Cosmography in f ( Q ) gravity Mandal, Sanjay; Wang, Deng; Sahoo, P. K.
Physical review. D,
12/2020, Letnik:
102, Številka:
12
Journal Article
Recenzirano
Cosmography is an ideal tool to investigate the cosmic expansion history of the Universe in a model-independent way. The equations of motion in modified theories of gravity are usually very ...complicated; cosmography may select practical models without imposing arbitrary choices a priori. We use the model-independent way to derive f(z) and its derivatives up to fourth order in terms of measurable cosmographic parameters. We then fit those functions into the luminosity distance directly. We perform the MCMC analysis by considering three different sets of cosmographic functions. Using the largest supernovae Ia Pantheon sample, we derive the constraints on the Hubble constant H0 and the cosmographic functions, and find that the former two terms in Taylor expansion of luminosity distance work dominantly in f(Q) gravity.
f
(
R
,
T
) gravity is an extended theory of gravity in which the gravitational action contains general terms of both the Ricci scalar
R
and the trace of the energy-momentum tensor
T
. In this way,
...f
(
R
,
T
) models are capable of describing a non-minimal coupling between geometry (through terms in
R
) and matter (through terms in
T
). In this article we construct a cosmological model from the simplest non-minimal matter–geometry coupling within the
f
(
R
,
T
) gravity formalism, by means of an effective energy-momentum tensor, given by the sum of the usual matter energy-momentum tensor with a dark energy contribution, with the latter coming from the matter–geometry coupling terms. We apply the energy conditions to our solutions in order to obtain a range of values for the free parameters of the model which yield a healthy and well-behaved scenario. For some values of the free parameters which are submissive to the energy conditions application, it is possible to predict a transition from a decelerated period of the expansion of the universe to a period of acceleration (dark energy era). We also propose further applications of this particular case of the
f
(
R
,
T
) formalism in order to check its reliability in other fields, rather than cosmology.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Energy conditions in f ( Q ) gravity Mandal, Sanjay; Sahoo, P. K.; Santos, J. R. L.
Physical review. D,
07/2020, Letnik:
102, Številka:
2
Journal Article
Recenzirano
A complete theory of gravity impels us to go beyond Einstein's general relativity. One promising approach lies in a new class of teleparallel theory of gravity named f(Q), where the nonmetricity Q is ...responsible for the gravitational interaction. The important roles any of these alternative theories should obey are the energy condition constraints. Such constraints establish the compatibility of a given theory with the causal and geodesic structure of space-time. In this work, we present a complete test of energy conditions for f(Q) gravity models. The energy conditions allowed us to fix our free parameters, restricting the families of f(Q) models compatible with the accelerated expansion our Universe passes through. Our results strengthen the viability of f(Q) theory, leading us close to the dawn of a complete theory for gravitation.
Microalgae are receiving increasing attention worldwide as an alternative and renewable source for energy production. Through various conversion processes, microalgae can be used to produce many ...different kinds of biofuels, which include biodiesel, bio-syngas, bio-oil, bio-ethanol, and bio-hydrogen. However, large scale production of microalgal biofuels, via many available conversion techniques, faces a number of technical challenges which have made the current growth and development of the algal biofuel industry economically unviable. Therefore, in addition to algae culture and growth, it is also essential to develop cost-effective technologies for efficient biomass harvesting, lipid extraction and biofuels production. This review aims to collate and present an overview of current harvesting, oil extraction and biofuels production technologies from microalgae. Since much of the current studies on oil extraction are focused on biodiesel production from microalga, this study, apart from discussing the various biodiesel production techniques in the later sections, has also done a detailed discussion on the production techniques of other biofuels.
Baryogenesis in f(Q,T) gravity Bhattacharjee, Snehasish; Sahoo, P. K.
The European physical journal. C, Particles and fields,
03/2020, Letnik:
80, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The article communicates exploration of gravitational baryogenesis in presence of
f
(
Q
,
T
)
gravity where
Q
denote the nonmetricity and
T
the trace of the energy momentum tensor. We study various ...baryogenesis interactions proportional to
Q
˙
and
Q
˙
f
Q
for the
f
(
Q
,
T
)
gravity model
f
(
Q
,
T
)
=
α
Q
n
+
1
+
β
T
, where
α
,
β
and
n
are model parameters. Additionally we report the viable parameter spaces for which an observationally consistent baryon-to-entropy can be generated. Our results indicate that
f
(
Q
,
T
)
gravity can contribute significantly and consistently to the phenomenon of gravitational baryognesis.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Although the Pöschl-Teller potential is widely known for its ability to describe diatomic molecular energy spectra and vibrational excitations, the current effort focuses on parameterizing the ...above-mentioned potential for nuclear systems. The differential equation methodology to the problem in the representation space leads to the derivation of regular and Jost solutions for the Pöschl-Teller potential. For nucleon-nucleon and nucleon-nucleus systems, bound state energies and scattering phase shifts are computed using the derived Jost function. Using the phase parameters, the elastic scattering cross sections and analyzing powers have been calculated. The outcomes closely match the experimental ones.
New high-precision observations are now possible to constrain different gravity theories. To examine the accelerated expansion of the Universe, we used the newly proposed
f
(
Q
,
T
) gravity, where
...Q
is the non-metricity, and
T
is the trace of the energy–momentum tensor. The investigation is carried out using a parameterized effective equation of state with two parameters,
m
and
n
. We have also considered the linear form of
f
(
Q
,
T
)
=
Q
+
b
T
, where
b
is constant. By constraining the model with the recently published 1048 Pantheon sample, we were able to find the best fitting values for the parameters
b
,
m
, and
n
. The model appears to be in good agreement with the observations. Finally, we analyzed the behavior of the deceleration parameter and equation of state parameter. The results support the feasibility of
f
(
Q
,
T
) as a promising theory of gravity, illuminating a new direction towards explaining the Universe dark sector.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In this work, we propose the modeling of static wormholes within the f(R,T) extended theory of gravity perspective. We present some models of wormholes, which are constructed from different ...hypotheses for their matter content, i.e., different relations for their pressure components (radial and lateral) and different equations of state. The solutions obtained for the shape function of the wormholes obey the necessary metric conditions. They show a behavior similar to those found in previous references about wormholes, which also happens to our solutions for the energy density of such objects. We also apply the energy conditions for the wormholes’ physical content.
Wormholes in exponential f(R, T) gravity Moraes, P. H. R. S.; Sahoo, P. K.
The European physical journal. C, Particles and fields,
08/2019, Letnik:
79, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Alternative gravity is nowadays an extremely important tool to address some persistent observational issues, such as the dark sector of the universe. They can also be applied to stellar astrophysics, ...leading to outcomes one step ahead of those obtained through General Relativity. In the present article we test a novel
f
(
R
,
T
) gravity model within the physics and geometry of wormholes. The
f
(
R
,
T
) gravity is a reputed alternative gravity theory in which the Ricci scalar
R
in the Einstein-Hilbert gravitational lagrangian is replaced by a general function of
R
and
T
, namely
f
(
R
,
T
), with
T
representing the trace of the energy-momentum tensor. We propose, for the first time in the literature, an exponential form for the dependence of the theory on
T
. We derive the field equations as well as the non-continuity equation and solve those to wormhole metric and energy-momentum tensor. The importance of applying alternative gravity to wormholes is that through these theories it might be possible to obtain wormhole solutions satisfying the energy conditions, departing from General Relativity well-known outcomes. In this article, we indeed show that it is possible to obtain wormhole solutions satisfying the energy conditions in the exponential
f
(
R
,
T
) gravity. Naturally, there is still a lot to do with this model, as cosmological, galactical and stellar astrophysics applications, and the reader is strongly encouraged to do so, but, anyhow, one can see the present outcomes as a good indicative for the theory.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Viscous cosmology in the Weyl-type f(Q, T) gravity Gadbail, Gaurav N.; Arora, Simran; Sahoo, P. K.
The European physical journal. C, Particles and fields,
12/2021, Letnik:
81, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Bulk viscosity is the only viscous influence that can change the background dynamics in a homogeneous and isotropic universe. In the present work, we analyze the bulk viscous cosmological model with ...the bulk viscosity coefficient of the form
ζ
=
ζ
0
+
ζ
1
H
+
ζ
2
H
˙
H
+
H
where,
ζ
0
,
ζ
1
and
ζ
2
are bulk viscous parameters, and
H
is the Hubble parameter. We investigate the impact of the bulk viscous parameter on dynamics of the universe in the recently proposed Weyl-type
f
(
Q
,
T
) gravity, where
Q
is the non-metricity, and
T
is the trace of the matter energy–momentum tensor. The exact solutions to the corresponding field equations are obtained with the viscous fluid and the linear model of the form
f
(
Q
,
T
)
=
α
Q
+
β
6
κ
2
T
, where
α
and
β
are model parameters. Further, we constrain the model parameters using the 57 points Hubble dataset the recently released 1048 points Pantheon sample and the combination Hz + BAO + Pantheon, which shows our model is good congeniality with observations. We study the possible scenarios and the evolution of the universe through the deceleration parameter, the equation of state (EoS) parameter, the statefinder diagnostics, and the Om diagnostics. It is observed that the universe exhibits a transition from a decelerated to an accelerated phase of the universe under certain constraints of model parameters.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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