We investigate plane symmetric spacetime filled with perfect fluid in the C-field cosmology of Hoyle and Narlikar. A new class of exact solutions has been obtained by considering the creation field C as a function of ...We investigate plane symmetric spacetime filled with perfect fluid in the C-field cosmology of Hoyle and Narlikar. A new class of exact solutions has been obtained by considering the creation field C as a function of time only. To get the deterministic solution, it has been assumed that the rate of creation of matter-energy density is proportional to the strength of the existing C-field energy density. Several physical aspects and geometrical properties of the models are discussed in detail, especially showing that some of our solutions of C-field cosmology are free from singularity in contrast to the Big Bang cosmology. A comparative study has been carried out between two models, one singular and the other nonsingular, by contrasting the behaviour of the physical parameters. We note that the model in a unique way represents both the features of the accelerating as well as decelerating universe depending on the parameters and thus seems to provide glimpses of the oscillating or cyclic model of the universe without invoking any other agent or theory in allowing cyclicity.展开更多
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...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.展开更多
The objective of this work is to generate a general formalism of f(R,L(X))-gravity in the context of dark energy under the framework of K-essence emergent geometry with the Dirac-Born-Infeld(DBI) variety of action,whe...The objective of this work is to generate a general formalism of f(R,L(X))-gravity in the context of dark energy under the framework of K-essence emergent geometry with the Dirac-Born-Infeld(DBI) variety of action,where R is the familiar Ricci scalar,L(X) is the DBI type non-canonical Lagrangian with X=1/2g^(μν)▽_(μ)φ▽_(ν)φ,and φ is the K-essence scalar field.The emergent gravity metric(G_(μν)) and the well known gravitational metric(g^(μν))are not conformally equivalent.We have constructed a modified field equation using the metric formalism in f(R,L(X))-gravity incorporating the corresponding Friedmann equations into the framework of the background gravitational metric,which is of Friedmann-Lemaitre-Robertson-Walker(FLRW) type.The solution of the modified Friedmann equations have been deduced for the specific choice of f(R,L(X)),which is of Starobinsky-type,using the power law expansion method.The consistency of the model with the accelerating phase of the universe has been shown when we restrict ourselves to consider the value of the dark energy density as φ^(2)=8/9=0.888 <1,which indicates that the present universe is dark-energy dominated.Graphical plots for the energy density(ρ),pressure(p),and equation of state parameter(ω) with respect to(w.r.t.) time(t) based on parametric values are interestingly consistent with the dark energy domination theory,and hence the accelerating features.We also highlight the corresponding energy conditions and constraints of the f(R,L(X)) theory with a basic example.展开更多
In this study,we evaluate power law inflation(PLI)with a monomial potential and obtain a novel exact solution.It is well known that the conventional PLI with an exponential potential is inconsistent with the Planck da...In this study,we evaluate power law inflation(PLI)with a monomial potential and obtain a novel exact solution.It is well known that the conventional PLI with an exponential potential is inconsistent with the Planck data.Unlike the standard PLI,the present model does not encounter the graceful exit problem,and the results agree fairly well with recent observations.In our analysis,we calculate the spectral index and the tensor-to-scalar ratio,both of which agree very well with recent observational data and are comparable with those of other modified inflationary models.The employed technique reveals that the large cosmological constant decreases with the expansion of the universe in the case of the PLI.The coupling of the inflaton with gravitation is the primary factor in this technique.The basic assumption here is that the two metric tensors in the gravitational and inflaton parts correspond to different conformal frames,which contradicts with the conventional PLI,where the inflaton is directly coupled with the background metric tensor.This fact has direct applications to different dark energy models and the assisted quintessence theory.展开更多
In this study,we investigate the collapsing scenario for the k-essence emergent Vaidya spacetime in the context of massive gravity's rainbow.For this study,we consider that the background metric is Vaidya spacetim...In this study,we investigate the collapsing scenario for the k-essence emergent Vaidya spacetime in the context of massive gravity's rainbow.For this study,we consider that the background metric is Vaidya spacetime in massive gravity's rainbow.We show that the k-essence emergent gravity metric closely resembles the new type of generalized Vaidya massive gravity metric with the rainbow deformations for null fluid collapse,where we consider the k-essence scalar field as a function solely of the advanced or the retarded time.The k-essence emergent Vaidya massive gravity rainbow mass function is also different.This new type k-essence emergent Vaidya massive gravity rainbow metric satisfies the required energy conditions.The existence of a locally naked central singularity and the strength and strongness of the singularities for the rainbow deformations of the k-essence emergent Vaidya massive gravity metric are the interesting outcomes of the present work.展开更多
基金DST,Government of India,for providing financial support under the INSPIRE Fellowship
文摘We investigate plane symmetric spacetime filled with perfect fluid in the C-field cosmology of Hoyle and Narlikar. A new class of exact solutions has been obtained by considering the creation field C as a function of time only. To get the deterministic solution, it has been assumed that the rate of creation of matter-energy density is proportional to the strength of the existing C-field energy density. Several physical aspects and geometrical properties of the models are discussed in detail, especially showing that some of our solutions of C-field cosmology are free from singularity in contrast to the Big Bang cosmology. A comparative study has been carried out between two models, one singular and the other nonsingular, by contrasting the behaviour of the physical parameters. We note that the model in a unique way represents both the features of the accelerating as well as decelerating universe depending on the parameters and thus seems to provide glimpses of the oscillating or cyclic model of the universe without invoking any other agent or theory in allowing cyclicity.
基金TRC Project(Grant No.BFP/RGP/CBS-/19/099),the Sultanate of Omancontinuous support and encouragement from the administration of University of Nizwa。
文摘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.
基金the DSTB,Government of West Bengal,India for financial support through the Grants No.:322(Sanc.)/ST/P/S&T/16G-3/2018 dated06.03.2019。
文摘The objective of this work is to generate a general formalism of f(R,L(X))-gravity in the context of dark energy under the framework of K-essence emergent geometry with the Dirac-Born-Infeld(DBI) variety of action,where R is the familiar Ricci scalar,L(X) is the DBI type non-canonical Lagrangian with X=1/2g^(μν)▽_(μ)φ▽_(ν)φ,and φ is the K-essence scalar field.The emergent gravity metric(G_(μν)) and the well known gravitational metric(g^(μν))are not conformally equivalent.We have constructed a modified field equation using the metric formalism in f(R,L(X))-gravity incorporating the corresponding Friedmann equations into the framework of the background gravitational metric,which is of Friedmann-Lemaitre-Robertson-Walker(FLRW) type.The solution of the modified Friedmann equations have been deduced for the specific choice of f(R,L(X)),which is of Starobinsky-type,using the power law expansion method.The consistency of the model with the accelerating phase of the universe has been shown when we restrict ourselves to consider the value of the dark energy density as φ^(2)=8/9=0.888 <1,which indicates that the present universe is dark-energy dominated.Graphical plots for the energy density(ρ),pressure(p),and equation of state parameter(ω) with respect to(w.r.t.) time(t) based on parametric values are interestingly consistent with the dark energy domination theory,and hence the accelerating features.We also highlight the corresponding energy conditions and constraints of the f(R,L(X)) theory with a basic example.
文摘In this study,we evaluate power law inflation(PLI)with a monomial potential and obtain a novel exact solution.It is well known that the conventional PLI with an exponential potential is inconsistent with the Planck data.Unlike the standard PLI,the present model does not encounter the graceful exit problem,and the results agree fairly well with recent observations.In our analysis,we calculate the spectral index and the tensor-to-scalar ratio,both of which agree very well with recent observational data and are comparable with those of other modified inflationary models.The employed technique reveals that the large cosmological constant decreases with the expansion of the universe in the case of the PLI.The coupling of the inflaton with gravitation is the primary factor in this technique.The basic assumption here is that the two metric tensors in the gravitational and inflaton parts correspond to different conformal frames,which contradicts with the conventional PLI,where the inflaton is directly coupled with the background metric tensor.This fact has direct applications to different dark energy models and the assisted quintessence theory.
文摘In this study,we investigate the collapsing scenario for the k-essence emergent Vaidya spacetime in the context of massive gravity's rainbow.For this study,we consider that the background metric is Vaidya spacetime in massive gravity's rainbow.We show that the k-essence emergent gravity metric closely resembles the new type of generalized Vaidya massive gravity metric with the rainbow deformations for null fluid collapse,where we consider the k-essence scalar field as a function solely of the advanced or the retarded time.The k-essence emergent Vaidya massive gravity rainbow mass function is also different.This new type k-essence emergent Vaidya massive gravity rainbow metric satisfies the required energy conditions.The existence of a locally naked central singularity and the strength and strongness of the singularities for the rainbow deformations of the k-essence emergent Vaidya massive gravity metric are the interesting outcomes of the present work.