QFT in the flat chart of de Sitter space

We study the correlators for interacting quantum field theory in the flat chart of de Sitter space at all orders in perturbation. The correlators are calculated in the in-in formalism which are often applied to the calculations in the cosmological perturbation. It is shown that these correlators are de Sitter invariant. They are compared with the correlators calculated based on the Euclidean field theory. We then find that these two correlators are identical. This correspondence has been already shown graph by graph but we give an alternative proof of it by direct calculation.Comment: 24 pages, 7 figures. References added with some minor corrections. To appear in Phys. Rev.

Generation of Field-Aligned Currents During Substorm Expansion: An Update

We investigated generation processes of field-aligned currents (FACs) that are abruptly intensified at the beginning of the substorm expansion phase by tracing a packet of the Alfvén wave backward in time from the onset position in the ionosphere in the global magnetohydrodynamics (MHD) simulation. The generation region is found in the near-Earth plasma sheet, in which (a) azimuthally moving plasma pulls the magnetic field line, and performs negative work against the magnetic tension force to excite the Alfvén waves, (b) FACs are generated from the requirement of Ampère and Faraday laws, and (c) field-perpendicular current is converted to FACs. We call this near-Earth FAC dynamo. The plasma involved originates in the tail lobe region. When near-Earth reconnection occurs in the plasma sheet, the plasma is accelerated earthward by the Lorentz force, and decelerated by the plasma pressure gradient force, followed by the Lorentz force. The flow is deflected to the west and east directions by the plasma pressure gradient force and the Lorentz force, resulting in the excitation of Alfvén waves and FACs. The Alfvén waves propagate along the magnetic field in the rest frame of the moving plasma. When it arrives at the ionosphere, the auroral electrojet starts developing and the substorm expansion phase begins. The near-Earth FAC dynamo can be distinguished from the near-Earth dynamo (J · E < 0, where J is the current density and E is the electric field). We suggest that the evolution of the substorm can be understood in terms of the development of FACs

Evolution of auroral substorm as viewed from MHD simulations: dynamics, energy transfer and energy conversion

An auroral substorm is a visual manifestation of large-scale, transient disturbances taking place in space surrounding the Earth, and is one of the central issues in the space plasma physics. While a number of studies have been conducted, a unified picture of the overall evolution of the auroral substorm has not been drawn. This paper is aimed to overview the recently obtained results of global magnetohydrodynamics (MHD) simulations in a context of a priori presence of anomalous resistivity leading to magnetic reconnection, and to illuminate what the global MHD simulation can sufficiently reproduce the auroral transients during the auroral substorm. Some auroral transients are found to be seamlessly reproduced by the MHD simulation, including complicated auroral structures moving equatorward during the growth phase, auroral brightening starting to appear near the equatorward border of the preexisting auroral arc, and an auroral surge traveling westward. Possible energy transfer and conversion from the solar wind to the Earth are also overviewed on the basis of the MHD simulation. At least, 4 dynamo regions appear sequentially in the course of the development of the auroral substorm. Although the MHD simulation reproduces some transients, further studies are needed to investigate the role of kinetic processes