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1-Loop Divergences of Quantum Gravity Using Conformal Parametrization  [PDF]
G. de Berredo-Peixoto,A. B. Penna-Firme,I. L. Shapiro
Physics , 2001, DOI: 10.1142/S0217732300002929
Abstract: We calculate the one-loop divergences for quantum gravity with cosmological constant, using new parametrization of quantum metric. The conformal factor of the metric is treated as an independent variable. As a result the theory possesses an additional degeneracy and one needs an extra conformal gauge fixing. We verify the on shell independence of the divergences from the parameter of the conformal gauge fixing, and find a special conformal gauge in which the divergences coincide with the ones obtained by t'Hooft and Veltman (1974). Using conformal invariance of the counterterms one can restore the divergences for the conformal metric-scalar gravity.
Towards a Covariant Loop Quantum Gravity  [PDF]
Etera R. Livine
Physics , 2006,
Abstract: We review the canonical analysis of the Palatini action without going to the time gauge as in the standard derivation of Loop Quantum Gravity. This allows to keep track of the Lorentz gauge symmetry and leads to a theory of Covariant Loop Quantum Gravity. This new formulation does not suffer from the Immirzi ambiguity, it has a continuous area spectrum and uses spin networks for the Lorentz group. Finally, its dynamics can easily be related to Barrett-Crane like spin foam models.
Towards Loop Quantum Gravity without the time gauge  [PDF]
Francesco Cianfrani,Giovanni Montani
Physics , 2008, DOI: 10.1103/PhysRevLett.102.091301
Abstract: The Hamiltonian formulation of the Holst action is reviewed and it is provided a solution of second-class constraints corresponding to a generic local Lorentz frame. Within this scheme the form of rotation constraints can be reduced to a Gauss-like one by a proper generalization of Ashtekar-Barbero-Immirzi connections. This result emphasizes that the Loop Quantum Gravity quantization procedure can be applied when the time-gauge condition does not stand.
Computing Black Hole entropy in Loop Quantum Gravity from a Conformal Field Theory perspective  [PDF]
Ivan Agullo,Enrique F. Borja,Jacobo Diaz-Polo
Physics , 2009, DOI: 10.1088/1475-7516/2009/07/016
Abstract: Motivated by the analogy proposed by Witten between Chern-Simons and Conformal Field Theories, we explore an alternative way of computing the entropy of a black hole starting from the isolated horizon framework in Loop Quantum Gravity. The consistency of the result opens a window for the interplay between Conformal Field Theory and the description of black holes in Loop Quantum Gravity.
Towards new background independent representations for Loop Quantum Gravity  [PDF]
Madhavan Varadarajan
Physics , 2007, DOI: 10.1088/0264-9381/25/10/105011
Abstract: Recently, uniqueness theorems were constructed for the representation used in Loop Quantum Gravity. We explore the existence of alternate representations by weakening the assumptions of the so called LOST uniqueness theorem. The weakened assumptions seem physically reasonable and retain the key requirement of explicit background independence. For simplicity, we restrict attention to the case of gauge group U(1).
Two-loop Renormalization in Quantum Gravity near Two Dimensions  [PDF]
Toshiaki Aida,Yoshihisa Kitazawa,Jun Nishimura,Asato Tsuchiya
Physics , 1995, DOI: 10.1016/0550-3213(95)00071-Y
Abstract: We study two--loop renormalization in $(2+\epsilon)$--dimensional quantum gravity. As a first step towards the full calculation, we concentrate on the divergences which are proportional to the number of matter fields. We calculate the $\beta$ functions and show how the nonlocal divergences as well as the infrared divergences cancel among the diagrams. Although the formalism includes a subtlety concerning the general covariance due to the dynamics of the conformal mode, we find that the renormalization group allows the existence of a fixed point which possesses the general covariance. Our results strongly suggest that we can construct a consistent theory of quantum gravity by the $\epsilon$ expansion around two dimensions.
Towards a Loop Quantum Gravity and Yang-Mills Unification  [PDF]
Stephon Alexander,Antonino Marciano,Ruggero Altair Tacchi
Physics , 2011, DOI: 10.1016/j.physletb.2012.07.034
Abstract: We propose a new method of unifying gravity and the Standard Model by introducing a spin-foam model. We realize a unification between an SU(2) Yang-Mills interaction and 3D general relativity by considering a Spin(4) Plebanski action. The theory is quantized a la spin-foam by implementing the analogue of the simplicial constraints for the broken phase of the Spin(4) SO(4) symmetry. A natural 4D extension of the theory is shown. We also present a way to recover 2-point correlation functions between the connections as a first way to implement scattering amplitudes between particle states, aiming to connect Loop Quantum Gravity to new physical predictions.
Three dimensional Loop Quantum Gravity: towards a self-gravitating Quantum Field Theory  [PDF]
Karim Noui
Physics , 2006, DOI: 10.1088/0264-9381/24/2/005
Abstract: In a companion paper, we have emphasized the role of the Drinfeld double DSU(2) in the context of three dimensional Riemannian Loop Quantum Gravity coupled to massive spinless point particles. We make use of this result to propose a model for a self-gravitating quantum field theory (massive spinless non-causal scalar field) in three dimensional Riemannian space. We start by constructing the Fock space of the free self-gravitating field: the vacuum is the unique DSU(2) invariant state, one-particle states correspond to DSU(2) unitary irreducible simple representations and any multi-particles states is obtained as the symmetrized tensor product between simple representations. The associated quantum field is defined by the usual requirement of covariance under DSU(2). Then, we introduce a DSU(2)-invariant self-interacting potential (the obtained model is a Group Field Theory) and compute explicitely the lowest order terms (in the self-interaction coupling constant $\lambda$) of the propagator and of the three-points function. Finally, we compute the lowest order quantum gravity corrections (in the Newton constant G) to the propagator and to the three-points function.
A Theory for the Conformal Factor in Quantum $R^2$ Gravity  [PDF]
E. Elizalde,S. D. Odintsov
Physics , 1994, DOI: 10.1016/0370-2693(94)90588-6
Abstract: A new theory for the conformal factor in R$^2$-gravity is developed. The infrared phase of this theory, which follows from the one-loop renormalization group equations for the whole quantum R$^2$-gravity theory is described. The one-loop effective potential for the conformal factor is found explicitly and a mechanism for inducing Einstein gravity at the minimum of the effective potential for the conformal factor is suggested. A comparison with the effective theory of the conformal factor induced by the conformal anomaly, and also aiming to describe quantum gravity at large distances, is done.
Newtonian gravity in loop quantum gravity  [PDF]
Lee Smolin
Physics , 2010,
Abstract: We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime.
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