226 research outputs found
Seed Magnetic Fields Generated by Primordial Supernova Explosions
The origin of the magnetic field in galaxies is an open question in
astrophysics. Several mechanisms have been proposed related, in general, with
the generation of small seed fields amplified by a dynamo mechanism. In
general, these mechanisms have difficulty in satisfying both the requirements
of a sufficiently high strength for the magnetic field and the necessary large
coherent scales. We show that the formation of dense and turbulent shells of
matter, in the multiple explosion scenario of Miranda and Opher (1996, 1997)
for the formation of the large-scale structures of the Universe, can naturally
act as a seed for the generation of a magnetic field. During the collapse and
explosion of Population III objects, a temperature gradient not parallel to a
density gradient can naturally be established, producing a seed magnetic field
through the Biermann battery mechanism. We show that seed magnetic fields can be produced in this multiple explosion scenario on
scales of the order of clusters of galaxies (with coherence length ) and up to on scales of galaxies ().Comment: Accepted for publication in MNRAS, 5 pages (MN plain TeX macros v1.6
file). Also available at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS"
and then "ARTICLES"
Dependence of the MHD shock thickness on the finite electrical conductivity
The results of MHD plane shock waves with infinite electrical conductivity
are generalized for a plasma with a finite conductivity. We derive the
adiabatic curves that describe the evolution of the shocked gas as well as the
change in the entropy density. For a parallel shock (i.e., in which the
magnetic field is parallel to the normal to the shock front) we find an
expression for the shock thickness which is a function of the ambient magnetic
field and of the finite electrical conductivity of the plasma. We give
numerical estimates of the physical parameters for which the shock thickness is
of the order of, or greater than, the mean free path of the plasma particles in
a strongly magnetized plasma.Comment: 8 pages, uses standard revtex, to appear in Journal of Plasma Physic
Generalized Non-Commutative Inflation
Non-commutative geometry indicates a deformation of the energy-momentum
dispersion relation for massless particles.
This distorted energy-momentum relation can affect the radiation dominated
phase of the universe at sufficiently high temperature. This prompted the idea
of non-commutative inflation by Alexander, Brandenberger and Magueijo (2003,
2005 and 2007). These authors studied a one-parameter family of
non-relativistic dispersion relation that leads to inflation: the
family of curves . We show here how the
conceptually different structure of symmetries of non-commutative spaces can
lead, in a mathematically consistent way, to the fundamental equations of
non-commutative inflation driven by radiation. We describe how this structure
can be considered independently of (but including) the idea of non-commutative
spaces as a starting point of the general inflationary deformation of
. We analyze the conditions on the dispersion relation that
leads to inflation as a set of inequalities which plays the same role as the
slow roll conditions on the potential of a scalar field. We study conditions
for a possible numerical approach to obtain a general one parameter family of
dispersion relations that lead to successful inflation.Comment: Final version considerably improved; Non-commutative inflation
rigorously mathematically formulate
A conceptual problem for non-commutative inflation and the new approach for non-relativistic inflationary equation of state
In a previous paper, we connected the phenomenological non-commutative
inflation of Alexander, Brandenberger and Magueijo (2003) and Koh S and
Brandenberger (2007) with the formal representation theory of groups and
algebras and analyzed minimal conditions that the deformed dispersion relation
should satisfy in order to lead to a successful inflation. In that paper, we
showed that elementary tools of algebra allow a group like procedure in which
even Hopf algebras (roughly the symmetries of non-commutative spaces) could
lead to the equation of state of inflationary radiation. In this paper, we show
that there exists a conceptual problem with the kind of representation that
leads to the fundamental equations of the model. The problem comes from an
incompatibility between one of the minimal conditions for successful inflation
(the momentum of individual photons is bounded from above) and the group
structure of the representation which leads to the fundamental inflationary
equations of state. We show that such a group structure, although
mathematically allowed, would lead to problems with the overall consistency of
physics, like in scattering theory, for example. Therefore, it follows that the
procedure to obtain those equations should be modified according to one of two
possible proposals that we consider here. One of them relates to the general
theory of Hopf algebras while the other is based on a representation theorem of
Von Neumann algebras, a proposal already suggested by us to take into account
interactions in the inflationary equation of state. This reopens the problem of
finding inflationary deformed dispersion relations and all developments which
followed the first paper of Non-commutative Inflation.Comment: Phys. Rev. D, 2013, in pres
Using foreCAT deflections and rotations to constrain the early evolution of CMEs
To accurately predict the space weather effects of the impacts of coronal mass ejection (CME) at Earth one must know if and when a CME will impact Earth and the CME parameters upon impact. In 2015 Kay et al. presented Forecasting a CME's Altered Trajectory (ForeCAT), a model for CME deflections based on the magnetic forces from the background solar magnetic field. Knowing the deflection and rotation of a CME enables prediction of Earth impacts and the orientation of the CME upon impact. We first reconstruct the positions of the 2010 April 8 and the 2012 July 12 CMEs from the observations. The first of these CMEs exhibits significant deflection and rotation (34° deflection and 58° rotation), while the second shows almost no deflection or rotation (<3° each). Using ForeCAT, we explore a range of initial parameters, such as the CME's location and size, and find parameters that can successfully reproduce the behavior for each CME. Additionally, since the deflection depends strongly on the behavior of a CME in the low corona, we are able to constrain the expansion and propagation of these CMEs in the low corona.C.K.'s research was supported by an appointment to the NASA Postdoctoral Program at NASA GSFC, administered by the Universities Space Research Association under contract with NASA. A.V. acknowledges support from JHU/APL. R.C.C. acknowledges the support of NASA contract S-136361-Y to NRL. The SECCHI data are produced by an international consortium of the NRL, LMSAL, and NASA GSFC (USA), RAL and Univ. of Birmingham (UK), MPS (Germany), CSL (Belgium), IOTA and IAS (France). (JHU/APL; S-136361-Y - NASA)Published versio
Using ForeCAT Deflections and Rotations to Constrain the Early Evolution of CMEs
To accurately predict the space weather effects of coronal mass ejection
(CME) impacts at Earth one must know if and when a CME will impact Earth, and
the CME parameters upon impact. Kay et al. (2015b) presents Forecasting a CME's
Altered Trajectory (ForeCAT), a model for CME deflections based on the magnetic
forces from the background solar magnetic field. Knowing the deflection and
rotation of a CME enables prediction of Earth impacts, and the CME orientation
upon impact. We first reconstruct the positions of the 2008 April 10 and the
2012 July 12 CMEs from the observations. The first of these CMEs exhibits
significant deflection and rotation (34 degrees deflection and 58 degrees
rotation), while the second shows almost no deflection or rotation (<3 degrees
each). Using ForeCAT, we explore a range of initial parameters, such as the CME
location and size, and find parameters that can successfully reproduce the
behavior for each CME. Additionally, since the deflection depends strongly on
the behavior of a CME in the low corona (Kay et al. (2015a, 2015b)), we are
able to constrain the expansion and propagation of these CMEs in the low
corona.Comment: accepted in Ap
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