932 research outputs found
The 21st century propulsion
The prediction of future space travel in the next millennium starts by examining the past and extrapolating into the far future. Goals for the 21st century include expanded space travel and establishment of permanent manned outposts, and representation of Lunar and Mars outposts as the most immediate future in space. Nuclear stage design/program considerations; launch considerations for manned Mars missions; and far future propulsion schemes are outlined
Tricritical behavior of the massive chiral Gross-Neveu model
The phase diagram of the massive chiral Gross-Neveu model (the
1+1-dimensional Nambu-Jona-Lasinio model at large N) is investigated in the
vicinity of the tricritical point. Using the derivative expansion, the grand
canonical potential is cast into the form of a Ginzburg-Landau effective
action. Minimization of this action by variational and numerical methods
reveals both 1st and 2nd order phase transitions to a chiral crystal phase,
separated by a tricritical line. These findings are contrasted to the massive
Gross-Neveu model with discrete chiral symmetry where only 2nd order
transitions have been observed.Comment: 10 pages, 10 figures; v2: More details about perturbation theory
given, cf Eqs. (46-48
Dark spinor models in gravitation and cosmology
We introduce and carefully define an entire class of field theories based on
non-standard spinors. Their dominant interaction is via the gravitational field
which makes them naturally dark; we refer to them as Dark Spinors. We provide a
critical analysis of previous proposals for dark spinors noting that they
violate Lorentz invariance. As a working assumption we restrict our analysis to
non-standard spinors which preserve Lorentz invariance, whilst being non-local
and explicitly construct such a theory. We construct the complete
energy-momentum tensor and derive its components explicitly by assuming a
specific projection operator. It is natural to next consider dark spinors in a
cosmological setting. We find various interesting solutions where the spinor
field leads to slow roll and fast roll de Sitter solutions. We also analyse
models where the spinor is coupled conformally to gravity, and consider the
perturbations and stability of the spinor.Comment: 43 pages. Several new sections and details added. JHEP in prin
Statefinder diagnostic in a torsion cosmology
We apply the statefinder diagnostic to the torsion cosmology, in which an
accounting for the accelerated universe is considered in term of a
Riemann-Cartan geometry: dynamic scalar torsion. We find that there are some
typical characteristic of the evolution of statefinder parameters for the
torsion cosmology that can be distinguished from the other cosmological models.
Furthermore, we also show that statefinder diagnostic has a direct bearing on
the critical points. The statefinder diagnostic divides the torsion parameter
into differential ranges, which is in keeping with the requirement of
dynamical analysis. In addition, we fit the scalar torsion model to ESSENCE
supernovae data and give the best fit values of the model parameters.Comment: 18 pages, 15 figures, accepted paper in JCA
Phase structure of the massive chiral Gross-Neveu model from Hartree-Fock
The phase diagram of the massive chiral Gross-Neveu model (the massive
Nambu-Jona-Lasinio model in 1+1 dimensions) is constructed. In the large N
limit, the Hartree-Fock approach can be used. We find numerically a chiral
crystal phase separated from a massive Fermi gas phase by a 1st order
transition. Using perturbation theory, we also construct the critical sheet
where the homogeneous phase becomes unstable in a 2nd order transition. A
tricritical curve is located. The phase diagram is mapped out as a function of
fermion mass, chemical potential and temperature and compared with the one of
the discrete chiral Gross-Neveu model. As a by-product, we illustrate the
crystal structure of matter at zero temperature for various densities and
fermion masses.Comment: 12 pages, 16 figure
Conformal Invariance in Einstein-Cartan-Weyl space
We consider conformally invariant form of the actions in Einstein, Weyl,
Einstein-Cartan and Einstein-Cartan-Weyl space in general dimensions() and
investigate the relations among them. In Weyl space, the observational
consistency condition for the vector field determining non-metricity of the
connection can be obtained from the equation of motion. In Einstein-Cartan
space a similar role is played by the vector part of the torsion tensor. We
consider the case where the trace part of the torsion is the Kalb-Ramond type
of field. In this case, we express conformally invariant action in terms of two
scalar fields of conformal weight -1, which can be cast into some interesting
form. We discuss some applications of the result.Comment: 10 pages, version to appear MPL
Upstream-binding factor is sequestered into herpes simplex virus type 1 replication compartments
Previous reports have shown that adenovirus recruits nucleolar protein upstream-binding factor (UBF) into adenovirus DNA replication centres. Here, we report that despite having a different mode of viral DNA replication, herpes simplex virus type 1 (HSV-1) also recruits UBF into viral DNA replication centres. Moreover, as with adenovirus, enhanced green fluorescent protein-tagged fusion proteins of UBF inhibit viral DNA replication. We propose that UBF is recruited to the replication compartments to aid replication of HSV-1 DNA. In addition, this is a further example of the role of nucleolar components in viral life cycle
The Bogoliubov/de Gennes system, the AKNS hierarchy, and nonlinear quantum mechanical supersymmetry
We show that the Ginzburg-Landau expansion of the grand potential for the
Bogoliubov-de Gennes Hamiltonian is determined by the integrable nonlinear
equations of the AKNS hierarchy, and that this provides the natural
mathematical framework for a hidden nonlinear quantum mechanical supersymmetry
underlying the dynamics.Comment: 25 pages, 4 figures; published versio
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