Nonlinear polarizabilities of atoms from their ground-state densities

Using density based perturbation theory [M.K. Harbola, A. Banerjee, Phys. Lett. A 222, 315 (1996)], we calculate the static hyperpolarizabilty for spherical atoms and ions from their ground-state densities. Since densities are being employed, calculations are performed using approximate functionals for the kinetic and the exchange-correlation energies. Use of densities - instead of the wavefunctions or Kohn-Sham orbitals - reduces the computational effort substantially. The results obtained are within of those calculated from the corresponding orbital-based calculations. Received: 23 June 1997 / Revised: 25 September 1997 / Accepted: 24 December 1997     

The three-boson bound state in massive QED2

We derive the (matrix-valued) Feynman rules of mass perturbation theory of the massive Schwinger model for non-zero vacuum angleϑ. Further, we discuss the properties of the three-boson bound state and compute — by a partial resummation of the mass perturbation series — its mass and its partial decay widths. This work was supported by a research stipendium of the Vienna University.     

Exciton-exciton collisions and conversion of interwell excitons in GaAs/AlGaAs superlattices

The ratio of the densities of intra-and interwell excitons in a symmetric system of coupled quantum wells — a superlattice based on a GaAs/AlGaAs heterostructure — is investigated over a wide range of optical excitation power densities. Conversion of interwell excitons into intrawell excitons as a result of exciton-exciton collisions is observed at high exciton densities. Direct evidence for such a conversion mechanism is the square-root dependence of the interwell exciton density on the optical excitation level. The decrease in the lifetime of interwell excitons with increasing excitation density, as measured directly by time-resolved spectroscopy methods, confirms the explanation proposed for the effect. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 623–628 (25 April 1997)     

Calculation of optical polarizability of atoms with two open shells in the Hartree-Fock approximation

Time-dependent Hartree-Fock equations (the Huzinaga method) in terms of density functionals have been obtained for a multielectronic system with two open shells of different symmetry species subjected to a time-dependent external perturbation. Based on these, the equations of time-dependent “bound” perturbation theory have been written in the orbital representation. The dynamic dipole polarizability of a number of atoms with two open shells with s¹pⁿ-configurations has been calculated using an optimized basis set of Slater-type atomic orbitals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 458–462, July–August, 2008.     

Parameters of the discharge plasmas of surface-plasma sources of negative hydrogen ions

The main parameters of the plasma of high-current hydrogen-cesium glow discharges of surface-plasma (planotron and Penning) sources of negative hydrogen ions are determined using contact-free spectroscopic methods and compared for identical discharge current densities. The elemental and charge composition of the plasma is established. The temperature of the hydrogen atoms and the energy of the visible-range radiation of the plasma discharge are measured and estimates of the electron density in the plasma are made. The dynamics of the change in the parameters of the discharge plasma of a Penning source — the densities of hydrogen atoms, cesium atoms and ions, and molybdenum atoms — is tracked during a discharge pulse with spatial resolution along two coordinates. It is observed that cesium atoms and ions and molybdenum atoms are pent up near the cathode surface. Zh. Tekh. Fiz. 68, 32–38 (October 1998)     

Relativistic correction to the dipole polarizability of a hydrogenic ion

The first relativistic correction of orderα ² to the dipole polarizability of a hydrogenic ion has been investigated by using mean excitation energy of the ion within the second-order perturbation theory. The density-dependent mean excitation energy is estimated via Bethe theory for the stopping cross section for a moving point charge interacting with the hydrogenic ion. In this approach only the unperturbed Dirac wavefunctions are required to evaluate the appropriate matrix elements. The first relativistic correction turns out to be − (13/12)(αZ)². This has the correct sign and is within 5% of the exact result which is −(28/27)(αZ)².     

The wideband attenuation of short radio waves on mid-latitude paths during X-ray flares in January 2005

We present the results of the ionosphere oblique chirp sounding on the Cyprus—Nizhny Novgorod, Cyprus—Rostov-on-Don, and Moscow—Rostov-on-Don mid-latitude paths during X-ray flares in January 17, 19, and 20, 2005. It is found that during strong flares the blackout of short radio waves was observed over the entire frequency range of chirp sounding on the Cyprus—Nizhny Novgorod and Cyprus—Rostov-on-Don paths. Modeling of the electron-density profiles in the lower ionosphere based on absorption of short radio waves on the Moscow—Rostov-on-Don path at different stages of the decay of the X-ray radiation intensity is carried out. It is shown that at the instant corresponding to the maximum value of the flare radiation flux, the electron density in the lower ionosphere at altitudes 60–80 km increased by a factor of about 10 and 100 for flares with radiation flux densities 5·10⁻² and 3·10⁻¹ erg/(cm ²·s) in the wavelength range 0.5–4.0 Å which took place in January 19 and 20, respectively. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 1–8, January 2007.     

Cosmological solution in the scalar—tensor theory of gravity

We consider the problem of exact integration of the field equations in the scalar—tensor theory of gravity for the case in which matter is an ideal fluid and the metric for space is given in Robertson—Walker form. We obtain a solution (in quadratures) for an arbitrary equation of state and an arbitrary time-dependent density for matter. Tomsk State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 124–127, January, 1997.     

The exciton many-body theory extended to any kind of composite bosons

We have recently constructed a many-body theory for composite excitons, in which the possible carrier exchanges between N excitons can be treated exactly through a set of dimensionless “Pauli scatterings” between two excitons. Many-body effects with free excitons turn out to be rather simple because these excitons are the exact one-pair eigenstates of the semiconductor Hamiltonian, in the absence of localized traps. They consequently form a complete orthogonal basis for one-pair states. As essentially all quantum particles known as bosons are composite bosons, it is highly desirable to extend this free exciton many-body theory to other kinds of “cobosons” — a contraction for composite bosons — the physically relevant ones being possibly not the exact one-pair eigenstates of the system Hamiltonian. The purpose of this paper is to derive the “Pauli scatterings” and the “interaction scatterings” of these cobosons in terms of their wave functions and the interactions which exist between the fermions from which they are constructed. It is also explained how to calculate many-body effects in such a very general composite boson system.     

An alternative definition of the electron propagator in the superoperator form and its relation to linear response theory in a coupled-cluster framework

In this paper it is shown that (i) there exists an alternative definition of the superoperator resolvent for calculation of difference energy satisfying linked cluster theorem for a coupled-cluster choice of the ground-state function which may even be approximate; (ii) the pole-structure of this propagator-like function in superoperator form is shown to contain information similar to that contained in the conventional propagator. (iii) It is demonstrated that suitable “Killer conditions” and completeness of the “operator manifold”—essential for understanding the pole-structure of the propagator—can be established both for an exact and an approximate ground state function in a coupled-cluster form. (iv) It is also demonstrated that difference energies calculated with these propagator-like functions are identical to those obtained from a linear response theory in a coupled-cluster form put forward recently by Mukherjeeet al and Monkhorst.     

Shiva diagrams for composite-boson many-body effects: how they work

The purpose of this paper is to show how the diagrammatic expansion in fermion exchanges of scalar products of N-composite-boson (“coboson”) states can be obtained in a practical way. The hard algebra on which this expansion is based, will be given in an independent publication. Due to the composite nature of the particles, the scalar products of N-coboson states do not reduce to a set of Kronecker symbols, as for elementary bosons, but contain subtle exchange terms between two or more cobosons. These terms originate from Pauli exclusion between the fermionic components of the particles. While our many-body theory for composite bosons leads to write these scalar products as complicated sums of products of “Pauli scatterings” between two cobosons, they in fact correspond to fermion exchanges between any number P of quantum particles, with 2 ≤P≤N. These P-body exchanges are nicely represented by the so-called “Shiva diagrams”, which are topologically different from Feynman diagrams, due to the intrinsic many-body nature of the Pauli exclusion from which they originate. These Shiva diagrams in fact constitute the novel part of our composite-exciton many-body theory which was up to now missing to get its full diagrammatic representation. Using them, we can now “see” through diagrams the physics of any quantity in which enters N interacting excitons — or more generally N composite bosons —, with fermion exchanges included in an exact — and transparent — way.     

Quantum field theory in curved spacetime,the operator product expansion,and dark energy

To make sense of quantum field theory in an arbitrary (globally hyperbolic) curved spacetime, the theory must be formulated in a local and covariant manner in terms of locally measurable field observables. Since a generic curved spacetime does not possess symmetries or a unique notion of a vacuum state, the theory also must be formulated in a manner that does not require symmetries or a preferred notion of a “vacuum state” and “particles”. We propose such a formulation of quantum field theory, wherein the operator product expansion (OPE) of the quantum fields is elevated to a fundamental status, and the quantum field theory is viewed as being defined by its OPE. Since the OPE coefficients may be better behaved than any quantities having to do with states, we suggest that it may be possible to perturbatively construct the OPE coefficients—and, thus, the quantum field theory. By contrast, ground/vacuum states—in spacetimes, such as Minkowski spacetime, where they may be defined—cannot vary analytically with the parameters of the theory. We argue that this implies that composite fields may acquire nonvanishing vacuum state expectation values due to nonperturbative effects. We speculate that this could account for the existence of a nonvanishing vacuum expectation value of the stress-energy tensor of a quantum field occurring at a scale much smaller than the natural scales of the theory. Fourth Award in the 2008 Essay Competition of the Gravity Research Foundation.     

Muon capture by16O—using a microscopic theory of particle-hole states

The partial capture rates for the process,μ ⁻ +¹⁶O (g·s) →¹⁶N (2⁻, 1⁻, 0⁻, 3⁻) +v _μ have been calculated using the particle-hole wavefunctions obtained using self-consistent procedure. In deriving these wavefunctions, the effectiveN-N interaction has been constructed from the bare Hamada-Johnston interaction. The terms in the muon capture Hamiltonian that depend on the momentum of the capturing proton have been included and their importance in 0⁺ → 0⁻ transition is exhibited. The agreement with the available experimental data is good. The need to incorporate meson exchange effects in 0⁺ → 0⁻ transition is pointed out.     

Formation of a chaotic layer of nonlinear resonance by a two-frequency perturbation

A new effect [V. V. Vecheslavov, Zh. éksp. Teor. Fiz. 109, 2208 (1996) (JETP 82, 1190 (1996)]—the appearance of low-frequency secondary harmonics in the separatrix mapping of a system—is discussed in detail for the example of a pendulum with a two-frequency perturbation. It is shown that there exist regions of values of the perturbation parameters where these harmonics make the main contribution to the formation of the chaotic layer of the fundamental resonance. The results of analytical and numerical determinations of the amplitudes of the secondary harmonics are compared. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 12, 989–994 (25 June 1996)     

The quantum-chemical modeling of the reaction of nitroso oxides with olefins

The density functional theory method was used to localize minima on the singlet potential energy surfaces of the nitroso oxide—ethylene, phenylnitroso oxide—tetramethylethylene, phenylnitroso oxide—hexene-1, and phenylnitroso oxide-styrene systems and on the triplet potential energy surfaces of the nitroso oxide—ethylene and phenylnitroso oxide-hexene-1 systems. The energetically favorable path was found to be that of (3 + 2) cycloaddition with the formation of five-membered rings, which decomposed into nitrone and carbonyl compound with the simultaneous dissociation of the C-C and C-O bonds. The influence of cis-trans isomerism of nitroso oxides on their reactivity with respect to olefins was studied.     

Magneto-absorption in cylindrical quantum dots

The absorption of light in an ensemble of non-interacting cylindrical quantum dots in the presence of a magnetic field is discussed using a model consisting of dots with rectangular infinitely-high potential barriers. The ensemble’s absorption coefficient is calculated — as well as the threshold frequency of absorption — as a function of the applied magnetic field and the quantum dot size. Theoretical results are compared with experimental data on magneto-luminescence in an In_0.53Ga_0.47As/InP cylindrical quantum dot system. In addition, using a perturbation theory framework, the influence of excitonic effects on the behaviour of the electron-hole energetic spectrum of said system is discussed.     

Calculation of spectroscopic parameters of diatomic van der walls molecules: Inert gas atom-halogen atom

Based on the effective pseudopotential method with the use of a new form of the polarization interaction potential that is obtained from calculating the major polarization diagrams of perturbation theory in the Thomas-Fermi approximation a calculation of interatomic potentials in the “halogen atom in the ground state F—inert gas atom Br” system is performed. The results of calculating on its basis the quasimolecular terms of the sought van der Waals system that ascertain the available data are given. Comparison with the available experimental and theoretical data is made. Odessa Hydrometeorological Institute, 15, L'vovskaya St., Odessa, 270016. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 256–259, March–April, 1997.     

Conformational analysis of allyl halides from the calculation of indirect spin-spin coupling

A theoretical study on the conformation of allyl halides from the calculation of nuclear spin-spin coupling constants by adopting the finite perturbation theory (FPT), is carried out in terms of the self-consistent, semi-empirical INDO (intermediate neglect of differential overlap) approximation of molecular orbital theory. Results of the calculations performed using ‘s’ and ‘p’ valence orbitals alone (‘sp’ basis) at INDO level approximation seem to replicate the experimental trend quite satisfactorily. Despite the overall agreement of the theoretical values with the experimental ones, the uncertainties in the INDO parametrization scheme lead to overestimation of certain coupling constants. The calculations also show that the orientation of the coupled protons with respect to the substituent halogen atom is an important factor to be considered.