In this work we investigate corrections of the quintessence regime of the dark energy on the Joule-Thomson (JT) effect of the Reissner Nordström anti de Sitter (RNAdS) black hole. The quintessence ...dark energy has equation of state as
p
q
=
ω
ρ
q
in which
−
1
<
ω
<
−
1
3
. Our calculations are restricted to ansatz:
ω
= − 1 (the cosmological constant regime) and
ω
=
−
2
3
(quintessence dark energy). To study the JT expansion of the AdS gas under the constant black hole mass, we calculate inversion temperature
T
i
of the quintessence RNAdS black hole where its cooling phase is changed to heating phase at a particular (inverse) pressure
P
i
. Position of the inverse point {
T
i
,
P
i
} is determined by crossing the inverse curves with the corresponding Gibbons-Hawking temperature on the T-P plan. We determine position of the inverse point versus different numerical values of the mass
M
and the charge
Q
of the quintessence AdS RN black hole. The cooling-heating phase transition (JT effect) is happened for
M
>
Q
in which the causal singularity is still covered by the horizon. Our calculations show sensitivity of the inverse point {
T
i
,
P
i
} position on the T-P plan to existence of the quintessence dark energy just for large numerical values of the AdS RN black holes charge
Q
. In other words the quintessence dark energy dose not affect on position of the inverse point when the AdS RN black hole takes on small charges.
By considering AdS charged black hole in the context of extended thermodynamic as the working substance we use it as a heat engine. We investigate the effect of hairy charge on the evolution of ...efficiency and Carnot efficiency along with electric charge. Because of interesting thermodynamic behavior of hairy black holes it would be natural to know their effects when we use black hole as a heat engine. We show that the hairy charge increases the efficiency, and so maximum temperature would be happened for bigger Maxwell charge when this hairy charge grows. For the fixed electric charges, the efficiency has a minimum value. In fact all critical points describe physical states except when the charge removed. If the electric charge takes a zero value then the hairy charge must be negative. We also seek behavior of the system for large charges which is provided a model with low-temperature thermodynamics.
Context.
The Λ cold dark matter (ΛCDM) scenario is able to describe the Universe at large scales, but clearly shows some serious difficulties at small scales. The core-cusp question is one of these ...difficulties: the inner dark matter (DM) density profiles of spiral galaxies generally appear to be cored, without the
r
−1
profile that is predicted by
N
-body simulations in the above scenario.
Aims.
It is well known that in a more physical context, the baryons in the galaxy might backreact and erase the original cusp through supernova explosions. Before the efficiency and the presence of this effect is investigated, it is important to determine how wide and frequent the discrepancy between observed and
N
-body-predicted profiles is and what its features are.
Methods.
We used more than 3200 quite extended rotation curves (RCs) of good quality and high resolution of disk systems that included normal and dwarf spirals as well as low surface brightness galaxies. The curves cover all magnitude ranges. All these RCs were condensed into 26 coadded RCs, each of them built with individual RCs of galaxies of similar luminosity and morphology. We performed mass models of these 26 RCs using the Navarro-Frenk-White (NFW) profile for the contribution of the DM halo to the circular velocity and the exponential Freeman disk for the contribution of the stellar disk.
Results.
The fits are generally poor in all the 26 cases: in several cases, we find
χ
red
2
> 2. Moreover, the best-fitting values of three parameters of the model (
c
,
M
D
, and
M
vir
) combined with those of their 1
σ
uncertainty clearly contradict well-known expectations of the ΛCDM scenario. We also tested the scaling relations that exist in spirals with the outcome of the current mass modeling: the modeling does not account for these scaling relations.
Conclusions.
The results of testing the NFW profile in disk systems indicate that this DM halo density law cannot account for the kinematics of the whole family of disk galaxies. It is therefore mandatory for the success of the ΛCDM scenario in any disk galaxy of any luminosity or maximum rotational velocity to transform initial cusps into the observed cores.
We use a modified Einstein-Maxwell gravity to study stability of an electrostatic spherical star. Correction terms in this model are scalars which are made from contraction of Ricci tensor and ...electromagnetic vector potential. Our motivation to use this kind of exotic Einstein-Maxwell gravity is inevitable influence of cosmic magnetic field in inflation of the universe which is observed now but its intensity suppresses in the usual gauge invariant Einstein-Maxwell gravity. In this work, we use approach of dynamical systems to obtain stability conditions of such a star and we investigate interaction parts effect of the model on the stability.
Using scalar–vector–tensor Brans Dicke (VBD) gravity (Ghaffarnejad in Gen Relativ Gravit 40:2229,
2008
; Gen Relativ Gravit 41:2941,
2009
) in presence of self interaction BD potential
V
(
ϕ
)
and ...perfect fluid matter field action we solve corresponding field equations via dynamical system approach for flat Friedmann Robertson Walker metric (FRW). We obtained three type critical points for
Λ
C
D
M
vacuum de Sitter era where stability of our solutions are depended to choose particular values of BD parameter
ω
. One of these fixed points is supported by a constant potential which is stable for
ω
<
0
and behaves as saddle (quasi stable) for
ω
≥
0
. Two other ones are supported by a linear potential
V
(
ϕ
)
∼
ϕ
which one of them is stable for
ω
=
0.27647
. For a fixed value of
ω
there is at least 2 out of 3 critical points reaching to a unique critical point. Namely for
ω
=
-
0.16856
(
-
0.56038
)
the second (third) critical point become unique with the first critical point. In dust and radiation eras we obtained one critical point which never become unique fixed point. In the latter case coordinates of fixed points are also depended to
ω
. To determine stability of our solutions we calculate eigenvalues of Jacobi matrix of 4D phase space dynamical field equations for de Sitter, dust and radiation eras. We should point also potentials which support dust and radiation eras must be similar to
V
(
ϕ
)
∼
ϕ
-
1
2
and
V
(
ϕ
)
∼
ϕ
-
1
respectively. In short our study predicts that radiation and dust eras of our VBD–FRW cosmology transmit to stable de Sitter state via non-constant potential (effective variable cosmological parameter) by choosing
ω
=
0.27647
.
Nonsingular Ayon-Beato-Garcia (ABG) spherically symmetric static black hole (BH) with charge to mass ratio q=g/2m is metric solution of Born Infeld nonlinear Maxwell-Einstein theory. Central region ...of the BH behaves as (anti-)de Sitter for (|q|>1) |q|<1. In the case where |q|=1, the BH central region behaves as Minkowski flat metric. Nonlinear Electromagnetic (NEM) fields counterpart causes deviation of light geodesics and so light rays will be forced to move on from effective metric. In this paper we study weak and strong gravitational lensing of light rays by seeking effects of NEM fields counterpart on image locations and corresponding magnification. We set our calculations to experimentally observed Sgr A⁎ BH. In short we obtained the following: for large distances, the NEM counterpart is negligible and it reduces to linear Maxwell fields. The NEM field enlarges radius of the BH photon sphere linearly by raising |q|>1 but decreases by raising |q|≤1. Sign of deflection angle of bending light rays is changed in presence of NEM effects with respect to ones obtained in absence of NEM fields. Absolute value of deflection angle rises by increasing |q|→1. Image locations in weak deflection limit (WDL) decrease (increases) by raising 0<|q|<1 in presence (absence) of NEM fields. By raising the closest distance of the bending light rays image locations in WDL change from left (right) to right (left) in absence (presence) of NEM fields. In WDL, radius of Einstein rings and corresponding magnification centroid become larger (smaller) in presence (absence) of NEM fields. Angular separation called s between the innermost and outermost relativistic images increases (decreases) by increasing 0<|q|<1 in absence (presence) of NEM fields. Corresponding magnification r decreases (increases) by raising 0<|q|<1 in absence (presence) of NEM fields.
We obtain renormalized stress tensor of a mass-less, charge-less dynamical quantum scalar field, minimally coupled with a spherically symmetric static Lukewarm black hole. In two dimensional analog ...the minimal coupling reduces to the conformal coupling and the stress tensor is found to be determined by the nonlocal contribution of the anomalous trace and some additional parameters in close relation to the work presented by Christensen and Fulling. Lukewarm black holes are a special class of Reissner-Nordström-de Sitter space times where its electric charge is equal to its mass. Having the obtained renormalized stress tensor we attempt to obtain a time-independent solution of the well known metric back reaction equation. Mathematical derivations predict that the final state of an evaporating quantum Lukewarm black hole reduces to a remnant stable mini black hole with moved locations of the horizons. Namely the perturbed black hole (cosmological) horizon is compressed (extended) to scales which is smaller (larger) than the corresponding classical radius of the event horizons. Hence there is not obtained an deviation on the cosmic sensor-ship hypothesis.
Pauli (or Einstein) frame is used to study the Brans-Dicke gravity theory, minimally coupled with dilatonic Brans-Dicke scalar field, whose solutions involve degenerate metrics. Some of these ...solutions exhibit transitions from an Euclidean domain to a Lorentzian space-time corresponding to a spatially flat Robertson-Walker cosmology.
The \(\Lambda\) cold dark matter (\(\Lambda\)CDM) scenario well describes the Universe at large scales, but shows some serious difficulties at small scales: the inner dark matter (DM) density ...profiles of spiral galaxies generally appear to be cored, without the \(r^{-1}\) predicted by N-body simulations in the above scenario. In a more physical context, the baryons in the galaxy might backreact and erase the original cusp through supernova explosions. Before that this effect be investigated, it is important to determine how wide and frequent the discrepancy between observed and N-body predicted profiles is and what its features are. We used more than 3200 quite extended rotation curves (RCs) of good quality and high resolution of disk systems. The curves cover all magnitude ranges. These RCs were condensed into 26 coadded RCs, each of them built with individual RCs of galaxies of similar luminosity and morphology. We performed mass models of these 26 RCs using the Navarro-Frenk-White (NFW) profile for the contribution of the DM halo to the circular velocity and the exponential Freeman disk for that of the stellar disk. The fits are generally poor in all the 26 cases: in several cases, we find \(\chi^2_{red}>2\). Moreover, the best-fitting values of three parameters of the model (\(c\), \(M_D\), and \(M_{vir}\)) combined with those of their 1\(\sigma\) uncertainty clearly contradict well-known expectations of the \(\Lambda\)CDM scenario. We also tested the scaling relations that exist in spirals with the fitting outcome: the modeling does not account for these scaling relations. Therefore, NFW halo density law cannot account for the kinematics of the whole family of disk galaxies. It is therefore mandatory for the \(\Lambda CDM\) scenario in any disk galaxy of any luminosity to transform initial cusps into the observed cores.
Using scalar-vector-tensor Brans Dicke (VBD) gravity 3 in presence of self interaction BD potential \(V(\phi)\) and perfect fluid matter field action we solve corresponding field equations via ...dynamical system approach for flat Friedmann Robertson Walker metric (FRW). We obtained 3 type critical points for \(\Lambda CDM\) vacuum de Sitter era where stability of our solutions are depended to choose particular values of BD parameter \(\omega.\) One of these fixed points is supported by a constant potential which is stable for \(\omega<0\) and behaves as saddle (quasi stable) for \(\omega\geq0.\) Two other ones are supported by a linear potential \(V(\phi)\sim\phi\) which one of them is stable for \(\omega=0.27647.\) For a fixed value of \(\omega\) there is at least 2 out of 3 critical points reaching to a unique critical point. Namely for \(\omega=-0.16856(-0.56038)\) the second (third) critical point become unique with the first critical point. In dust and radiation eras we obtained 1 critical point which never become unique fixed point. In the latter case coordinates of fixed points are also depended to \(\omega.\) To determine stability of our solutions we calculate eigenvalues of Jacobi matrix of 4D phase space dynamical field equations for de Sitter, dust and radiation eras. We should be point also potentials which support dust and radiation eras must be similar to \(V(\phi)\sim\phi^{-\frac{1}{2}}\) and \(V(\phi)\sim\phi^{-1}\) respectively. In short our study predicts that radiation and dust eras of our VBD-FRW cosmology transmit to stable de Sitter state via non-constant potential (effective variable cosmological parameter) by choosing \(\omega=0.27647\).
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