5,145 research outputs found
Photon spheres in Einstein and Einstein-Gauss-Bonnet theories and circular null geodesics in axially-symmetric spacetimes
In this article we extend a recent theorem proven by Hod (Phys. Lett. B, {\bf
727}, 345--348, 2013) to -dimensional Einstein and Einstein-Gauss-Bonnet
theories, which gives an upper bound for the photon sphere radii of spherically
symmetric black holes. As applications of these results we give a universal
upper bound for the real part of quasinormal modes in the WKB limit and a
universal lower bound for the position of the first relativistic image in the
strong lensing regime produced by these type of black holes. For the
axially-symmetric case, we also make some general comments (independent of the
underlying gravitational theory) on the relation between circular null
geodesics and the fastest way to circle a black hole.Comment: In this post-publisher version two typos were corrected: the
signature of the metric in eq.(1) and a factor in eq.(102). We thanks Gary
Gibbons and Chris Pope for bringing to our attention these typo
About the coordinate time for photons in Lifshitz Space-times
In this paper we studied the behavior of radial photons from the point of
view of the coordinate time in (asymptotically) Lifshitz space-times, and we
found a generalization to the result reported in previous works by Cruz et. al.
[Eur. Phys. J. C {\bf 73}, 7 (2013)], Olivares et. al. [Astrophys. Space Sci.
{\bf 347}, 83-89 (2013)], and Olivares et. al. [arXiv: 1306.5285]. We
demonstrate that all asymptotically Lifshitz space-times characterized by a
lapse funcion which tends to one when , present the
same behavior, in the sense that an external observer will see that photons
arrive at spatial infinity in a finite coordinate time. Also, we show that
radial photons in the proper system cannot determine the presence of the black
hole in the region , because the proper time results to be
independent of the lapse function .Comment: 5 pages, 4 figures, accepted for publication on EPJ
Gravitational Rutherford scattering and Keplerian orbits for electrically charged bodies in heterotic string theory
Properties of the motion of electrically charged particles in the background
of the Gibbons-Maeda-Garfinkle-Horowitz-Strominger (GMGHS) black hole is
presented in this paper. Radial and angular motion are studied analytically for
different values of the fundamental parameter. Therefore, gravitational
Rutherford scattering and Keplerian orbits are analysed in detail. Finally,
this paper complements previous work by Fernando for null geodesics (Phys. Rev.
D 85: 024033, 2012), Olivares & Villanueva (Eur. Phys. J. C 73: 2659, 2013) and
Blaga (Automat. Comp. Appl. Math. 22, 41 (2013); Serb. Astron. J. 190, 41
(2015)) for time-like geodesics.Comment: 11 pages, 12 figure
Massive neutral particles on heterotic string theory
The motion of massive particles in the background of a charged black hole in
heterotic string theory, which is characterized by a parameter , is
studied in detail in this paper. Since it is possible to write this space-time
in the Einstein frame, we perform a quantitative analysis of the time-like
geodesics by means of the standard Lagrange procedure. Thus, we obtain and
solve a set of differential equations and then we describe the orbits in terms
of the elliptic -Weierstra{\ss} function. Also, by making an elementary
derivation developed by Cornbleet (Am. J. Phys. \textbf{61} 7, (1993) 650 -
651) we obtain the correction to the angle of advance of perihelion to first
order in , and thus, by comparing with Mercury's data we give an
estimation for the value of this parameter, which yields an {\it heterotic
solar charge} .
Therefore, in addition to the study on null geodesics performed by Fernando
(Phys. Rev. D {\bf 85}, (2012) 024033), this work completes the geodesic
structure for this class of space-time.Comment: 12 pages, 8 figures. Accepted for publication on EPJ
A Jacobian elliptic single-field inflation
In the scenario of single-field inflation, this field is done in terms of
Jacobian elliptic functions. This approach provides, when constrained to
particular cases, analytic solutions already known in the past, generalizing
them to a bigger family of analytical solutions. The emergent cosmology is
analysed using the Hamilton-Jacobi approach and then, the main results are
contrasted with the recent measurements obtained from the Planck 2015 data.Comment: 7 pages, 5 figure
The golden ratio in Schwarzschild-Kottler black holes
In this paper we show that the golden ratio is present in the
Schwarzschild-Kottler metric. For null geodesics with maximal radial
acceleration, the turning points of the orbits are in the golden ratio . This is a general result which is independent of the value and
sign of the cosmological constant
Geodesic Structure of Lifshitz Black Holes in 2+1 Dimensions
We present a study of the geodesic equations of a black hole space-time which
is a solution of the three-dimensional NMG theory and is asymptotically
Lifshitz with and as found in [Ayon-Beato E., Garbarz A., Giribet
G. and Hassaine M., Phys. Rev. {\bf D} 80, 104029 (2009)]. By means of the
corresponding effective potentials for massive particles and photons we find
the allowed motions by the energy levels. Exact solutions for radial and
non-radial geodesics are given in terms of the Weierstrass elliptic ,
, and functions.Comment: 10 pages, 6 figures, accepted for publication in Eur. Phys. J.
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