Types Of Effective Interactions Research Articles

Polarons in binary Bose–Einstein condensates

Bose polarons are quasiparticles formed through the interaction between impurities and Bose–Einstein condensates. In this paper, we derive an effective Fröhlich Hamiltonian using the generalized Bogoliubov transformation. The effective Fröhlich Hamiltonian encompasses two types of effective interactions: impurity-density (ID) coupling and impurity-spin (IS) coupling. Furthermore, we employ the Lee–Low–Pines variational approach to investigate the relevant properties of Bose polarons induced by the ID and IS coupling. These properties include the ground state energy, effective mass, and average number of virtual phonons. Our findings reveal that the contribution resulting from IS couplings to the ground energy decreases to zero near the miscible–immiscible boundary. Additionally, the increase of the IS coupling induces a greater number of virtual phonons, impeding the movement of impurities and leading to a significant increase in the effective mass of Bose polarons.

The Boltzmann distribution function for equilibrium fluctuations

A complex of issues related to the problem of proving the Boltzmann formula for the probability density (distribution) w(η) of the values of a certain set of parameters η of an equilibrium system is investigated. The classical Boltzmann formula expresses this distribution through the non-equilibrium free energy of the system F (η) , which depends on the mentioned parameters. This is possible because after the occurrence of fluctuations, the system finds itself in a non-equilibrium state, which evolves further to equilibrium. The specified parameters are chosen according to the problem under consideration. In the theory of phase transitions, they are called the order parameters. Questions under consideration include definition and construction of the free energy F (η) of a non-equilibrium system and distribution w(η ) for it in the microscopic theory. The approaches of Landau, Leontovich, and Peletminsky are discussed. It is proposed to investigate the results for states in the vicinity of equilibrium. The leading ideas of the research are considering the non-equilibrium state as being realized in the presence of an appropriate external field, using the Gibbs formula for the non-equilibrium system entropy, and applying the Boltzmann formula as a definition of the free energy of the non-equilibrium system. The article is a continuation of the authors' works and sets the task of clarifying some of their statements as well as simplifying and clarifying the calculations. Among other things, the following are discussed: the formula for the expansion of the free energy of the system in powers of the field, the simplification of the distribution w(η ) calculation, the normalization of the approximate expressions for the distribution w(η) , the possibilities of studying the free energy of the equilibrium system using our expression for the effective Landau Hamiltonian, the refinement of the calculation of the non-equilibrium free energy of a spatially inhomogeneous system, the investigation of new types of effective interactions with the Landau Hamiltonian.

Study of the Electric Quadrupole Moments for some Scandium Isotopes Using Shell Model Calculations with Different Interactions

The electric quadrupole moments for some scandium isotopes (41, 43, 44, 45, 46, 47Sc) have been calculated using the shell model in the proton-neutron formalism. Excitations out of major shell model space were taken into account through a microscopic theory which is called core polarization effectives. The set of effective charges adopted in the theoretical calculations emerging about the core polarization effect. NushellX@MSU code was used to calculate one body density matrix (OBDM). The simple harmonic oscillator potential has been used to generate the single particle matrix elements. Our theoretical calculations for the quadrupole moments used the two types of effective interactions to obtain the best interaction compared with the experimental data. The theoretical results of the quadrupole moments for some scandium isotopes performed with FPD6 interaction and Bohr-Mottelson effective charge agree with experimental values.

Glass transition of charged particles in two-dimensional confinement.

The glass transition of mesoscopic charged particles in two-dimensional confinement is studied by mode-coupling theory. We consider two types of effective interactions between the particles, corresponding to two different models for the distribution of surrounding ions that are integrated out in coarse-grained descriptions. In the first model, a planar monolayer of charged particles is immersed in an unbounded isotropic bath of ions, giving rise to an isotropically screened Debye-Hückel (Yukawa)-type effective interaction. The second, experimentally more relevant system is a monolayer of negatively charged particles that levitate atop a flat horizontal electrode, as frequently encountered in laboratory experiments with complex (dusty) plasmas. A steady plasma current toward the electrode gives rise to an anisotropic effective interaction potential between the particles, with an algebraically long-ranged in-plane decay. In a comprehensive parameter scan that covers the typical range of experimentally accessible plasma conditions, we calculate and compare the mode-coupling predictions for the glass transition in both kinds of systems.

Confronting the direct search of low mass dark matter from CoGeNT data with antiproton PAMELA data

If the excess events from the CoGeNT experiment arise from elastic scatterings of a light dark matter off the nuclei, crossing symmetry implies non-vanishing annihilation cross-sections of the light dark matter into hadronic final states inside the galactic halo, which we confront with the anti-proton spectrum measured by the PAMELA collaboration. We consider two types of effective interactions between the dark matter and the quarks: 1) contact interactions from integrating out heavy particles and 2) long-range interactions due to the electromagnetic properties of the dark matter. The lack of excess in the anti-proton spectrum results in tensions for a scalar and, to a less extent, a vector dark matter interacting with the quarks through the Higgs portal.

Cosmological birefringence induced by neutrino current

We review our recent work, Geng et al. (J. Cosmol. Astropart. Phys. 09, 010 (2007)) on the cosmological birefringence. We propose a new type of effective interactions in terms of the CPT-even dimension-six Chern–Simons-like term to generate the cosmological birefringence. We use the neutrino number asymmetry to induce a nonzero rotation polarization angle in the data of the cosmic microwave background-radiation polarization.PACS Nos.: 98.80.Cq, 98.80.Es, 11.30.Fs

Bond-Dilution-Induced Quantum Phase Transitions in Heisenberg Antiferromagnets

Bond-dilution effects on the ground state of the square-lattice antiferromagnetic Heisenberg model, consisting of coupled bond-alternating chains, are investigated by means of the quantum Monte Carlo simulation. It is found that, when the ground state of the non-diluted system is a non-magnetic state with a finite spin gap, a sufficiently weak bond dilution induces a disordered state with a mid gap in the original spin gap, and under a further stronger bond dilution an antiferromagnetic long-range order emerges. While the site-dilution-induced long-range order is induced by an infinitesimal concentration of dilution, there exists a finite critical concentration in the case of bond dilution. We argue that this essential difference is due to the occurrence of two types of effective interactions between induced magnetic moments in the case of bond dilution, and that the antiferromagnetic long-range-ordered phase does not appear until the magnitudes of the two interactions become comparable.

Hartree-Fock calculations on unstable nuclei with several types of effective interactions

Spherical Hartree-Fock calculations are carried out using several types of effective interactions. As well as the Skyrme and the Gogny interactions, a new interaction with Yukawa form is developed by modifying the M3Y interaction. Effects of the effective interactions on the gap at N = 16 are investigated. It is confirmed that the (σ · σ) (τ · τ) interaction plays a certain role in the occurrence of the N = 16 magic number in the neutron-rich region. This study shows that the M3Y-type interaction is useful to properly take into account spin-isospin characters in the mean-field theories, and to make a correspondence between the mean-field theories and the shell model.