Relativistic addition of interactions in constraint Hamiltonian mechanics

The problem of constructing separable N-particle interactions for given two-body forces in the constraint Hamiltonian approach to relativistic classical mechanics is tackled in two different ways. A formal expression for the N-particle constraints is given in terms of a classical wave operator. An (independent) iterative scheme for these constraints is carried out. Explicit formulas for the three-particle interactions are written down, accurate up to second order in the two-body coupling constants and symmetric with respect to particle permutations.     

Optical pulling force on nanoparticle clusters with gain due to Fano-like resonance

We demonstrate that, in a simple linearly-polarized plane wave, the optical pulling forces on nanoparticle clusters with gain can be induced by the Fano-like resonance. The numerical results based on the full-wave calculation show that the optical pulling forces can be attributed to the recoil forces for the nanoparticle clusters composed of dipolar nanoparticles with three different configurations. Interestingly, the recoil forces giving rise to optical pulling forces are exactly dominated by the coupling term between the electric and magnetic dipoles excited in the nanoparticle clusters, while other higher-order terms have a negligible contribution. In addition, the optical pulling force can be tailored by modulating the Fano-like resonance via either the particle size or the gain magnitude, offering an alternative freedom degree for optical manipulations of particle clusters.     

New experimental limits on non-Newtonian forces in the micrometer range

We report measurements of the short-range forces between two macroscopic gold-coated plates using a torsion pendulum. The force is measured for separations between 0.7 and 7 μm and is well described by a combination of the Casimir force, including the finite-temperature correction, and an electrostatic force due to patch potentials on the plate surfaces. We use our data to place constraints on the Yukawa-type "new" forces predicted by theories with extra dimensions. We establish a new best bound for force ranges 0.4-4 μm and, for forces mediated by gauge bosons propagating in (4+n) dimensions and coupling to the baryon number, extract a (4+n)-dimensional Planck scale lower limit of M(*)>70 TeV.     

On the Interplay of Magnetic and Molecular Forces in Curie–Weiss Ferrofluid Models

We consider a mean-field continuum model of classical particles in R ^d with Ising or Heisenberg spins. The interaction has two ingredients, a ferromagnetic spin coupling and a spin-independent molecular force. We show that a feedback between these forces gives rise to a first-order phase transition with simultaneous jumps of particle density and magnetization per particle, either at the threshold of ferromagnetic order or within the ferromagnetic region. If the direct particle interaction alone already implies a phase transition, then the additional spin coupling leads to an even richer phase diagram containing triple (or higher order) points.     

Particle simulations of space weather

We review the application of particle simulation techniques to the full kinetic study of space weather events. We focus especially on the methods designed to overcome the difficulties created by the tremendous range of time and space scales present in the physical systems. We review the aspects of the derivation of the particle in cell (PIC) method relevant to the discussion. We consider first the explicit formulation highlighting its severe limitations due to the presence of stability constraints. Next we introduce implicit methods designed to remove such constraints. We describe both fully implicit methods based on the use of non-linear iteration solvers and semi-implicit methods based on the linearization of the coupling and on simpler linear solvers. We focus the discussion on the implicit moment method but remark its differences from the direct implicit method. The application of adaptive methods within PIC is discussed. Finally practical considerations about the implementation of the implicit PIC method on massively parallel computers to conduct studies of space weather events are given.     

General properties of the decay amplitudes for massless particles

We derive the kinematical constraints which characterize the decay of any massless particle in flat space-time. We show that in perturbation theory the decay probabilities of photons and Yang-Mills bosons vanish to all orders and the decay probability of gravitons vanishes to one-loop order for graviton loops and to all orders for matter loops. A general power counting argument indicates in which conditions a decay of a massless particle could be possible: the Lagrangian should contain a self-coupling without derivatives and with a coupling constant of positive mass dimension.     

Neutron optics of noncentrosymmetric crystals: New possibility of searches for the neutron electric dipole moment and CP-violating forces

New neutron-optics effects, which were predicted and discovered quite recently in noncentrosymmetric crystals and which can be used to study the fundamental properties of the neutron, are discussed. In particular, strong electric fields of strength up to 10⁸ or 10⁹ V/cm may act in such crystals on the neutron, and this provides new possibilities for measuring the neutron electric dipole moment (EDM) by the crystal-diffraction method. It also becomes possible to perform searches for pseudomagnetic forces acting on neutrons and violating CP invariance. For the range of such forces that satisfies the condition λ _A < 10^?5 cm, the best constraints on the product of the scalar and pseudoscalar coupling constants have already been obtained for the interaction induced by the exchange of a light pseudoscalar (axion-like) particle. The present-day status and prospects of neutron-optics crystal-diffraction experiments aimed at searches for the neutron EDM and pseudomagnetic forces are considered.     

Relativistic Dynamics of Vector Bosons in the Field of Gravitational Radiation

We consider a model of the state evolution of relativistic vector bosons, which includes both the dynamical equations for the particle four-velocity and the equations for the polarization four-vector evolution in the field of a nonlinear plane gravitational wave. In addition to the gravitational minimal coupling, tidal forces linear in curvature tensor are suggested to drive the particle state evolution. The exact solutions of the evolutionary equations are obtained. Birefringence and tidal deviations from the geodesic motion are discussed.     

Angular momentum coupling and Optical Reference Geometry in Kerr space-time

We study in the framework of the Optical Reference Geometry the manner in which the coupling of the angular momentum of a test particle with that of a Kerr black hole affects the Newtonian forces acting on the particle.     

Production of <Superscript>149</Superscript>Tb in Alpha-Particle-Induced Nuclear Reactions

The sensitivity of the method of neutron scattering to novel neutron–nucleon interactions is analyzed. Upper limits on the coupling constant of such interactions are imposed using the available data on neutron powder diffraction on polycrystalline silicon. For the forces acting at ranges of λ < 10^–11 m, these upper limits are already competitive with the best existing constraints on their coupling constant. A dedicated experiment can help improve the sensitivity to this coupling constant by nearly two orders of magnitude.     

Force network ensemble: a new approach to static granular matter

An ensemble approach for force distributions in static granular packings is developed. This framework is based on the separation of packing and force scales, together with an a priori flat measure in the force phase space under the constraints that the contact forces are repulsive and balance on every particle. We show how the formalism yields realistic results, both for disordered and regular triangular "snooker ball" configurations, and obtain a shear-induced unjamming transition of the type proposed recently for athermal media.     

Resonant radiation pressure on neutral particles in a waveguide

A theoretical analysis of electromagnetic forces on neutral particles in a hollow waveguide is presented. We show that the effective scattering cross section of a very small (Rayleigh) particle can be strongly modified inside a waveguide. The coupling of the scattered dipolar field with the waveguide modes induces a resonant enhanced backscattering state of the scatterer-guide system close to the onset of new modes. The particle effective cross section can then be as large as the wavelength even far from any transition resonance. As we will show, a small particle can be strongly accelerated along the guide axis while being highly confined in a narrow zone of the cross section of the guide.     

Modeling force transmission in granular materials

The probability density function of contact forces in granular materials has been extensively studied and modeled as an outstanding signature of granular microstructure. Arguing that particle environments play a fundamental role in force transmission, we analyze the effects of steric constraints with respect to force balance condition and show that each force may be considered as resulting from a balance between lower and larger forces in proportions that mainly depend on steric effects. This idea leads to a general model that predicts an analytical expression of force density with a single free parameter. This expression fits well our simulation data and generically predicts the exponential fall-off of strong forces, a small peak below the mean force and the non-zero probability of vanishingly small forces.     

On the Importance of Testing Gravity at Distances Less Than 1cm

If the mechanism responsible for the smallness of the vacuum energy is consistent with local quantum field theory, general arguments suggest the existence of at least one unobserved scalar particle with Compton wavelength bounded from below by one tenth of a millimeter. We show that this bound is saturated if vacuum energy is a substantial component of the energy density of the universe. Therefore, the success of cosmological models with a significant vacuum energy component suggests the existence of new macroscopic forces with range in the sub-millimeter region. There are virtually no experimental constraints on the existence of quanta with this range of interaction.     

Search for a new gauge boson in electron-nucleus fixed-target scattering by the APEX experiment

We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.     

New exclusion limits for dark gauge forces from beam-dump data

We re-analyze published proton beam dump data taken at the U70 accelerator at IHEP Serpukhov with the ν-calorimeter I experiment in 1989 to set mass-coupling limits for dark gauge forces. The corresponding data have been used for axion and light Higgs particle searches in Blümlein et al. (1991, 1992) [1] and [2] before. We determine new mass and coupling exclusion bounds for dark gauge bosons.     

Core-particle coupling and polarization effects

The unpaired particle in an odd-mass transitional nucleus exerts forces on the rest of the system leading to an effective shape which is in general dependent on thej-orbital occupied by the extra particle. To account for this polarization effect we propose to modify the collective matrix elements by a phenomenological polarization factor. This enables us to describe also such band structures by the core-particle coupling model for which the common coupling rules seem to fail. Selecting a typical case the model is applied to¹²³I in order to demonstrate the important role of the polarization. The calculation reproduces fairly well all band structures including theirM1 andE2 decay properties.