Hamiltonian Constraint Analysis of Vector Field Theories with Spontaneous Lorentz Symmetry Breaking
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Immirzi Parameter Without Immirzi Ambiguity: Conformal Loop Quantization of Scalar-Tensor Gravity
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aberdeen University Research Archive PHYSICAL REVIEW D 96, 084011 (2017) Immirzi parameter without Immirzi ambiguity: Conformal loop quantization of scalar-tensor gravity † Olivier J. Veraguth* and Charles H.-T. Wang Department of Physics, University of Aberdeen, King’s College, Aberdeen AB24 3UE, United Kingdom (Received 25 May 2017; published 5 October 2017) Conformal loop quantum gravity provides an approach to loop quantization through an underlying conformal structure i.e. conformally equivalent class of metrics. The property that general relativity itself has no conformal invariance is reinstated with a constrained scalar field setting the physical scale. Conformally equivalent metrics have recently been shown to be amenable to loop quantization including matter coupling. It has been suggested that conformal geometry may provide an extended symmetry to allow a reformulated Immirzi parameter necessary for loop quantization to behave like an arbitrary group parameter that requires no further fixing as its present standard form does. Here, we find that this can be naturally realized via conformal frame transformations in scalar-tensor gravity. Such a theory generally incorporates a dynamical scalar gravitational field and reduces to general relativity when the scalar field becomes a pure gauge. In particular, we introduce a conformal Einstein frame in which loop quantization is implemented. We then discuss how different Immirzi parameters under this description may be related by conformal frame transformations and yet share the same quantization having, for example, the same area gaps, modulated by the scalar gravitational field. DOI: 10.1103/PhysRevD.96.084011 I. -
An Invitation to the New Variables with Possible Applications
An Invitation to the New Variables with Possible Applications Norbert Bodendorfer and Andreas Thurn (work by NB, T. Thiemann, AT [arXiv:1106.1103]) FAU Erlangen-N¨urnberg ILQGS, 4 October 2011 N. Bodendorfer, A. Thurn (FAU Erlangen) An Invitation to the New Variables ILQGS, 4 October 2011 1 Plan of the talk 1 Why Higher Dimensional Loop Quantum (Super-)Gravity? 2 Review: Hamiltonian Formulations of General Relativity ADM Formulation Extended ADM I Ashtekar-Barbero Formulation Extended ADM II 3 The New Variables Hamiltonian Viewpoint Comparison with Ashtekar-Barbero Formulation Lagrangian Viewpoint Quantisation, Generalisations 4 Possible Applications of the New Variables Solutions to the Simplicity Constraint Canonical = Covariant Formulation? Supersymmetry Constraint Black Hole Entropy Cosmology AdS / CFT Correspondence 5 Conclusion N. Bodendorfer, A. Thurn (FAU Erlangen) An Invitation to the New Variables ILQGS, 4 October 2011 2 Plan of the talk 1 Why Higher Dimensional Loop Quantum (Super-)Gravity? 2 Review: Hamiltonian Formulations of General Relativity ADM Formulation Extended ADM I Ashtekar-Barbero Formulation Extended ADM II 3 The New Variables Hamiltonian Viewpoint Comparison with Ashtekar-Barbero Formulation Lagrangian Viewpoint Quantisation, Generalisations 4 Possible Applications of the New Variables Solutions to the Simplicity Constraint Canonical = Covariant Formulation? Supersymmetry Constraint Black Hole Entropy Cosmology AdS / CFT Correspondence 5 Conclusion N. Bodendorfer, A. Thurn (FAU Erlangen) An Invitation to the -
Instructions to Authors
www.elsevier.com/locate/physletb Instructions to authors Aims and Scope Physics Letters B ensures the rapid publication of letter-type communications in the fields of Nuclear Physics, Particle Physics and Astrophysics. Articles should influence the physics community significantly. Submission Electronic submission is strongly encouraged. The electronic file, accompanied by a covering message, should be e-mailed to one of the Editors indicated below. If electronic submission is not feasible, submission in print is possible, but it will delay publication. In the latter case manuscripts (one original + two copies), accompanied by a covering letter, should be sent to one of the following Editors: L. Alvarez-Gaumé, Theory Division, CERN, CH-1211 Geneva 23, Switzerland, E-mail address: Luis.Alvarez-Gaume@CERN. CH Theoretical High Energy Physics (General Theory) J.-P. Blaizot, ECT*, Strada delle Tabarelle, 266, I-38050 Villazzano (Trento), Italy, E-mail address: [email protected]. FR Theoretical Nuclear Physics M. Cvetic,ˇ David Rittenhouse Laboratory, Department of Physics, University of Pennsylvania, 209 S, 33rd Street, Philadelphia, PA 19104-6396, USA, E-mail address: [email protected] Theoretical High Energy Physics M. Doser, EP Division, CERN, CH-1211 Geneva 23, Switzerland, E-mail address: [email protected] Experimental High Energy Physics D.F. Geesaman, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA, E-mail address: [email protected] Experimental Nuclear Physics H. Georgi, Department of Physics, Harvard University, Cambridge, MA 02138, USA, E-mail address: Georgi@PHYSICS. HARVARD.EDU Theoretical High Energy Physics G.F. Giudice, CERN, CH-1211 Geneva 23, Switzerland, E-mail address: [email protected] Theoretical High Energy Physics N. -
Asymptotically Flat Boundary Conditions for the U(1)3 Model for Euclidean Quantum Gravity
universe Article Asymptotically Flat Boundary Conditions for the U(1)3 Model for Euclidean Quantum Gravity Sepideh Bakhoda 1,2,* , Hossein Shojaie 1 and Thomas Thiemann 2,* 1 Department of Physics, Shahid Beheshti University, Tehran 1983969411, Iran; [email protected] 2 Institute for Quantum Gravity, FAU Erlangen—Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany * Correspondence: [email protected] (S.B.); [email protected] (T.T.) 3 Abstract: A generally covariant U(1) gauge theory describing the GN ! 0 limit of Euclidean general relativity is an interesting test laboratory for general relativity, specially because the algebra of the Hamiltonian and diffeomorphism constraints of this limit is isomorphic to the algebra of the corresponding constraints in general relativity. In the present work, we the study boundary conditions and asymptotic symmetries of the U(1)3 model and show that while asymptotic spacetime translations admit well-defined generators, boosts and rotations do not. Comparing with Euclidean general relativity, one finds that the non-Abelian part of the SU(2) Gauss constraint, which is absent in the U(1)3 model, plays a crucial role in obtaining boost and rotation generators. Keywords: asymptotically flat boundary conditions; classical and quantum gravity; U(1)3 model; asymptotic charges Citation: Bakhoda, S.; Shojaie, H.; 1. Introduction Thiemann, T. Asymptotically Flat In the framework of the Ashtekar variables in terms of which General Relativity (GR) Boundary Conditions for the U(1)3 is formulated as a SU(2) gauge theory [1–3], attempts to find an operator corresponding to Model for Euclidean Quantum the Hamiltonian constraint of the Lorentzian vacuum canonical GR led to the result [4] that Gravity. -
Spontaneous Lorentz Violation, Nambu-Goldstone Modes, And
SPONTANEOUS LORENTZ VIOLATION, NAMBU-GOLDSTONE MODES, AND MASSIVE MODES ROBERT BLUHM Department of Physics and Astronomy, Colby College Waterville, ME 04901, USA In any theory with spontaneous symmetry breaking, it is important to account for the massless Nambu-Goldstone and massive Higgs modes. In this short review, the fate of these modes is examined for the case of a bumblebee model, in which Lorentz symmetry is spontaneously broken. 1 Spontaneous Lorentz violation Spontaneous symmetry breaking has three well-known consequences. The first is Goldstone’s theorem, which states that massless Nambu-Goldstone (NG) modes should appear when a continuous symmetry is spontaneously broken. The second is that massive Higgs modes can appear, consisting of excitations out of the degenerate minimum. The third is the Higgs mechanism, which can occur when the broken symmetry is local. In conventional particle physics, these processes involve a scalar field with a nonzero vacuum expectation value that induces spontaneous breaking of gauge symmetry. However, in this paper, these processes are examined for the case where it is a vector field that has a nonzero vacuum value and where the symmetry that is spontaneously broken is Lorentz symmetry. The idea of spontaneous Lorentz violation is important in quantum-gravity theory. For example, in string field theory, mechanisms have been found that can lead to spontaneous Lorentz violation.1 It has also been shown that sponta- neous Lorentz breaking is compatible with geometrical consistency conditions 2 arXiv:1008.1805v1 [hep-th] 10 Aug 2010 in gravity, while explicit Lorentz breaking is not. The Standard-Model Extension (SME) describes Lorentz-violating inter- actions at the level of effective field theory. -
Gravity with Explicit Diffeomorphism Breaking
S S symmetry Article Gravity with Explicit Diffeomorphism Breaking Robert Bluhm * and Yumu Yang Department of Physics and Astronomy, Colby College, Waterville, ME 04901, USA; [email protected] * Correspondence: [email protected] Abstract: Modified theories of gravity that explicitly break diffeomorphism invariance have been used for over a decade to explore open issues related to quantum gravity, dark energy, and dark matter. At the same time, the Standard-Model Extension (SME) has been widely used as a phenomenological framework in investigations of spacetime symmetry breaking. Until recently, it was thought that the SME was suitable only for theories with spontaneous spacetime symmetry breaking due to consistency conditions stemming from the Bianchi identities. However, it has recently been shown that, particularly with matter couplings included, the consistency conditions can also be satisfied in theories with explicit breaking. An overview of how this is achieved is presented, and two examples are examined. The first is massive gravity, which includes a nondynamical background tensor. The second is a model based on a low-energy limit of Hoˇrava gravity, where spacetime has a physically preferred foliation. In both cases, bounds on matter–gravity interactions that explicitly break diffeomorphisms are obtained using the SME. Keywords: gravity; explicit diffeomorphism breaking; Standard-Model Extension 1. Introduction Citation: Bluhm, R.; Yang, Y. Gravity Diffeomorphism invariance is a fundamental symmetry in Einstein’s General Relativity with Explicit Diffeomorphism (GR). As a result of this symmetry and the Bianchi identities, when matter and gravity interact Breaking. Symmetry 2021, 13, 660. in GR, the energy-momentum of the matter fields is guaranteed to be covariantly conserved https://doi.org/10.3390/sym when the matter fields obey their equations of motion. -
Cosmological Plebanski Theory
General Relativity and Gravitation (2011) DOI 10.1007/s10714-009-0783-0 RESEARCHARTICLE Karim Noui · Alejandro Perez · Kevin Vandersloot Cosmological Plebanski theory Received: 17 September 2008 / Accepted: 2 March 2009 c Springer Science+Business Media, LLC 2009 Abstract We consider the cosmological symmetry reduction of the Plebanski action as a toy-model to explore, in this simple framework, some issues related to loop quantum gravity and spin-foam models. We make the classical analysis of the model and perform both path integral and canonical quantizations. As for the full theory, the reduced model admits two disjoint types of classical solutions: topological and gravitational ones. The quantization mixes these two solutions, which prevents the model from being equivalent to standard quantum cosmology. Furthermore, the topological solution dominates at the classical limit. We also study the effect of an Immirzi parameter in the model. Keywords Loop quantum gravity, Spin-foam models, Plebanski action 1 Introduction Among the issues which remain to be understood in Loop Quantm Gravity (LQG) [1; 2; 3], the problem of the dynamics is surely one of the most important. The regularization of the Hamiltonian constraint proposed by Thiemann [4] was a first promising attempt towards a solution of that problem. However, the technical dif- ficulties are such that this approach has not given a solution yet. Spin Foam mod- els [5] is an alternative way to explore the question: they are supposed to give a combinatorial expression of the Path integral of gravity, and should allow one to compute transition amplitudes between states of quantum gravity, or equivalently to compute the dynamics of a state. -
Covariant Quantum Gravitational Corrections to Scalar and Tensor Field Models
Covariant Quantum Gravitational Corrections to Scalar and Tensor Field Models A thesis submitted in partial fulfilment of the requirements for the award of the degree of DOCTOR OF PHILOSOPHY by SANDEEP AASHISH 1610511 arXiv:2007.13150v1 [gr-qc] 26 Jul 2020 to the DEPARTMENT OF PHYSICS INDIAN INSTITUTE OF SCIENCE EDUCATION AND RESEARCH BHOPAL Bhopal - 462 066 April, 2020 Covariant Quantum Gravitational Corrections to Scalar and Tensor Field Models A thesis submitted in partial fulfilment of the requirements for the award of the degree of DOCTOR OF PHILOSOPHY by SANDEEP AASHISH 1610511 to the DEPARTMENT OF PHYSICS INDIAN INSTITUTE OF SCIENCE EDUCATION AND RESEARCH BHOPAL Bhopal - 462 066 April, 2020 ACADEMIC INTEGRITY AND COPYRIGHT DISCLAIMER I hereby declare that this thesis is my own work and, to the best of my knowledge, it contains no materials previously published or written by any other person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at IISER Bhopal or any other educational institution, except where due acknowledgement is made in the thesis. I certify that all copyrighted material incorporated into this thesis is in compliance with the Indian Copyright (Amendment) Act, 2012 and that I have received written permission from the copyright owners for my use of their work, which is beyond the scope of the law. I agree to indemnify and save harmless IISER Bhopal from any and all claims that may be asserted or that may arise from any copyright violation. April, 2020 Sandeep Aashish IISER, Bhopal Dr. Sukanta Panda (Supervisor) ii ACKNOWLEDGEMENTS This thesis is the culmination of contributions from a number of people, who have know- ingly and unknowingly encouraged me to persist through this incredible journey spanning a plethora of experiences. -
Loop Quantum Gravity: an Inside View
Loop Quantum Gravity: An Inside View T. Thiemann∗ MPI f. Gravitationsphysik, Albert-Einstein-Institut, Am M¨uhlenberg 1, 14476 Potsdam, Germany and Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, ON N2L 2Y5, Canada Preprint AEI-2006-066 Abstract This is a (relatively) non – technical summary of the status of the quantum dynamics in Loop Quantum Gravity (LQG). We explain in detail the historical evolution of the subject and why the results obtained so far are non – trivial. The present text can be viewed in part as a response to an article by Nicolai, Peeters and Zamaklar. We also explain why certain no go conclusions drawn from a mathematically correct calculation in a recent paper by Helling et al are physically incorrect. arXiv:hep-th/0608210v1 29 Aug 2006 ∗[email protected],[email protected] 1 Contents 1 Introduction 3 2 Classical preliminaries 6 3 Canonical quantisation programme 8 4 Status of the quantisation programme for Loop Quantum Gravity (LQG) 12 4.1 CanonicalquantumgravitybeforeLQG . .............. 12 4.2 Thenewphasespace................................ ......... 13 4.3 Quantumkinematics ............................... .......... 16 4.3.1 Elementaryfunctions. .......... 16 4.3.2 Quantum ∗ algebra ..................................... 17 − 4.3.3 Representations of A ..................................... 18 4.3.4 The kinematical Hilbert space and its properties . ................. 19 4.4 Quantumdynamics................................. ......... 21 4.4.1 Reduction of Gauss – and spatial diffeomorphism constraint............... 21 4.4.1.1 Gaussconstraint. .. .. .. .. .. .. .. .. ..... 21 4.4.1.2 Spatial diffeomorphism constraint . .......... 22 4.4.2 Reduction of the Hamiltonian constraint . ............... 23 4.4.2.1 Hamiltonian constraint . ....... 25 4.4.2.2 Master Constraint Programme . ....... 32 4.4.2.2.1 Graph changing Master constraint . -
Aspects of Spontaneous Lorentz Violation
Aspects of Spontaneous Lorentz Violation Robert Bluhm Colby College IUCSS School on CPT & Lorentz Violating SME, Indiana University, June 2012 Outline: I. Review & Motivations II. Spontaneous Lorentz Violation III. Nambu-Goldstone Modes & Higgs Mech. IV. Examples: Bumblebee & Tensor Models V. Conclusions I. Review & Motivations Lorentz symmetry comes in two varieties: global ⇒ symmetry of special relativity - field theories invariant under global LTs local ⇒ symmetry of general relativity - Lorentz symmetry holds locally Previous talk looked at how to construct the SME in the presence of gravity SME lagrangian observer scalar formed from tensors, covariant derivatives, spinors, gamma matrices, etc. & SME coeffs. SME with Gravity includes gravity, SM, and LV sectors Have 2 symmetries in gravity: • local Lorentz symmetry • spacetime diffeomorphisms GR involves tensors on a curved spacetime manifold ⇒ spacetime tensor components Tλµν. To reveal the local Lorentz symmetry, introduce local tensor components in Lorentz frames ⇒ local Lorentz frame components Tabc. These components are connected by a vierbein vierbein: ⇒ relates local and manifold frames ⇒ tetrad of spacetime coord. vectors ⇒ can accommodate spinors In a vierbein formalism, must also introduce a spin connection appears in cov. derivs. spin connection: ⇒ of local tensors In Riemann spacetime with (metric) ⇒ spin connection is determined by the vierbein ⇒ not independent degrees of freedom Can also introduce torsion Tλµν = Γλµν - Γλνµ ⇒ spin connection becomes dynamically independent -
Gravity Theories with Background Fields and Spacetime Symmetry Breaking
S S symmetry Article Gravity Theories with Background Fields and Spacetime Symmetry Breaking Robert Bluhm Colby College, Department of Physics and Astronomy, Mayflower Hill 5862, Waterville, Maine, 04901, USA; [email protected] Received: 25 September 2017; Accepted: 10 October 2017; Published: 16 October 2017 Abstract: An overview is given of effective gravitational field theories with fixed background fields that break spacetime symmetry. The behavior of the background fields and the types of excitations that can occur depend on whether the symmetry breaking is explicit or spontaneous. For example, when the breaking is spontaneous, the background field is dynamical and massless Nambu–Goldstone and massive Higgs excitations can appear. However, if the breaking is explicit, the background is nondynamical, and in this case additional metric or vierbein excitations occur due to the loss of local symmetry, or these excitations can be replaced by dynamical scalar fields using a Stückelberg approach. The interpretation of Noether identities that must hold in each case differs, depending on the type of symmetry breaking, and this affects the nature of the consistency conditions that must hold. The Noether identities also shed light on why the Stückelberg approach works, and how it is able to restore the broken spacetime symmetry in a theory with explicit breaking. Keywords: gravity; background fields; Lorentz violation; Noether identities. 1. Introduction Some of the most important open questions in physics concern gravity. These include the question of how General Relativity (GR) merges with the Standard Model (SM) of particle interactions in a quantum theory. Additional open questions concern the nature of dark energy and dark matter in gravity theories and cosmology. -
Gravitational Dynamics—A Novel Shift in the Hamiltonian Paradigm
universe Article Gravitational Dynamics—A Novel Shift in the Hamiltonian Paradigm Abhay Ashtekar 1,* and Madhavan Varadarajan 2 1 Institute for Gravitation and the Cosmos & Physics Department, The Pennsylvania State University, University Park, PA 16802, USA 2 Raman Research Institute, Bangalore 560 080, India; [email protected] * Correspondence: [email protected] Abstract: It is well known that Einstein’s equations assume a simple polynomial form in the Hamil- tonian framework based on a Yang-Mills phase space. We re-examine the gravitational dynamics in this framework and show that time evolution of the gravitational field can be re-expressed as (a gauge covariant generalization of) the Lie derivative along a novel shift vector field in spatial directions. Thus, the canonical transformation generated by the Hamiltonian constraint acquires a geometrical interpretation on the Yang-Mills phase space, similar to that generated by the diffeomor- phism constraint. In classical general relativity this geometrical interpretation significantly simplifies calculations and also illuminates the relation between dynamics in the ‘integrable’ (anti)self-dual sector and in the full theory. For quantum gravity, it provides a point of departure to complete the Dirac quantization program for general relativity in a more satisfactory fashion. This gauge theory perspective may also be helpful in extending the ‘double copy’ ideas relating the Einstein and Yang-Mills dynamics to a non-perturbative regime. Finally, the notion of generalized, gauge covariant Lie derivative may also be of interest to the mathematical physics community as it hints at some potentially rich structures that have not been explored. Keywords: general relativity dynamics; gauge theory; hamiltonian framework Citation: Ashtekar, A.; Varadarajan, M.