119255191
A unified constraint on the Lorentz invariance violation from both short and long GRBs
Possible Lorentz invariance violation (LIV) has been investigated for a long time based on observations of GRBs. These arguments relied on the assumption that photons with different energy are emitted at the same place and time. In this work, we try to take account of the intrinsic time delay Delta t(int) between emissions of low and high energy photons by using the magnetic jet model. The possible LIV effects are discussed in a unified scenario both for long and short Fermi-detected GRBs. This leads to a unique quantum gravity energy scale M(1)c(2) similar to 1.0 x 10(20) GeV respecting the linear dispersion relation. (C) 2012 Elsevier B.V. All rights reserved.
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.
118473600
Galaxy Rotation Curves in the Grumiller's Modified Gravity
The effective potential in the Grumiller's modified gravity includes the Newtonian potential and a Rindler term. The fitting to the rotation curve data of eight galaxies suggests a universal Rindler acceleration a approximate to 0.30 x 10(-10) ms(-2). We do a two-parameter fit first, with the mass-to-light ratio ((sic)(*)) and the Rindler acceleration (a) as free parameters. It is found that the data of six out of the eight galaxies fit well with the prediction of theory in the range 0 r less than or similar to 40 kpc, although the theoretical curves show a tendency of arising beyond this range. The Rindler accelerations of the six well-fitted galaxies have the same magnitude, with an average value (a) over bar approximate to 0.30 x 10(-10) ms(-2). Inspired by this fact, we then carry out a one-parameter ((sic)(*)) fit to the six galaxies, with a fixed at (a) over bar, and find that the theory can still reproduce the observation. The value of Rindler acceleration we get here is a quarter of that of Milgrom's modified Newtonian dynamics. For the rest two galaxies, NGC 5055 and DDO 154, the fitting results are significantly improved if the photometric scale length (h) is included as another free parameter.
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 $cH_{0}/2\pi\sim10^{-10}~\mathrm{m\,s}^{-2}$.
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.
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.
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.
119225338
Strings on bubbling geometries
We study gauge theory operators which take the form of a product of a trace with a Schur polynomial, and their string theory duals. These states represent strings excited on bubbling AdS geometries which are dual to the Schur polynomials. These geometries generically take the form of multiple annuli in the phase space plane. We study the coherent state wavefunction of the lattice, which labels the trace part of the operator, for a general Young tableau and their dual description on the droplet plane with a general concentric ring pattern. In addition we identify a density matrix over the coherent states on all the geometries within a fixed constraint. This density matrix may be used to calculate the entropy of a given ensemble of operators. We finally recover the BMN string spectrum along the geodesic near any circle from the ansatz of the coherent state wave-function.
118398823
M2-M5 systems in = 6 Chern-Simons theory
We study two aspects of M5-branes in N = 6 U(N) × U(N) Chern-Simons gauge theory. We first examine multiple M2-branes ending on a M5-brane. We study Basu-Harvey type cubic equations, fuzzy funnel configurations, and derive the M5-brane tension from the N = 6 theory. We also find a limit in which the above M2-M5 system reduces to a D2-D4 system and we recover the Nahm equation from the N = 6 theory. We then examine domain wall configurations in mass-deformed N = 6 theory with a manifest SU(2) × SU(2) × U(1) global symmetry. We derive tensions of domain walls connecting between arbitrary M5-brane vacua of the deformed theory and observe their consistency with gravity dual expectations.
117989993
Magnetically induced spin reorientation on the surface of a topological insulator (a surface magnetic topological insulator MBE film)
The surface of topological insulators is proposed as a promising platform for spintronics and quantum information applications. In particular, when time- reversal symmetry is broken, topological surface states are expected to exhibit a wide range of exotic spin phenomena for potential implementation in electronics. Such devices need to be fabricated using nanoscale artificial thin films. It is of critical importance to study the spin behavior of artificial topological MBE thin films associated with magnetic dopants, and with regards to quantum size effects related to surface-to-surface tunneling as well as experimentally isolate time-reversal breaking from non-intrinsic surface electronic gaps. Here we present observation of the first (and thorough) study of magnetically induced spin reorientation phenomena on the surface of a topological insulator. Our results reveal dramatic rearrangements of the spin configuration upon magnetic doping contrasted with chemically similar nonmagnetic doping as well as with quantum tunneling phenomena in ultra-thin high quality MBE films. While we observe that the spin rearrangement induced by quantum tunneling occurs in a time-reversal invariant fashion, we present critical and systematic observation of an out-of-plane spin texture evolution correlated with magnetic interactions, which breaks time-reversal symmetry, demonstrating microscopic TRB at a Kramers' point on the surface.
119087062
Effects of iron doping on the topological insulator surfaces
Topological insulators embody a newly discovered state of matter characterized by conducting spin-momentum locked surface states that span the bulk band gap. So far, most of the study on topological insulator surfaces has been limited to understanding their properties without strong Coulomb perturbation or breaking of time reversal symmetry. We have used deposited iron, with a large positive ionization state and significant magnetic moment as a strong probe to modify the surface electronic structure of the Bi2Se3 surface at the gap energy scale. We observe that such perturbation leads to the creation of multiple Dirac fermions consistent with Z2 or Mod(2) symmetry. Taken collectively, these results are a helpful guide in manipulating topological surfaces for probing fundamental physics or developing device applications.