We explore the shifted f(R)(∝ R) model with δ as a distinguishing physical parameter for the stud... more We explore the shifted f(R)(∝ R) model with δ as a distinguishing physical parameter for the study of constraints at local scales. The corresponding dynamics confronted with different geodesics (null and non-null) along with its conformal analogue is investigated. For null geodesics, we discuss the light deflection angle, whereas for non-null geodesics under the weak field limit, we investigate the perihelion advance of the Mercury orbit in f(R) Schwarzschild background, respectively. The extent of an additional force, appearing for non-null geodesics, depends on δ. Such phenomenological investigations allow us to strictly constrain δ to be approximately O(10−6) with a difference of unity in orders at galactic and planetary scales and seems to provide a unique f(R) at local scales. Further, at late cosmic time, we analyse the constraint on δ via the bare scalar self-interaction Einstein frame potential to provide a null test of dark energy. We constrain the deviation parameter, | δ ...
An attempt has been made to explore the galactic dynamics via the rotational velocity beyond the ... more An attempt has been made to explore the galactic dynamics via the rotational velocity beyond the Einstein's geometric theory of gravity. It is inspired from the geometric relation obtained in the power law f(R) gravity model in vacuum. We analyse the action with a small positive deviation from the Einstein-Hilbert action (taking R as f(R)∝ R^1+δ) at the galactic scales for the explanation of cosmological dark matter problem and obtain the contribution of dynamical f(R) background geometry in accelerating the test mass. In the weak field limits, we obtain the effective acceleration of the test mass due to a massive spherically symmetric source in f(R) background and develop an equation for the rotational velocity. We test the viability of the model by tracing the motion of test mass outside the typical galactic visible boundaries without considering any dark matter halo profile. We obtain a nice agreement in the outer regions (up to few tens of kpc beyond the visible boundary) of...
We propose a model of the evolution of the tachyonic scalar field over two phases in the universe... more We propose a model of the evolution of the tachyonic scalar field over two phases in the universe. The field components do not interact in phase I, while in the subsequent phase II, they change flavours due to relative suppression of the radiation contribution. In phase II, we allow them to interact mutually with time-independent perturbation in their equations of state, as Shifted Cosmological Parameter (SCP) and Shifted Dust Matter (SDM). We determine the solutions of their scaling with the cosmic redshift in both phases. We further suggest the normalized Hubble function diagnostic, which, together with the low- and high-redshift H(z) data and the concordance values of the present density parameters from the CMBR, BAO statistics etc., constrains the strength of interaction, by imposing the viable conditions to break degeneracy in 3-parameter (γ, ε, ϕ̇^2) space. The range of redshifts (z=0.1 to z=1.75) is chosen to highlight the role of interaction during structure formation, and i...
We discuss the expansion of the universe in the FRLW model assuming that the source of dark energ... more We discuss the expansion of the universe in the FRLW model assuming that the source of dark energy is either tachyonic scalar field or quintessence. The tachyonic scalar field with exponential and power-law potential (function of homogeneous scalar field ϕ) both gives exponential expansion of the universe. It is found that this behaviour is not distinguishable from the quintessence with respect to these potentials.
We explore the scalar field obtained under the conformal transformation of the spacetime metric g... more We explore the scalar field obtained under the conformal transformation of the spacetime metric g_μν from the Jordan frame to the Einstein frame in f(R) gravity. This scalar field is the result of the modification in the gravitational part of the Einstein's general relativistic theory of gravity. For f(R)=R^1+δ/R_c^δ, we find the effective potential of the scalar field and calculate the mass of the scalar field particle "scalaron". It is shown that the mass of the scalaron depends upon the energy density of standard matter in the background. The interaction between standard matter and scalaron is weak in the high curvature regime. This linkage between the mass of the scalaron and the background leads to the physical effects of dark matter and is expected to reflect the anisotropic propagation of scalaron in moving baryonic matter fields as in merging clusters (Bullet cluster, the Abell 520 system, MACS etc.). Such scenario also satisfies the local gravity constraints o...
We investigate a form of f ( R ) = R 1 + δ / R c δ and study the viability of the model for infla... more We investigate a form of f ( R ) = R 1 + δ / R c δ and study the viability of the model for inflation in the Jordan and the Einstein frames. We have extended this form to f ( R ) = R + R 1 + δ / R c δ in an attempt to solve the problems of the former model. This model is further analyzed by using the power spectrum indices of inflation and the reheating temperature. During the inflationary evolution, the model predicts a value of the δ parameter very close to one (δ = 0.98), while the reheating temperature T re ∼ 10 16 GeV at δ = 0.98 is consistent with the standard approach to inflation and observations. We calculate the slow roll parameters for the minimally coupled scalar field within the framework of our models. It is found that the values of the scalar spectral index and tensor-to-scalar ratio are very close to the recent observational data, including those released by Planck. Further, we find the scalar spectral index and the tensor-to-scalar ratio are exactly the same in the ...
We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon ... more We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon in power-law f(R) gravity theory of the type $$f(R)\propto R^{1+\delta }$$ f ( R ) ∝ R 1 + δ with $$\delta<<1$$ δ < < 1 for interpreting the clustered dark matter effects. We utilize the single effective point like potential (Newtonian potential + f(R) background potential) obtained under the weak field limit to study the combined observations of galaxy rotation curve beyond the optical disk size and their lensing profile in f(R) frame work. We calculate the magnitude of light deflection angle with the characteristic length scale (because of Noether symmetry in f(R) theories) appearing in the effective f(R) rotational velocity profile of a typical galaxy with the model parameter $$\delta \approx O(10^{-6})$$ δ ≈ O ( 10 - 6 ) constrained in previous work. For instance, we work with the two nearby controversial galaxies NGC 5533 and NGC 4138 and explore their galactic features ...
We propose a time-varying cosmological constant with a fixed equation of state, which evolves mai... more We propose a time-varying cosmological constant with a fixed equation of state, which evolves mainly through its interaction with the background during most of the long history of the universe. However, such interaction does not exist in the very early and the latetime universe and produces the acceleration during these eras when it becomes very nearly a constant. It is found that after the initial inflationary phase, the cosmological constant, that we call as lambda parameter, rolls down from a large constant value to another but very small constant value and further dominates the present epoch showing up in form of the dark energy driving the acceleration. Key words: Cosmology; cosmological constant; dark energy PACS:
arXiv: General Relativity and Quantum Cosmology, 2020
We investigate a form of $ f(R) = {R^{1+\delta}}/{R_c^{\delta}}$ and study the viability of the m... more We investigate a form of $ f(R) = {R^{1+\delta}}/{R_c^{\delta}}$ and study the viability of the model for inflation in the Jordan and the Einstein frames. This model is further analysed by using the power spectrum indices of the inflation and the reheating temperature. During the inflationary evolution, the model predicts a value of $\delta$ parameter very close to one ($\delta=0.98$), while the reheating temperature $T_{re} \sim 10^{17}$ GeV at $\delta=0.98$ is consistent with the standard approach to inflation and observations. We calculate the slow roll parameters for the minimally coupled scalar field within the framework of our model. It is found that the values of the scalar spectral index and tensor-to-scalar ratio are very close to the recent observational data, including those released by Planck 2018. We also show that the Jordan and the Einstein frames are equivalent when $\delta \sim 1 $ by using the scalar spectral index, tensor-to-scalar ratio and reheating temperature.
The cosmological arrow of time may be linked to the thermodynamic arrow by second law of thermody... more The cosmological arrow of time may be linked to the thermodynamic arrow by second law of thermodynamics. The time asymmetry is also associated with dissipative fluid as Tolman introduced a viscous fluid to generate an arrow of time in cyclic cosmology. An arrow of time in cyclic cosmology has been shown using scalar field.In this work we find out the cosmological arrow of time in f(R) gravity. Here we use the relation between a new scalar field and $f(R)$. The dynamics of this new scalar field may emerge the arrow of time.
We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon ... more We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon in powerlaw f (R) gravity theory of the type f (R) ∝ R 1+δ with δ \u003c\u003c 1 for interpreting the clustered dark matter effects. We utilize the single effective point like potential (Newtonian potential + f (R) background potential) obtained under the weak field limit to study the combined observations of galaxy rotation curve beyond the optical disk size and their lensing profile in f (R) frame work. We calculate the magnitude of light deflection angle with the characteristic length scale (because of Noether symmetry in f (R) theories) appearing in the effective f (R) rotational velocity profile of a typical galaxy with the model parameter δ ≈ O(10 −6) constrained in previous work. For instance, we work with the two nearby controversial galaxies NGC 5533 and NGC 4138 and explore their galactic features by analysing the lensing angle profiles in f (R) background. We also contrast the...
An attempt has been made to explore the geometric effects of f(R) action on the galactic dynamics... more An attempt has been made to explore the geometric effects of f(R) action on the galactic dynamics under the weak field approximation. The rotational velocity is calculated beyond the Einstein’s geometric theory of gravity. It is inspired by the cosmological geometric relation obtained in the power-law f(R) gravity model in vacuum. We analyse the action with a small positive deviation from the Einstein–Hilbert gravity action (taking R as $$f(R)\propto R^{1+\delta }$$f(R)∝R1+δ) at the galactic scales for the explanation of the flatness paradox associated with the clustered galactic dark matter. We obtain the contribution of a dynamical f(R) cosmological background geometry on accelerating the test mass. Furthermore, the integrated effective acceleration of the test mass due to a massive spherically symmetric source in f(R) background is calculated via the study of geodesics for the suitable spacetime metric and an equation for the effective rotational velocity has been developed. We t...
SRI JNPG COLLEGE REVELATION A JOURNAL OF POPULAR SCIENCE
The pathways to the search of truth in science inevitably meander through the rights and wrongs, ... more The pathways to the search of truth in science inevitably meander through the rights and wrongs, often with the right claims but wrong foundations, or wrong claims even when our knowledge tells us otherwise. Since the final frontiers always recede from us, we can’t see very far into the future and the search for the ultimate truth remains a wild-goose-chase. So, brooding over reaching the destinations must be replaced by sheer joy of the fetching journey. This article explains such pathways, wonders and delights through a process of learning.
International Journal of Modern Physics: Conference Series
A strong follow up of a previous proposal (ICHEP, Valencia 2014) is made leading to the first exp... more A strong follow up of a previous proposal (ICHEP, Valencia 2014) is made leading to the first experiment to observe the gravitational waves at the collision sites at the colliders such as the Large Hadron Collider at CERN. The amplitudes have been calculated with regard to the sensitivity of the detector. Compared with the standard model physics, it is shown to have a measurable impact on the particle motions and corresponds to ‘missing’ energy in form of the gravitational wave loss. This is unlike the cosmological detectors like BICEP2 etc. where the indirect B mode polarization on CMBR were masked by dust. In contrast, this experiment would be the first experiment where the energy-momentum tensor of the source can be controlled.
We explore the shifted f(R)(∝ R) model with δ as a distinguishing physical parameter for the stud... more We explore the shifted f(R)(∝ R) model with δ as a distinguishing physical parameter for the study of constraints at local scales. The corresponding dynamics confronted with different geodesics (null and non-null) along with its conformal analogue is investigated. For null geodesics, we discuss the light deflection angle, whereas for non-null geodesics under the weak field limit, we investigate the perihelion advance of the Mercury orbit in f(R) Schwarzschild background, respectively. The extent of an additional force, appearing for non-null geodesics, depends on δ. Such phenomenological investigations allow us to strictly constrain δ to be approximately O(10−6) with a difference of unity in orders at galactic and planetary scales and seems to provide a unique f(R) at local scales. Further, at late cosmic time, we analyse the constraint on δ via the bare scalar self-interaction Einstein frame potential to provide a null test of dark energy. We constrain the deviation parameter, | δ ...
An attempt has been made to explore the galactic dynamics via the rotational velocity beyond the ... more An attempt has been made to explore the galactic dynamics via the rotational velocity beyond the Einstein's geometric theory of gravity. It is inspired from the geometric relation obtained in the power law f(R) gravity model in vacuum. We analyse the action with a small positive deviation from the Einstein-Hilbert action (taking R as f(R)∝ R^1+δ) at the galactic scales for the explanation of cosmological dark matter problem and obtain the contribution of dynamical f(R) background geometry in accelerating the test mass. In the weak field limits, we obtain the effective acceleration of the test mass due to a massive spherically symmetric source in f(R) background and develop an equation for the rotational velocity. We test the viability of the model by tracing the motion of test mass outside the typical galactic visible boundaries without considering any dark matter halo profile. We obtain a nice agreement in the outer regions (up to few tens of kpc beyond the visible boundary) of...
We propose a model of the evolution of the tachyonic scalar field over two phases in the universe... more We propose a model of the evolution of the tachyonic scalar field over two phases in the universe. The field components do not interact in phase I, while in the subsequent phase II, they change flavours due to relative suppression of the radiation contribution. In phase II, we allow them to interact mutually with time-independent perturbation in their equations of state, as Shifted Cosmological Parameter (SCP) and Shifted Dust Matter (SDM). We determine the solutions of their scaling with the cosmic redshift in both phases. We further suggest the normalized Hubble function diagnostic, which, together with the low- and high-redshift H(z) data and the concordance values of the present density parameters from the CMBR, BAO statistics etc., constrains the strength of interaction, by imposing the viable conditions to break degeneracy in 3-parameter (γ, ε, ϕ̇^2) space. The range of redshifts (z=0.1 to z=1.75) is chosen to highlight the role of interaction during structure formation, and i...
We discuss the expansion of the universe in the FRLW model assuming that the source of dark energ... more We discuss the expansion of the universe in the FRLW model assuming that the source of dark energy is either tachyonic scalar field or quintessence. The tachyonic scalar field with exponential and power-law potential (function of homogeneous scalar field ϕ) both gives exponential expansion of the universe. It is found that this behaviour is not distinguishable from the quintessence with respect to these potentials.
We explore the scalar field obtained under the conformal transformation of the spacetime metric g... more We explore the scalar field obtained under the conformal transformation of the spacetime metric g_μν from the Jordan frame to the Einstein frame in f(R) gravity. This scalar field is the result of the modification in the gravitational part of the Einstein's general relativistic theory of gravity. For f(R)=R^1+δ/R_c^δ, we find the effective potential of the scalar field and calculate the mass of the scalar field particle "scalaron". It is shown that the mass of the scalaron depends upon the energy density of standard matter in the background. The interaction between standard matter and scalaron is weak in the high curvature regime. This linkage between the mass of the scalaron and the background leads to the physical effects of dark matter and is expected to reflect the anisotropic propagation of scalaron in moving baryonic matter fields as in merging clusters (Bullet cluster, the Abell 520 system, MACS etc.). Such scenario also satisfies the local gravity constraints o...
We investigate a form of f ( R ) = R 1 + δ / R c δ and study the viability of the model for infla... more We investigate a form of f ( R ) = R 1 + δ / R c δ and study the viability of the model for inflation in the Jordan and the Einstein frames. We have extended this form to f ( R ) = R + R 1 + δ / R c δ in an attempt to solve the problems of the former model. This model is further analyzed by using the power spectrum indices of inflation and the reheating temperature. During the inflationary evolution, the model predicts a value of the δ parameter very close to one (δ = 0.98), while the reheating temperature T re ∼ 10 16 GeV at δ = 0.98 is consistent with the standard approach to inflation and observations. We calculate the slow roll parameters for the minimally coupled scalar field within the framework of our models. It is found that the values of the scalar spectral index and tensor-to-scalar ratio are very close to the recent observational data, including those released by Planck. Further, we find the scalar spectral index and the tensor-to-scalar ratio are exactly the same in the ...
We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon ... more We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon in power-law f(R) gravity theory of the type $$f(R)\propto R^{1+\delta }$$ f ( R ) ∝ R 1 + δ with $$\delta<<1$$ δ < < 1 for interpreting the clustered dark matter effects. We utilize the single effective point like potential (Newtonian potential + f(R) background potential) obtained under the weak field limit to study the combined observations of galaxy rotation curve beyond the optical disk size and their lensing profile in f(R) frame work. We calculate the magnitude of light deflection angle with the characteristic length scale (because of Noether symmetry in f(R) theories) appearing in the effective f(R) rotational velocity profile of a typical galaxy with the model parameter $$\delta \approx O(10^{-6})$$ δ ≈ O ( 10 - 6 ) constrained in previous work. For instance, we work with the two nearby controversial galaxies NGC 5533 and NGC 4138 and explore their galactic features ...
We propose a time-varying cosmological constant with a fixed equation of state, which evolves mai... more We propose a time-varying cosmological constant with a fixed equation of state, which evolves mainly through its interaction with the background during most of the long history of the universe. However, such interaction does not exist in the very early and the latetime universe and produces the acceleration during these eras when it becomes very nearly a constant. It is found that after the initial inflationary phase, the cosmological constant, that we call as lambda parameter, rolls down from a large constant value to another but very small constant value and further dominates the present epoch showing up in form of the dark energy driving the acceleration. Key words: Cosmology; cosmological constant; dark energy PACS:
arXiv: General Relativity and Quantum Cosmology, 2020
We investigate a form of $ f(R) = {R^{1+\delta}}/{R_c^{\delta}}$ and study the viability of the m... more We investigate a form of $ f(R) = {R^{1+\delta}}/{R_c^{\delta}}$ and study the viability of the model for inflation in the Jordan and the Einstein frames. This model is further analysed by using the power spectrum indices of the inflation and the reheating temperature. During the inflationary evolution, the model predicts a value of $\delta$ parameter very close to one ($\delta=0.98$), while the reheating temperature $T_{re} \sim 10^{17}$ GeV at $\delta=0.98$ is consistent with the standard approach to inflation and observations. We calculate the slow roll parameters for the minimally coupled scalar field within the framework of our model. It is found that the values of the scalar spectral index and tensor-to-scalar ratio are very close to the recent observational data, including those released by Planck 2018. We also show that the Jordan and the Einstein frames are equivalent when $\delta \sim 1 $ by using the scalar spectral index, tensor-to-scalar ratio and reheating temperature.
The cosmological arrow of time may be linked to the thermodynamic arrow by second law of thermody... more The cosmological arrow of time may be linked to the thermodynamic arrow by second law of thermodynamics. The time asymmetry is also associated with dissipative fluid as Tolman introduced a viscous fluid to generate an arrow of time in cyclic cosmology. An arrow of time in cyclic cosmology has been shown using scalar field.In this work we find out the cosmological arrow of time in f(R) gravity. Here we use the relation between a new scalar field and $f(R)$. The dynamics of this new scalar field may emerge the arrow of time.
We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon ... more We explore a new realisation of the galactic scale dynamics via gravitational lensing phenomenon in powerlaw f (R) gravity theory of the type f (R) ∝ R 1+δ with δ \u003c\u003c 1 for interpreting the clustered dark matter effects. We utilize the single effective point like potential (Newtonian potential + f (R) background potential) obtained under the weak field limit to study the combined observations of galaxy rotation curve beyond the optical disk size and their lensing profile in f (R) frame work. We calculate the magnitude of light deflection angle with the characteristic length scale (because of Noether symmetry in f (R) theories) appearing in the effective f (R) rotational velocity profile of a typical galaxy with the model parameter δ ≈ O(10 −6) constrained in previous work. For instance, we work with the two nearby controversial galaxies NGC 5533 and NGC 4138 and explore their galactic features by analysing the lensing angle profiles in f (R) background. We also contrast the...
An attempt has been made to explore the geometric effects of f(R) action on the galactic dynamics... more An attempt has been made to explore the geometric effects of f(R) action on the galactic dynamics under the weak field approximation. The rotational velocity is calculated beyond the Einstein’s geometric theory of gravity. It is inspired by the cosmological geometric relation obtained in the power-law f(R) gravity model in vacuum. We analyse the action with a small positive deviation from the Einstein–Hilbert gravity action (taking R as $$f(R)\propto R^{1+\delta }$$f(R)∝R1+δ) at the galactic scales for the explanation of the flatness paradox associated with the clustered galactic dark matter. We obtain the contribution of a dynamical f(R) cosmological background geometry on accelerating the test mass. Furthermore, the integrated effective acceleration of the test mass due to a massive spherically symmetric source in f(R) background is calculated via the study of geodesics for the suitable spacetime metric and an equation for the effective rotational velocity has been developed. We t...
SRI JNPG COLLEGE REVELATION A JOURNAL OF POPULAR SCIENCE
The pathways to the search of truth in science inevitably meander through the rights and wrongs, ... more The pathways to the search of truth in science inevitably meander through the rights and wrongs, often with the right claims but wrong foundations, or wrong claims even when our knowledge tells us otherwise. Since the final frontiers always recede from us, we can’t see very far into the future and the search for the ultimate truth remains a wild-goose-chase. So, brooding over reaching the destinations must be replaced by sheer joy of the fetching journey. This article explains such pathways, wonders and delights through a process of learning.
International Journal of Modern Physics: Conference Series
A strong follow up of a previous proposal (ICHEP, Valencia 2014) is made leading to the first exp... more A strong follow up of a previous proposal (ICHEP, Valencia 2014) is made leading to the first experiment to observe the gravitational waves at the collision sites at the colliders such as the Large Hadron Collider at CERN. The amplitudes have been calculated with regard to the sensitivity of the detector. Compared with the standard model physics, it is shown to have a measurable impact on the particle motions and corresponds to ‘missing’ energy in form of the gravitational wave loss. This is unlike the cosmological detectors like BICEP2 etc. where the indirect B mode polarization on CMBR were masked by dust. In contrast, this experiment would be the first experiment where the energy-momentum tensor of the source can be controlled.
International Journal of Modern Physics: Conference Series
The fixed points for the dynamical system in the phase space have been calculated with dark matte... more The fixed points for the dynamical system in the phase space have been calculated with dark matter in the [Formula: see text] gravity models. The stability conditions of these fixed points are obtained in the ongoing accelerated phase of the universe, and the values of the Hubble parameter and Ricci scalar are obtained for various evolutionary stages of the universe. We present a range of some modifications of general relativistic action consistent with the [Formula: see text]CDM model. We elaborate upon the fact that the upcoming cosmological observations would further constrain the bounds on the possible forms of [Formula: see text] with greater precision that could in turn constrain the search for dark matter in colliders.
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