2025

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Browsing 2025 by Author "ARSAL KAMAL"

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    Impact of modified theories of gravity on the propagation of gravitational waves.
    (UMT Lahore, 2025-07-02) ARSAL KAMAL
    This thesis investigates the fluctuations of GWs in FLRW and Bianchi Type-I universe models within framework of f(R, Tφ) theory. To incorporate GWs into these backgrounds, we employ the axial and polar perturbation techniques established by Regge and Wheeler, simultaneously perturbing the corresponding scalar field as well as its potential in each case. We aim to examine the effect of scalar field on GWs through the modified gravity model. In each scenario, we mainly formulate field equations for unperturbed and perturbed cases. By solving these two sets of field equations simultaneously, along with the perturbed scalar field and its potential, we obtain a set of differential equations involving unknown perturbation parameters. The resulting equations are solved using the separation of variables method, yielding solutions for both the temporal and spatial components. Furthermore, we analyze the perturbation parameters graphically by varying the model parameter λ. The graphical analysis in FRW case as well as Bianchi Type-I scenario, revealed that the scalar field influences propagation of axial and polar GWs. Our results highlight influence of scalar field on GWs propagation, particularly through variations in model parameter. Graphical analysis observed that how scalar field influences the temporal components of the perturbations. Meanwhile, the spatial part remains unaffected by the scalar field. These findings offer insights into the interaction between scalar fields and GWs, with implications for early universe dynamics and modified gravity theories.