The present work deals with some WH solutions in <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>Q</mi><mo stretchy='false'>)</mo></math> gravity theory for non-constant red-shift function subject to a power law model of <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>Q</mi><mo stretchy='false'>)</mo></math>, <italic>Q</italic> being the non-metricity scalar. Important properties of a WH configuration like the asymptotic flatness, traversability, flairing out condition and energy conditions have been checked for the obtained solutions. Shadows for these WHs have been determined and effect of non-metricity has been discussed. Finally, the paper gives an essence of quasinormal modes and gray body factors for traversable WHs in general and <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>Q</mi><mo stretchy='false'>)</mo></math> wormholes in particular indicating a distinct signature of non-metricity influencing these observational tools.

India

Madhukrishna Chakraborty

Thailand

Malaysia

Subenoy Chakraborty

Exploring traversable wormholes in <italic>f</italic>( <italic>Q</italic>) gravity: Shadows and quasinormal modes

The present work analyses Raychaudhuri equation (RE) in Einstein gravity for two interacting fluids. Focusing theorem, a consequence of RE, is directly related to the singularity theorems of Penrose and Hawking. In the present work, the signature of the Raychaudhuri scalar or convergence scalar has been examined for two types of interaction forms namely, (i) $$Q=H(\alpha \rho _1+\beta \rho _2)$$ (linear) and (ii) $$Q=\dfrac{H\xi \rho _1\rho _2}{\alpha \rho _1+\beta \rho _2}$$ (non-linear). Finally, the phenomena of focusing of a congruence of geodesics and possible avoidance of singularity have been discussed based on the nature of the two fluids and the interaction term operating between them.

Implications of Raychaudhuri equation and geodesic focusing in interacting two fluid systems

The present work deals with Noether symmetry approach in a modified teleparallel gravity for classical quantum cosmological description. In the background of homogeneous and isotropic flat Friedmann–Lema $$\hat{\text{ i }}$$ tre–Robertson–Walker (FLRW) model, the Noether symmetry vector with the associated conserved charge identifies a cyclic variable so that the modified Einstein field equations get simplified and becomes solvable in the present model. In quantum cosmology, the operator version of the conserved associated momentum identifies the oscillatory part of the wave function and consequently it is possible to have the complete wave as the solution of the Wheeler–DeWitt (WD) equation. Finally, it has been examined whether classical singularity can be avoided or not by quantum description.

Dipankar Laya

Shriton Hembrom

Sourav Dutta

A study of classical and quantum cosmology in modified teleparallel gravity and the role of Noether symmetry

A detailed symmetry analysis has been done for the present multi scalar-torsion gravity theory in the background of flat Friedmann Lema $$\hat{\text{ i }}$$  <math> <mover> <mrow> <mspace width="0.333333em"></mspace> <mtext>i</mtext> <mspace width="0.333333em"></mspace> </mrow> <mo>^</mo> </mover> </math>  tre Robertson Walker (FLRW) space-time. Not only the Noether symmetry from the invariance of the Lagrangian has been determined and associated conserved quantities are evaluated, but also the conformal symmetry of the physical metric (i.e., metric of the kinetic part) has been investigated to evaluate homothetic and killing vector fields. Finally, a through study of quantum cosmology both by canonical approach and by considering quantum trajectories has been presented.

Roshni Bhaumik

Symmetry analysis in multi scalar-torsion cosmological model with quantum description

An investigation has been done for possible existence of evolving wormhole (WH) solution in the background of inhomogeneous Lemaitre–Tolman–Bondi (LTB) space-time geometry. Using separable product form of the geometric (or area) radius, the shape function can be evaluated in terms of the functional part of the radial coordinate in the area radius. The conditions for a viable WH configuration have been examined.

A study on existence of wormhole in Lemaitre–Tolman–Bondi model

The paper deals with a cosmological model containing two scalar fields which can be considered as an extension of the Brans–Dicke scalar field model. Due to highly coupled non linear field equations, Noether symmetry analysis has been imposed and as a result the Lagrangian as well as the field equations become much simple in form to have the classical solutions. The relevant cosmological parameters are analyzed graphically. Finally, quantum cosmology has been studied by constructing the Wheeler–DeWitt equation and the solution of this second order partial differential equation has been done using this symmetry analysis.

Classical and quantum cosmology for two scalar field Brans–Dicke type theory: a Noether symmetry approach

The paper deals with Warm Inflationary scenario in FLRW with torsion both from theoretical and observational point of view. In the background of flat FLRW model the Hubble parameter is found to be proportional to the torsion function and warm inflation is examined both in weak and strong dissipation regimes for the power law choice of potential using slow-roll approximation with quasi-stable criteria for radiation. The slow-roll parameters, no.of e-folds, scalar spectral index, and tensor-to-scalar ratio are determined in the present model for mainly three choices of the dissipation coefficient  $$\Gamma $$  <math> <mi>Γ</mi> </math>   using the Planck data set. Finally, we focus on single-field chaotic quartic potential with the above choices of the dissipation coefficient to confront the warm inflation observational predictions directly with the latest observational data set.

Gopal Sardar

Akash Bose

Theoretical and observational prescription of warm-inflation in FLRW universe with torsion

The present work deals with a complex scalar field in scalar tensor gravity theory in the background of spatially flat Friedmann–Lema $${\hat{i}}$$  <math> <mover> <mi>i</mi> <mo>^</mo> </mover> </math>  tre–Robertson–Walker (FLRW) geometry. Noether symmetry analysis has been used to determine the classical cosmological solution of a scalar field in scalar–tensor theory with the scalar field as a nonminimally coupled complex field. Noether symmetry analysis is not only used to find a symmetry vector and potential but also it helps in finding an appropriate transformation  $$(a,~\phi ,~\theta )\rightarrow (u,~v,~\theta )$$  <math> <mrow> <mo>(</mo> <mi>a</mi> <mo>,</mo> <mspace width="3.33333pt"></mspace> <mi>ϕ</mi> <mo>,</mo> <mspace width="3.33333pt"></mspace> <mi>θ</mi> <mo>)</mo> <mo>→</mo> <mo>(</mo> <mi>u</mi> <mo>,</mo> <mspace width="3.33333pt"></mspace> <mi>v</mi> <mo>,</mo> <mspace width="3.33333pt"></mspace> <mi>θ</mi> <mo>)</mo> </mrow> </math>   in the augmented space so that one of the new variables becomes cyclic. In quantum cosmology, the Wheeler–DeWitt (WD) equation has been formed in the minisuperspace and its solution i.e. the wave function of the universe has been evaluated by using the operator version of the conserved (Noether) charge. Finally, the nature of the classical solution has been discussed from the observational point of view and the cosmological singularity has been examined both classically and quantum mechanically.

Noether symmetry analysis in scalar tensor cosmology: a study of classical and quantum cosmology

The present study analyses the wormhole solution both in the dRGT-f(R, T) massive gravity and Einstein massive gravity. In both the models, the anisotropic pressure solution in ultrastatic wormhole geometry gives rise to the shape function that involves massive gravity parameters  $$ \gamma $$  <math> <mi>γ</mi> </math>   and  $$ \Lambda $$  <math> <mi>Λ</mi> </math>  . However, the terms consisting of  $$ \gamma $$  <math> <mi>γ</mi> </math>   and  $$ \Lambda $$  <math> <mi>Λ</mi> </math>   acts in such a way that the spacetime loses asymptotic flatness. Similar to the black hole solution in massive gravity, this inconsistency arises due to the repulsive effect of gravity which can be represented by the photon deflection angle that goes negative after a certain radial distance. It is investigated that the repulsive effect induced in the massive gravitons push the spacetime geometry so strongly that the asymptotic flatness is effected. On the other hand, in this model, one can have a wormhole with ordinary matter at the throat that satisfies all the energy conditions while the negative energy density is sourced by massive gravitons. Finally, using the TOV equation, it is found that the model is stable under the hydrostatic equilibrium condition.

Ayanendu Dutta

Dhritimalya Roy

Nihal Pullisseri

Wormhole formation in massive gravity: an analytic description

The present cosmological model deals with modified f(R, T) gravity theory with  $$f(R,T)=R+h(T)$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>R</mi> <mo>,</mo> <mi>T</mi> <mo>)</mo> <mo>=</mo> <mi>R</mi> <mo>+</mo> <mi>h</mi> <mo>(</mo> <mi>T</mi> <mo>)</mo> </mrow> </math>   in the background of homogeneous and isotropic FLRW space-time model. Four choices of h(T) have been studied and examined from two observational data sets. It is found that model III, namely, the linear combination of power law and logarithmic form is more consistent with observed data than the others. However, all four considered models are a worse fit than the LCDM model.

Observational constraints on f(R, T) gravity with  $$f(R,T) = R + h(T)$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>R</mi> <mo>,</mo> <mi>T</mi> <mo>)</mo> <mo>=</mo> <mi>R</mi> <mo>+</mo> <mi>h</mi> <mo>(</mo> <mi>T</mi> <mo>)</mo> </mrow> </math>