
Nayem SkSaidabad Maindra Chandra Vidyapith, Murshidabad, West Bengal, India (742103) · Physics
Nayem Sk
Ph.D.
About
29
Publications
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Introduction
I (Dr. Nayem Sheikh) am now trying to solve the unsolved problems in Cosmology and Astronomy. I have already completed my Ph.D. degree from University of Kalyani, India.
Skills and Expertise
Additional affiliations
March 2006 - present
Saidabad Manindra Chandra Vidyapith
Position
- Assistant Teacher
Description
- Teaching and Research
Education
December 2012 - January 2018
University of Kalyani
Field of study
- Cosmology
Publications
Publications (29)
Unlike F ( R ) gravity, pure F ( T ) gravity in the vacuum dominated era does not produce any form, viable to study cosmological evolution. Factually, it does not even produce any dynamics. This eerie situation may be circumvented by associating a scalar field, which can also drive inflation in the very early universe. Here, we particularly show th...
Unlike F(R) gravity, pure metric F(T) gravity in the vacuum dominated era, ends up with an imaginary action and is therefore not feasible. This eerie situation may only be circumvented by associating a scalar field, which can also drive inflation in the very early universe. We show that, despite diverse claims, F(T) theory admits Noether symmetry o...
We study early universe with a particular form of F(T) Telleparallel gravity theory, in which inflation is driven by a scalar field. To ensure slow rollover, two different potentials are chosen in a manner, such that they remain almost flat for large initial value of the scalar field. Inflationary parameters show wonderful fit with the presently av...
We study early universe with a particular form of F(T) teleparallel gravity theory, in which inflation is driven by a scalar field. To ensure slow rollover, two different potentials are chosen in a manner, such that they remain almost flat for large initial value of the scalar field. Inflationary parameters show wonderful fit with the presently ava...
F(R) theory of gravity unifies early inflation with late time cosmic acceleration, admits Newtonian limit and passes the solar test single-handedly. However, in order to select a particular form of F(R) out of indefinitely many, Noether symmetry was invoked as a selection rule. We have shown that Noether symmetry gives R^ (3/2) along with a conserv...
F(R) theory of gravity is claimed to admit a host of conserved currents under the imposition of Noether symme-
try following various techniques. However, for a constrained system such as gravity, Noether symmetry is not
on-shell. As a result, the symmetries do not necessarily satisfy the field equations in general, constraints in par-
ticular, unle...
F(R) theory of gravity is claimed to admit a host of conserved currents under the imposition of Noether symmetry following various techniques. However, for a constrained system such as gravity, Noether symmetry is not on-shell. As a result, the symmetries do not necessarily satisfy the field equations in general, constraints in particular, unless t...
Under conformal transformation, [Formula: see text] theory of gravity in Palatini formalism leads to a Brans–Dicke type of scalar-tensor equivalent theory with a wrong sign in the effective kinetic energy term. This means that the effective scalar acts as the dark energy and so late-time cosmic acceleration in the matter-dominated era is accountabl...
Under conformal transformation, f(R) theory of gravity in Palatini formalism leads to a Brans-Dicke type of scalar-tensor equivalent theory with a wrong sign in the effective kinetic energy term. This means, the effective scalar acts as the dark energy and so late-time cosmic acceleration in matter-dominated era is accountable. However, we unveil s...
Classical equivalence between Jordan's and Einstein's frame counterparts of F(R) theory of gravity has recently been questioned, since the two produce different Noether symmetries, which couldn't be translated back and forth using transformation relations. Here we add the Hamiltonian constraint equation, which is essentially the time-time component...
Classical equivalence between Jordan's and Einstein's frame counterparts of F(R) theory of gravity has recently been questioned, since the two produce different Noether symmetries, which couldn't be translated back and forth using transformation relations. Here we add the Hamiltonian constraint equation, which is essentially the time-time component...
Hao Wei et.al. has claimed in $\mathrm{Phys. Lett. \textbf{B707}, 298 (2012)}$ that Noether symmetry in the context of teleparallel $f(T)$ theory of gravity admits $f(T)\propto T^{n}$, (where $n$ is arbitrary) in matter domain era in Friedman- Robertson-Walker universe. But, it has been shown that the conserved current obtained under the process do...
Hao Wei et.al. has claimed in $\mathrm{Phys. Lett. \textbf{B707}, 298 (2012)}$ that Noether symmetry in the context of teleparallel $f(T)$ theory of gravity admits $f(T)\propto T^{n}$, (where $n$ is an arbitrary) in matter domain era in Friedmann- Robertson universe. But, it has been shown that the conserved current obtained under the process does...
In metric formalism, Noether symmetry of (Formula presented.) theory of gravity in vacuum and in the presence of pressureless dust yields (Formula presented.) along with the conserved current (Formula presented.) in Robertson–Walker metric and nothing else. However, Roshan and Shojai have claimed in [Palatini (Formula presented.) gravity and Noethe...
In metric formalism, Noether symmetry of F(R) theory of gravity in vacuum and in the presence of pressureless dust yields $F(R)\propto R^\frac{3}{2}$ along with the conserved current $\frac{d}{dt} (a\sqrt R)$ in Robertson-Walker metric and nothing else. However, Roshan et.al. had claimed in $\mathrm{Phys. Lett. \textbf{B668}, 238 (2008)}$ \cite{o}...
Whether Jordan's and Einstein's frame descriptions of F(R) theory of gravity are physically equivalent, is a long standing debate. However, none questioned on true mathematical equivalence, since classical field equations may be translated from one frame to the other following a transformation relation. Nevertheless, true mathematical equivalence i...
Whether Jordan's and Einstein's frame descriptions of F(R) theory of gravity are physically equivalent, is a long standing debate. However, practically none questioned on true mathematical equivalence, since classical field equations may be translated from one frame to the other following a transformation relation. Here we show that neither Noether...
Issue of branched Hamiltonian appearing in the presence of velocities with
degree higher than two in the Lagrangian, has not been resolved uniquely as
yet. However, often such terms appear with higher order theory, gravity in
particular. Here we show that an appropriate canonical formulation of higher
order theory takes care of the issue elegantly....
Metric variation of higher order theory of gravity requires to fix the Ricci
scalar in addition to the metric tensor at the boundary. Fixing Ricci scalar at
the boundary implies that the classical solutions are fixed once and forever to
the de-Sitter or anti de-Sitter solutions. Here, we justify such requirement
from the standpoint of Noether Symme...
Metric variation of higher order theory of gravity requires to fix the Ricci scalar(R) in addition to the metric tensor at the boundary. Fixing R at the boundary implies that the classical solutions are fixed once and forever to the De-Sitter or anti De-Sitter solutions. Here, we justify such requirement from the standpoint of Noether Symmetry.
Noether symmetry of F(R) theory of gravity in vacuum and in the presence of
pressureless dust yields F(R) \propto R^{3/2} along with the conserved current
\frac{d}{dt}(a\sqrt R) in Robertson-Walker metric and nothing else. Still some
authors recently claimed to have obtained four conserved currents setting F(R)
\propto R^{3/2} a-priori, taking time...
It has been shown earlier that Noether symmetry does not admit a form of F (R) corresponding to an action in which F (R) is coupled to scalar-tensor action for gravity or even for pure F (R) gravity taking anisotropic model into account. Here, we prove that F(R) theory of gravity does not admit Noether symmetry even if it is coupled to Tachyonic fi...
Recently, some authors have made a falsifiable claim that Noether gauge
symmetry for F(R) theory of gravity coupled to a tachyon field enforces gauge
to vanish and leads to F(R) \propto R^2, with a tachyon potential V(\phi)
\propto \phi^{-4}. Here, we show that the analysis is completely wrong since
the conserved current does not satisfy the field...
Noether gauge symmetry for F(R) theory of gravity has been explored recently.
The fallacy is that, even after setting gauge to vanish, the form of F(R)
\propto R^n (where n \neq 1, is arbitrary) obtained in the process, has been
claimed to be an outcome of gauge Noether symmetry. On the contrary, earlier
works proved that any nonlinear form other t...
Canonization of F(R) theory of gravity to explore Noether symmetry is
performed treating R - 6(\frac{\ddot a}{a} + \frac{\dot a^2}{a^2} +
\frac{k}{a^2}) = 0 as a constraint of the theory in Robertson-Walker
space-time, which implies that R is taken as an auxiliary variable. Although it
yields correct field equations, Noether symmetry does not allow...
Noether symmetry of F(R) theory of gravity in vacuum or in matter dominated
era yields three-half power law of R. We show that this particular curvature
invariant term is very special in the context of isotropic and homogeneous
cosmological model as it makes the first fundamental form cyclic. As a result,
it allows a unique power law solution, typi...