432 research outputs found
Stability analysis of Lower Dimensional Gravastars in noncommutative geometry
The Ba\~{n}ados, Teitelboim and Zanelli \cite{BTZ1992}, black hole solution
is revamped from the Einstein field equations in (2 + 1)-dimensional anti-de
Sitter spacetime, in a context of noncommutative geometry \cite{Rahaman(2013)}.
In this article, we explore the exact gravastar solutions in three-dimension
anti-de Sitter space given in the same geometry. As a first step we derive BTZ
solution assuming the source of energy density as point-like structures in
favor of smeared objects, where the particle mass M, is diffused throughout a
region of linear size and is described by a Gaussian function
of finite width rather than a Dirac delta function. We matched our interior
solution to an exterior BTZ spacetime at a junction interface situated outside
the event horizon. Furthermore, stability analysis is carried out for the
dynamic case for the specific case when under radial
perturbations about static equilibrium solutions. To give theoretical support
we also trying to explore their physical properties and characteristics.Comment: 3 figure
Saturated-absorption spectroscopy: Eliminating crossover resonances using co-propagating beams
We demonstrate a new technique for saturated-absorption spectroscopy using
co-propagating beams that does not have the problem of crossover resonances.
The pump beam is locked to a transition and its absorption signal is monitored
while the probe beam is scanned. As the probe comes into resonance with another
transition, the pump absorption is reduced and the signal shows a Doppler-free
dip. We use this technique to measure hyperfine intervals in the line of
Rb with a precision of 70 kHz, and to resolve hyperfine levels in the
line of K that are less than 10 MHz apart.Comment: 3 pages, 4 figures. To appear in Optics Letter
Charged Thin-shell Gravastars in Noncommutative Geometry
In this paper we construct a charged thin-shell gravastar model within the
context of noncommutative geometry. To do so, we choose the interior of the
nonsingular de Sitter spacetime with an exterior charged noncommutative
solution by cut-and-paste technique and apply the generalized junction
conditions. We then investigate the stability of a charged thin-shell gravastar
under linear perturbations around the static equilibrium solutions as well as
the thermodynamical stability of the charged gravastar. We find the stability
regions by choosing appropriate parameter values which is located sufficiently
close to the event horizon.Comment: 8 pages, twocolumn, Accepted in EPJC for publicatio
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