Microscopic particle-vibrator model: A new fermion-boson expansion

The elements for a microscopic foundation of the particle-vibrator model are derived in the form of a new fermion-boson expansion in which valence particles or holes added to a closed shell are treated essentially as fermion degrees of freedom, while particle-hole excitations of the closed shell itself are treated as bosons. The Pauli principle is completely fulfilled without redundancy. The generalizations of both the non-unitary Dyson and the unitary Holstein-Primak off representations are given, as well as an equivalent intermediate unitary representation.     

Microscopic derivation of kinetic equations for interacting optical two-level systems

Kinetic equations are derived for optical two-level atoms interacting with a molecular subsystem treated as a thermostat. It is assumed that the kinetics is determined by the electric dipole interaction perturbed by the thermal motion. Dynamic parts of the kinetic equations coincide with the corresponding terms of optical Bloch equations, whereas nonlinear relaxation and shift terms have the specific form and are absent in the phenomenological generalized Bloch equations. It is shown that the relaxation kinetics can be substantially different from the exponential one and depends on the initial state of the system. In particular, the inversion relaxation is frozen at small deviations from the equilibrium. The possibility of observation of the optical bistability is discussed.     

Superalgebra and fermion-boson symmetry

Fermions and bosons are quite different kinds of particles, but it is possible to unify them in a supermultiplet, by introducing a new mathematical scheme called superalgebra. In this article we discuss the development of the concept of symmetry, starting from the rotational symmetry and finally arriving at this fermion-boson (FB) symmetry.     

Microscopic dynamics in a strongly interacting Bose-Einstein condensate

An initially stable 85Rb Bose-Einstein condensate (BEC) was subjected to a carefully controlled magnetic field pulse near a Feshbach resonance. This pulse probed the strongly interacting regime for the BEC, with the diluteness parameter (na(3)) ranging from 0.01 to 0.5. Condensate number loss resulted from the pulse, and for triangular pulses shorter than 1 ms, decreasing the pulse length actually increased the loss, until very short time scales (approximately 10 micros) were reached. The observed time dependence is very different from that expected in traditional inelastic loss processes, suggesting the presence of new microscopic BEC physics.     

Microscopic open systems

Microscopic open systems are defined by optimally controlled (with respect to the minimal average energy) randomly perturbed evolutions. It is shown that these evolutions are compatible with quantum ground states. New representations and interpretations of ground states revealed by these evolutions are stressed and discussed. Harmonic oscillator and hydrogen atom are briefly described as examples of microscopic open systems.     

The gauge-covariant formulation of interacting strings and superstrings

The local gauge-covariant free actions of open and closed bosonic strings and superstrings are constructed. The unique local covariant actions for interacting bosonic strings (open and closed) are determined and the corresponding one for superstrings is proposed.     

Microscopic formulation of black holes in string theory

In this report we review the microscopic formulation of the five-dimensional black hole of type IIB string theory in terms of the D1–D5 brane system. The emphasis here is more on the brane dynamics than on supergravity solutions. We show how the low energy brane dynamics, combined with crucial inputs from AdS/CFT correspondence, leads to a derivation of black hole thermodynamics and the rate of Hawking radiation. Our approach requires a detailed exposition of the gauge theory and conformal field theory of the D1–D5 system. We also discuss some applications of the AdS/CFT correspondence in the context of black hole formation in three dimensions by thermal transition and by collision of point particles.     

Microscopic approach to the interacting boson model: (II). Extension to neutron-proton systems and applications

Earlier work on the microscopic foundation of the interacting boson model is extended to neutron-proton systems, and a numerical application to the Sm isotopes is given. The calculated excitation energies turn out to be systematically larger than the experimental values, but good agreement is obtained for some qualitative features such as level orderings and the character of the spectrum. Renormalization effects due to the coupling with hexadecupole degrees of freedom (g-boson) are estimated and found to be rather small. The validity of the IBA truncation scheme is discussed in detail.     

Microscopic study of configuration mixing in the interacting boson model

The microscopic foundation of the configuration-mixing interacting boson model, as proposed by Duval and Barrett, is explored. In this model, the normal shell-model configurations are supplemented by intruder configurations that arise by exciting a proton pair from one major shell to the next. A computationally-efficient generalized-seniority formalism for treating the mixing of these two configurations is described. Boson mixing parameters are obtained using the Otsuka-Arima-Iachello mapping procedure. Specific application to configuration mixing in the Cd isotopes is reported. The successes and failures of the calculations are assessed and suggestions for future work are made.     

Microscopic description of heavy-ion collisions in terms of interacting RPA modes

Starting from the TDHF equation, the equations of motion for the single-particle density matrices refering to projectile and target are derived in an approximative way in a translating and rotating reference frame. An expansion of the fluctuating part of the transformed density in terms of generalized RPA modes in the ph as well as the pp(hh) channel leads to a system of non-linear coupled equations which simultaneously determine the time development of the collective coordinates and momenta of the relative motion, of the intrinsic angular momentum, and of the amplitudes of coherent surface excitations of the fragments. In a schematic calculation the formalism is applied to the angular momentum dissipation in the excitation of damped giant dipole modes.     

Microscopic foundation of the interacting boson model in thes d-shell nuclei

Starting from an isospin invariant shell-model hamiltonian, we describe a method for deriving microscopically the IBM-hamiltonian appropriate to lights d-shell nuclei. The key ingredients of our approach are:a) the Belyaev-Zelevinsky-Marshalek (BZM) bosonization procedure;b) two successive unitary transformations that extract the “maximally decoupled” collective bosons with angular momentaJ=0(s _ππ ⁺ ,s _νν ⁺ ,s _πν ⁺ ) andJ =2(d _ππ ⁺ ,d _νν ⁺ ,d _πν ⁺ (T=0),d _πν ⁺ (T=1)). The method is applied to obtain the low-energy spectra and the electron scattering form factors for the 0 ₁ ⁺ →2 ₁ ⁺ transitions in²⁰Ne and²⁴Mg. Good agreement with the exact shell-model results is achieved. The inclusion of proton-neutron bosons (s _πν ⁺ ,d _πν ⁺ (T=1),d _πν ⁺ (T=0)), as well as the renormalization of boson parameters due to the non-collective degrees of freedom, are shown to play a crucial role.     

Adiabatic pumping in interacting systems

A dc current can be pumped through an interacting system by periodically varying two independent parameters such as the magnetic field and a gate potential. We present a general expression for the adiabatic pumping current in interacting systems, written in terms of instantaneous properties of the system at equilibrium, and find the limits of its applicability. This expression generalizes the scattering approach for noninteracting particles. We apply our formula for a quantum critical system that exhibits the two-channel Kondo effect, where single particle excitations are not well defined. We find that if the quantum critical point is contained in the pumping trajectory, the pumped spin between the channels approaches h, and if it is not contained in the trajectory, the spin approaches zero when the temperature T --> 0. We discuss the non-Fermi liquid features of this system at finite T.     

On the decoupling of interacting systems

It is shown that the one electron energy matrix of a system composed of similar interacting subsystems does not, in general, provide a unique determination of the energy matrix of the subsystems. A criterion for making this separation is proposed.     

Permutation complexity of interacting dynamical systems

The coupling complexity index is an information measure introduced within the framework of ordinal symbolic dynamics. This index is used to characterize the complexity of the relationship between dynamical system components. In this work, we clarify the meaning of the coupling complexity by discussing in detail some cases leading to extreme values, and present examples using synthetic data to describe its properties. We also generalize the coupling complexity index to the multivariate case and derive a number of important properties by exploiting the structure of the symmetric group. The applicability of this index to the multivariate case is demonstrated with a real-world data example. Finally, we define the coupling complexity rate of random and deterministic time series. Some formal results about the multivariate coupling complexity index have been collected in an Appendix.     

Double-resonance spectroscopy of interacting Rydberg-atom systems

The energy level spectrum of a many-body system containing two shared, collective Rydberg excitations is measured using cold atoms in an optical dipole trap. Two pairs of independently tunable laser pulses are employed to spectroscopically probe the spectrum in a double-resonance excitation scheme. Depending on the magnitude of an applied electric field, the Rydberg-atom interactions can vary from resonant dipole-dipole to attractive or repulsive van der Waals, leading to characteristic signatures in the measured spectra. Our results agree with theoretical estimates of the magnitude and sign of the interactions.     

Dynamics of disordered interacting quantum systems

Starting from the Liouville-von Neumann equation for the state operator, a functional integral representation of the generating functional for time-temperature dependent Green's functions in interacting disordered quantum systems is constructed. In the framework of this method, quenched averages can be performed without introducing additional, unphysical degrees of freedom, like, e.g., in then-replica method. For interaction-free systems, the dynamical origin of the Schäfer-Wegner symmetry is pointed out. For interacting systems we derive a matrix field theory with a single matrix field, which includes all interaction effects without approximations.     

Microscopic theory of charge-density wave systems

An effective action (in imaginary time) for the phase of the order parameter is derived using the path integral formulation of the microscopic theory. After analytic continuation, the classical equation of motion is derived. Dissipation is found to arise from impurity scattering and from the screened Coulomb interaction with normal electrons. Similarities to a recent theory of Josephson junctions are discussed.     

Hamiltonian formulation of the theory of interacting gravitational and electron fields

The action which describes the interaction of gravitational and electron fields is expressed in canonical form. In addition to general covariance, it exhibits the local Lorentz invariance associated with four-dimensional rotations of the local orthonormal frames. The corresponding Hamiltonian constraints are derived and their (Dirac) bracket relations given. The derivative coupling of the gravitational tetrad and spinor fields is not present in the Hamiltonian, but rather in the unusual bracket relations of the field variables in the theory. If the timelike leg of the tetrad field is fixed to be normal to the x^o = constant hyper-surfaces (“time gauge”) the derivative coupling drops from the theory in the sense that the relation between the gravitational velocities and momenta is the same as when the spinor fields are absent.     

Oscillator model for the relativistic fermion-boson system

The solvable quantum mechanical model for the relativistic two-body system composed of spin-1/2 and spin-0 particles is constructed. The model includes the oscillator-type interaction through a combination of Lorentz-vector and Lorentz-tensor potentials. The analytical expressions for the wave functions and the order of the energy levels are discussed.