132 research outputs found
Geodesic equations and algebro-geometric methods
For an investigation of the physical properties of gravitational fields the
observation of massive test particles and light is very useful. The
characteristic features of a given space-time may be decoded by studying the
complete set of all possible geodesic motions. Such a thorough analysis can be
accomplished most effectively by using analytical methods to solve the geodesic
equation. In this contribution, the use of elliptic functions and their
generalizations for solving the geodesic equation in a wide range of well known
space-times, which are part of the general Pleba\'nski-Demia\'nski family of
solutions, will be presented. In addition, the definition and calculation of
observable effects like the perihelion shift will be presented and further
applications of the presented methods will be outlined.Comment: 8 pages, no figures; based on presentation at the conference
"Relativity and Gravitation: 100 Years after Einstein in Prague," Prague,
2012. Relativity and Gravitation, volume 157 of Springer Proceedings in
Physics, p 91. Springer International Publishing, 201
The complete set of solutions of the geodesic equations in the space-time of a Schwarzschild black hole pierced by a cosmic string
We study the geodesic equations in the space-time of a Schwarzschild black
hole pierced by an infinitely thin cosmic string and give the complete set of
analytical solutions of these equations for massive and massless particles,
respectively. The solutions of the geodesic equations can be classified
according to the particle's energy and angular momentum, the ratio between the
component of the angular momentum aligned with the axis of the string and the
total angular momentum, the deficit angle of the space-time and as well the
horizon radius (or mass) of the black hole. For bound orbits of massive test
particles we calculate the perihelion shift, we discuss light deflection and
comment on the Newtonian limit.Comment: 21 pages; section 3 shortened, references added; accepted for
publication in Phys. Rev.
Analytical solution of the geodesic equation in Kerr-(anti) de Sitter space-times
The complete analytical solutions of the geodesic equations in Kerr-de Sitter
and Kerr-anti-de Sitter space-times are presented. They are expressed in terms
of Weierstrass elliptic p, zeta, and sigma functions as well as hyperelliptic
Kleinian sigma functions restricted to the one-dimensional theta-divisor. We
analyze the dependency of timelike geodesics on the parameters of the
space-time metric and the test-particle and compare the results with the
situation in Kerr space-time with vanishing cosmological constant. Furthermore,
we systematically can find all last stable spherical and circular orbits and
derive the expressions of the deflection angle of flyby orbits, the orbital
frequencies of bound orbits, the periastron shift, and the Lense-Thirring
effect.Comment: 18 pages, 11 figure
Geodesic motion in the space-time of a cosmic string
We study the geodesic equation in the space-time of an Abelian-Higgs string
and discuss the motion of massless and massive test particles. The geodesics
can be classified according to the particles energy, angular momentum and
linear momentum along the string axis. We observe that bound orbits of massive
particles are only possible if the Higgs boson mass is smaller than the gauge
boson mass, while massless particles always move on escape orbits. Moreover,
neither massive nor massless particles can ever reach the string axis for
non-vanishing angular momentum. We also discuss the dependence of light
deflection by a cosmic string as well as the perihelion shift of bound orbits
of massive particles on the ratio between Higgs and gauge boson mass and the
ratio between symmetry breaking scale and Planck mass, respectively.Comment: 20 pages including 14 figures; v2: references added, discussion on
null geodesics extended, numerical results adde
Lense-Thirring Precession in Pleba\'nski-Demia\'nski spacetimes
An exact expression of Lense-Thirring precession rate is derived for
non-extremal and extremal Pleba\'nski-Demia\'nski spacetimes. This formula is
used to find the exact Lense-Thirring precession rate in various axisymmetric
spacetimes, like: Kerr, Kerr-Newman, Kerr-de Sitter etc. We also show, if the
Kerr parameter vanishes in Pleba\'nski-Demia\'nski(PD) spacetime, the
Lense-Thirring precession does not vanish due to the existence of NUT charge.
To derive the LT precession rate in extremal Pleba\'nski-Demia\'nski we first
derive the general extremal condition for PD spacetimes. This general result
could be applied to get the extremal limit in any stationary and axisymmetric
spacetimes.Comment: 9 pages, Some special modifications are mad
Nucleonic resonance excitations with linearly polarized photon in
In this work, an improved quark model approach to the meson
photo-production with an effective Lagrangian is presented. The {\it t}-channel
{\it natural}-parity exchange is taken into account through the Pomeron
exchange, while the {\it unnatural}-parity exchange is described by the
exchange. With a very limited number of parameters, the available experimental
data in the low energy regime can be consistently accounted for. We find that
the beam polarization observables show sensitivities to some {\it s}-channel
individual resonances in the quark model symmetry limit.
Especially, the two resonances and , which belong
to the representation , have dominant contributions
over other excited states. Concerning the essential motivation of searching for
"missing resonances" in meson photo-production, this approach provides a
feasible framework, on which systematic investigations can be done.Comment: 16 pages, Revtex, 9 eps figures, to appear in PR
Co-design with aligned and non-aligned knowledge partners: implications for research and coproduction of sustainable food systems
We discuss two different strategies to initiate a process of identifying a focused sustainability challenge, and co-defining and co-designing alternative pathways to more sustainable food systems. One strategy was based on working with a relatively closely aligned network of private sector, civil society and academic organisations, whilst the other involved working with a more plural, non-aligned group, ranging from representatives of agricultural social movements, through to the domestic seed industry and government officials, to academic agronomists. This paper reflects on the distinct benefits and challenges involved in each strateg
The Pioneer Anomaly
Radio-metric Doppler tracking data received from the Pioneer 10 and 11
spacecraft from heliocentric distances of 20-70 AU has consistently indicated
the presence of a small, anomalous, blue-shifted frequency drift uniformly
changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was
interpreted as a constant sunward deceleration of each particular spacecraft at
the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of
the Newton's gravitational inverse-square law has become known as the Pioneer
anomaly; the nature of this anomaly remains unexplained. In this review, we
summarize the current knowledge of the physical properties of the anomaly and
the conditions that led to its detection and characterization. We review
various mechanisms proposed to explain the anomaly and discuss the current
state of efforts to determine its nature. A comprehensive new investigation of
the anomalous behavior of the two Pioneers has begun recently. The new efforts
rely on the much-extended set of radio-metric Doppler data for both spacecraft
in conjunction with the newly available complete record of their telemetry
files and a large archive of original project documentation. As the new study
is yet to report its findings, this review provides the necessary background
for the new results to appear in the near future. In particular, we provide a
significant amount of information on the design, operations and behavior of the
two Pioneers during their entire missions, including descriptions of various
data formats and techniques used for their navigation and radio-science data
analysis. As most of this information was recovered relatively recently, it was
not used in the previous studies of the Pioneer anomaly, but it is critical for
the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living
Reviews in Relativit
Electromagnetic Fields of Slowly Rotating Compact Magnetized Stars in Braneworld
We study the structure of electromagnetic field of slowly rotating magnetized
star in a Randall-Sundrum II type braneworld. The star is modeled as a sphere
consisting of perfect highly magnetized fluid with infinite conductivity and
frozen-in dipolar magnetic field. Maxwell's equations for the external magnetic
field of the star in the braneworld are analytically solved in approximation of
small distance from the surface of the star. We have also found numerical
solution for the electric field outside the rotating magnetized neutron star in
the braneworld in dependence on brane tension. The influence of brane tension
on the electromagnetic energy losses of the rotating magnetized star is
underlined. Obtained "brane" corrections are shown to be relevant and have
non-negligible values. In comparison with astrophysical observations on pulsars
spindown data they may provide an evidence for the brane tension and, thus,
serve as a test for the braneworld model of the Universe.Comment: 11 pages, 5 figure
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