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Covariant models of loop quantum gravity generically imply dynamical signature change at high density. This article presents detailed derivations that show the fruitful interplay of this new kind of signature change with wave-function…

General Relativity and Quantum Cosmology · Physics 2021-05-27 Martin Bojowald , Suddhasattwa Brahma

We present the exact solution of a scalar field theory defined with noncommuting position and momentum variables. The model describes charged particles in a uniform magnetic field and with an interaction defined by the Groenewold-Moyal…

High Energy Physics - Theory · Physics 2009-11-10 E. Langmann , R. J. Szabo , K. Zarembo

Semiclassical states in isotropic loop quantum cosmology are employed to show that the improved dynamics has the correct classical limit. The effective Hamiltonian for the quantum cosmological model with a massless scalar field is thus…

General Relativity and Quantum Cosmology · Physics 2009-02-27 You Ding , Yongge Ma , Jinsong Yang

We offer a new, physically transparent argument for the existence of the critical, universal maximum matter density in loop quantum cosmology for the case of a flat Friedmann-Lemaitre-Robertson-Walker cosmology with scalar matter. The…

General Relativity and Quantum Cosmology · Physics 2013-01-23 David A. Craig

In this letter, we investigate the cosmic expansion scenario of the universe in the framework of $f(R,L_m)$ gravity theory. We consider a non-linear $f(R,L_m)$ model, specifically, $f(R,L_m)=\frac{R}{2}+L_m^n + \beta$, where $n$ and $\beta$…

General Relativity and Quantum Cosmology · Physics 2023-11-02 Lakhan V. Jaybhaye , Raja Solanki , Sanjay Mandal , P. K. Sahoo

In a sense of deformation quantization, noncommutative (NC) geometry introduces a quantum structure of spacetime. Using the twist-deformation formalism, we show that the dynamical effects of spacetime noncommutativity can amount to a…

High Energy Physics - Theory · Physics 2025-07-17 Dušan Đorđević , Dragoljub Gočanin

The so-called canonical noncommutativity is based on a constant noncommutative parameter ($\theta$). However, this formalism breaks Lorentz invariance and one way to recover it is to define the NC parameter as a variable, an extra…

High Energy Physics - Theory · Physics 2015-01-09 Everton M. C. Abreu , M. J. Neves , Vahid Nikoofard

The noncommutativity of the space-time had important implications for the very early Universe, when its size was of the order of the Planck length. An important implication of this effect is the deformation of the standard dispersion…

General Relativity and Quantum Cosmology · Physics 2018-10-09 Yunxin Ye , Tiberiu Harko , Shi-Dong Liang

The idea that coherent oscillations of a scalar field, oscillating over a time period that is much shorter than the cosmological timescale, can exhibit cold dark matter (CDM) like behavior was previously established. In our work we first…

General Relativity and Quantum Cosmology · Physics 2025-12-24 Priyanka Saha , Dipanjan Dey , Kaushik Bhattacharya

In this work, we will explore the effects of non-commutativity in fractional classical and quantum schemes using the anisotropicc Bianchi Type I cosmological model coupled to a scalar field in the K-essence formalism. We introduce…

General Relativity and Quantum Cosmology · Physics 2024-05-28 J. Socorro , J. Juan Rosales , Leonel Toledo-Sesma

We examine the cosmological implications of space-time non-commutativity, discovering yet another realization of the varying speed of light model. Our starting point is the well-known fact that non-commutativity leads to deformed dispersion…

High Energy Physics - Theory · Physics 2010-01-06 Stephon H. S. Alexander , João Magueijo

We extend our analysis for scalar fields in a Robertson-Walker metric to the electromagnetic field and Dirac fields by the method of invariants. The issue of the relation between conformal properties and particle production is re-examined…

General Relativity and Quantum Cosmology · Physics 2008-11-26 F. Finelli , A. Gruppuso , G. Venturi

In loop quantum cosmology, non-perturbative quantum gravity effects lead to the resolution of the big bang singularity by a quantum bounce without introducing any new degrees of freedom. Though fundamentally discrete, the theory admits a…

General Relativity and Quantum Cosmology · Physics 2010-05-12 Gonzalo J. Olmo , Parampreet Singh

Quantum electrodynamics (QED) in a strong constant magnetic field is investigated from the viewpoint of its connection with noncommutative QED. It turns out that within the lowest Landau level (LLL) approximation the 1-loop contribution of…

High Energy Physics - Theory · Physics 2009-11-11 Michio Hashimoto

Massless and massive scalar fields and massless spinor fields are considered at arbitrary temperatures in four dimensional ultrastatic curved spacetime. Scalar models under consideration can be either conformal or nonconformal and include…

High Energy Physics - Theory · Physics 2016-08-25 Yu. V. Gusev , A. I Zelnikov

We investigate the evolution of a spatially flat Friedmann-Robertson-Walker (FRW) universe in the framework of scalar non-metricity theory of gravity. In the model, we consider dark matter (DM) and dark energy (DE) described by the scalar…

General Relativity and Quantum Cosmology · Physics 2025-08-05 Bikash Chandra Roy , Bikash Chandra Paul

In this work we carry out a noncommutative analysis of several Friedmann-Robert-Walker models, coupled to different types of perfect fluids and in the presence of a cosmological constant. The classical field equations are modified, by the…

High Energy Physics - Theory · Physics 2015-06-03 E. M. C. Abreu , M. V. Marcial , A. C. R. Mendes , W. Oliveira , G. Oliveira-Neto

We explore the extension of quantum cosmology outside the homogeneous approximation, using the formalism of loop quantum gravity. We introduce a model where some of the inhomogeneous degrees of freedom are present, providing a tool for…

General Relativity and Quantum Cosmology · Physics 2008-12-18 Carlo Rovelli , Francesca Vidotto

The simplest flavor of the Effective Field Theory of Large Scale Structure is based on Newtonian equations and describes the nonlinear matter density and velocity using Einstein-de-Sitter kernels. Even in the presence of massive neutrinos,…

Cosmology and Nongalactic Astrophysics · Physics 2026-05-07 Christian Fidler , Julien Lesgourgues , Antonia Mattes , Azadeh Moradinezhad Dizgah , Simon Neuland

The aim of this review is to outline a full route from the fundamental principles of algebraic quantum field theory on curved spacetime in its present-day form to explicit phenomenological applications which allow for comparison with…

Mathematical Physics · Physics 2013-09-02 Klaus Fredenhagen , Thomas-Paul Hack