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In this paper we explore the effects of a Generalized Uncertainty Principle (GUP) on Schwarzschild black hole. In particular, we incorporate the effects of GUP into the Parikh-Wilczek tunneling process for Hawking radiation. To this effect, we observe that results obtained due to GUP correction resemble that of the Reissner-Nordstr\"{om} black hole, showing similarities to the nature of an electric charge. We also find that, within this framework, the emission is not purely thermal, thus addressing the information loss problem through the correlation function., Comment: 7 pages, 1 figure

In this paper, we invoke a generalized uncertainty principle (GUP) in the symmetry-reduced cosmological Hamiltonian for a universe driven by a quintessence scalar field with potential. Our study focuses on semi-classical regime. In particular, we derive the GUP-distorted Friedmann, Raychaudhuri, and the Klein-Gordon equation. This is followed by a systematic analysis of the qualitative dynamics for the choice of potential $V(\phi)= V_0 \sinh^{-n}{(\mu \phi)}$. This involves constructing an autonomous dynamical system of equations by choosing appropriate dynamical variables, followed by a qualitative study using linear stability theory. Our analysis shows that incorporating GUP significantly changes the existing fixed points compared to the limiting case without quantum effects by switching off the GUP., Comment: 12. arXiv admin note: text overlap with arXiv:2404.09049

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 early epoch of the evolution. 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 contribution. In addition, we confirm the existence of an inflationary epoch and analyze the behavior of relevant cosmological parameters with respect to the strength of GUP distortion.

We consider a formulation of the Brans-Dicke theory in Jordan's frame for Bianchi-I spacetime within the framework of loop quantum gravity. The robustness of singularity resolutions due to the quantum effects is explicitly verified in the context of two quantization schemes typically used in the literature. We present an exploration of the effects of quantum geometry on the background dynamics, which is also illustrated through some explicit numerical examples and showing the absence of the singularity., Comment: 13 pages, 4 figures

The strange behaviour of the universe's dark sector offers us the flexibility to address cosmological problems with different approaches. Using this flexibility, we consider a possible exchange of energy among the dark sector components as a viable candidate model. In the present work, we investigate the interaction between two scalar fields within the generalization of a two-component chiral cosmology. We also show that there exists a unique equivalence between fields and fluids description of interacting dark sector model. Later, a detailed analysis of the dynamics of the dark energy-dark matter model with coupling in both kinetic and potential parts has been performed using a method of qualitative analysis of dynamical systems. Moreover, the cosmological viability of this model is analyzed for the potential of an exponential form via the phase-space study of autonomous system for various cosmological parameters., Comment: 21+6 pages, Supported New figures, Few modification, references added

A non-canonical scalar tachyon field is a viable candidate for dark energy and has been found to be in good agreement with observational data. Background data alone cannot completely rule out degeneracy between this model and others. To further constrain the parameters, apart from the distance measurements, we study perturbations in the tachyon scalar field and how they affect matter clustering. We consider two tachyon potentials for this study, an inverse square potential and an exponential potential. We study the evolution of the gravitational potential, matter density contrast, and dark energy density contrast, and compare them with the evolution in the $\Lambda CDM $ model. Although perturbations in dark energy at sub-Hubble scales are negligible in comparison with matter perturbations, they cannot be ignored at Hubble and super-Hubble scales ($\lambda_p > 1000$ Mpc). We also study the evolution of growth function and growth rate of matter, and find that the growth rate is significantly suppressed in dark energy dominated era with respect to the growth rate for $\Lambda CDM$ model. A comparison of these models with Redshift Space Distortion growth rate data is presented by way of calculating $f\sigma_8(z)$. There is a tension of $2.9\sigma$ ($2.26\sigma$ ) between growth rate data and Planck-2015 (Planck-2018) Cosmic Microwave Background Radiation data for $\Lambda CDM$ model. We present constraints on free parameters of these models and show that perturbations in the tachyon scalar field reduce this tension between different data sets., Comment: 29 pages, 16 figures, modified abstract, more detailed discussion, published in JCAP

Recently the background independent nonperturbative quantization technique has been extended to theories of gravity and the corresponding quantum effective cosmology has been derived, which provides us with necessary avenue to explore the pre-inflationary dynamics. Brans-Dicke loop quantum cosmology (BDLQC) is one such theory whose effective background dynamics is considered in this article. Starting with a quantum bounce, we explore the pre-inflationary dynamics of a universe sourced by a scalar field with the Starobinsky potential in BDLQC. Our study is based on the idea that though Einstein's and Jordan's frames are classically equivalent up to a conformal transformation in Brans-Dick theory, it is not true after quantization. Taking the Jordan frame as the physical one we explore in detail the bouncing scenario which is followed by a phase of slow roll inflation. The three phases of the evolution of the universe namely, bouncing, transition from quantum bounce to classical universe and the slow roll inflation, are noted for an initially kinetic energy dominated bounce. In addition, to be consistent with observational data, we also find out the allowed data space of initial conditions that would produce 60 e-folds of expansion during the slow roll inflation., Comment: 18 pages, 8 figures, 1 table. Published in Commun. Theor. Phys. 71 (2019) 1205-1218

In this article we explore the pre-inflationary background dynamics of an FLRW universe sourced by a scalar field with monodromy potential in LQC framework. In particular we calculate the number of e-folds, $N_{inf}$, produced during the slowly rolling phase of the inflation and find out the critical value of the ratio of the kinetic to potential energy, $r_w^c$, at the quantum bounce that is required to produce $N_{inf}\simeq 60.$ Two different monodromy potentials, namely, linear and quadratic with a modulation term are investigated to this effect. The effects on the value of $N_{inf}$ due to parameters associated with the strength, decay constant and the phase factor of the modulation term are calculated. In addition to this we present the qualitative picture of the background dynamics by carrying out a dynamical system analysis. We produce the phase portraits and carry out a detailed linear stability analysis of the finite fixed points, if any, for each of the potentials., Comment: revtex4, seven figures and five tables. Version to appear in JCAP

In this paper, we study the pre-inflationary dynamics for the power-law potential $(V(\phi) \propto \phi^n)$ with $n<2$ in the framework of loop quantum cosmology. In the case where the kinetic energy of the inflaton dominates at the initial, the evolution of the universe can always be divided into three different phases prior to preheating: {\em bouncing, transition and slow-roll inflation}. During the bouncing phase, the evolution of the expansion factor is independent not only on the initial conditions but also the inflationary potentials, and is given explicitly by an analytical solution. In contrast, for the potential energy dominated initial conditions, this universality is lost. We also obtain total number of e-folds during the slow-roll inflation, whereby physically viable models are identified. In addition, we present phase space analysis for the inflationary potentials under consideration and compare our results with the ones obtained previously for different potentials., Comment: revtex4, 11 figure and 4 tables. Some typos are corrected, and new references are added. Phys. Rev. D96 (2017) 123533

We investigate the cosmology of a class of model with noncanonical scalar field and matter both in FRW closed and open background. Writing the Einstein Equations in terms of dimensionless dynamical variables suitable for studying bouncing solutions, a fixed point analysis is carried out. Cosmological solutions satisfying the stability and bouncing conditions are obtained., Comment: 15 pages, 10 figures. arXiv admin note: substantial text overlap with arXiv:1501.01765

We investigate the cosmology of a class of model with noncanonical scalar field and matter in an anisotropic time dependent background. Writing the Einstein Equations in terms of dimensionless dynamical variables appropriately defined for bouncing solutions, we find all the fixed points. From the bouncing conditions and stability of fixed points, solutions describing non singular bounce are obtained., Comment: 13 pages, 6 figures. arXiv admin note: text overlap with arXiv:1406.3992

We investigate the cosmology of a class of model with noncanonical scalar field and matter in an anisotropy background. We find fixed points and their stability which constraints equation of state parameter for the matter. This is done after expressing the Einstein equations in terms of dimensionless variables. Similarly we define a set of suitable dynamical variables for studying bouncing solutions. The condition for nonsingular bounce is obtained. Here we show, numerically, that solution that of a cyclic universe exist for the certain form of kinetic term of noncanonical scalar field and the time period of cycle depends on the kinetic term of noncanonical scalar field. In certain case we find that a cyclic universe can be approximated to be a single bouncing scenario for the entire evolution of the dynamical variables. Resemblling an eternal bouncing scenario, this model may also be free from BKL instability. Also, the univerese isotropize in the expansion phase and this isotropization can be delayed to some extent by tuning the the parameter of the model., Comment: This paper has been withdrawn by the author due to error in the analysis

In this paper we investigate the fate of the universe with an anisotropic background sourced by anisotropic matter. We see the behaviour of the Raychaudhuri Equation and investigate wheather a congrurence of time like geodesics focus to a point in a universe with Bianchi I background which is dictated by anisotropic sources like cosmic strings, domain walls, magnetic field and lorentz violating magnetic field each separately. Thus, Focussing theorem has been checked both for initially contracting and diverging universe with each of these anisotropic sources., Comment: 6 pages, 10 figures

We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de~Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union~2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found., Comment: 21 pages, 12 figures, matches journal version