16233799
Bulge formation in very late-type galaxies
The dynamical evolution of super star clusters (SSCs) moving in the background of a dark matter halo has been investigated as a possible event responsible for the formation of bulges in late-type spirals. The underlying physical processes include sinking of SSCs due to the dynamical friction and stripping of SSCs on their way to the center. Based on the assumption of a universal density profile for the dark matter halo, and an isothermal model for the SSCs, our simulations have yielded bulges that are similar in many aspects to the observational ones. In particular, the derived surface density profiles can be well fitted by an exponential structure with nuclear cusps, which is consistent with HST observations.The preliminary simulations with the Burkert density profile yield very instructive predictions on the bulge formation, which is surely worth further investigating.
119331816
An Equilibrium Dark Matter Halo with the Burkert Profile
In this paper a prescription for generating an equilibrium spherical system depicted with cuspy density profiles is extended to a core density profile, the Burkert profile, which is observationally more suitable to dwarfs. By using a time-saving Monte Carlo method instead of N-body simulations, we show that the Burkert halo, which is initialized with a distribution function that depends only on energy, is in a practically stable equilibrium. The one generated with the local Maxwellian approximation is unstable, where the flat core density structure tends to steepen. This is fundamentally different from a previous study on a halo with a cuspy density profile. The deviation of the unstable “Burkert” from the initial Burkert profile is found to be closely related to taking a Gaussian as the velocity distribution at any given point. The significance of not using the local Maxwellian approximation is further demonstrated by exploring the dynamical evolution of compact super star clusters (SSCs) in the Burkert halo. In particular, the local Maxwellian approximation results in underestimating the dynamical friction and overestimating sinking time scale. Accordingly, this leads to a lower probability of forming massive bulges and young nuclear star clusters in bulgeless galaxies.
121494708
Requirements for scattering solutions and the causal Green's function of the Bethe--Salpeter equation
We investigate the conditions necessary for the existence of scattering solutions to the Bethe-Salpeter equation. We work with the causal Green's function in both timelike and spacelike regions of $x\ensuremath{-}{x}^{\ensuremath{'}}$. Our results indicate that high-momentum or small-relative-time limits must be taken. In the small-relative-time limit, suitable restrictions on the interaction $I(x)$ must also be considered.
121270760
The complex EAS hybrid arrays in Tibet
The Tibet hybrid experiment is an extensive air shower experiment that operated at Yangbajing (E90°31', N30°06'; 4300 m above sea level) in Tibet, China, since 1996. This multi-detector system is used to observe air showers of high energy celestial gamma-ray origin and that of nuclear-component origin. Both observations aim to investigate the origin of cosmic rays using different methods. In this paper, based on the energy spectrum of the nuclear component and its chemical composition around the knee, we would like to discuss whether they could be described by the theoretical picture of the diffusive shock acceleration at SNRs. The consistency of the experimental data with rigidity dependent cutoff spectrum of CRs is examined using Tibet data and KASCADE data. It is found that both experimental data cannot be fully interpreted by such a simple approach. The sharp knee observed by Tibet experiment suggests the contribution of nearby source(s).
53540874
Dark matter induced nucleon decay: model and signatures
A bstractIf dark matter (DM) carries anti-baryon number, a DM particle may annihilate with a nucleon by flipping to anti-DM. Inspired by Hylogenesis models, we introduce a single component DM model where DM is asymmetric and carries B and L as -1/2. It can annihilate with a nucleon to an anti-lepton and an anti-DM at leading order or with an additional meson at sub-leading order. Such signals may be observed in proton decay experiments. If DM is captured in the Sun, the DM induced nucleon decay can generate a large flux of anti-neutrinos, which could be observed in neutrino experiments. Furthermore, the anti-DM particle in the final state obtains a relatively large momentum (few hundred MeV), and escapes the Sun. These fast-moving anti-DM particles could also induce interesting signals in various underground experiments.
122685473
Ladder approximation, scalar-exchange mesons, and Bethe--Salpeter scattering states
118612347
Collisions of Jets of Particles from Active Galactic Nuclei with Neutralino Dark Matter
We examine the possibility that energetic Standard Model particles contained in the jets produced by active galactic nuclei (AGN) may scatter off of the dark matter halo which is expected to surround the AGN. In particular, if there are nearby states in the dark sector which can appear resonantly in the scattering, the cross section can be enhanced and a distinctive edge feature in the energy spectrum may appear. We examine bounds on supersymmetric models which may be obtained from the Fermi Gamma-ray Space Telescope observation of the nearby AGN Centaurus A.