Physical properties and maximum allowable mass-radius relation of complexity-free compact stellar objects within modified f(R,T)gravity formalism

This paper investigates the physical properties and predicted radii of compact stars generated by the Tolman-IV complexity-free model within the background of modified gravity theory,particularly the f(R,T)-gravity theory,under complexity formalism for a spherically symmetric spacetime proposed by L.Herrera[Phys Rev D 97:044010,2018].By solving the resulting set of differential equations,we obtain the explicit forms of the energy-momentum(EM)tensor components,including the density,radial pressure,and tangential pressure.The influence of the parameterχon various physical properties of the star is thoroughly investigated.The model undergoes a series of rigorous tests to determine its physical relevance.The findings indicate that the model exhibits regularity,stability,and a surface with vanishing pressure.The boundary of this surface is determined by carefully selecting the parameter space.The complexity method employed in f(R,T)gravity offers an interesting approach for developing astrophysical models that are consistent with observable events as demonstrated by recent experiments.In this regard,we use observational data from the GW190814 event,detected by the LIGO and Virgo observatories,to investigate the validity of the Tolman-IV model in f(R,T)gravity.The analysis includes comparing the model's predictions with the observed characteristics of the compact object involved in the merger.In addition,data from two-millisecond pulsars,PSR J1614-2230 and PSR J0952-0607,are incorporated to further constrain the theoretical theories.However,we present a diagram depicting the relationship between the total mass and radius of the compact object candidates for different values ofχ.

Plasmonic enhancement of upconversion emission in Ag@NaYF4:Er^3+/Yb^3+phosphor

In this article upconversion luminescence of silver nanoparticles（AgNPs） coated NaYF4：Er3＋/Yb3＋phosphor nano-particles was investigated.The prepared samples were characterized through various techniques.The surface plasmon band is observed for prepared AgNPs by analyzing UV-vis measurements and is used to enhance the upconversion emission.From the upconversion measurement the emission bands are observed at 522,546,and 656 nm corresponding to the 2 H11/2→ 4115/2,4 S3/2→4 I15/2and 4 F9/2→4 I15/2 levels,respectively.The upconversion emission intensity of the above bands is found to enhance for sample containing 1 mmol AgNPs.Decay time of 4 S3/2 and 4F9/2 levels is found to decrease on coating of AgNPs and hence intensity enhancement is assumed due to the surface plasmon resonance（SPR） effect.

Static fluid spheres admitting Karmarkar condition

We explore a new relativistic anisotropic solution of the Einstein field equations for compact stars based on embedding class one condition.For this purpose,we use the embedding class one methodology by employing the Karmarkar condition.Employing this methodology,we obtain a particular differential equation that connects both the gravitational potentials e^λ and e^ν.We solve this particular differential equation choosing a simple form of generalized gravitational potential grr to describe a complete structure of the space-time within the stellar configuration.After determining this space-time geometry for the stellar models,we discuss thermodynamical observables including radial and tangential pressures,matter density,red-shift,velocity of sound,etc.,in the stellar models.We also perform a complete graphical analysis,which shows that our models satisfy all the physical and mathematical requirements of ultra-high dense collapsed structures.Further,we discuss the moment of inertia and M-R curve for rotating and non-rotating stars.

Relativistic compact stars with charged anisotropic matter

In this article, we perform a detailed theoretical analysis of new exact solutions with anisotropic fluid distribution of matter for compact objects subject to hydrostatic equilibrium. We present a family solution to the Einstein-Maxwell equations describing a spherically symmetric, static distribution of a fluid with pressure anisotropy.We implement an embedding class one condition to obtain a relation between the metric functions. We generalize the properties of a spherical star with hydrostatic equilibrium using the generalised Tolman-Oppenheimer-Volkoff(TOV)equation. We match the interior solution to an exterior Reissner-Nordstr?m one, and study the energy conditions,speed of sound, and mass-radius relation of the star. We also show that the obtained solutions are compatible with observational data for the compact object Her X-1. Regarding our results, the physical behaviour of the present model may serve for the modeling of ultra compact objects.

Anisotropic stars in modified gravity:An extended gravitational decoupling approach

In this study,we conduct an investigation on decoupling gravitational sources under the framework of f(R,T)gravity.Basically,the complete geometric deformation technique is employed,which facilitates finding the exact solutions to the anisotropic astrophysical system smoothly without imposing any particular ansatz for the deformation function.In addition,we used 5-dimensional Euclidean spacetime in order to describe the embedding Class Ⅰ spacetime in order to obtain a solvable spherical physical system.The resulting solutions are both physically interesting and viable with new possibilities for investigation.Notably,the present investigation demonstrates that the mixture of f(R,T)+CGD translates to a scenario beyond the pure GR realm and helps to enhance the features of the interior astrophysical aspects of compact stellar objects.To determine the physical acceptability and stability of the stellar system based on the obtained solutions,we conducted a series of physical tests that satisfied all stability criteria,including the nonsingular nature of density and pressure.