3,840 research outputs found
Testing Single-Parameter Classical Standpoint Cosmology
Experimental tests of homogeneous-universe classical standpoint cosmology are
proposed after presentation of conceptual considerations that encourage this
radical departure from the standard model. Among predictions of the new model
are standpoint age equal to Hubble time, energy-density parameter , and relations between redshift, Hubble-scale distribution of
matter and galaxy luminosity and angular diameter. These latter relations
coincide with those of the standard model for zero deceleration. With eye to
further tests, geodesics of the non-Riemannian standpoint metric are explicitly
given. Although a detailed thermodynamic ``youthful-standpoint'' approximation
remains to be developed (for particle mean free path small on standpoint
scale), standpoint temperature depending only on standpoint age is a natural
concept, paralleling energy density and redshift that perpetuates thermal
spectrum for cosmic background radiation. Prospects for primordial
nucleosynthesis are promising.Comment: 27 pages, latexed, math_macros.tex used, full postscript available
from: http://theor1.lbl.gov/www/theorgroup/papers/37162.p
Weak Classical-Gravity Source in Standpoint Cosmology
Guided by a linearized approximation to Einstein theory, an interim
prescription for ``weak source of gravity'' - - in ``particle'' energy-momentum
distributed along standpoint light cone - - is formulated for (classical)
standpoint cosmology.Comment: 11 pages, uses math_macros.tex, late
Transition from collisionless to collisional MRI
Recent calculations by Quataert et al. (2002) found that the growth rates of
the magnetorotational instability (MRI) in a collisionless plasma can differ
significantly from those calculated using MHD. This can be important in hot
accretion flows around compact objects. In this paper we study the transition
from the collisionless kinetic regime to the collisional MHD regime, mapping
out the dependence of the MRI growth rate on collisionality. A kinetic closure
scheme for a magnetized plasma is used that includes the effect of collisions
via a BGK operator. The transition to MHD occurs as the mean free path becomes
short compared to the parallel wavelength 2\pi/k_{\Par}. In the weak magnetic
field regime where the Alfv\'en and MRI frequencies are small compared
to the sound wave frequency k_{\Par} c_0, the dynamics are still effectively
collisionless even if , so long as the collision frequency \nu
\ll k_{\Par} c_{0}; for an accretion flow this requires \nu \lsim \Omega
\sqrt{\beta}. The low collisionality regime not only modifies the MRI growth
rate, but also introduces collisionless Landau or Barnes damping of long
wavelength modes, which may be important for the nonlinear saturation of the
MRI.Comment: 20 pages, 4 figures, submitted to ApJ with a clearer derivation of
anisotropic pressure closure from drift kinetic equatio
Exploring the S-Matrix of Massless Particles
We use the recently proposed generalised on-shell representation for
scattering amplitudes and a consistency test to explore the space of tree-level
consistent couplings in four-dimensional Minkowski spacetime. The extension of
the constructible notion implied by the generalised on-shell representation,
i.e. the possibility to reconstruct at tree level all the scattering amplitudes
from the three-particle ones, together with the imposition of the consistency
conditions at four-particle level, allow to rediscover all the known theories
and their algebra structure, if any. Interestingly, this analysis seems to
leave room for high-spin couplings, provided that at least the requirement of
locality is weakened. We do not claim to have found tree-level consistent
high-spin theories, but rather that our methods show signatures of them and
very likely, with a suitable modification, they can be a good framework to
perform a systematic search.Comment: 44 pages, 1 figur
TOPOLOGICAL ELECTROMAGNETISM FOR QUARKS AND LEPTONS
As outgrowth of a topological bootstrap theory of strong interactions and precursor to a corresponding theory of weak interactions, we propose a representation of electromagnetic interactions for "elementary" hadrons and leptons through combinatorial topology. The representation supports the prediction of four lepton doublets
U(1)-decoupling, KK and BCJ relations in SYM
We proved the color reflection relation, U(1)-decoupling, Kleiss-Kuijf and
Bern-Carrasco-Johansson relation for color-ordered Super
Yang-Mills theory using SYM version BCFW recursion relation,
which depends only on the general properties of super-amplitudes. This verified
the conjectured matter fields BCJ relation. We also show that color reflection
relation and U(1)-decoupling relation are special cases of KK relation, if we
consider the KK relation as a general relation, then the former two relations
come out naturally as the special cases.Comment: 17 page
Dissipation in intercluster plasma
We discuss dissipative processes in strongly gyrotropic, nearly collisionless
plasma in clusters of galaxies (ICM). First, we point out that Braginsky
theory, which assumes that collisions are more frequent that the system's
dynamical time scale, is inapplicable to fast, sub-viscous ICM motion. Most
importantly, the electron contribution to collisional magneto-viscosity
dominates over that of ions for short-scale Alfvenic motions. Thus, if a
turbulent cascade develops in the ICM and propagates down to scales
kpc, it is damped collisionally not on ions, but on electrons. Second, in high
beta plasma of ICM, small variations of the magnetic field strength, of
relative value , lead to development of anisotropic pressure
instabilities (firehose, mirror and cyclotron). Unstable wave modes may provide
additional resonant scattering of particles, effectively keeping the plasma in
a state of marginal stability. We show that in this case the dissipation rate
of a laminar, subsonic, incompressible flows scales as inverse of plasma beta
parameter. We discuss application to the problem of ICM heating.Comment: 4 pages, accepted by ApJ Let
The Riemann Surface of a Static Dispersion Model and Regge Trajectories
The S-matrix in the static limit of a dispersion relation is a matrix of a
finite order N of meromorphic functions of energy in the plane with
cuts . In the elastic case it reduces to N functions
connected by the crossing symmetry matrix A. The scattering of
a neutral pseodoscalar meson with an arbitrary angular momentum l at a source
with spin 1/2 is considered (N=2). The Regge trajectories of this model are
explicitly found.Comment: 5 pages, LaTe
Application of dispersion relations to low-energy meson-nucleon scattering
Relativistic dispersion relations are used to derive equations for low-energy S-, P-, and D-wave meson-nucleon scattering under the assumption that the (3,3) resonance dominates the dispersion integrals. The P-wave equations so obtained differ only slightly from those of the static fixed-source theory. The conclusions of the static theory are re-examined in the light of their new derivation
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