21 research outputs found
A simple model for explaining Galaxy Rotation Curves
A new simple expression for the circular velocity of spiral galaxies is
proposed and tested against HI Nearby Galaxy Survey (THINGS) data set. Its
accuracy is compared with the one coming from MOND.Comment: 9 pages, 3 figures, 2 tables; this article is connected to
arXiv:1705.0413
Partial wave analysis of the Dirac fermions scattered from Reissner - Nordstr\" om charged black holes
The asymptotic form of Dirac spinors in the field of the Reissner-Nordstrom
black hole are derived for the scattering states (with ) obtaining the
phase shifts of the partial wave analysis of Dirac fermions scattered from
charged black holes. The elastic scattering and absorption are studied giving
analytic formulas for the partial amplitudes and cross sections. A graphical
study is performed for analysing the differential cross section
(forward/backward scattering) and the polarization degree as functions of
scattering angle.Comment: 6 two-column pages, 5 figures, a new figure with absorption included
and new comment
Partial wave analysis of the Dirac fermions scattered from Schwarzschild black holes
Asymptotic analytic solutions of the Dirac equation, giving the scattering
modes (of the continuous energy spectrum, ) in Schwarzschild's chart
and Cartesian gauge, are used for building the partial wave analysis of Dirac
fermions scattered by black holes. The contribution of the bound states to
absorption and possible resonant scattering is neglected because of some
technical difficulties related to the discrete spectrum that is less studied so
far. In this framework, the analytic expressions of the differential cross
section and induced polarization degree are derived in terms of scattering
angle, mass of the black hole, energy and mass of the fermion. Moreover, the
closed form of the absorption cross section due to the scattering modes is
derived showing that in the high-energy limit this tends to the event horizon
area regardless of the fermion mass (including zero). A graphical study
presents the differential cross section analyzing the forward/backward
scattering (known also as glory scattering) and the polarization degree as
functions of scattering angle. The graphical analysis shows the presence of
oscillations in scattering intensity around forward/backward directions,
phenomena known as spiral scattering. The energy dependence of the differential
cross section is also established by using analytical and graphical methods.Comment: 34 page