119247814
GAMMA-RAY POLARIZATION INDUCED BY COLD ELECTRONS VIA COMPTON PROCESSES
The polarization measurement is an important tool to probe the prompt emission mechanism in gamma-ray bursts (GRBs). The synchrotron photons can be scattered by cold electrons in the outflow via Compton scattering (CS) processes. The observed polarization depends on both the photon energy and the viewing angle. With the typical bulk Lorentz factor Gamma similar to 200, photons with energy E > 10 MeV tend to have smaller polarization than photons with energy E < 1 MeV. At the right viewing angle, i.e., theta similar to Gamma(-1), the polarization achieves its maximal value, and the polarization angle changes 90 degrees relative to the initial polarization direction. Thus, the synchrotron radiation plus CS model can naturally explain the 90 degrees change of the polarization angle in GRB 100826A.
118885274
The change of GRB polarization angles in the magnetic-dominated jet model
The polarimetric measurement on the prompt phase of GRB 100826A shows that the polarization angle changes similar to 90 degrees between two adjacent time intervals. We will show that this phenomenon can be naturally interpreted in the framework of the magnetic-dominated jet (MDJ) model. The MDJ model suggests that the bulk Lorentz factor of the outflow increases as Gamma proportional to r(1/3), until reaching a saturated value Gamma(sat). Electrons move in the globally ordered magnetic field advected by the jet from the central engine and produce synchrotron photons. The polarized synchrotron photons travel alone the jet direction and then collide with the cold electrons at the front of the jet. After the Compton scattering process, these photons escape from the jet and are detected by the observer locating slightly off-axis. If photons are emitted before the bulk Lorentz factor saturates, the change of polarization angle is a natural result of the acceleration of the outflow.
10026539
Constraining anisotropy of the universe from different groups of type-Ia supernovae
Recently released Planck data and other astronomical observations show that the universe may be anisotropic on large scales. Inspired by this, anisotropic cosmological models have been proposed. We note that the Finsler–Randers spacetime provides an appropriate framework for the anisotropic cosmology. By adding an arbitrary 1-form to the Friedmann–Robertson–Walker line element, a privileged axis in the universe is picked out. The distance–redshift relation is modified to be direction-dependent. We wish that the anisotropic cosmological model may be tested crossly by independent observations. Type-Ia supernovae (SNe Ia) calibrated from four different light curve fitters are used to constrain the possible anisotropy of the universe. The magnitudes of anisotropy are all between 2–5 %, but the systematic uncertainty cannot be excluded. The directions of the privileged axis seem to differ from each other. The statistical significance is not high enough to make a convincing conclusion. Nevertheless, the $$1\sigma $$1σ contours in the $$(l,b)$$(l,b) plane obtained from four groups of SNe Ia have an overlap, centering at $$(l,b)\approx (170^{\circ }, 0^{\circ })$$(l,b)≈(170∘,0∘). Monte Carlo simulation shows that the anisotropy is unlikely to be caused by the selection effect.
119212709
Constraining the anisotropy of the universe from supernovae and gamma-ray bursts
Recently, an anisotropic cosmological model was proposed. An arbitrary one-form, which picks out a privileged axis in the universe, was added to the Friedmann Robertson Walker (FRW) line element. The distance-redshift relation was modified such that it is direction-dependent. In this paper, we use the Union2 dataset and 59 high-redshift gamma-ray bursts (C.:411Es) to give constraints on the anisotropy of the universe. The results show that the magnitude of anisotropy is about D = 0.044 0.018, and the privileged axis points toward the direction (to, ho) = (306.1" 18.7", 18.2" 11.2') in the galactic coordinate system. The anisotropy is small and the isotropic cosmological model is an excellent approximation.
119108453
Effects of spacetime anisotropy on the galaxy rotation curves
The observations on galaxy rotation curves show significant discrepancies from the Newtonian theory. This issue could be explained by the effect of the anisotropy of the spacetime. Conversely, the spacetime anisotropy could also be constrained by the galaxy rotation curves. Finsler geometry is a kind of intrinsically anisotropic geometry. In this paper, we study the effect of the spacetime anisotropy at galactic scales in the Finsler spacetime. It is found that the Finslerian model has close relations with the Milgrom’s MOND. By performing the best-fit procedure to the galaxy rotation curves, we find that the anisotropic effects of the spacetime become significant when the Newtonian acceleration GM/r2 is smaller than the critical acceleration a0. Interestingly, the critical acceleration a0, although varies between different galaxies, is in the order of magnitude $cH_{0}/2\pi\sim10^{-10}~\mathrm{m\,s}^{-2}$.
118372786
GAMMA-RAY POLARIZATION OF THE SYNCHROTRON SELF-COMPTON PROCESS FROM A HIGHLY RELATIVISTIC JET
The high polarization observed in the prompt phase of some gamma-ray bursts invites extensive study of the emission mechanism. In this paper, we investigate the polarization properties of the synchrotron self-Compton (SSC) process from a highly relativistic jet. Amagnetic-dominated, baryon-loaded jet ejected from the central engine travels with a large Lorentz factor. Shells with slightly different velocities collide with each other and produce shocks. The shocks accelerate electrons to a power-law distribution and, at the same time, magnify the magnetic field. Electrons move in the magnetic field and produce synchrotron photons. Synchrotron photons suffer from the Compton scattering (CS) process and then are detected by an observer located slightly off-axis. We analytically derive the formulae of photon polarization in the SSC process in two magnetic configurations: a magnetic field in the shock plane and perpendicular to the shock plane. We show that photons induced by the SSC process can be highly polarized, with the maximum polarization Pi similar to 24% in the energy band [0.5, 5] MeV. The polarization depends on the viewing angles, peaking in the plane perpendicular to the magnetic field. In the energy band [0.05, 0.5] MeV, in which most gamma-ray polarimeters are active, the polarization is about twice that in the Thomson limit, reaching Pi similar to 20%. This implies that the Klein-Nishina effect, which is often neglected in the literature, should be carefully considered.
55602833
A new platform for topological quantum phenomena : Topological Insulator states in thermoelectric Heusler-related ternary compounds
Topological insulators (TI) realize a novel state of quantum matter that are distinguished by topological invariants of bulk band structure rather than spontaneously broken symmetries. A number of exotic quantum phenomena have been predicted to exist in multiply-connected geometries which require an enormous amount of materials flexibility. We have extended our previous search for TI materials from binary (Bi2X3 series) to the thermoelectric ternary compounds. We discover that the distorted LuPtSb is the first ternary compound harboring a 3D topological insulator state. We also show that the half-Heusler LuPtSb-type series is a natural platform that hosts a range of candidate compounds, alloys and artificial heterostructures (quantum-wells). We also discovered several different paradigms of trivial and non-trivial topological ordering in this class, including a metallic nontrivial topological state in YAuPb. Some of these materials are grown (results will be reported separately).
38766511
BESIII luminosity readout design based on embedded system
Zero-Degree Detector (ZDD) is a new Detector of Beijing Electron Spectrometer III (BESIII) for both double gamma event detection and luminosity monitoring to substitute the old luminosity monitor. A new luminosity readout is described in this paper which is designed in double width AMC/MTCA form factor with a large Xilinx Virtex5 FPGA in addition to normal electronic signal formation. A FPGA embedded PowerPC is used for data reading, accumulation and data transmission over a gigabit Ethernet. The setting of parameters like the discriminator threshold in Front End electronics is done via a special serial link under control of firmware in the same FPGA. This readout system has been put in operation since fall of 2012.
7503241
Kac-Moody extensions of 3-algebras and M2-branes
We study the 3-algebraic structure involved in the recently shown M2-branes worldvolume gauge theories. We first extend an arbitrary finite dimensional 3-algebra into an infinite dimensional 3-algebra by adding a mode number to each generator. A unique central charge in the algebra of gauge transformations appears naturally in this extension. We present an infinite dimensional extended 3-algebra with a general metric and also a different extension with a Lorentzian metric. We then study ordinary finite dimensional 3-algebras with different signatures of the metric, focusing on the cases with a negative eigenvalue and the cases with a zero eigenvalue. In the latter cases we present a new algebra, whose corresponding theory is a decoupled abelian gauge theory together with a free theory with global gauge symmetry, and there is no negative kinetic term from this algebra.
206531826
Topological Phase Transition and Texture Inversion in a Tunable Topological Insulator
Two types of bulk insulator are realized in the same family of compounds through chemical doping. The recently discovered three-dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into a topological state by modulating the spin-orbit interaction or the crystal lattice, driving the system through a topological quantum phase transition. By directly measuring the topological quantum numbers and invariants, we report the observation of a phase transition in a tunable spin-orbit system, BiTl(S1–δSeδ)2, in which the topological state formation is visualized. In the topological state, vortex-like polarization states are observed to exhibit three-dimensional vectorial textures, which collectively feature a chirality transition as the spin momentum–locked electrons on the surface go through the zero carrier density point. Such phase transition and texture inversion can be the physical basis for observing fractional charge (±e/2) and other fractional topological phenomena.
119224646
Giant gravitons and correlators
A bstractWe calculate non-extremal correlators of Schur polynomials and single trace operators. We analyse their dual descriptions from the approach of the variation of DBI and WZ actions of the giant gravitons. We show a regularization procedure under which the extremal correlators of Schur polynomials and single trace operators match exactly with string theory computation. Other aspects of the extremal and non-extremal correlators are also discussed.