting information on the shift of the ω mass in the nuclear medium we analyze data obtained at ELSA from where claims for evidence of a mass shift of the ω have been made. We develop a Monte Carlo simulation code which takes into account the possible reactions in the experimental set-up of (γA → π⁰γX) in the vicinity of the ω production region with subsequent ω → π⁰γ decay. We compare our results with experiment for the distribution of π⁰γ invariant masses and conclude that the distribution is compatible with an enlarged ω width of about 90MeV at nuclear-matter density and no shift in the mass. This change in the width would be compatible with the preliminary results obtained from the transparency ratio in the A-dependence of ω production. The discrepancy of the present conclusions with former claims of an evidence for a shift of the ω mass stems from a different choice of background which is discussed in the paper.     

Dielectric parameterization of raman lineshapes for GaP with a plasma of charge carriers

We have studied the Raman lineshapes of several samples of GaP with appreciable carrier concentrations. There is no feature identifiable as a plasma resonance, but there are pronounced effects of interaction with the LO phonon resonance. For analysis we have developed a model along lines laid down by Barker and Loudon, employing Nyquist relations to calculate infrared fluctuations which scatter light. We introduce a response matrix α(ω) withseveral resonances; and we uncover some points which seem to be new, for coupled-mode scattering systems in general. In the GaP-plasma problem the data do not necessitate inclusion of the scattering amplitude from the plasma; we ascribe this to large plasma damping rates (ωτ≲1). This provides an account for the lack of any apparent plasma resonance in the scattering and for the modified appearance of the LO phonon, relative to the pure crystal. We emphasize that the following parameters suffice: Lorentz parameters measured in linear infrared experiments, the nonlinear parameterC from a visible-infrared mixing experiment, and the plasma frequency and damping fit to each sample. Beyond treatment of the plasma problem, the theory bears more generally on the conditions under which an LO Raman lineshape measures locally the shape of 〈E ²〉_ω. Also it bears upon the analysis of polariton linewidths to infer the variation of the phonon damping Γ(ω). This work was supported by the National Science Foundation Grant No. GH 32401. It is based on a major segment of the thesis of D.T. Hon, submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Physics) in the Faculty of the Graduate School of the University of Southern California.     

Logical stochastic resonance in bistable system under α-stable noise

An autonomous stochastic system with nonlinear time-delayed feedback is investigated employing the stochastic simulation method. In the autonomous stochastic system with quadratic time-delayed feedback or under positive feedback, the nonlinear delay time fails to possess the role improving the noisy state of the system. In the autonomous stochastic system with cubic time-delayed feedback and under negative feedback, the nonlinear delay time can improve the noisy state, tuning the signal output, and generating incoherence and coherence maximization. We reveal a new kind of anti-coherence and coherence resonance phenomena induced by the nonlinear time delay in the autonomous stochastic system without external periodic force, discussing further the effects of the noise strength, the control parameter, and the feedback strength on anti-coherence and coherence resonance.     

L<Superscript>1</Superscript> Stability of Spatially Periodic Solutions in Relativistic Gas Dynamics

This paper proves the well posedness of spatially periodic solutions of the relativistic isentropic gas dynamics equations. The pressure is given by a γ-law with initial data of large amplitude, provided γ − 1 is sufficiently small. As a byproduct of our techniques, we obtain the same results for the classical case. At the limit c → + ∞, the solutions of the relativistic system converge to the solutions of the classical one, the convergence rate being 1/c ². We also construct the semigroup of solutions of the Cauchy problem for initial data with bounded total variation, which can be large, as long as γ − 1 is small.     

Density perturbation of unparticle dark matter in the flat Universe

The unparticle has been suggested as a candidate of dark matter. We investigated the growth rate of the density perturbation for unparticle dark matter in the flat Universe. First, we consider the model in which the unparticle is the sole dark matter and find that the growth factor can be approximated well by f=(1+3ω _u )Ω _u ^γ , where ω _u is the equation of state of unparticle. Our results show that the presence of ω _u modifies the behavior of the growth factor f. For the second model where the unparticle co-exists with cold dark matter, the growth factor has a new approximation f=(1+3ω _u )Ω _u ^γ +α Ω _m and α is a function of ω _u . Thus the growth factor of the unparticle is quite different from that of the usual dark matter. This information can help us know more about unparticle and the early evolution of the Universe.     

Investigation of in-medium ω photoproduction

Recent experimental results on the in-medium modification of the ω meson are discussed. The experiment described was performed at the ELSA accelerator facility in Bonn using the combined detector system of Crystal Barrel and TAPS. Theω-meson was identified via the reaction γ+A → ω +X → π⁰ γ +X     

ω(→ π+π?π0) meson photoproduction on proton

The cross-section for the π ⁺ π ⁻ π ⁰ invariant mass distribution in the γp reaction in the GeV region is calculated. This reaction is assumed to proceed through the formation of the ω-meson in the intermediate state, because the production cross-section for this meson in the γp reaction in the GeV region is significant and it has a large branching ratio (88.8%) in the π ⁺ π ⁻ π ⁰ channel. The cross-sections for this reaction are calculated using the energy-dependent reaction amplitude, f _γp→ωp(0), extracted from the latest ω-meson photoproduction data. We use established procedure to calculate other factors, like width and propagator of the ω-meson, so that our calculation can provide reliable cross-section. The calculated results reproduce the measured π ⁺ π ⁻ π ⁰ invariant mass distribution spectra in the γp reaction.     

Periodic and Quasi-Periodic Orbits¶for the Standard Map

We consider both periodic and quasi-periodic solutions for the standard map, and we study the corresponding conjugating functions, i.e. the functions conjugating the motions to trivial rotations. We compare the invariant curves with rotation numbers ω satisfying the Bryuno condition and the sequences of periodic orbits with rotation numbers given by their convergents ω _N = p _N /q _N . We prove the following results for N→ ∞: (1) for rotation numbers ω _N N we study the radius of convergence of the conjugating functions and we find lower bounds on them, which tend to a limit which is a lower bound on the corresponding quantity for ω; (2) the periodic orbits consist of points which are more and more close to the invariant curve with rotation number ω; (3) such orbits lie on analytical curves which tend uniformly to the invariant curve. Received: 14 December 2001 / Accepted: 16 March 2002?Published online: 2 October 2002     

Thermal Conductivity of the Toda Lattice with Conservative Noise

We study the thermal conductivity of the one dimensional Toda lattice perturbed by a stochastic dynamics preserving energy and momentum. The strength of the stochastic noise is controlled by a parameter γ. We show that heat transport is anomalous, and that the thermal conductivity diverges with the length n of the chain according to κ(n)∼n ^α , with 0<α≤1/2. In particular, the ballistic heat conduction of the unperturbed Toda chain is destroyed. Besides, the exponent α of the divergence depends on γ.     

Existence and Modulation of Uniform Sliding States in Driven and Overdamped Particle Chains

In this paper we are mainly concerned with existence and modulation of uniform sliding states for particle chains with damping γ and external driving force F. If the on-site potential vanishes, then for each F > 0 there exist trivial uniform sliding states x _n (t) = n ω + ν t + α for which the particles are uniformly spaced with spacing ω > 0, the sliding velocity of each particle is ν = F/γ, and the phase α is arbitrary. If the particle chain with convex interaction potential is placed in a periodic on-site potential, we show under some conditions the existence of modulated uniform sliding states of the form

ρ(ω) → π0π0γ, ρ(ω) → ηπ0γ decays in the local quark Nambu-Jona-Lasinio model

The branching ratios and photon spectra of the rare processes ρ(ω) → π ⁰ π ⁰ γ, ρ(ω) → ηπ ⁰ γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered: the quark box and the pole diagrams with scalar (σ, α ₀(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π ⁰ π ⁰ γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ ⁰ γ. The text was submitted by the authors in English.     

A new optical method for measuring the electron-phonon interaction parameter λ〈Ω2〉 using the spectral dependence of the relaxation rate

The spectral dependence of the electron-phonon relaxation rate γ_e−ph(ℏω) in metals is studied in pump-supercontinuum-probe (PSCP) experiments with femtosecond time resolution. Investigation of this spectral dependence, which exhibits a substantial slowing of the relaxation rate γ_e−ph(ℏω) near the Fermi level E _F , using the parametrization γ_e−ph(ℏω)∝λ〈Ω²〉 (ℏω−E _F )² makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω²〉. The parameter λ〈Ω²〉 for YBa₂Cu₃O_7−δ is analyzed using this method. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 329–332 (10 September 1999)     

Long Time Stability of Some Small Amplitude Solutions in Nonlinear Schrödinger Equations

We consider small perturbations of the Zakharov–Shabat nonlinear Schr?dinger equation on [0,π] with vanishing or periodic boundary conditions; we prove a Nekhoroshev type result for solutions starting in the neighbourhood (in the H ¹ topology) of the majority of small amplitude finite dimensional invariant tori of the linearized system. More precisely we will prove that along the considered solutions all the actions of the linearized system are approximatively constant up to times growing exponentially with the inverse of a suitable small parameter. Received: 10 December 1996 / Accepted: 17 March 1997     

<Emphasis Type="Italic">Om</Emphasis> Diagnostic for Two-Parameter <Emphasis Type="Italic">ω</Emphasis><Subscript><Emphasis Type="Italic">σ</Emphasis></Subscript> in Dilaton Dark Energy

Om diagnostic is a good geometric method to differentiate one dark energy model from LCDM. We apply three different two-parameter equation of state ω _σ (EOS) to Dilaton Dark energy (DDE) model and investigate the Om diagnostic for these cases. We obtain that DDE model can be easily distinguished from LCDM no matter which case is considered. We also investigate the influence of coupled parameter α on the evolutive behavior of Om−z. According to the numerical result of Om, we get the current value of equation of state ω _σ0=−0.939 which fits the observational data well.     

Decay of transient nutation in two-level spin systems

This paper reports the results of an experimental study of the decay of transient NMR nutations in a two-level spin system with homogeneous line broadening. The NMR nutation signals in glycerin were studied for 10⩽ω ₁ T ₂⩽150, where ω ₁=γH ₁, with γ the gyromagnetic ratio and H ₁ the amplitude of the magnetic component of the radio-frequency field, and T ₂ is the transverse relaxation time. It is found that in a high-power field (ω ₁ T ₂≫1) the nutation decay rate is independent of ω ₁ and is quantitatively described by Bloch’s model. The data is compared with the data on non-Bloch (ω ₁-dependent) EPR-nutation decay in quartz (R. Boscaino, F. M. Gelardi, and J. P. Corb, Phys. Rev. B 48, 7077 (1993)). Zh. éksp. Teor. Fiz. 111, 1207–1213 (April 1997)     

具有时滞反馈的非对称双稳系统中的振动共振研究

研究了具有时滞反馈的非对称双稳系统中的振动共振现象. 在绝热近似条件下, 应用快慢变量分离法得到系统响应振幅的解析表达式Q, 分析了时滞参数α和不对称参数r对振动共振现象的影响. 结果表明: 在Q-α平台上, α可以诱导响应幅值的极大值以输入高频信号和低频信号的周期出现. 不对称参数并不影响共振发生的位置, 但是能够增强响应幅值. 在Q-B (B为高频信号振幅)平台上, 共振发生的位置B_VR随着α呈现两种不同的周期关系, 且周期分别为输入高频信号和低频信号的周期. 在Q-Ω (Ω高频信号频率)平台上, 随着时滞参数的增大, 当B较小时, 在Ω的小值区间内, Q呈现出多重共振现象, 在Ω的大值区间, Q趋于定值.     

Electric fields and currents in the planetary electric generator model. II. Sharp inhomogeneity of angular velocity of the plasma envelope

In the framework of the planetary-generator model, we study electric fields and, currents in a nonuniformly rotating plasma envelope with inhomogeneous conductivity surrounding a magnetized rotating planet. The angular velocity ω_p of the plasma envelope and the conductivity profile in its lower layers are taken in accordance with the experimental data, while the flow in the upper layers is modified in such a way that a sharp angular-velocity gradient (discontinuity) occurs at some altitude h₂: ω_p(h₂−0, Θ, = ω₀+γ₂sin²Θ, ω_p(h₂+γ₃sin²Θ =W ₆+γ₃sin₂Θ . If the parameters ω₀ and γ₂ are fixed, the profile of this discontinuity, is determined by W₆ and γ₃. It is shown that the parameter plane (γ₂, W₆) consists of certain regions, and the bifurcations of current structure, such as variations in the number of current loops or their configuration, occur upon crossing the boundaries of these regions. The topology of the current lines in the plasma envelope and inside the planet is strongly dependent on the parameters γ₃ and W₆. It was found that the unique point, corresponding to a system in which no current flows in the external region of the envelope, exists on the plane (γ₃, W₆). This point is located at the intersection of the boundaries seqarating the parameters-plane regions corresponding to the topology of the current system. Solution of the problem reveals that the plasma-envelope regions with strong inhomogeneity of the angular velocity play a considerable role in the generation of plasmasphere currents. The planetary-generator model allows one to reconstruct the topology of the current system of a planet only if data on its upper-plasmasphere flows are known at any polar angle. Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 7, pp. 595–606, July, 2000.     

Bimodal fission in binary and ternary spontaneous fission of 252Cf

The hot bimodal fission of ²⁵²Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the “hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode. The text was submitted by the authors in English.     

Study of in-medium <Emphasis Type="Italic">ω</Emphasis>-meson properties in <Emphasis Type="Italic">Ap</Emphasis> and <Emphasis Type="Italic">pA</Emphasis> collisions

The possibility to investigate the in-medium properties of the vector ω mesons at normal nuclear density is considered. The folding model and simulations with the RQMD generator have been used for studying of the ω-resonance production in Ap and pA reactions and its ω → π ⁰ γ → 3γ decay. We show that measurements in the inverse Ap kinematics is an effective way to get information about the ω-meson mass modification especially in not yet explored range of small meson momenta relative to the projectile nuclei where the strength of the effect is expected to be most strong. The traditional pA kinematics appears to be more preferable for the investigation of the in-medium ω-meson width. Using of compact electromagnetic calorimeter provides the possibility to collect large statistics and study the momentum dependencies of both the ω-meson mass and width at the density of normal nuclei.     

Breakdown of the linear current regime in periodic structures

We study the effect of a weak nonlinearity in media on the linear regime of current flow in two-dimensional periodic structures with two equal component concentrations. We find that the asymptotic behavior of the electric field and current as functions of the distance between the angles in heterogeneous media is determined by the parameter h=σ ₂/σ ₁ (here σ ₁ and σ ₂ are the linear conductivities of the cells) and the external magnetic field B. This dependence leads to divergence of the higher-order moments of field and current at certain critical values h _c and B _c and to divergence of the response functions related to the higher-order moments. For square cells the effective nonlinear conductivity diverges at h⩽h _c, with . For structures of general shape we find the dependence of h _c on the angles and the external magnetic field. We show that for a given structure the linear regime of current flow in the system can be reversibly transformed into a nonlinear one by varying the magnetic field strength. The critical field B _c is approximately determined from the condition ω _c τ∼1, where ω _c and τ ⁻¹ are, respectively, the cyclotron frequency and the collision rate. Finally, we discuss the feasibility of detecting these effects experimentally. Zh. éksp. Teor. Fiz. 112, 643–660 (August 1997)