37,923 research outputs found
Particle collisions near a three-dimensional warped AdS black hole
In this paper we consider the warped AdS black hole solution of
topologically massive gravity with a negative cosmological constant, and we
investigate the possibility that it acts as a particle accelerator by analyzing
the energy in the center of mass (CM) frame of two colliding particles in the
vicinity of its horizon, which is known as the Ba\~nados, Silk and West (BSW)
process. Mainly, we show that the critical angular momentum of the
particle decreases when the parameter that controls the stretching deformation
() increases. Also, we show that despite the particle with can exist
for certain values of the conserved energy outside the horizon, it will never
reach the event horizon; therefore, the black hole can not act as a particle
accelerator with arbitrarily high CM energy on the event horizon. However, such
particle could also exist inside the outer horizon being the BSW process
possible on the inner horizon. On the other hand, for the extremal warped
AdS black hole, the particle with and energy could exist
outside the event horizon and the CM energy blows up on the event horizon if
its conserved energy fulfill the condition
, being the BSW process possible.Comment: 11 pages, 6 figure
Fermionic greybody factors of two and five-dimensional dilatonic black holes
We study fermionic perturbations in the background of a two and
five-dimensional dilatonic black holes. Then, we compute the reflection and
transmission coefficients and the absorption cross section for fermionic
fields, and we show numerically that the absorption cross section vanishes in
the low and high frequency limit. Also we find that beyond a certain value of
the horizon radius the absorption cross section for five-dimensional
dilatonic black hole is constant. Besides, we have find that the absorption
cross section decreases for higher angular momentum, and it decreases when the
mass of the fermionic field increases.Comment: Accepted in EPJ
Fast-to-Alfv\'en mode conversion mediated by Hall current. II Application to the solar atmosphere
Coupling between fast magneto-acoustic and Alfv\'en waves can be observe in
fully ionized plasmas mediated by stratification and 3D geometrical effects. In
Paper I, Cally & Khomenko (2015) have shown that in a weakly ionized plasma,
such as the solar photosphere and chromosphere, the Hall current introduces a
new coupling mechanism. The present study extends the results from Paper I to
the case of warm plasma. We report on numerical experiments where mode
transformation is studied using quasi-realistic stratification in thermodynamic
parameters resembling the solar atmosphere. This redresses the limitation of
the cold plasma approximation assumed in Paper I, in particular allowing the
complete process of coupling between fast and slow magneto-acoustic modes and
subsequent coupling of the fast mode to the Alfv\'en mode through the Hall
current. Our results confirm the efficacy of the mechanism proposed in Paper I
for the solar case. We observe that the efficiency of the transformation is a
sensitive function of the angle between the wave propagation direction and the
magnetic field, and of the wave frequency. The efficiency increases when the
field direction and the wave direction are aligned for increasing wave
frequencies. After scaling our results to typical solar values, the maximum
amplitude of the transformed Alfv\'en waves, for a frequency of 1 Hz,
corresponds to an energy flux (measured above the height of peak Hall coupling)
of , based on an amplitude of 500 at
, which is sufficient to play a major role in both quiet and active
region coronal heating
Fermionic field perturbations of a three-dimensional Lifshitz black hole in conformal gravity
We study the propagation of massless fermionic fields in the background of a
three-dimensional Lifshitz black hole, which is a solution of conformal
gravity. The black hole solution is characterized by a null dynamical exponent.
Then, we compute analytically the quasinormal modes, the area spectrum, and the
absorption cross section for fermionic fields. The analysis of the quasinormal
modes shows that the fermionic perturbations are stable in this background. The
area and entropy spectrum are evenly spaced. At the low frequency limit, it is
observed that there is a range of values of the angular momentum of the mode
that contributes to the absorption cross section, whereas it vanishes at the
high frequency limit. In addition, by a suitable change of variables a
gravitational soliton can also be obtained and the stability of the quasinormal
modes are studied and ensured.Comment: 14 pages; 3 figures. arXiv admin note: text overlap with
arXiv:1407.639
Peeping into the SU(2) Gauge Vacuum
We study thermalised configurations of SU(2) gauge fields by cooling. An
analysis of the effect of cooling is presented and global and statistical
information is extracted.Comment: 3 pages, uuencoded compressed postscript file, contribution to LAT 9
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