17271354
Spinning particles in scalar-tensor gravity
We develop a new model of a spinning particle in Brans–Dicke spacetime using a metric-compatible connection with torsion. The particle's spin vector is shown to be Fermi-parallel (by the Levi-Civita connection) along its worldline (an autoparallel of the metric-compatible connection) when neglecting spin-curvature coupling.
119240145
Quantum fluctuations in planar domain wall space–times: A possible origin of primordial preferred direction
Abstract We study the gravitational effects of a planar domain wall on quantum fluctuations of a massless scalar field during inflation. By obtaining an exact solution of the scalar field equation in de-Sitter space, we show that the gravitational effects of the domain wall break the rotational invariance of the primordial power spectrum without affecting the translational invariance. The strength of rotational violation is determined by one dimensionless parameter β , which is a function of two physical parameters, the domain wall surface tension σ and cosmological constant Λ . In the limit of small β , the leading effect of rotational violation of the primordial power spectrum is scale-invariant.
17610587
Linearized Torsion Waves in a Tensor-Tensor Theory of Gravity
We investigate a linearized tensor-tensor theory of gravity with torsion and a perturbed torsion wave solution is discovered in background Minkowski spacetime with zero torsion. Furthermore, gauge transformations of any perturbed tensor field are derived in general background non-Riemannian geometries. By calculating autoparallel deviations, both longitudinal and transverse polarizations of the torsion wave are discovered.
119282479
Momentum-space representation of the Feynman propagator in Riemann-Cartan spacetime
We first construct generalized normal coordinates by using autoparallels, instead of geodesics, in an arbitrary Riemann-Cartan spacetime. With the aid of generalized normal coordinates and their associated orthonormal frames, we obtain a momentum-space representation of the Feynman propagator for scalar fields, which is a direct generalization of Bunch and Parker's works to curved spacetime with torsion. We further derive the proper-time representation in n-dimensional Riemann-Cartan spacetime from the momentum-space representation. It leads us to obtain the renormalization of the one-loop effective Lagrangians of free scalar fields by using dimensional regularization. When the torsion tensor vanishes, our resulting momentum-space representation returns to the standard Riemannian results.
118253971
How can one observe gravitational angular momentum radiation from a dynamical source near null infinity
To answer a question of how can one observed angular momentum radiation near null infinity, one can first transform the dynamical twisting vacuum solution and make it satisfy Bondi coordinate conditions in the asymptotical region of the null infinity. We then obtain the Bondi-Sachs news function and also find the relationship of how does the angular momentum contribute to the news functions from the exact solution sense. By using the Komar's integral of angular momentum, the gravitational angular momentum flux of the dynamical twisting space-time can be obtained. All of our results can be compared with the Kerr solution, Robbinson-Trautmann or Schwarzschild solution. This study can provide a theoretical basis to understand the correlations of gravitational radiations near a rotating dynamical horizon and null infinity.
118692827
Local and global structure of domain wall space-times
We present a general proof on the equivalence of the comoving-coordinate approach, where the wall is fixed at a constant coordinate variable, and moving-wall approach, where the wall is moving in a background static space-time, in the domain wall space-times without reflection symmetry. We further provide a general procedure to construct the comoving coordinates in the domain wall space-times, where the two regions separated by an infinite thin wall have different cosmological constant $\Lambda$ and Schwartzschild mass $M$. By solving Israel's junction conditions in the thin-wall limit, the gravitational fields of spherical, planar and hyperbolic domain wall space-times with M=0 in the two different comoving coordinate systems are obtained. We finally discuss the global structure of these domain wall space-times.
17362035
Existence of the Solution for the 't Hooft-Polyakov Monopole
Author(s): McLeod, J. Bryce; Wang, Chie Bing | Abstract: In this paper we give a mathematical proof of the existence of the time independent and spherically symmetric solution to the 't Hooft-Polyakov model of magnetic monopole by using 2D-shooting method.
119207341
Split flows in bubbled geometries
We propose a procedure to clarify part of the physical sector in the five dimensional bubble geometries based on ideas similar to the split attractor flow conjecture proposed by Denef. This procedure involves building some simple tree-like graphs that we call skeletons without referring to the moduli space. The skeleton (tree) exists if and only if it passes the existence conditions which are purely based on some local CTC’s (closed timelike curves) checking. Then, we propose the conjecture similar to Denef’s version which states that every existing skeleton (tree) should correspond to some solution in which the global absence of CTC’s is ensured. Furthermore, we propose two pictures to identify this correspondence explicitly and use some numerical examples to show how this procedure works. We also analyze the physical sector of the simplest bubbled supertube and see how the existence conditions constrain the charge parameter space.
119131032
Algebraic Bethe ansatz for singular solutions
The Bethe equations for the isotropic periodic spin-1/2 Heisenberg chain with N sites have solutions containing i/2, -i/2 that are singular: both the corresponding energy and the algebraic Bethe ansatz vector are divergent. Such solutions must be carefully regularized. We consider a regularization involving a parameter that can be determined using a generalization of the Bethe equations. These generalized Bethe equations provide a practical way of determining which singular solutions correspond to eigenvectors of the model.
14842099
Bullets in a Core-Collapse Supernova Remnant: The Vela Remnant
We use two-dimensional hydrodynamical simulations to investigate the properties of dense ejecta clumps (bullets) in a core-collapse supernova remnant, motivated by the observation of protrusions probably caused by clumps in the Vela supernova remnant. The ejecta, with an inner flat and an outer steep power-law density distribution, were assumed to freely expand into an ambient medium with a constant density, ~0.1 H atoms cm-3 for the case of Vela. At an age of 104 yr, the reverse shock front is expected to have moved back to the center of the remnant. Ejecta clumps with an initial density contrast χ ~ 100 relative to their surroundings are found to be rapidly fragmented and decelerated. In order to cause a pronounced protrusion on the blast wave, as observed in the Vela remnant, χ ~ 1000 may be required. In this case, the clump should be near the inflection point in the ejecta density profile, at an ejecta velocity ~3000 km s-1. These results apply to moderately large clumps; smaller clumps would require an even larger density contrast. Clumps can create ring structure in the shell of the Vela remnant, and we investigate the possibility that RX J0852-4622, an apparent supernova remnant superposed on Vela, is actually part of the Vela shell. Radio observations support this picture, but the possible presence of a compact object argues against it. The Ni bubble effect or compression in a pulsar wind nebula are possible mechanisms to produce the clumping.
119195614
MHD Simulations of Parker Instability Undergoing Cosmic-Ray Diffusion
Parker instability arises from the presence of magnetic fields in a plasma in a gravitational field such as the interstellar medium (ISM), wherein the magnetic buoyant pressure expels the gas and causes the gas to move along the field lines. The process of mixing of this instability in the ISM near the Galactic plane is investigated. The initial ISM is assumed to consist of two fluids: plasma gas and cosmic-ray particles, in hydrostatic equilibrium, coupled with a uniform, azimuthally-aligned magnetic field. The evolution of the instability is explored in two models: an isothermal exponential-declining density model and a two-layered, hyperbolic tangent temperature model. After a small perturbation, the unstable gas aggregates at the bottom of the magnetic loops and forms dense blobs. The growth rate of the instability decreases as the coupling between the cosmic rays and the plasma becomes stronger (meaning a smaller CR diffusion coefficient). The mixing is enhanced by the cosmic-ray diffusion, while the shape of the condensed gas depends sensitively on the initial equilibrium conditions. The hyperbolic tangent temperature model produces a more concentrated and round shape of clumps at the foot points of rising magnetic arches, like the observed giant molecular cloud, whereas the exponential density model gives rise to a filamentary morphology of the clumpy structure. When considering a minimum perpendicular or cross field diffusion of cosmic rays, which is often substantially smaller than the parallel coefficient $\kappa_{\|}$, around $2%-4%$ of $\kappa_{\|}$, the flow speed is significantly increased such that the magnetic loops extend to a greater altitude. We speculate that the galactic wind flow perpendicular to the galactic disk may be facilitated by Parker instabilities through the cross field diffusion of cosmic rays.