5,827 research outputs found
Resgate de germoplasma vegetal de espĂ©cies-alvo na ĂĄrea de influĂȘncia do Aproveitamento HidrelĂ©trico Barra Grande (RS, SC).
bitstream/CENARGEN/29675/1/doc223.pd
Bopp-Podolsky black holes and the no-hair theorem
Bopp-Podolsky electrodynamics is generalized to curved space-times. The
equations of motion are written for the case of static spherically symmetric
black holes and their exterior solutions are analyzed using Bekenstein's
method. It is shown the solutions split-up into two parts, namely a
non-homogeneous (asymptotically massless) regime and a homogeneous
(asymptotically massive) sector which is null outside the event horizon. In
addition, in the simplest approach to Bopp-Podolsky black holes, the
non-homogeneous solutions are found to be Maxwell's solutions leading to a
Reissner-Nordstr\"om black hole. It is also demonstrated that the only exterior
solution consistent with the weak and null energy conditions is the Maxwell's
one. Thus, in light of energy conditions, it is concluded that only Maxwell
modes propagate outside the horizon and, therefore, the no-hair theorem is
satisfied in the case of Bopp-Podolsky fields in spherically symmetric
space-times.Comment: 9 pages, updated to match published versio
de Broglie-Proca and Bopp-Podolsky massive photon gases in cosmology
We investigate the influence of massive photons on the evolution of the
expanding universe. Two particular models for generalized electrodynamics are
considered, namely de Broglie-Proca and Bopp-Podolsky electrodynamics. We
obtain the equation of state (EOS) for each case using
dispersion relations derived from both theories. The EOS are inputted into the
Friedmann equations of a homogeneous and isotropic space-time to determine the
cosmic scale factor . It is shown that the photon non-null mass does not
significantly alter the result valid for a massless photon
gas; this is true either in de Broglie-Proca's case (where the photon mass
is extremely small) or in Bopp-Podolsky theory (for which is extremely
large).Comment: 8 pages, 2 figures; v2 matches the published versio
Four-dimensional topological Einstein-Maxwell gravity
The complete on-shell action of topological Einstein-Maxwell gravity in
four-dimensions is presented. It is shown explicitly how this theory for SU(2)
holonomy manifolds arises from four-dimensional Euclidean N=2 supergravity. The
twisted local BRST symmetries and twisted local Lorentz symmetries are given
and the action and stress tensor are shown to be BRST-exact. A set of
BRST-invariant topological operators is given. The vector and antisymmetric
tensor twisted supersymmetries and their algebra are also found.Comment: Published version. Expanded discussion of new results in the
introduction and some clarifying remarks added in later sections. 22 pages,
uses phyzz
How can one probe Podolsky Electrodynamics?
We investigate the possibility of detecting the Podolsky generalized
electrodynamics constant . First we analyze an ion interferometry apparatus
proposed by B. Neyenhuis, et al (Phys. Rev. Lett. 99, (2007) 200401) who looked
for deviations from Coulomb's inverse-square law in the context of Proca model.
Our results show that this experiment has not enough precision for measurements
of . In order to set up bounds for we investigate the influence of
Podolsky's electrostatic potential on the ground state of the Hydrogen atom.
The value of the ground state energy of the Hydrogen atom requires Podolsky's
constant to be smaller than 5.6 fm, or in energy scales larger than 35.51 MeV.Comment: 12 pages, 2 figure
Avaliação de adubos orgĂąnicos, elaborados a partir de resĂduos de pescado, no cultivo da batata (Solanum tuberosum) em bases ecolĂłgicas.
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