21,860 research outputs found
Lagrangians for Massive Dirac Chiral Superfields
A variant for the superspin one-half massive superparticle in , , based on Dirac superfields, is offered. As opposed to the
current known models that use spinor chiral superfields, the propagating fields
of the supermultiplet are those of the lowest mass dimensions possible: scalar,
Dirac and vector fields. Besides the supersymmetric chiral condition, the Dirac
superfields are not further constrained, allowing a very straightforward
implementation of the path-integral method. The corresponding superpropagators
are presented. In addition, an interaction super Yukawa potential, formed by
Dirac and scalar chiral superfields, is given in terms of their component
fields. The model is first presented for the case of two superspin one-half
superparticles related by the charged conjugation operator, but in order to
treat the case of neutral superparticles, the Majorana condition on the Dirac
superfields is also studied. We compare our proposal with the known models of
spinor superfields for the one-half superparticle and show that it is
equivalent to them.Comment: 22 pages. Matches published versio
Brownian motion of black holes in stellar systems with non-Maxwellian distribution for the stars field
A massive black hole at the center of a dense stellar system, such as a
globular cluster or a galactic nucleus, is subject to a random walk due
gravitational encounters with nearby stars. It behaves as a Brownian particle,
since it is much more massive than the surrounding stars and moves much more
slowly than they do. If the distribution function for the stellar velocities is
Maxwellian, there is a exact equipartition of kinetic energy between the black
hole and the stars in the stationary state. However, if the distribution
function deviates from a Maxwellian form, the strict equipartition cannot be
achieved. The deviation from equipartition is quantified in this work by
applying the Tsallis q-distribution for the stellar velocities in a
q-isothermal stellar system and in a generalized King model.Comment: Presented at XXVI Int. Astronomical Union General Assembly, Symp.
238, Prague, Czech Republic, Aug 21-25 200
Gravity with extra dimensions and dark matter interpretation: A straightforward approach
Any connection between dark matter and extra dimensions can be cognizably
evinced from the associated effective energy-momentum tensor. In order to
investigate and test such relationship, a higher dimensional spacetime endowed
with a factorizable general metric is regarded to derive a general expression
for the stress tensor -- from the Einstein-Hilbert action -- and to elicit the
effective gravitational potential. A particular construction for the case of
six dimensions is provided, and it is forthwith revealed that the missing mass
phenomenon may be explained, irrespective of the dark matter existence.
Moreover, the existence of extra dimensions in the universe accrues the
possibility of a straightforward mechanism for such explanation. A
configuration which density profile coincides with the Newtonian potential for
spiral galaxies is constructed, from a 4-dimensional isotropic metric plus
extra-dimensional components. A Miyamoto-Nagai \emph{ansatz} is used to solve
Einstein equations. The stable rotation curves associated to such system are
computed, in full compliance to the observational data, without fitting
techniques. The density profiles are reconstructed and compared to that ones
obtained from the Newtonian potential.Comment: 13 pages, 6 figure
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