Absence of a True Vortex-Glass Phase above the Bragg Glass Transition Line in Bi-2212

In magnetic measurements on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) single crystals, a general peak with a dynamical feature on both $S-H$ and $S-T$ curves was found with S the magnetic relaxation rate. At higher fields, the characteristic exponent $\mu$ becomes negative, together with the positive curvature of $logE$ vs. $logj$ and the scaling based on the 2D vortex glass theory or plastic creep theory, we conclude that the vortex motion above the second peak is plastic when $j\to 0$ and there is no vortex glass phase at finite temperatures in Bi-2212. The peak of S is then explained as the crossover between different meta-stable vortex states.Comment: 10 pages, 5 figures, To appear in Physica

Hamiltonian Map to Conformal Modification of Spacetime Metric: Kaluza-Klein and TeVeS

It has been shown that the orbits of motion for a wide class of nonrelativistic Hamiltonian systems can be described as geodesic flows on a manifold and an associated dual. This method can be applied to a four dimensional manifold of orbits in spacetime associated with a relativistic system. We show that a relativistic Hamiltonian which generates Einstein geodesics, with the addition of a world scalar field, can be put into correspondence with another Hamiltonian with conformally modified metric. Such a construction could account for part of the requirements of Bekenstein for achieving the MOND theory of Milgrom in the post-Newtonian limit. The constraints on the MOND theory imposed by the galactic rotation curves, through this correspondence, would then imply constraints on the structure of the world scalar field. We then use the fact that a Hamiltonian with vector gauge fields results, through such a conformal map, in a Kaluza-Klein type theory, and indicate how the TeVeS structure of Bekenstein and Sanders can be put into this framework. We exhibit a class of infinitesimal gauge transformations on the gauge fields ${\cal U}_\mu$ which preserve the Bekenstein-Sanders condition ${\cal U}_\mu {\cal U}^\mu = -1$. The underlying quantum structure giving rise to these gauge fields is a Hilbert bundle, and the gauge transformations induce a non-commutative behavior to the fields, i.e., they become of Yang-Mills type. Working in the infinitesimal gauge neighborhood of the initial Abelian theory, we show that in the Abelian limit the Yang-Mills field equations provide nonlinear terms which may avoid the caustic singularity found by Contaldi, et al.Comment: Plain TeX, 8 pages. Proceedings of Conference of International Association for Relativistic Dynamics, Thessaloniki, Greece, June 2008. Revision includes discussion of field norm preserving gauge on Hilbert bundle and nonlinear contributions to field equations in Abelian limi

Black Hole Solutions and Pressure Terms in Induced Gravity with Higgs Potential

We study the quintessential properties of the Black Hole solutions in a scalar--tensor theory of gravity with Higgs potential in view of the static and spherically symmetric line element. In view of our earlier results, Reissner--Nordstr\"om-like and Schwarzschild Black Hole solutions are derived with the introduction of a series-expansion method to solve the field equations without and with Higgs field mass. The physical consequences of the Black Hole solutions and the solutions obtained in the weak field limit are discussed in detail by the virtue of the equation-of-state parameter, the scalar-field excitations and the geodesic motion. The appearance of naked singularities is also discussed together with the dependence of Black Hole horizons on the field excitations, which are themselves dependent on pressure terms which effectively screen the mass terms. A possible connection to flat rotation curves following the interaction with the scalar field is also presented in the weak field limit of gravity, together with a discussion of dynamical effects of scalar fields and pressure terms on mass.Comment: 28 pages, 4 figures, contents and figures modified, major revision, results are unchanged, published in Classical and Quantum Gravit

Kinematics and Performance Analysis of 2R2T Parallel Manipulator with Partially Decoupled Motion

© 2019, Chinese Society of Agricultural Machinery. All right reserved. A novel parallel manipulator with two rotations and two translations was proposed. The moving platform of the parallel manipulator was connected to the fixed base through four kinematic limbs. Four prismatic joints can be used as actuations to fully control the motion of manipulator. The mobility and motion characteristic of the manipulator were analyzed by using Lie Group theory. Position model of the parallel manipulator was established. Inverse and forward position solutions were analyzed. It was demonstrated that the analytical expressions can be obtained for the inverse and forward position solutions. Partially decoupled motion characteristic of the manipulator was analyzed. Position of the moving platform can be determined by two limbs. Singularity analysis was conducted based on Jacobian matrix. Singular configurations, including inverse kinematic singularity, forward kinematic singularity and combined singularity were analyzed. Workspace and singularity curves were determined. It was found that the singularities located near the boundary of the workspace and the parallel manipulator had relatively high rotational capability. The rotational ranges in two directions were -44°~60° and -35°~52°, respectively. Performance analysis was carried out by using the method of motion/force transmission. Performance distribution over the orientation workspace was sketched. Global performance index was used in optimal design of the manipulator. The proposed parallel manipulator can be used in many fields such as five axis machine and motion simulator

F-theory Yukawa Couplings and Supersymmetric Quantum Mechanics

The localized fermions on the intersection curve $\Sigma$ of D7-branes, are connected to a N=2 supersymmetric quantum mechanics algebra. Due to this algebra the fields obey a global U(1) symmetry. This symmetry restricts the proton decay operators and the neutrino mass terms. Particularly, we find that several proton decay operators are forbidden and the Majorana mass term is the only one allowed in the theory. A special SUSY QM algebra is studied at the end of the paper. In addition we study the impact of a non-trivial holomorphic metric perturbation on the localized solutions along each matter curve. Moreover, we study the connection of the localized solutions to an N=2 supersymmetric quantum mechanics algebra when background fluxes are turned on.Comment: References added, New Material Added, Published versio

Geometry and Motion in General Relativity

A classic problem in general relativity, long studied by both physicists and philosophers of physics, concerns whether the geodesic principle may be derived from other principles of the theory, or must be posited independently. In a recent paper [Geroch & Weatherall, "The Motion of Small Bodies in Space-Time", Comm. Math. Phys. (forthcoming)], Bob Geroch and I have introduced a new approach to this problem, based on a notion we call "tracking". In the present paper, I situate the main results of that paper with respect to two other, related approaches, and then make some preliminary remarks on the interpretational significance of the new approach. My main suggestion is that "tracking" provides the resources for eliminating "point particles"---a problematic notion in general relativity---from the geodesic principle altogether.Comment: 26 pages, 1 figure. Forthcoming in a future volume of the Einstein Studies serie