We investigate the celebrated Raychaudhuri equation (RE) within the framework of a modified gravity inspired by Finsler geometry. We further discuss the classical focusing theorem in different cosmological scenarios. Moreover, we attempt to find some analogy of the modified Finsler RE with the first Friedmann equation and find the first integral. We analyze the cosmological singularity using a Harmonic Oscillator approach in this modified dynamics. Finally, we incorporate quantum corrections to the Finsler-modified RE and discuss the existence and/or avoidance of the initial big-bang singularity by a semi-classical approaches namely,the Wheeler–DeWitt quantization formalism.

India

Madhukrishna Chakraborty

Subenoy Chakraborty

Raychaudhuri equation and its consequences in Finsler-modified gravity: classical and quantum analysis

This article opens new window to obtain accelerating scaling attractors without any need of dark energy. We study cosmological dynamics in a two-fluid system where pressureless dark matter (DM) undergoes adiabatic particle creation and exchanges energy with a barotropic fluid. Considering six widely used interaction prescriptions, we formulate the corresponding autonomous systems in a compact phase space and perform a unified dynamical analysis. We find that accelerating scaling attractors, namely late-time states where both fluids coexist with fixed energy fractions, arise only when the interaction is controlled by the DM density and energy flows from DM to the second fluid. Such attractors appear in the global and local DM-based interactions, and in the global mixed case, but are entirely absent when the interaction depends on the second fluid or on local mixed terms, which instead drive the universe to a DM-dominated accelerating phase. These results clarify the unique conditions under which matter creation can mimic dark-energy-like behaviour without introducing a dark-energy component.

Sudip Halder

Spain

Jaume de Haro

South Africa

Supriya Pan

Greece

Chile

China

Emmanuel N. Saridakis

Tapan Saha

Accelerating scaling solutions from dark matter particle creation

In this work, we construct novel traversable wormhole solutions supported by gravitational particle creation mechanism and study their physical viability through energy conditions, throat dynamics and asymptotic behavior. We further study their geometry through the lens of embedding diagrams. Subsequently, we explore their observational signatures, focusing on the shadow structure, quasinormal spectra, and greybody factors obtained via the WKB approximation. In doing so, we aim to provide a comprehensive framework where particle creation naturally sustains traversable wormholes and simultaneously enriches their phenomenology in a testable manner.

Thailand

Malaysia

Traversable wormholes induced by particle creation mechanism: from geometry to observations

The paper deals with the study of some novel traversable Wormholes (TWHs) in the presence of Casimir effect, a well known quantum phenomenon in conjunction with classical electric charge and a massless scalar field with vanishing potential. The paper delves deep into exploring the interplay of General Relativity (GR) and Quantum Field Theory (QFT) to shape realistic models of Wormhole (WH) space-times. Further, it studies the geometry and stability of these WHs both on qualitative as well as on quantitative grounds. Finally, the paper provides valuable insights regarding the observational signatures like shadows, quasinormal modes (QNMs) and grey body factors (GBFs) concerning the TWHs so constructed.

Casimir-driven traversable wormholes: Geometry, stability and observable signatures

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.

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.