22 research outputs found
D-dimensional charged Anti-de-Sitter black holes in f (T) gravity
No full textAbstract We present a D-dimensional charged Anti-de-Sitter black hole solutions in f (T) gravity, where f (T) = T + βT 2 and D ≥ 4. These solutions are characterized by flat or cylindrical horizons. The interesting feature of these solutions is the existence of inseparable electric monopole and quadrupole terms in the potential which share related momenta, in contrast with most of the known charged black hole solutions in General Relativity and its extensions. Furthermore, these solutions have curvature singularities which are milder than those of the known charged black hole solutions in General Relativity and Teleparallel Gravity. This feature can be shown by calculating some invariants of curvature and torsion tensors. Furthermore, we calculate the total energy of these black holes using the energy-momentum tensor. Finally, we show that these charged black hole solutions violate the first law of thermodynamics in agreement with previous results
Energy and momentum of a spherically symmetric dilaton frame as regularized by teleparallel gravity
No full textIsotropic compact stellar model in Rastall's gravitational theory
No full textIs Rastall's theory of gravity equivalent to Einstein's general relativity theory? This question has sparked a significant debate, prompting researchers to delve into the topic. To investigate further, we apply Rastall's theory's field equation to a spacetime characterized by spherical symmetry. This leads us to encounter a system of non-linear differential equations that is overdetermined. To address this, we make assumptions about the specific form of the metric potential's temporal component, denoted as gtt. Additionally, we impose constraints to eliminate the anisotropic condition, resulting in a vanishing effect. These steps allow us to determine the form of grr and ultimately achieve an isotropic spacetime. Furthermore, our investigation focuses on the potential of obtaining a set of parameters that align with the observed behavior of pulsars. To achieve this, we employ junction conditions to match the interior spacetime with the exterior Schwarzschild configuration, thereby constraining the model's relevant constants. Subsequently, we employ the pulsar SAXJ1748.9−2021, characterized by a measured mass of M=1.81±0.31,M⊙ and a radius of R=11.7±1.7 km, to numerically explore the physical properties of the model. Stability is assessed using the Tolman-Oppenheimer-Volkoff equation and the adiabatic index. Our findings suggest that Rastall's parameter, a key distinction of Rastall's theory from Einstein's general relativity, can play a crucial role in forming a realistic, compact object consistent with observational data. Furthermore, we verify the model's validity by comparing it with various observed masses and radii of different pulsars, ensuring a satisfactory fit between the model proposed in this study and the observed data
Special N-dimensional charged anti-de-Sitter black holes in f(Q) gravitational theory
No full textIn this study, we introduce a toroidal solution for charged anti-de Sitter black holes in N dimensions within the framework of the quadratic form of f(Q) gravity, employing the coincident gauge condition [1]. We assume f(Q) to take the form f(Q)=Q+12αQ2−2Λ, where N≥4. These black hole solutions are characterized by flat or cylindrical horizons. A notable feature of these solutions is the presence of both electric monopole and quadrupole components in the potential field. These monopole and quadrupole components are inseparable and exhibit interconnected momenta, distinguishing them from the known charged solutions in the linear case of non-metricity theory. Furthermore, we demonstrate that the curvature singularities of these solutions are less severe than those in charged general relativity solutions. Finally, we calculate thermodynamic parameters, including entropy, Hawking temperature, and Gibbs free energy. These calculations confirm the stability of our model
Constraining linear form of f(R,G,T) gravity from astrophysical observations of the Pulsar U1724
No full textThis study explores the structure of compact stars using an extended theory of gravity known as f(R,G,T) gravity, where R, is the Ricci scalar, G, the Gauss-Bonnet invariant, and T the trace of the energy-momentum tensor. Focusing on massive radio pulsars, specifically neutron stars with masses greater than 1.8 solar masses, utilize these extreme astrophysical environments to test gravity in regimes unreachable by Earth-based experiments. We adopt a linear form of the theory, f(R,G,T)=R+αG+βT, with α,1 and β are dimensional constants, and derive an exact analytical solution for anisotropic perfect fluid spheres in hydrostatic equilibrium. This model incorporates the compactness factor C=2GMRc2, to describe all physical properties within the stellar interior. To constrain the model, we employ observational data from the pulsar U1724, using its mass and radius to fix the parameters at their upper bounds: α1=αR2=±0.023 and β1=βκ2=±0.001. The resulting model is consistent with physical viability and observational constraints. Notably, the squared sound speed in this framework remains below the theoretical limit (cs2<c2/3), contrasting with general relativity results. Without assuming a specific equation of state, the model exhibits linear behavior and predicts a core density several times higher than nuclear saturation density (ρnuc=2.6×1014 g/cm3), with surface density ρs, also exceeding this threshold. Additionally, the derived mass-radius relation agrees well with existing astrophysical observations
Analytic charged BHs in f(R) gravity
No full textIn this article, we seek exact charged spherically symmetric black holes (BHs) with considering f(R) gravitational theory. This BH is characterized by convolution and error functions. Those two functions depend on a constant of integration which is responsible to make such a solution deviate from Einstein's general relativity (GR). The error function which constitutes the charge potential of the Maxwell field depends on the constant of integration and when this constant is vanishing we can not reproduce Reissner-Nordström BH in the lower order of f(R). This means that we can not reproduce Reissner-Nordström BH in lower-order–curvature theory, i.e., in GR limit f(R)=R, we can not get the well known charged BH. We study the physical properties of these BHs and show that it is asymptotically approached as a flat spacetime or approach AdS/dS spacetime. Also, we calculate the invariants of the BHS and show that the singularities are milder than those of BH's of GR. Additionally, we derive the stability condition through the use of geodesic deviation. Moreover, we study the thermodynamics of our BH and show the effect of the higher-order–curvature theory. Finally, we study the stability analysis using the odd-type mode and show that all the BHs are stable and have radial speed equal to one
Topology and stability of a (2+1)-dimensional black hole in f(Q) gravity
No full textIn this work, we construct a novel exact solution in the framework of symmetric teleparallel gravity (STG), specifically in the context of three-dimensional f(Q) gravity, where Q is the non-metricity scalar. Utilizing a spherically symmetric (2+1)-dimensional metric and the coincident gauge condition, we derive a new class of black hole solutions characterized by an analytic form of f(Q) that generalizes the Banados-Teitelboim-Zanelli (BTZ) solution. The resulting solution generalizes the BTZ black hole by incorporating a dimensional deformation parameter a1, yielding deviations from general relativity due to non-metricity corrections. This solution reduces to the standard BTZ geometry in the limit of vanishing deformation parameter a1, while exhibiting distinctive features when a1≠0, including deviation in curvature and non-metricity scalars. We conduct a thorough analysis of the thermodynamic properties of the resulting black hole, including its Hawking temperature, entropy, and heat capacity, confirming its thermodynamic stability and demonstrating the validity of the first law of thermodynamics. Furthermore, we explore the topological classification of the black hole using the generalized free energy method, demonstrating the existence of nontrivial topological charges associated with its horizon structure
Role of Stearoyl-CoA desaturase-1 (SCD1) in the activation of epidermal growth factor receptor (EGFR) in lung cancer cells
No full textCancer cells activate lipogenic enzymes, including StearoylCoA Desaturase-1 (SCD1), the key enzyme that converts saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA). Previously, we established that SCD1 regulates lipogenesis, cell proliferation and invasiveness in lung cancer cells, as well as tumor formation in mice. We recently reported that SCD1 modulates the PI3K/Akt pathway, a central signaling cascade, along with ERK, which are involved in the regulation of lipid biosynthesis, growth and survival of mammalian cells. Growth factor-activated tyrosine kinase receptors, such as epidermal growth factor (EGF) receptors (EGFR), are main activators of Akt and ERK signals, two cascades that are most often deranged in cancer. A hallmark of cancer is the metabolic shift towards macromolecular synthesis to support cell replication. SCD1 expression increases in cancer cells. The molecular mechanisms by which SCD1 regulates the biological phenotype of cancer cells is still unknown. The poor prognosis and ineffective treatments of some cancers, such as lung cancer, calls for better understanding of their mechanisms and for finding novel targets that, like SCD1, modulate the Akt and ERK pathways. Here we provide evidence that SCD1 activity controls the activation of EGFR and its downstream signaling targets, Akt and ERK. Using H460 human lung cancer cells, we observed that the activating phosphorylation of Tyr1068 and Tyr1086 residues in EGFR upon EGF stimulation was markedly impaired when SCD1 activity was blocked with CVT-11127, a novel small molecule SCD inhibitor. In addition, supplementation with oleic acid, the product of SCD1, restored EGF-induced phosphorylation of EGFR but not the full phosphorylation of Akt. Finally, abrogation of SCD1 dramatically altered distribution of rafts and non-raft domains, suggesting that the regulation of EGFR function by SCD1 may involve the alteration of membrane lipid domains. All results are representative of 3 separate experiments. In conclusion, our data indicate that SCD1 may coordinate the regulation of lipid biosynthesis and the transduction signals that control cancer cell metabolism, proliferation, survival and tumorigenesis by modulating EGFR activation, which subsequently modifies the Akt and ERK signaling platforms. Our findings also suggest SCD1 is a potential target for novel pharmacological interventions in lung cancer.M.S.Includes bibliographical referencesby Mary Nashe
The key role of Lagrangian multiplier in mimetic gravitational theory in the frame of isotropic compact star
No full textRecently, the mimetic gravitational theory has gained much attention in the frame of cosmology as well as in the domain of astrophysics. In this study, we show that in the frame of mimetic gravitation theory we are not able to derive an isotropic model. Therefore, we turn our attention to mimetic gravitational theory coupled with the Lagrangian multiplier. The field equations of a static isotropic gravitational system that controls the geometry and dynamics of star structure are studied in the frame of mimetic theory coupled with a Lagrangian multiplier using a non-linear equation of state. An energy density is assumed from where all the other unknowns are fixed and a new isotropic model is derived. The physical analysis of this model is studied from different viewpoints and consistent results compatible with a realistic isotropic star are investigated analytically and graphically. Finally, we show that the model under consideration is stable using the adiabatic index procedure
Generic phase portrait analysis of finite-time singularities and generalized Teleparallel gravity
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