Quantum Gravitational Corrections Research Articles

Near-extremal Kerr-like ECO in the Kerr/CFT correspondence in higher spin perturbations

The Kerr/CFT correspondence has been established to explore the quantum theory of gravity in the near-horizon geometry of an extreme Kerr black holes. The quantum gravitational corrections on the near-horizon region may manifest in form of a partially reflective membrane that replace the horizon. In such modification, the black holes now can be seen as a horizonless exotic compact object (ECO). In this paper, we consider the properties of Kerr-like ECOs in near-extremal condition using Kerr/CFT correspondence. We study the quasinormal modes and absorption cross-section in that background and compare these by using CFT dual computation. The corresponding dual CFT one needs to incorporate finite size/finite N effects in the dual CFT terminology. We also extend the dual CFT analysis for higher spin perturbations such as photon and graviton. We find consistency between properties of the ECOs from gravity sides and from CFT sides. The quasinormal mode spectrum is in line with non-extreme case, where the differences are in the length of the circle, on which the dual CFT lives, and phase shift of the incoming perturbation. The absorption cross-section has oscillatory feature that start to disappear near extremal limit. The particle spin determines the phase shift and conformal weight. We also obtain that the echo time-delay depends on the position of the membrane and extremality of the ECOs.

Near-extremal Kerr-like ECO in the Kerr/CFT Correspondence

The Kerr/CFT correspondence has been established to explore the quantum theory of gravity in the near-horizon geometry of a extreme Kerr black holes. The horizon can be replaced by partially reflective membrane due to quantum gravitational corrections on the near-horizon region. Because of this modification, black holes now can be seen as a horizonless exotic compact object (ECO). In this work, with Kerr/CFT correspondence we study the properties of Kerr-like ECO in near-extremal condition. We compute the quasinormal modes and absorption cross-section and compare the results with CFT computation. The dual CFT one needs to consider finite size/finite N effects in the dual CFT terminology. We find consistency between properties of the ECOs from gravity side and from CFT side. The quasinormal mode spectrum is in line with non-extreme case with differences in the length of the circle where the dual CFT lives, and phase shift of the incoming perturbation. The absorption cross-section has oscillatory feature that start to vanish in near extremal limit. We also show that the echo time-delay depends on the position of the membrane and extremality of the ECOs.

Neutral current neutrino-electron scattering and generalized uncertainty principle

In this article, we study the effect of quantum gravitational corrections on neutrino electron scattering in electroweak theory SU(2) L × U(1) Y . We consider a neutrino that scatters off an electron by an exchange of a massive neutral gauge boson. In the minimal length formalism, starting from the equation of motion for a massive gauge field we obtain the propagator. And currents are obtained from the action for a massless Dirac fermion. Scattering amplitudes and differential cross sections as function of inelasticity variable y are obtained using expressions of the propagator and leptonic current. All usual expressions are recovered when the deformation parameter α tends to zero. We find that quantum gravitational effects become important only for a highly energetic process with a momentum transfer being much greater than the neutral gauge boson mass.

Constraining Snyder and GUP models with low-mass stars

We investigate the application of an equation of state that incorporates corrections derived from the Snyder model (and the Generalized Uncertainty Principle) to describe the behaviour of matter in a low-mass star. Remarkably, the resulting equations exhibit striking similarities to those arising from modified Einstein gravity theories. By modeling matter with realistic considerations, we are able to more effectively constrain the theory parameters, surpassing the limitations of existing astrophysical bounds. The bound we obtain is β0≤4.5×1047\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta _0 \\le 4.5 \ imes 10^{47}$$\\end{document}. We underline the significance of realistic matter modeling in order to enhance our understanding of effects arising in quantum gravity phenomenology and implications of quantum gravitational corrections in astrophysical systems.

Quantum thermodynamics of an Reissner-Nordström black hole

In this paper, we will go beyond equilibrium description to properly investigate the evaporation of a Reissner-Nordström black hole. Thus, we will explicitly apply techniques of non-equilibrium quantum thermodynamics to this black hole. As the non-equilibrium effects would become important at the quantum scale, we will incorporate the quantum gravitational corrections by using an Reissner-Nordström black hole. We will start by developing a novel first law. Then we will investigate the quantum gravitational corrections to the Parikh-Wilczek formalism, and introduce Kullback-Leibler divergence to quantify the effects of corrections. Furthermore, we will demonstrate that the non-thermal nature of radiation in the Parikh-Wilczek formalism can be directly related to the average quantum work done on the emitted particles using non-equilibrium quantum thermodynamics. This is because the average quantum work done is a unitary process in non-equilibrium quantum thermodynamics. We will use the Ramsey scheme for emitted particles to calculate this quantum work distribution for the emitted particles.

Estimation of Correction of Ground State Energy of Hydrogen Atom in Presence of Quadratic GUP

Abstract: String Theory, Quantum Geometry, Loop Quantum Gravity and Black Hole physic all predict the existence of a observable minimal length at Planck scale. For example, in case of string theory it is conjectured that a particle described as a string does not interact at distances smaller than its size. As a consequence, the HUP has to be generalized to take into account this aspect. The models which are designed to implement the minimal length scale and/or the maximum momentum in different physical systems entered into the literature as the Generalized Uncertainty Principle (GUP). Here, quadratic GUP model has been used to estimate the quantum-gravitational correction of ground state energy of hydrogen atom (H-atom).

The semiclassical limit of quantum gravity and the problem of time

The question about the appearance of time in the semiclassical limit of quantum gravity continues to be discussed in the literature. It is believed that a temporal Schrödinger equation for matter fields on the background of a classical gravitational field must be true. To obtain this equation, the Born–Oppenheimer approximation for gravity is used. However, the origin of time in this equation is different in works of various authors. For example, in the papers of Kiefer and his collaborators, time is a parameter along a classical trajectory of gravitational field; in the works of Montani and his collaborators, the origin of time is introducing the Kuchař–Torre reference fluid; in the extended phase space approach, the origin of time is the consequence of existing of the observer in a fixed reference frame. We discuss and compare these approaches. To make the calculations transparent, we illustrate them with the model of a closed isotropic universe. In each approach, one obtains some Schrödinger equation for matter fields with quantum gravitational corrections, but the form of the equation and the corrections depend on additional assumptions which are rather arbitrary. None of the approaches can explain how time had appeared in the Early Universe, since it is supposed that classical gravity and, therefore, classical spacetime had already come into being.

Quantum-gravitational corrections to the power spectrum for a closed universe

We study the quantum-gravitational corrections to the power spectrum of a gauge-invariant inflationary scalar perturbations in a closed model of a universe. We consider canonical quantum gravity as an approach to quantizing gravity. This leads to the Wheeler-DeWitt equation, which has been studied by applying a semiclassical Born–Oppenheimer type of approximation. At the corresponding orders of approximation, we recover both the uncorrected and quantum-gravitationally corrected Schrödinger equations for the perturbation modes from which we calculate the quantum-gravitational corrections to the power spectrum in the slow-roll regime. The results are compared to the power spectra for the flat model of the universe.

Quantum gravity corrections to the fall of an apple

We consider the motion of a massive particle in a static, weakly-curved spacetime where the gravitational field is taken to be quantized. We find that Newton's law of free-fall is modified by quantum-gravitational corrections, in addition to the known special-relativistic and post-Newtonian modifications. The quantum-gravitational corrections take the form of stochastic noise in the particle trajectory, where the statistical properties of the noise depend on the quantum state of the gravitational field.

Logarithmic correction to black hole entropy in universal low-energy string theory models

We calculate the logarithmic correction to the entropy of asymptotically flat and AdS black holes (rotating, non-rotating, charged, and uncharged) embedded in Einstein-Maxwell-dilaton (EMD) theories with U(1)-charged. The leading quantum gravitational corrections are achieved in both extremal and non-extremal limits of black hole temperature by designing a common Euclidean gravity setup that evaluates the “logarithmic term” from one-loop effective actions via heat kernel method-based calculations. EMD theories are universal building blocks of compactified string theory or supergravity models in 4D. For a concrete example, we generalize the entire setup and calculate logarithmic corrections for black holes in U(1)2-charged EMD models intersecting with mathcal{N} = 4 ungauged and gauged bosonic supergravity. In contrast to flat backgrounds, all the AdS4 results are found to be non-topological, providing a wider “infrared window” into the microscopic degrees of freedom of black holes in string theory.

Quantum gravitational corrections to particle creation by black holes

We calculate quantum gravitational corrections to the amplitude for the emission of a Hawking particle by a black hole. We show explicitly how the amplitudes depend on quantum corrections to the exterior metric (quantum hair). This reveals the mechanism by which information escapes the black hole. The quantum state of the black hole is reflected in the quantum state of the exterior metric, which in turn influences the emission of Hawking quanta.

On the Appearance of Time in the Classical Limit of Quantum Gravity

A possible solution of the problem of time in the Wheeler–DeWitt quantum geometrodynamics is that time appears within a semiclassical limit. Following this line of thinking, one can come to the Schrodinger equation for matter fields in curved spacetime with quantum-gravitational corrections. In the present paper, we study the semiclassical limit in the case of a closed isotropic model with a scalar field decomposed into modes. We analyse calculations made within frameworks of three approaches. The first approach was proposed by Kiefer and Singh. Since the Wheeler–DeWitt equation does not contain a time derivative, it is constructed by means of a special mathematical procedure, a time variable being a parameter along a classical trajectory of gravitational field. The second method was suggested in the paper of Maniccia and Montani, who introduced the Kuchař–Torre reference fluid as an origin of time. Furthermore, the third is the extended phase space approach to the quantisation of gravity. In this approach, the temporal Schrodinger equation is argued to be more fundamental than the Wheeler–DeWitt equation, and there is no problem of time. Time is introduced due to fixing a reference frame of a certain observer, who can register the macroscopic consequences of quantum gravitational phenomena in the Very Early Universe. To go to the semiclassical limit, the Born–Oppenheimer approximation for gravity is used. In each of the approaches, in the order of O(1/M), a temporal Schrödinger equation for matter fields in curved spacetime with quantum gravitational corrections is obtained. However, equations and corrections are different in various approaches, and the results depend on the additional assumptions made within the scopes of these approaches.

Black hole thermodynamics in asymptotically safe gravity

We have investigated the black hole thermodynamics and the phase transition for renormalized group improved asymptotically safe Schwarzschild black hole. This geometry takes into account the quantum gravitational correction in the running gravitational constant identifying \(G(r) \equiv G(k=k(r))\). We studied various thermodynamic quantity like the Hawking temperature, specific heat and entropy for the general parameter \(\gamma \) for quantum corrected Schwarzschild metric. We have noticed that the coefficient of the leading quantum correction, that is, the logarithmic correction gets affected by the presence of \(\gamma \). We further study the local temperature, thermal stability of the black hole and the free energy considering a cavity enclosing the black hole. According to the local specific heat, there exists three black hole states, among them the large and tiny black hole are thermally stable states. We further investigate the on-shell free energy and find that no Hawking-Page phase transition occurs here unlike the ordinary Schwarzschild black hole. The black hole state always prevails for all temperatures. Also, we have found two critical points, \(T_{c1}\) and \(T_{c2}\), corresponding to the phase transition from one black hole state to another.

Beyond the Born Rule in Quantum Gravity

We have recently developed a new understanding of probability in quantum gravity. In this paper we provide an overview of this new approach and its implications. Adopting the de Broglie–Bohm pilot-wave formulation of quantum physics, we argue that there is no Born rule at the fundamental level of quantum gravity with a non-normalisable Wheeler–DeWitt wave functional $$\Psi$$ . Instead the universe is in a perpetual state of quantum nonequilibrium with a probability density $$P\ne \left| \Psi \right| ^{2}$$ . Dynamical relaxation to the Born rule can occur only after the early universe has emerged into a semiclassical or Schrödinger approximation, with a time-dependent and normalisable wave functional $$\psi$$ , for non-gravitational systems on a classical spacetime background. In that regime the probability density $$\rho$$ can relax towards $$\left| \psi \right| ^{2}$$ (on a coarse-grained level). Thus the pilot-wave theory of gravitation supports the hypothesis of primordial quantum nonequilibrium, with relaxation to the Born rule taking place soon after the big bang. We also show that quantum-gravitational corrections to the Schrödinger approximation allow quantum nonequilibrium $$\rho \ne \left| \psi \right| ^{2}$$ to be created from a prior equilibrium ( $$\rho =\left| \psi \right| ^{2}$$ ) state. Such effects are very tiny and difficult to observe in practice.

Sign Switching Dark Energy from a Running Barrow Entropy

Barrow proposed that the area law of the entropy associated with a horizon might receive a “fractal correction” due to quantum gravitational effects—in place of S∝A, we have instead S∝A1+δ/2, where 0⩽δ⩽1 measures the deviation from the standard area law (δ=0). Based on black hole thermodynamics, we argue that the Barrow entropy should run (i.e., energy scale dependent), which is reasonable given that quantum gravitational corrections are expected to be important only in the high-energy regime. When applied to the Friedmann equation, we demonstrate the possibility that such a running Barrow entropy index could give rise to a dynamical effective dark energy, which is asymptotically positive and vanishing, but negative at the Big Bang. Such a sign switching dark energy could help to alleviate the Hubble tension. Other cosmological implications are discussed.

Cosmology with modified continuity equation in asymptotically safe gravity

We study FLRW cosmology, taking into account quantum gravitational corrections in the formalism of the exact renormalization group flow of the effective action for gravity. We calculate the quantum corrected scale factor, energy density, and entropy production at late times, taking different choices of cut-off functions. Our approach is in line with previous studies which involve the running Newton constant G(k) in the definition of energy–momentum tensor, and then imposing the covariant conservation identity of the Einstein tensor. The quantum corrections obtained in this approach are different from what are found by letting the conservation equation remain the same as for a scale-independent Newton constant. The main observation made here is that different cut-off identifications results in different late time cosmologies. Further, the choices made also led to exact analytical solutions for the Hubble parameter in terms of the cosmological time and scale factor.

Generalizing event shapes: in search of lost collider time

We introduce a new class of collider-type observables in conformal field theories which we call generalized event shapes. They are defined as matrix elements of light-ray operators that are sensitive to the longitudinal, or time-dependent, structure of the state produced in the collision. Generalized event shapes can be studied using both correlation functions and scattering amplitudes. They are infrared finite and smoothly transit over to the familiar event shapes. We compute them in planar mathcal{N} = 4 super-Yang-Mills theory at weak and strong coupling, and study their physical properties. We show that at strong coupling both the stringy and quantum-gravitational corrections to the energy-energy correlation exhibit longitudinal broadening that manifests itself through the presence of long-time tails in the energy flux measured by the detectors.

Quantum thermodynamics of a quantum sized AdS black hole

In this paper, we investigate the effects of non-perturbative quantum gravitational corrections on a quantum sized AdS black hole. It will be observed that these non-perturbative quantum gravitational corrections modify the stability of this black hole. We will use the non-equilibrium quantum thermodynamics to investigate the evaporation of this black hole between two states. We will analyze the effects of non-perturbative quantum gravitational corrections on this non-equilibrium quantum thermodynamics. We will explicitly obtain the quantum work distribution for this black hole, as it evaporates between two states. It will be observed that this quantum work distribution is modified due to non-perturbative quantum gravitational corrections.

Quantum thermodynamics of an M2-M5 brane system

We will investigate a system of M2-M5 branes as a black M2-M5 bound state. The behavior of this system will be investigated at short distances. At such scales, we will have to incorporate quantum gravitational corrections to the supergravity solutions. We will study the non-equilibrium quantum thermodynamics of this black M2-M5 bound state. The quantum work for this solution will be obtained using the Jarzynski equality. We will also study the corrections to the thermodynamic stability of this system from quantum gravitational corrections. We will use the concept of a novel quantum mass to analyze the quantum gravitational corrections to the information geometry of this system. This will be done using effective quantum metrics for this system.

Large logarithms from quantum gravitational corrections to a massless, minimally coupled scalar on de Sitter

We consider single graviton loop corrections to the effective field equation of a massless, minimally coupled scalar on de Sitter background in the simplest gauge. We find a large temporal logarithm in the approach to freeze-in at late times, but no correction to the feeze-in amplitude. We also find a large spatial logarithm (at large distances) in the scalar potential generated by a point source, which can be explained using the renormalization group with one of the higher derivative counterterms regarded as a curvature-dependent field strength renormalization. We discuss how these results set the stage for a project to purge gauge dependence by including quantum gravitational corrections to the source which disturbs the effective field and to the observer who measures it.