The Search for Quantum Gravity Signals (original) (raw)
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New Quantum Gravity Phenomenology
2005
The idea that quantum gravity manifestations would be associated with a violation of Lorentz invariance is very strongly bounded and faces serious theoretical challenges. This leads us to consider an alternative scheme for such phenomenological search. We discuss the underlying viewpoint and briefly mention its possible connections with current theoretical ideas. We also outline the new experimental avenues that would be open along these lines.
Towards a New Approach to Quantum Gravity Phenomenology
2005
The idea that quantum gravity manifestations would be associated with a violation of Lorentz invariance is very strongly bounded and faces serious theoretical challenges. This leads us to consider an alternative line of thought for such phenomenological search. We discuss the underlying viewpoint and briefly mention its possible connections with current theoretical ideas. We also outline the challenges that the experimental search of the effects would seem to entail.
Quantum Gravity Phenomenology and Lorentz Violation
Springer Proceedings in Physics, 2005
In most fields of physics it goes without saying that observation and prediction play a central role, but unfortunately quantum gravity (QG) has so far not fit that mold. Many intriguing and ingenious ideas have been explored, but it seems safe to say that without both observing phenomena that depend on QG, and extracting reliable predictions from candidate theories that can be compared with observations, the goal of a theory capable of incorporating quantum mechanics and general relativity will remain unattainable.
SCIENCE WITHOUT BORDERS. Transactions of the International Academy of Science.H&E. Vol.2. Innsbruck, 2005/2006, pp.204-216. ISSN 2070-0334 ISBN 978-9952-451-04-7, 2006
Quantum mechanics, the third constituent part of quantum theory of gravity, was created in 1925 by W.Heizenberg and E.Schrodinger, but in its initial wording the theory of gravity wasn't paid attention to. Nevertheless, it was a great success, as were waiting for their explanation for a long time the experimental observations, where dominated namely quantum effects, but relativist effects played little or trifling role. Despite the active researches during a few last ten years, the quantum gravity hasn't been built. The main difficulty in its construction is that two physical theories which it tries to connect together – the quantum mechanics and general theory of relativity (GTR) – are guided by different set of principles /5/. So, the quantum mechanics is formulated as a theory of moving of particles against the background of external space-time. There isn't external space-time in the whole theory of relativity: it is the dynamic variable theory itself. In view of mentioned problems the attempt to do the quantification of classical theory of gravity (GTR) causes many technical problems. The situation is aggravated by the fact that the direct experiments in the sphere of quantum gravity aren't accessible to modern technologies. In this connection, in the search of right formulating of quantum gravity, it can be guided only by theoretical calculations. What way is the transmission of gravitational energy carried out in quantum gravity? It is supposed that the gravitational powers are transmitted by means of special particles, which don't have the masses – gravitons. The main distinctive peculiarity of elementary particles of different families is a spin, which can be represented as a result of revolving of particles on their axes. Spin of electrons, protons and neutrons is ½, and the spin of particles which don't have mass, as, for example, photon, is 1. Consequently, all exchange particles of strong and electromagnetic interaction has a spin equal to 1, that is why the equal particles are repelled (for example, two electrons), and the particles with opposite charges are gravitated (for example, electron and proton). It is considered that graviton has a spin equal to 2, as all interactions with the exchange with particles which have a spin equal to 2, are characterized only by attraction /9/. In 1976 D.A.Freedman, P.van Nivenscheizen and S. Ferrara, and independently of them S.Deser and B.Zumino was elaborated a theory of super-gravity. In this theory is considered the only kind of particle – super-particles. This particle can be as any particle, which carries out the interaction, including a quark or lepton (" light " particle, for example, electron), connecting on this way the gravity with the rest interactions and particles. Using this approach, there appears the opportunity to build a theory of gravity, having been based on the notion of graviton which has a spin 2, at that the particles of the substance are interacted, exchanging with gravitons in accordance with the equations of the general theory of relativity of Einstein. SCIENCE WITHOUT BORDERS. Transactions of the International Academy of Science.H&E. Vol.2. Innsbruck, 2005/2006, pp.204-216. ISSN 2070-0334 ISBN 978-9952-451-04-7
Experimental search for quantum gravity
2010
We offer a brief survey of existent and planned experimental tests for quantum gravity. First, we outline the questions we wish to address, and then introduce some of the phenomenological models that are currently used in quantum gravity, both with and without a lowered Planck scale. After that, we summarize experimental areas where these models can be tested or constrained and discuss the status of the field.
Possible astrophysical probes of quantum gravity
2002
A satisfactory theory of quantum gravity will very likely require modification of our classical perception of space-time, perhaps by giving it a 'foamy' structure at scales of order the Planck length. This is expected to modify the propagation of photons and other relativistic particles such as neutrinos, such that they will experience a non-trivial refractive index even in vacuo. The implied spontaneous violation of Lorentz invariance may also result in alterations of kinematical thresholds for key astrophysical processes involving high energy cosmic radiation. We discuss experimental probes of these possible manifestations of the fundamental quantum nature of space-time using observations of distant astrophysical sources such as gamma-ray bursts and active galactic nuclei.
Quantum Vacuum Effects in Gravitational Fields: Theory and Detectability
This thesis is devoted to the study of quantum vacuum effects in the presence of strong gravitational fields. We shall see how the quantum vacuum interacts with black hole geometries and how it can play an important role in the interpretation of the gravitational entropy. In this respect particular attention will be given to the peculiar role of the extremal black hole solutions. From this branch of our research we shall try to collect some important hints about the relation between quantum gravity theories and the semiclassical results. After these investigations we shall move our attention toward possible experimental tests of particle creation from the quantum vacuum which is an indirect confirmation of the Hawking effect. This aim will lead us to study acoustic geometries and their way of "simulating" General Relativity structures, such as horizons and black holes. We shall study the stability of these structures and the problems related to setting up experimental detection of phonon Hawking flux from acoustic horizons. This research will naturally lead us to propose a new model for explaining the emission of light in the phenomenon of Sonoluminescence, based on the dynamical Casimir effect. Possible experimental tests of this proposal will be discussed. In this way we shall set up one of the few available models of quantum vacuum radiation amenable to observational test within the next few years. After this journey in the condensed matter world we shall move to the other arena where our efforts to test the effects of the quantum vacuum in gravitational fields can find a positive solution in the future: the high energy phenomena in the early universe. We shall concentrate our attention on inflation and its possible alternatives for solving the cosmological puzzles. This will lead us to propose a new way to reheat the universe after inflation via pure gravitational effects. We shall finally show how some known phenomena related to the vacuum polarization in the Casimir effects, can naturally suggest new ways to replace (or at least improve) the inflationary scenario. Conclusions Bibliography Notation Unless otherwise stated we shall use units for whichh = c = 1. We shall make explicit the dependence on the fundamental constants in the most important formulae. The Boltzmann constant is k B and the gravitational constant will be denoted as G N. The Greek indices take values 0. .. 3 while Latin indices denote spatial directions and range over 1. .. 3. The wide range of problems treated in this thesis has made it impossible to use the same metric signature through all of the work. Chapters 1 and 4 use the signature common in the literature of quantum field theory (+, −, −, −) with the Minkowski metric given by η µν = diag(1, −1, −1, −1). In chapters 2, 3 and 5 we use the signature commonly used by general relativists (−, +, +, +) with the Minkowski metric given by η µν = diag(−1, +1, +1, +1). These notations are consistent with standard reference books in the subject, which have been used as references for the review parts of this work. For purely general relativistic issues we have mainly * complex conjugate † or h.c. Hermitian conjugate ∂ µ or ∂ ∂x µ or ,µ Partial derivative ∇ µ or ;µ Covariant derivative ≡ g µν ∇ µ ∇ ν D'Alambertian operator ℜ (ℑ) Real (imaginary) part Tr Trace [A, B] = AB − BA Commutator {A, B} = AB + BA Anti-commutator κ surface gravity κ N = 8πG N rescaled Newton constant ρ mass density ε energy density r h event horizon radius g ⊕ Earth gravity acceleration We find that we inhabit an insignificant planet of a humdrum star lost in a galaxy tucked away in some forgotten corner of a universe in which there are far more galaxies than people.
Experimental tests for some quantum effects in gravitation
Annals of Physics, 1977
The existing impressive tests for general relativity are shown not to yield very useful information on the possible quantum gravitational interactions. The possibility is raised here that intrinsic spins may behave differently from orbital angular momenta in external gravitational fields. The dominant spin interactions are most generally characterized by three parameters oil, uZ, a3. All the metric theories of gravitation predict 01~ = (t2 = 0. Indirect limits posed on these parameters by existing data are not very meaningful (LX{ 5 lOlo). Feasible experiments based on the neutron electric dipole moment measurement techniques are discussed and shown to offer the possibility of measuring a1 N 1. Other possible experimental set ups are also briefly reviewed. The existence of these effects is shown to imply the breakdown of the equivalence principle. In particular, oil + 0, 01% $: 0 also implies the breakdown of discrete symmetries in gravitation (C, P, T). Theoretical frameworks that accommodate such effects are analyzed. A reinterpretation of Einstein's generalized gravitational theory as well as a recent theoretical proposal of Hayashi are shown to be sufficiently general for this purpose. Other important implications of these quantum effects are discussed in detail.
Observable Effects of Quantum Gravity
We discuss the generic phenomenology of quantum gravity and, in particular, argue that the observable effects of quantum gravity, associated with new, extended, non-local, non-particle-like quanta, and accompanied by a dynamical energy-momentum space, are not necessarily Planckian and that they could be observed at much lower and experimentally accessible energy scales. Essay written for the Gravity Research Foundation 2016 Awards for Essays on Gravita-tion. 1. The Quest for Quantum Gravity The two main legacies of 20th century physics are relativity and quantum theory. Both frameworks have been tested in numerous experiments, including the recent detection of gravitational waves by LIGO [1], and the completion of the fundamental quantum field theoretic framework of the Standard Model (SM) of particle physics, exemplified by the LHC discovery of the Higgs particle [2, 3]. However, the conceptual foundations of general relativity and quantum theory still stand apart. It is thus often stated that one of the most outstanding problems of physics is to find a unified habitat for these two great frameworks. That is the problem of quantum gravity [4]. In this essay, we address the question of the generic phenomenological effects of quantum gravity and especially the crucial role played by the minimal length. In particular, we argue that the observable effects of quantum gravity may not necessarily be Planckian (∼ 10 19 GeV) and that the essential phenomenology of quantum gravity may be observable at much lower, and experimentally accessible, energy scales. 2. Quantum Gravity and the Minimal Length We start our discussion with the concept of a minimal length, a feature expected of any candidate theory of quantum gravity, since gravity itself is characterized by the Planck scale ℓ P = G N /c 3 ∼ 10 −35 m. One can re-analyze the Heisenberg microscope gedanken experiment in the presence of gravity, and claim that the