Search for: All records

The prediction of a minimal length scale by various quantum gravity candidates (such as string/M theory, Doubly Special Relativity, Loop Quantum Gravity and others) have suggested modification of Heisenberg Uncertainty Principle (HUP), resulting in the Generalized Uncertainty Principle (GUP). In this short review, we investigate the origins of the GUP and examine higher-order models, focusing on the linear plus quadratic form of the GUP. We extend the concept of minimal length to minimal angular resolution, which plays a crucial role in modifying angular momentum and its associated algebra. A comparison is made between the standard angular momentum commutator algebra and that modified by the GUP. Finally, we review its application in the hydrogen atom spectra and and discuss future endeavors. 

Abstract In this paper, we study the quasi-normal modes (QNMs) of a scalar field in the background of a large class of quantum black holes that can be formed from gravitational collapse of a dust fluid in the framework of effective loop quantum gravity. The loop quantum black holes (LQBHs) are characterized by three free parameters, one of which is the mass parameter, while the other two are purely due to quantum geometric effects. Among these two quantum parameters, one is completely fixed by black hole thermodynamics and its effects are negligible for macroscopic black holes, while the second parameter is completely free (in principle). In the studies of the QNMs of such LQBHs, we pay particular attention to the difference of the QNMs between LQBHs and classical ones, so that they can be observed for the current and forthcoming gravitational wave observations, whereby place the LQBH theory directly under the test of observations. 

In this paper, we systematically study the evolution of the Universe within the framework of a modified loop quantum cosmological model (mLQC-I) using various inflationary potentials, including chaotic, Starobinsky, generalized Starobinsky, polynomials of the first and second kinds, generalized T-models and natural inflation. In all these models, the big bang singularity is replaced by a quantum bounce, and the evolution of the Universe, both before and after the bounce, is universal and weakly dependent on the inflationary potentials, as long as the evolution is dominated by the kinetic energy of the inflaton at the bounce. In particular, the pre-bounce evolution can be universally divided into three different phases: pre-bouncing, pre-transition, and pre-de Sitter. The pre-bouncing phase occurs immediately before the quantum bounce, during which the evolution of the Universe is dominated by the kinetic energy of the inflaton. Thus, the equation of state of the inflaton is about one, w(ϕ)≃1. Soon, the inflation potential takes over, so w(ϕ) rapidly falls from one to negative one. This pre-transition phase is very short and quickly turns into the pre-de Sitter phase, whereby the effective cosmological constant of Planck size takes over and dominates the rest of the contracting phase. Throughout the entire pre-bounce regime, the evolution of both the expansion factor and the inflaton can be approximated by universal analytical solutions, independent of the specific inflation potentials. 

In loop quantum cosmology, the slow-roll inflation is generic, and when the kinetic energy of the scalar field dominates at the bounce, the evolution of the Friedmann-Lemaître-Robertson-Walker universe will go through three distinguishable epochs, bouncing, transition, and finally slow-roll inflation, before the reheating commences. The bouncing dynamics are insensitive of the potential and initial conditions, so that the expansion factor and the scalar field can be described uniquely by a universal solution during this epoch. After about 105 Planck time, the epoch of transition starts and the universe rapidly turns over from the kinetic energy dominated state to the potential energy dominated one, whereby the slow-roll inflationary phase begins. In this paper, we consider the power law plateau potential and study the pre-inflationary cosmology for different sets of initial conditions, so that during the slow-roll inflation epoch enough e-folds will be produced. Considering the generalized reheating and comparing with the recent Planck 2018 data, we are able to constrain the total number of e-folds (NT) from the bounce till today to be consistent with the current observable universe. Depending on the matter driving the reheating (subject to the different dominant equations of states), we report the observationally allowed NT and reheating temperature and find in particular NT≃127, which is significantly different from the one NT≳141 obtained previously without considering the reheating phase. 

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.