Browsing by Author "Pathak S.D."

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    An extensive analysis of Schwarzschild exterior solution
    (2022-11-01) Rajeeb Kumar D.; Chowdhury N.; Pathak S.D.; Kumar U.; Sharma M.; Ojha V.K.; Mahidol University
    We pursue a detailed analysis of the Schwarzschild geometry around a spherically symmetric, non-rotating, uncharged source and aim to construct the Schwarzschild metric by considering trigonometric, hyperbolic and logarithmic functions of position and time and solving the Einstein field equation. We investigate whether the Schwarzschild exterior solution is indeed independent of the choice of the nature of the function for the first two metric elements in the general expression for the Schwarzschild metric, and is solely dependent upon the centrally symmetric nature of the geometry taken into account.
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    Distortion of quintessence dynamics by the generalized uncertainty principle
    (2025-02-01) Bhandari G.; Pathak S.D.; Sharma M.; Wang A.; Bhandari G.; Mahidol University
    In this paper, we introduce the generalized uncertainty principle (GUP) into the symmetry-reduced cosmological Hamiltonian for a universe influenced by a quintessence scalar field with potential. Our investigation centers on the semi-classical regime. Specifically, we derive the GUP-modified versions of the Friedmann, Raychaudhuri, and Klein–Gordon equations. Subsequently, we conduct a systematic analysis of the qualitative dynamics for the potential V(ϕ)=V0sinh−n(μϕ). This involves formulating an autonomous dynamical system using suitable dynamical variables, followed by a qualitative analysis through linear stability theory. Our findings reveal that incorporating GUP markedly alters the fixed points compared to the scenario without quantum effects, where GUP is not considered.
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    Dynamics of scalar fields from a generalized form of Lagrangian
    (2025-09-01) Kaur J.; Pathak S.D.; Khlopov M.; Krasnov M.; Sharma M.; Kaur J.; Mahidol University
    Scalar fields play a crucial role in Einstein's field equations, describing both the early- and late-time phenomenology of the universe. Despite numerous Lagrangians with distinct implications, a unified model has been lacking. We propose a generalized Lagrangian with two parameters, α and β, that encompasses quintessence, phantom, and tachyon fields. This framework captures their canonical dynamics, derives the background equations, and facilitates studies of cosmic evolution. Using the Om(z) diagnostic, we distinguish the evolutionary patterns of these fields from those of the cosmological constant, demonstrating smooth transitions between different behaviors. This cohesive structure enhances our understanding of dark energy and cosmic expansion, bridging theoretical versatility with observational constraints.
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    Generalized uncertainty principle and the Zeeman effect: Relativistic corrections unveiled
    (2025-03-01) Bhandari G.; Pathak S.D.; Sharma M.; Bhandari G.; Mahidol University
    In this paper, we calculate the relativistic corrections to the Zeeman effect for hydrogen-like atoms based on the Generalized Uncertainty Principle (GUP). We propose a relativistic GUP algebra using the Stetsko and Tkachuk approximation and incorporate these corrections into the Zeeman effect. In the relativistic limit, our results recover previously derived GUP corrections as well as the standard Lande energy shift expression when GUP effects are absent. This work presents a generalized expression that accounts for both relativistic and GUP corrections to the Zeeman effect.
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    GUP deformed background dynamics of phantom field
    (2024-11-01) Bhandari G.; Pathak S.D.; Sharma M.; Wang A.; Bhandari G.; Mahidol University
    Quantum gravity has been baffling the theoretical physicist for decades now, both for its mathematical obscurity and phenomenological testing. Nevertheless, the new era of precision cosmology presents a promising avenue to test the effects of quantum gravity. In this study, we consider a bottom-up approach. Without resorting to any candidate quantum gravity, we invoke a generalized uncertainty principle (GUP) directly into the cosmological Hamiltonian for a universe sourced by a phantom scalar field with potential to study the evolution of the universe in a very early epoch. This is followed by a systematic analysis of the dynamics, both qualitatively and quantitatively. Our qualitative analysis shows that the introduction of GUP significantly alters the existence of fixed points for the potential considered in this paper. In addition, we confirm the existence of an inflationary phase and analyze the behavior of relevant cosmological parameters with respect to the strength of the GUP distortion.
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    Inflection Point Dynamics of Minimally Coupled Tachyonic Scalar Fields
    (2025-04-01) Kaur J.; Pathak S.D.; Khlopov M.; Sharma M.; Kaur J.; Mahidol University
    In this paper, we explore the behavior of a minimally coupled tachyonic scalar field at an inflection point within an accelerating universe. We examine various cosmic expansion factors, including power-law, exponential, and a hybrid form combining power-law and exponential growth. For each of these scenarios, we derive the corresponding potentials of the tachyonic scalar field. Subsequently, we calculate the inflection points of the spatially homogeneous tachyonic scalar field for these potentials. To further analyze the system, we employ dynamical system analysis techniques to identify equilibrium points and assess their stability.
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    Quantum gravity corrections to Hawking radiation via GUP
    (2025-07-01) Bhandari G.; Pathak S.D.; Sharma M.; Khlopov M.Y.; Bhandari G.; Mahidol University
    In this paper, we explore the effects of the generalized uncertainty principle (GUP) on the tunneling process of a Schwarzschild black hole using two different approaches. First, we analyze the Parikh–Wilczek tunneling process for Hawking radiation within the GUP framework. Our results indicate that GUP corrections lead to outcomes similar to those of a Reissner–Nordström black hole, introducing an effect analogous to an electric charge, in agreement with findings from string theory and other quantum gravity models. Furthermore, we observe that the emission spectrum deviates from pure thermality, with correlations between emitted particles providing insights into the resolution of the information loss problem. Second, we examine the tunneling process using the Hamilton–Jacobi method, finding that both approaches yield the same GUP-modified Hawking temperature. These results reinforce the validity of GUP as a promising framework in the pursuit of a consistent theory of quantum gravity.
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    Quantum-Corrected Brans–Dicke cosmology
    (2025-01-01) Bhandari G.; Pathak S.D.; Sharma M.; Bhandari G.; Mahidol University
    In this paper, we explore the implication of the Generalized Uncertainty Principle (GUP) to theories beyond General Relativity. In particular, we obtain the effective dynamics for a class of scalar–tensor theory called Brans–Dicke in cosmological setting. To this effect, we obtain the GUP-modified Friedmann, Raychaudhuri and Klein–Gordon equations, along with the expressions for effective energy density and pressure. We identify the explicit additional terms that arise from the GUP corrections, providing deeper insights into the impact of quantum gravity effects on cosmological dynamics in the given context.