arXiv subjects

Yunguo Jiang

Publications and source records attributed to Yunguo Jiang.

29 records · Page 2Linked to original sources

arXiv2015

GRB Spectra in the complex of synchrotron and Compton processes

Under the steady state condition, the spectrum of electrons is investigated by solving the continuity equation under the complex radiation of both the synchrotron and Compton processes. The resulted GRB spectrum is a broken power law in both the fast and slow cooling phases. On the basis of this electron spectrum, the spectral indices of the Band function in four different phases are presented. In the complex radiation frame, the detail investigation on physical parameters reveals that both the reverse shock photosphere model and the forward shock with strong coupling model can answer the $α\sim -1$ problem. A possible marginal to fast cooling phase transition in GRB 080916C is discussed. The time resolved spectra in different pulses of GRB 100724B, GRB 100826A and GRB 130606B are investigated. We found that the flux is proportional to the peak energy in almost all pulses. The phases for different pulses are determined according to the spectral index revolution. We found the strong correlations between spectral indices and the peak energy in GRB 100826A, which can be explained by the Compton effect in the fast cooling phase. However, the complex scenario predicts a steeper index for the injected electrons, which challenges the acceleration mechanism in GRBs.

astro-ph.HE↗

arXiv2014

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 processes. The observed polarization depends on both the photon energy and the viewing angle. With the typical bulk Lorentz factor $Γ\sim 200$, 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. $θ\sim Γ^{-1}$, the polarization achieves its maximal value, and the polarization angle changes $90^{\circ}$ relative to the initial polarization direction. Thus, the synchrotron radiation plus Compton scattering model can naturally explain the $90^{\circ}$ change of the polarization angle in GRB 100826A.

astro-ph.HE↗

arXiv2014

Gamma-ray burst polarization via Compton scattering process

Synchrotron radiation and Compton scattering are widely accepted as the most likely emission mechanisms of some astrophysical phenomena, such as gamma-ray bursts (GRBs) and active galactic nuclei (AGNs). The measurement on polarization of photons provides a useful tool to distinguish different emission mechanisms and structures of the emission region. Based on the differential cross section of a polarized photon scattered by an unpolarized electron of any initial momentum, we derive analytical formula of polarization for beamed photons scattered by isotropic electrons with a power law distribution. Numerical calculations are carried out in four special cases: electrons at rest, Thomson limit, head-on collision and monochromatic electrons. It is found that the maximum polarization can be as high as $100\%$ for low energy photons, if the electrons are at rest. Although polarization is highly suppressed due to the isotropic electrons, a maximum value of $\sim 10\% \-- 20\%$ can still be achieved. Compton scattering process can be used to explain the polarization of GRB 041219A and GRB 100826A.

astro-ph.HE↗

arXiv2013

Mass deformed world-sheet action of semi-local vortices

The mass deformed effective world-sheet theory of semi local vortices was constructed via the field theoretical method. By Euler-Lagrangian equations, the Ansatze for both the gauge field and the adjoint scalar were solved, this ensures that zero modes of vortices are minimal excitations of the system. Up to the $1/g^2$ order, all profiles are solved. The mass deformed effective action was obtained by integrating out the transverse plane of the vortex string. The effective theory interpolates between the local vortex and the lump. Respecting certain normalization conditions, the effective theory shows a Seiberg-like duality, which agrees with the result of the Kähler quotient construction.

hep-th↗

arXiv2013

Polarization of photons scattered by electrons in any spectral distribution

Based on the quantum electrodynamics, we present a generic formalism of the polarization for beamed monochromatic photons scattered by electrons in any spectral distribution. The formulae reduce to the components of the Fano matrix when electrons are at rest. We mainly investigate the polarization in three scenarios, i.e., electrons at rest, isotropic electrons with a power law spectrum and thermal electrons. If the incident beam is polarized, the polarization is reduced significantly by isotropic electrons at large viewing angles, and the degree of polarization due to thermal electrons is about one times less than that of electrons in a power law. If the incident bean is unpolarized, soft $γ$-rays can lead to about 15% polarization at viewing angles around $π/4$. For isotropic electrons, one remarkable feature is that the polarization as a function of the incident photon energy always peaks roughly at 1 MeV, this is valid for both the thermal and power law cases. This feature can be used to distinguish the model of the inverse Compton scattering from that of the synchrotron radiation.

astro-ph.HE↗

arXiv2013

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 $Δt_{\rm int}$ 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 {\it Fermi}-detected GRBs. This leads to a unique quantum gravity energy scale $M_1c^2 \sim 1.0 \times 10^{20}$ GeV respecting the linear dispersion relation.

astro-ph.HE↗

arXiv2013

Constraining the Bulk Lorentz Factor of GRB Outflow in the Magnetic-dominated Jet Model

Recent observations by the Fermi-LAT showed that there are delayed arrivals of GeV photons relative to the onset of MeV photons in some GRBs. In order to avoid a large optical depth, the minimal value of the Lorentz factor has been estimated to be higher than 1000 in some brightest bursts. In this paper, we present a detailed calculation of the time delay between the MeV and GeV photons in the framework of the magnetic-dominated jet model. We find that the time delay strongly depends on the saturated bulk Lorentz factor of the jet. Inspired by this fact, we use this model to calculate the Lorentz factors of the four brightest Fermi bursts. The results indicate that the Lorentz factors are much smaller than that obtained from the "single-zone" scenario. The short GRB 090510 has a minimal Lorentz factor 385, while the three long bursts GRB 080916c, GRB090902b and GRB 090926 have almost the same Lorentz factors, with an average value near 260. Another interesting result is that, for long bursts, GeV photons are emitted after the bulk Lorentz factor saturates. For the short GRB, however, MeV and GeV photons are emitted at the same phase, i.e., either at the expansion phase or at the coast phase.

astro-ph.HE↗

arXiv2012

Non-Abelian vortices in the emergent U(2) gauge theory of the Hubbard model

By the spin-fermion formula, the Hubbard model on the honeycomb lattice is represented by a U(2) gauge theory in the mean field method, non-Abelian vortex solutions are constructed based on this theory. The quantization condition shows that the magnetic flux quanta are half-integer. There are $2k$ bosonic zero modes for $k$ winding vortices. For the fermions, there are 2 zero energy states (ZESs) corresponding to the single elementary vortex. In the vortex core and on the edge, the system are in the semi-metal phase with a spin gap and in the insulator phase with Néel order phase, and can be mapped to the superconductor in class A and CI, respectively.

cond-mat.supr-con↗

arXiv2011

Vortices and Monopoles in Mass-deformed SO and USp Gauge Theories

Effects of mass deformations on 1/2 Bogomol'nyi-Prasad-Sommerfield (BPS) non-Abelian vortices are studied in 4d N=2 supersymmetric U(1) \times SO(2n) and U(1) \times USp(2n) gauge theories, with Nf=2n quark multiplets. The 2d N=(2,2) effective worldsheet sigma models on the Hermitian symmetric spaces SO(2n)/U(n) and USp(2n)/U(n) found recently which describe the low-energy excitations of the orientational moduli of the vortices, are generalized to the respective massive sigma models. The continuous vortex moduli spaces are replaced by a finite number (2^{n-1} or 2^{n}) of vortex solutions. The 1/2 BPS kinks connecting different vortex vacua are magnetic monopoles in the 4d theory, trapped inside the vortex core, with total configurations being 1/4 BPS composite states. These configurations are systematically studied within the semi-classical regime.

hep-th↗

arXiv2010

Group Theory of Non-Abelian Vortices

We investigate the structure of the moduli space of multiple BPS non-Abelian vortices in U(N) gauge theory with N fundamental Higgs fields, focusing our attention on the action of the exact global (color-flavor diagonal) SU(N) symmetry on it. The moduli space of a single non-Abelian vortex, CP(N-1), is spanned by a vector in the fundamental representation of the global SU(N) symmetry. The moduli space of winding-number k vortices is instead spanned by vectors in the direct-product representation: they decompose into the sum of irreducible representations each of which is associated with a Young tableau made of k boxes, in a way somewhat similar to the standard group composition rule of SU(N) multiplets. The Kähler potential is exactly determined in each moduli subspace, corresponding to an irreducible SU(N) orbit of the highest-weight configuration.

hep-th↗

arXiv2010

Non-Abelian vortex dynamics: Effective world-sheet action

The low-energy vortex effective action is constructed in a wide class of systems in a color-flavor locked vacuum, which generalizes the results found earlier in the context of U(N) models. It describes the weak fluctuations of the non-Abelian orientational moduli on the vortex worldsheet. For instance, for the minimum vortex in SO(2N) x U(1) or USp(2N) x U(1) gauge theories, the effective action found is a two-dimensional sigma model living on the Hermitian symmetric spaces SO(2N)/U(N) or USp(2N)/U(N), respectively. The fluctuating moduli have the structure of that of a quantum particle state in spinor representations of the GNO dual of the color-flavor SO(2N) or USp(2N) symmetry, i.e. of SO(2N) or of SO(2N+1). Applied to the benchmark U(N) model our procedure reproduces the known CP(N-1) worldsheet action; our recipe allows us to obtain also the effective vortex action for some higher-winding vortices in U(N) and SO(2N) theories.

hep-th↗