Loop Quantum Gravity: an Inside View
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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. -
DIFFERENTIAL GEOMETRY FINAL PROJECT 1. Introduction for This
DIFFERENTIAL GEOMETRY FINAL PROJECT KOUNDINYA VAJJHA 1. Introduction For this project, we outline the basic structure theory of Lie groups relating them to the concept of Lie algebras. Roughly, a Lie algebra encodes the \infinitesimal” structure of a Lie group, but is simpler, being a vector space rather than a nonlinear manifold. At the local level at least, the Fundamental Theorems of Lie allow one to reconstruct the group from the algebra. 2. The Category of Local (Lie) Groups The correspondence between Lie groups and Lie algebras will be local in nature, the only portion of the Lie group that will be of importance is that portion of the group close to the group identity 1. To formalize this locality, we introduce local groups: Definition 2.1 (Local group). A local topological group is a topological space G, with an identity element 1 2 G, a partially defined but continuous multiplication operation · :Ω ! G for some domain Ω ⊂ G × G, a partially defined but continuous inversion operation ()−1 :Λ ! G with Λ ⊂ G, obeying the following axioms: • Ω is an open neighbourhood of G × f1g Sf1g × G and Λ is an open neighbourhood of 1. • (Local associativity) If it happens that for elements g; h; k 2 G g · (h · k) and (g · h) · k are both well-defined, then they are equal. • (Identity) For all g 2 G, g · 1 = 1 · g = g. • (Local inverse) If g 2 G and g−1 is well-defined in G, then g · g−1 = g−1 · g = 1. A local group is said to be symmetric if Λ = G, that is, every element g 2 G has an inverse in G.A local Lie group is a local group in which the underlying topological space is a smooth manifold and where the associated maps are smooth maps on their domain of definition. -
10 Group Theory and Standard Model
Physics 129b Lecture 18 Caltech, 03/05/20 10 Group Theory and Standard Model Group theory played a big role in the development of the Standard model, which explains the origin of all fundamental particles we see in nature. In order to understand how that works, we need to learn about a new Lie group: SU(3). 10.1 SU(3) and more about Lie groups SU(3) is the group of special (det U = 1) unitary (UU y = I) matrices of dimension three. What are the generators of SU(3)? If we want three dimensional matrices X such that U = eiθX is unitary (eigenvalues of absolute value 1), then X need to be Hermitian (real eigenvalue). Moreover, if U has determinant 1, X has to be traceless. Therefore, the generators of SU(3) are the set of traceless Hermitian matrices of dimension 3. Let's count how many independent parameters we need to characterize this set of matrices (what is the dimension of the Lie algebra). 3 × 3 complex matrices contains 18 real parameters. If it is to be Hermitian, then the number of parameters reduces by a half to 9. If we further impose traceless-ness, then the number of parameter reduces to 8. Therefore, the generator of SU(3) forms an 8 dimensional vector space. We can choose a basis for this eight dimensional vector space as 00 1 01 00 −i 01 01 0 01 00 0 11 λ1 = @1 0 0A ; λ2 = @i 0 0A ; λ3 = @0 −1 0A ; λ4 = @0 0 0A (1) 0 0 0 0 0 0 0 0 0 1 0 0 00 0 −i1 00 0 01 00 0 0 1 01 0 0 1 1 λ5 = @0 0 0 A ; λ6 = @0 0 1A ; λ7 = @0 0 −iA ; λ8 = p @0 1 0 A (2) i 0 0 0 1 0 0 i 0 3 0 0 −2 They are called the Gell-Mann matrices. -
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 -
Representation Theory
M392C NOTES: REPRESENTATION THEORY ARUN DEBRAY MAY 14, 2017 These notes were taken in UT Austin's M392C (Representation Theory) class in Spring 2017, taught by Sam Gunningham. I live-TEXed them using vim, so there may be typos; please send questions, comments, complaints, and corrections to [email protected]. Thanks to Kartik Chitturi, Adrian Clough, Tom Gannon, Nathan Guermond, Sam Gunningham, Jay Hathaway, and Surya Raghavendran for correcting a few errors. Contents 1. Lie groups and smooth actions: 1/18/172 2. Representation theory of compact groups: 1/20/174 3. Operations on representations: 1/23/176 4. Complete reducibility: 1/25/178 5. Some examples: 1/27/17 10 6. Matrix coefficients and characters: 1/30/17 12 7. The Peter-Weyl theorem: 2/1/17 13 8. Character tables: 2/3/17 15 9. The character theory of SU(2): 2/6/17 17 10. Representation theory of Lie groups: 2/8/17 19 11. Lie algebras: 2/10/17 20 12. The adjoint representations: 2/13/17 22 13. Representations of Lie algebras: 2/15/17 24 14. The representation theory of sl2(C): 2/17/17 25 15. Solvable and nilpotent Lie algebras: 2/20/17 27 16. Semisimple Lie algebras: 2/22/17 29 17. Invariant bilinear forms on Lie algebras: 2/24/17 31 18. Classical Lie groups and Lie algebras: 2/27/17 32 19. Roots and root spaces: 3/1/17 34 20. Properties of roots: 3/3/17 36 21. Root systems: 3/6/17 37 22. Dynkin diagrams: 3/8/17 39 23. -
Special Unitary Group - Wikipedia
Special unitary group - Wikipedia https://en.wikipedia.org/wiki/Special_unitary_group Special unitary group In mathematics, the special unitary group of degree n, denoted SU( n), is the Lie group of n×n unitary matrices with determinant 1. (More general unitary matrices may have complex determinants with absolute value 1, rather than real 1 in the special case.) The group operation is matrix multiplication. The special unitary group is a subgroup of the unitary group U( n), consisting of all n×n unitary matrices. As a compact classical group, U( n) is the group that preserves the standard inner product on Cn.[nb 1] It is itself a subgroup of the general linear group, SU( n) ⊂ U( n) ⊂ GL( n, C). The SU( n) groups find wide application in the Standard Model of particle physics, especially SU(2) in the electroweak interaction and SU(3) in quantum chromodynamics.[1] The simplest case, SU(1) , is the trivial group, having only a single element. The group SU(2) is isomorphic to the group of quaternions of norm 1, and is thus diffeomorphic to the 3-sphere. Since unit quaternions can be used to represent rotations in 3-dimensional space (up to sign), there is a surjective homomorphism from SU(2) to the rotation group SO(3) whose kernel is {+ I, − I}. [nb 2] SU(2) is also identical to one of the symmetry groups of spinors, Spin(3), that enables a spinor presentation of rotations. Contents Properties Lie algebra Fundamental representation Adjoint representation The group SU(2) Diffeomorphism with S 3 Isomorphism with unit quaternions Lie Algebra The group SU(3) Topology Representation theory Lie algebra Lie algebra structure Generalized special unitary group Example Important subgroups See also 1 of 10 2/22/2018, 8:54 PM Special unitary group - Wikipedia https://en.wikipedia.org/wiki/Special_unitary_group Remarks Notes References Properties The special unitary group SU( n) is a real Lie group (though not a complex Lie group). -
Group Theory - QMII 2017
Group Theory - QMII 2017 Reminder Last time we said that a group element of a matrix lie group can be written as an exponent: a U = eiαaX ; a = 1; :::; N: We called Xa the generators, we have N of them, they span a basis for the Lie algebra, and they can be found by taking the derivative with respect to αa at α = 0. The generators are closed under the Lie product (∼ [·; ·]), and related by the structure constants [Xa;Xb] = ifabcXc: (1) We end with the Jacobi identity [Xa; [Xb;Xc]] + [Xb; [Xc;Xa]] + [Xc; [Xa;Xb]] = 0: (2) 1 Representations of Lie Algebra 1.1 The adjoint rep. part- I One of the most important representations is the adjoint. There are two equivalent ways to defined it. Here we follow the definition by Georgi. By plugging Eq. (1) into the Jacobi identity Eq. (2) we get the following: fbcdfade + fabdfcde + fcadfbde = 0 (3) Proof: 0 = [Xa; [Xb;Xc]] + [Xb; [Xc;Xa]] + [Xc; [Xa;Xb]] = ifbcd [Xa;Xd] + ifcad [Xb;Xd] + ifabd [Xc;Xd] = − (fbcdfade + fcadfbde + fabdfcde) Xe (4) 1 Now we can define a set of matrices Ta s.t. [Ta]bc = −ifabc: (5) Then by using the relation of the structure constants Eq. (3) we get [Ta;Tb] = ifabcTc: (6) Proof: [Ta;Tb]ce = [Ta]cd[Tb]de − [Tb]cd[Ta]de = −facdfbde + fbcdfade = fcadfbde + fbcdfade = −fabdfcde = fabdfdce = ifabd[Td]ce (7) which means that: [Ta;Tb] = ifabdTd: (8) Therefore the structure constants themselves generate a representation. This representation is called the adjoint representation. The adjoint of su(2) We already found that the structure constants of su(2) are given by the Levi-Civita tensor. -
Groups and Representations the Material Here Is Partly in Appendix a and B of the Book
Groups and representations The material here is partly in Appendix A and B of the book. 1 Introduction The concept of symmetry, and especially gauge symmetry, is central to this course. Now what is a symmetry: you have something, e.g. a vase, and you do something to it, e.g. turn it by 29 degrees, and it still looks the same then we call the operation performed, i.e. the rotation, a symmetryoperation on the object. But if we first rotate it by 29 degrees and then by 13 degrees and it still looks the same then also the combined operation of a rotation by 42 degrees is a symmetry operation as well. The mathematics that is involved here is that of groups and their representations. The symmetry operations form the group and the objects the operations work on are in representations of the group. 2 Groups A group is a set of elements g where there exist an operation ∗ that combines two group elements and the results is a third: ∃∗ : 8g1; g2 2 G : g1 ∗ g2 = g3 2 G (1) This operation must be associative: 8g1; g2; g3 2 G :(g1 ∗ g2) ∗ g3 = g1 ∗ (g2 ∗ g3) (2) and there exists an element unity: 91 2 G : 8g 2 G : g ∗ 1 = 1 ∗ g = g (3) and for every element in G there exists an inverse: 8g 2 G : 9g−1 2 G : g ∗ g−1 = g−1 ∗ g = 1 (4) This is the general definition of a group. Now if all elements of a group commute, i.e. -
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. -
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. -
Hamiltonian Constraint Analysis of Vector Field Theories with Spontaneous Lorentz Symmetry Breaking
Colby College Digital Commons @ Colby Honors Theses Student Research 2008 Hamiltonian constraint analysis of vector field theories with spontaneous Lorentz symmetry breaking Nolan L. Gagne Colby College Follow this and additional works at: https://digitalcommons.colby.edu/honorstheses Part of the Physics Commons Colby College theses are protected by copyright. They may be viewed or downloaded from this site for the purposes of research and scholarship. Reproduction or distribution for commercial purposes is prohibited without written permission of the author. Recommended Citation Gagne, Nolan L., "Hamiltonian constraint analysis of vector field theories with spontaneous Lorentz symmetry breaking" (2008). Honors Theses. Paper 92. https://digitalcommons.colby.edu/honorstheses/92 This Honors Thesis (Open Access) is brought to you for free and open access by the Student Research at Digital Commons @ Colby. It has been accepted for inclusion in Honors Theses by an authorized administrator of Digital Commons @ Colby. 1 Hamiltonian Constraint Analysis of Vector Field Theories with Spontaneous Lorentz Symmetry Breaking Nolan L. Gagne May 17, 2008 Department of Physics and Astronomy Colby College 2008 1 Abstract Recent investigations of various quantum-gravity theories have revealed a variety of possible mechanisms that lead to Lorentz violation. One of the more elegant of these mechanisms is known as Spontaneous Lorentz Symmetry Breaking (SLSB), where a vector or tensor field acquires a nonzero vacuum expectation value. As a consequence of this symmetry breaking, massless Nambu-Goldstone modes appear with properties similar to the photon in Electromagnetism. This thesis considers the most general class of vector field theo- ries that exhibit spontaneous Lorentz violation{known as bumblebee models{and examines their candidacy as potential alternative explanations of E&M, offering the possibility that Einstein-Maxwell theory could emerge as a result of SLSB rather than of local U(1) gauge invariance. -
Characterization of SU(N)
University of Rochester Group Theory for Physicists Professor Sarada Rajeev Characterization of SU(N) David Mayrhofer PHY 391 Independent Study Paper December 13th, 2019 1 Introduction At this point in the course, we have discussed SO(N) in detail. We have de- termined the Lie algebra associated with this group, various properties of the various reducible and irreducible representations, and dealt with the specific cases of SO(2) and SO(3). Now, we work to do the same for SU(N). We de- termine how to use tensors to create different representations for SU(N), what difficulties arise when moving from SO(N) to SU(N), and then delve into a few specific examples of useful representations. 2 Review of Orthogonal and Unitary Matrices 2.1 Orthogonal Matrices When initially working with orthogonal matrices, we defined a matrix O as orthogonal by the following relation OT O = 1 (1) This was done to ensure that the length of vectors would be preserved after a transformation. This can be seen by v ! v0 = Ov =) (v0)2 = (v0)T v0 = vT OT Ov = v2 (2) In this scenario, matrices then must transform as A ! A0 = OAOT , as then we will have (Av)2 ! (A0v0)2 = (OAOT Ov)2 = (OAOT Ov)T (OAOT Ov) (3) = vT OT OAT OT OAOT Ov = vT AT Av = (Av)2 Therefore, when moving to unitary matrices, we want to ensure similar condi- tions are met. 2.2 Unitary Matrices When working with quantum systems, we not longer can restrict ourselves to purely real numbers. Quite frequently, it is necessarily to extend the field we are with with to the complex numbers.