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Extending dualities to trialities deepens the foundations of dynamicsMar 04 2015Dualities are often supposed to be foundational, but they may come into conflict with background independence, because a hidden fixed structures is needed to define the duality transformation. This conflict can be eliminated by extending a duality to ... More

Precedence and freedom in quantum physicsMay 16 2012A new interpretation of quantum mechanics is proposed according to which precedence, freedom and novelty play central roles. This is based on a modification of the postulates for quantum theory given by Masanes and Muller. We argue that quantum mechanics ... More

Generic predictions of quantum theories of gravityMay 04 2006I discuss generic consequences (sometimes called "soft predictions") of a class of background independent quantum theories of spacetime called causal spin network theories. These are theories whose kinematics and dynamics is based on the evolution of ... More

A real ensemble interpretation of quantum mechanicsApr 14 2011A new ensemble interpretation of quantum mechanics is proposed according to which the ensemble associated to a quantum state really exists: it is the ensemble of all the systems in the same quantum state in the universe. Individual systems within the ... More

Newtonian gravity in loop quantum gravityJan 20 2010Feb 22 2010We 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 ... More

Falsifiable predictions from semiclassical quantum gravityJan 12 2005Apr 18 2005Quantum gravity is studied in a semiclassical approximation and it is found that to first order in the Planck length the effect of quantum gravity is to make the low energy effective spacetime metric energy dependent. The diffeomorphism invariance of ... More

Three Dimensional Strings as Collective Coordinates of Four Dimensional Non-Perturbative Quantum GravitySep 12 1996A string theory in $3$ euclidean spacetime dimensions is found to describe the semiclassical behavior of a certain exact physical state of quantum general relativity in $4$ dimensions. Both the worldsheet and the three dimensional metric emerge as collective ... More

The fate of black hole singularities and the parameters of the standard models of particle physics and cosmologyApr 07 1994A cosmological scenario which explains the values of the parameters of the standard models of elementary particle physics and cosmology is discussed. In this scenario these parameters are set by a process analogous to natural selection which follows naturally ... More

Time, measurement and information loss in quantum cosmologyJan 15 1993Feb 08 1993An error in the gauge fixed quantization of section 3 is corrected. The result is a much simpler treatment of the clock field, leading to a simplification of the gauge fixed quantum theory and the treatment of the semiclassical limit.

Matrix universality of gauge and gravitational dynamicsMar 20 2008Mar 21 2008A simple cubic matrix model is presented, which has truncations that, it is argued, lead at the classical level to a variety of theories of gauge fields and gravity. These include Chern-Simons theory in d=3, and BF theory and general relativity in d=4. ... More

Twistor relative localityNov 01 2013We present a version of relative locality based on the geometry of twistor space. This can also be thought of as a new kind of deformation of twistor theory based on the construction of a bundle of twistor spaces over momentum space. Locality in space-time ... More

The quantization of unimodular gravity and the cosmological constant problemApr 30 2009A quantization of unimodular gravity is described, which results in a quantum effective action which is also unimodular, ie a function of a metric with fixed determinant. A consequence is that contributions to the energy momentum tensor of the form of ... More

Scientific alternatives to the anthropic principleJul 26 2004Jul 29 2004It is explained in detail why the Anthropic Principle (AP) cannot yield any falsifiable predictions, and therefore cannot be a part of science. Cases which have been claimed as successful predictions from the AP are shown to be not that. Either they are ... More

The future of spin networksFeb 17 1997The roles that spin networks play in gauge theories, quantum gravity and topological quantum field theory are briefly described, with an emphasis on the question of the relationships among them. It is argued that spin networks and their generalizations ... More

The G_Newton --> 0 Limit of Euclidean Quantum GravityFeb 22 1992Using the Ashtekar formulation, it is shown that the G_{Newton} --> 0 limit of Euclidean or complexified general relativity is not a free field theory, but is a theory that describes a linearized self-dual connection propagating on an arbitrary anti-self-dual ... More

Towards a background independent approach to M theoryAug 31 1998Work in progress is described which aims to construct a background independent formulation of M theory by extending results about background independent states and observables from quantum general relativity and supergravity to string theory. A list of ... More

A holographic formulation of quantum general relativityAug 31 1998Oct 31 1999We show that there is a sector of quantum general relativity which may be expressed in a completely holographic formulation in terms of states and operators defined on a finite boundary. The space of boundary states is built out of the conformal blocks ... More

Linking Topological Quantum Field Theory and Nonperturbative Quantum GravityMay 17 1995Jan 30 1996Quantum gravity is studied nonperturbatively in the case in which space has a boundary with finite area. A natural set of boundary conditions is studied in the Euclidean signature theory, in which the pullback of the curvature to the boundary is self-dual ... More

Experimental Signatures of Quantum GravityMar 16 1995Jan 30 1996I review several different calculations, coming from string theory, nonperturbative quantum gravity and analyses of black holes that lead to predictions of phenomena that would uniquely be signatures of quantum gravitational effects. These include: 1) ... More

Holographic relations in loop quantum gravityAug 09 2016It is shown that a relation between entropy and minimal area holds in loop quantum gravity, reminiscent of the Ryu-Takayanagi relation.

The thermodynamics of quantum spacetime historiesOct 13 2015We show that the simplicity constraints, which define the dynamics of spin foam models, imply, and are implied by, the first law of thermodynamics, when the latter is applied to causal diamonds in the quantum spacetime. This result reveals an intimate ... More

Non-local beablesJul 30 2015I discuss the idea that the beables underlying quantum physics are non-local and relational, and give an example of a dynamical theory of such beables based on a matrix model, which is the bosonic sector of the BFSS model. Given that the same model has ... More

Dynamics of the cosmological and Newton's constantJul 05 2015A modification of general relativity is presented in which Newton's constant and the cosmological constant become a conjugate pair of dynamical variables.

The case for background independenceJul 25 2005The aim of this paper is to explain carefully the arguments behind the assertion that the correct quantum theory of gravity must be background independent. We begin by recounting how the debate over whether quantum gravity must be background independent ... More

A quantization of topological M theoryMar 17 2005A conjecture is made as to how to quantize topological M theory. We study a Hamiltonian decomposition of Hitchin's 7-dimensional action and propose a formulation for it in terms of 13 first class constraints. The theory has 2 degrees of freedom per point, ... More

The cubic matrix model and a duality between strings and loopsJun 19 2000We find evidence for a duality between the standard matrix formulations of M theory and a background independent theory which extends loop quantum gravity by replacing SU(2) with a supersymmetric and quantum group extension of SU(16). This is deduced ... More

General relativity as the equation of state of spin foamMay 24 2012Building on recent significant results of Frodden, Ghosh and Perez (FGP) and Bianchi, I present a quantum version of Jacobson's argument that the Einstein equations emerge as the equation of state of a quantum gravitational system. I give three criteria ... More

On limitations of the extent of inertial frames in non-commutative relativistic spacetimesJul 05 2010Aug 10 2010We study the interplay of non-locality and Lorentz invariance in a version of deformed or doubly special relativity (DSR) based on kappa-Minkowski spacetime. We find that Einstein's procedure for an inertial observer to assign coordinates to distant events ... More

The status of cosmological natural selectionDec 18 2006The problem of making predictions from theories that have landscapes of possible low energy parameters is reviewed. Conditions for such a theory to yield falsifiable predictions for doable experiments are given. It is shown that the hypothesis of cosmological ... More

The present moment in quantum cosmology: challenges to the arguments for the elimination of timeApr 29 2001Barbour, Hawking, Misner and others have argued that time cannot play an essential role in the formulation of a quantum theory of cosmology. Here we present three challenges to their arguments, taken from works and remarks by Kauffman, Markopoulou and ... More

Finite, diffeomorphism invariant observables in quantum gravityFeb 10 1993Two sets of spatially diffeomorphism invariant operators are constructed in the loop representation formulation of quantum gravity. This is done by coupling general relativity to an anti- symmetric tensor gauge field and using that field to pick out sets ... More

Strings as perturbations of evolving spin-networksJan 06 1998A connection between non-perturbative formulations of quantum gravity and perturbative string theory is exhibited, based on a formulation of the non-perturbative dynamics due to Markopoulou. In this formulation the dynamics of spin network states and ... More

Galactic disks as reaction-diffusion systemsDec 03 1996A model of a galactic disk is presented which extends the homogeneous one zone models by incorporating propagation of material and energy in the disk. For reasonable values of the parameters the homogeneous steady state is unstable to the development ... More

Cosmology as a Problem in Critical PhenomenaMay 16 1995Several problems in cosmology and astrophysics are described in which critical phenomena of various types may play a role. These include the organization of the disks of spiral galaxies, various aspects of the problem of structure formation in icosmology, ... More

Positive energy in quantum gravityJun 10 2014This paper addresses the question of whether Witten's proof of positive ADM energy for classical general relativity can be extended to give a proof of positive energy for a non-perturbative quantization of general relativity. To address this question, ... More

Could deformed special relativity naturally arise from the semiclassical limit of quantum gravity?Aug 27 2008A argument is described for how deformed or doubly special relativity may arise in the semiclassical limit of a quantum theory of gravity. We consider a generic quantum theory of gravity coupled to matter, from which we use only the assumption that a ... More

Could quantum mechanics be an approximation to another theory?Sep 14 2006We consider the hypothesis that quantum mechanics is an approximation to another, cosmological theory, accurate only for the description of subsystems of the universe. Quantum theory is then to be derived from the cosmological theory by averaging over ... More

Quantum gravity with a positive cosmological constantSep 09 2002A quantum theory of gravity is described in the case of a positive cosmological constant in 3+1 dimensions. Both old and new results are described, which support the case that loop quantum gravity provides a satisfactory quantum theory of gravity. These ... More

Matrix models as non-local hidden variables theoriesJan 05 2002It is shown that the matrix models which give non-perturbative definitions of string and M theory may be interpreted as non-local hidden variables theories in which the quantum observables are the eigenvalues of the matrices while their entries are the ... More

Using neutron stars and primordial black holes to test theories of quantum gravityDec 15 1997Jan 06 1998Three observational tests of cosmological natural selection, a theory that follows from some hypotheses about quantum gravity, are described. If true, this theory explains the choices of the parameters of the standard model of particle physics. The first, ... More

Linking shape dynamics and loop quantum gravityJul 10 2014Shape dynamics is a reformulation of general relativity, locally equivalent to Einstein's theory, in which the refoliation invariance of the older theory is traded for local scale invariance. Shape dynamics is here derived in a formulation related to ... More

Classical paradoxes of locality and their possible quantum resolutions in deformed special relativityApr 05 2010Jul 05 2010In deformed or doubly special relativity (DSR) the action of the lorentz group on momentum eigenstates is deformed to preserve a maximal momenta or minimal length, supposed equal to the Planck length. The classical and quantum dynamics of a particle propagating ... More

The strong and weak holographic principlesMar 08 2000We review the different proposals which have so far been made for the holographic principle and the related entropy bounds and classify them into the strong, null and weak forms. These are analyzed, with the aim of discovering which may hold at the level ... More

A candidate for a background independent formulation of M theoryMar 19 1999Jan 10 2000A class of background independent membrane field theories are studied, and several properties are discovered which suggest that they may play a role in a background independent form of M theory. The bulk kinematics of these theories are described in terms ... More

The classical limit and the form of the hamiltonian constraint in nonperturbative quantum gravitySep 12 1996It is argued that some approaches to non-perturbative quantum general relativity lack a sensible continuum limit that reproduces general relativity. The basic problem is that generic physical states lack long ranged correlations, because the form of the ... More

Fermions and TopologyApr 07 1994The canonical theory of quantum gravity in the loop representation can be extended to incorporate topology change, in the simple case that this refers to the creation or annihilation of "minimalist wormholes" in which two points of the spatial manifold ... More

Temporal naturalismOct 31 2013Two people may claim both to be naturalists, but have divergent conceptions of basic elements of the natural world which lead them to mean different things when they talk about laws of nature, or states, or the role of mathematics in physics. These disagreements ... More

Quantum mechanics and the principle of maximal varietyJun 09 2015Quantum mechanics is derived from the principle that the universe contain as much variety as possible, in the sense of maximizing the distinctiveness of each subsystem. The quantum state of a microscopic system is defined to correspond to an ensemble ... More

Four principles for quantum gravityOct 06 2016Four principles are proposed to underlie the quantum theory of gravity. We show that these suffice to recover the Einstein equations. We also suggest that MOND results from a modification of the classical equivalence principle, due to quantum gravity ... More

A naturalist account of the limited, and hence reasonable, effectiveness of mathematics in physicsJun 11 2015The aim of this essay is to propose a conception of mathematics that is fully consonant with naturalism. By that I mean the hypothesis that everything that exists is part of the natural world, which makes up a unitary whole.

Lessons from Einstein's 1915 discovery of general relativityDec 23 2015There is a myth that Einstein's discovery of general relativity was due to his following beautiful mathematics to discover new insights about nature. I argue that this is an incorrect reading of the history and that what Einstein did was to follow physical ... More

A perspective on the landscape problemFeb 15 2012I discuss the historical roots of the landscape problem and propose criteria for its successful resolution. This provides a perspective to evaluate the possibility to solve it in several of the speculative cosmological scenarios under study including ... More

The black hole information paradox and relative localityAug 03 2011We argue that the recently proposed principle of relative locality offers a new way to resolve the black hole information puzzle.

How far are we from the quantum theory of gravity?Mar 20 2003Apr 11 2003An assessment is offered of the progress that the major approaches to quantum gravity have made towards the goal of constructing a complete and satisfactory theory. The emphasis is on loop quantum gravity and string theory, although other approaches are ... More

The exceptional Jordan algebra and the matrix stringApr 05 2001A new matrix model is described, based on the exceptional Jordan algebra. The action is cubic, as in matrix Chern-Simons theory. We describe a compactification that, we argue, reproduces, at the one loop level, an octonionic compactification of the matrix ... More

Covariant quantization of membrane dynamicsOct 25 1997A Lorentz covariant quantization of membrane dynamics is defined, which also leaves unbroken the full three dimensional diffeomorphism invariance of the membrane. Among the applications studied are the reduction to string theory, which may be understood ... More

Unification of the state with the dynamical lawJan 12 2012We address the question of why particular laws were selected for the universe, by proposing a mechanism for laws to evolve. Normally in physical theories, timeless laws act on time-evolving states. We propose that this is an approximation, good on time ... More

Unimodular loop quantum gravity and the problems of timeAug 10 2010We develop the quantization of unimodular gravity in the Plebanski and Ashtekar formulations and show that the quantum effective action defined by a formal path integral is unimodular. This means that the effective quantum geometry does not couple to ... More

Time and symmetry in models of economic marketsFeb 25 2009These notes discuss several topics in neoclassical economics and alternatives, with an aim of reviewing fundamental issues in modeling economic markets. I start with a brief, non-rigorous summary of the basic Arrow-Debreu model of general equilibrium, ... More

The Plebanski action extended to a unification of gravity and Yang-Mills theoryDec 06 2007Jul 25 2008We study a unification of gravity with Yang-Mills fields based on a simple extension of the Plebanski action to a Lie group G which contains the local lorentz group. The Coleman-Mandula theorem is avoided because the theory has no global spacetime symmetry. ... More

An invitation to loop quantum gravityAug 05 2004Jun 28 2005We describe the basic assumptions and key results of loop quantum gravity, which is a background independent approach to quantum gravity. The emphasis is on the basic physical principles and how one deduces predictions from them, at a level suitable for ... More

Chern-Simons theory in 11 dimensions as a non-perturbative phase of M theoryMar 25 1997Jan 06 1998A Chern-Simons theory in 11 dimensions, which is a piece of the 11 dimensional supergravity action, is considered as a quantum field theory in its own right. We conjecture that it defines a non-perturbative phase of M theory in which the metric and gravitino ... More

The Bekenstein Bound, Topological Quantum Field Theory and Pluralistic Quantum Field TheoryAug 31 1995Sep 01 1995An approach to quantum gravity and cosmology is proposed based on a synthesis of four elements: 1) the Bekenstein bound and the related holographic hypothesis of 't Hooft and Susskind, 2) topological quantum field theory, 3) a new approach to the interpretational ... More

M theory as a matrix extension of Chern-Simons theoryFeb 01 2000We study a new class of matrix models, the simplest of which is based on an Sp(2) symmetry and has a compactification which is equivalent to Chern-Simons theory on the three-torus. By replacing Sp(2) with the super-algebra Osp(1|32), which has been conjectured ... More

What can we learn from the study of non-perturbative quantum general relativity?Nov 15 1992I attempt to answer the question of the title by giving an annotated list of the major results achieved, over the last six years, in the program to construct quantum general relativity using the Ashtekar variables and the loop representation. A summary ... More

Recent Developments in Non-Perturbative Quantum GravityFeb 07 1992New results from the new variables/loop representation program of nonperturbative quantum gravity are presented, with a focus on results of Ashtekar, Rovelli and the author which greatly clarify the physical interpretation of the quantum states in the ... More

Gauge fixing in Causal Dynamical TriangulationsSep 04 2004May 09 2005We relax the definition of the Ambjorn-Loll causal dynamical triangulation model in 1+1 dimensions to allow for a varying lapse. We show that, as long as the spatially averaged lapse is constant in time, the physical observables are unchanged in the continuum ... More

The linearization of the Kodama stateOct 23 2003Oct 28 2003We study the question of whether the linearization of the Kodama state around classical deSitter spacetime is normalizable in the inner product of the theory of linearized gravitons on deSitter spacetime. We find the answer is no in the Lorentzian theory. ... More

Conservative solutions to the black hole information problemJan 20 2009We review the different options for resolution of the black hole loss of information problem. We classify them first into radical options, which require a quantum theory of gravity which has large deviations from semi-classical physics on macroscopic ... More

A possible solution to the problem of time in quantum cosmologyMar 09 1997We argue that in classical and quantum theories of gravity the configuration space and Hilbert space may not be constructible through any finite procedure. If this is the case then the "problem of time" in quantum cosmology may be a pseudo-problem, because ... More

Combinatorial dynamics in quantum gravitySep 22 1998We describe the application of methods from the study of discrete dynanmical systems to the problem of the continuum limit of evolving spin networks. These have been found to describe the small scale structure of quantum general relativity and extensions ... More

Gravity's RainbowMay 14 2003Feb 03 2004Non-linear special relativity (or doubly special relativity) is a simple framework for encoding properties of flat quantum space-time. In this paper we show how this formalism may be generalized to incorporate curvature (leading to what might be called ... More

Reversing the irreversible: from limit cycles to emergent time symmetryMar 27 2017In 1979 Penrose hypothesized that the arrows of time are explained by the hypothesis that the fundamental laws are time irreversible. That is, our reversible laws, such as the standard model and general relativity are effective, and emerge from an underlying ... More

Cosmological Histories for the New VariablesFeb 08 1994Feb 09 1994Histories and measures for quantum cosmology are investigated through a quantization of the Bianchi IX cosmology using path integral techniques. The result, derived in the context of Ashtekar variables, is compared with earlier work. A non-trivial correction ... More

Quantum Theory from Quantum GravityNov 18 2003Jun 14 2004We provide a mechanism by which, from a background independent model with no quantum mechanics, quantum theory arises in the same limit in which spatial properties appear. Starting with an arbitrary abstract graph as the microscopic model of spacetime, ... More

Extremal variety as the foundation of a cosmological quantum theoryMar 17 1992Dynamical systems of a new kind are described, which are motivated by the problem of constructing diffeomorphism invariant quantum theories. These are based on the extremization of a non-local and non-additive quantity that we call the variety of a system. ... More

Discreteness of area and volume in quantum gravityNov 02 1994We study the operator that corresponds to the measurement of volume, in non-perturbative quantum gravity, and we compute its spectrum. The operator is constructed in the loop representation, via a regularization procedure; it is finite, background independent, ... More

A note on the Plebanski action with cosmological constant and an Immirzi parameterAug 24 2009Jan 11 2010We study the field equations of the Plebanski action for general relativity when both the cosmological constant and an Immirzi parameter are present. We show that the Lagrange multiplier, which usually gets identified with the Weyl curvature, now acquires ... More

Fermion Doubling in Loop Quantum GravityJul 05 2015In this paper, we show that the Hamiltonian approach to loop quantum gravity has a fermion doubling problem. To obtain this result, we couple loop quantum gravity to a free massless scalar and a chiral fermion field, gauge fixing the many fingered time ... More

A Universe that does not know the timeJul 04 2018Sep 17 2018In this paper we propose that cosmological time is a quantum observable that does not commute with other quantum operators essential for the definition of cosmological states, notably the cosmological constant. This is inspired by properties of a measure ... More

Nonperturbative dynamics for abstract (p,q) string networksDec 16 1997Jan 06 1998We describe abstract (p,q) string networks which are the string networks of Sen without the information about their embedding in a background spacetime. The non-perturbative dynamical formulation invented for spin networks, in terms of causal evolution ... More

Quantum geometry with intrinsic local causalityDec 16 1997The space of states and operators for a large class of background independent theories of quantum spacetime dynamics is defined. The SU(2) spin networks of quantum general relativity are replaced by labelled compact two-dimensional surfaces. The space ... More

Causal evolution of spin networksFeb 13 1997A new approach to quantum gravity is described which joins the loop representation formulation of the canonical theory to the causal set formulation of the path integral. The theory assigns quantum amplitudes to special classes of causal sets, which consist ... More

Phenomenological Quantum GravityNov 14 2009If the history of science has taught us anything, it's that persistence and creativity makes the once impossible possible. It has long been thought experimental tests of quantum gravity are impossible. But during the last decade, several different approaches ... More

Spin foam models as energetic causal setsJun 30 2014Jul 28 2014Energetic causal sets are causal sets endowed by a flow of energy-momentum between causally related events. These incorporate a novel mechanism for the emergence of space-time from causal relations. Here we construct a spin foam model which is also an ... More

Quantum deformation of quantum gravityDec 09 1995We describe a deformation of the observable algebra of quantum gravity in which the loop algebra is extended to framed loops. This allows an alternative nonperturbative quantization which is suitable for describing a phase of quantum gravity characterized ... More

Eleven dimensional supergravity as a constrained topological field theoryMar 30 2000Sep 03 2000We describe a new first-order formulation of D=11 supergravity which shows that that theory can be understood to arise from a certain topological field theory by the imposition of a set of local constraints on the fields, plus a lagrange multiplier term. ... More

Lorentz invariance with an invariant energy scaleDec 11 2001Dec 18 2001We propose a modification of special relativity in which a physical energy, which may be the Planck energy, joins the speed of light as an invariant, in spite of a complete relativity of inertial frames and agreement with Einstein's theory at low energies. ... More

String theories with deformed energy momentum relations, and a possible non-tachyonic bosonic stringJan 13 2004Jan 18 2004We consider a prescription for introducing deformed dispersion relations in the bosonic string action. We find that in a subset of such theories it remains true that the embedding coordinates propagate linearly on the worldsheet. While both the string ... More

Disordered locality in loop quantum gravity statesFeb 07 2007Apr 21 2007We show that loop quantum gravity suffers from a potential problem with non-locality, coming from a mismatch between micro-locality, as defined by the combinatorial structures of their microscopic states, and macro-locality, defined by the metric which ... More

Holography in a quantum spacetimeOct 18 1999We propose a formulation of the holographic principle, suitable for a background independent quantum theory of cosmology. It is stated as a relationship between the flow of quantum information and the causal structure of a quantum spacetime. Screens are ... More

Gamma ray burst delay times probe the geometry of momentum spaceMar 29 2011We study the application of the recently proposed framework of relative locality to the problem of energy dependent delays of arrival times of photons that are produced simultaneously in distant events such as gamma ray bursts. Within this framework, ... More

General relativity with a topological phase: an action principleNov 18 2003An action principle is described which unifies general relativity and topological field theory. An additional degree of freedom is introduced and depending on the value it takes the theory has solutions that reduce it to 1) general relativity in Palatini ... More

Enhanced color gauge invariance and a new di-photon state at the LHCJan 12 2016Mar 17 2016We propose to interpret the possible resonance seen in di-photons at the LHC at 750 Gev as a bound state of a new pair of heavy gluons associated with an enhanced color gauge invariance. These have a conservation law which enforces their production and ... More

Mixmaster quantum cosmology in terms of physical dynamicsJul 07 1996An approach to quantum cosmology, relying on strengths of both canonical and path integral formalisms, is applied to the cosmological model, Bianchi type IX. Physical quantum states are constructed on the maximal slice of the cosmological history. A path ... More

Holographic Formulation of Quantum SupergravitySep 03 2000We show that ${\cal N}=1$ supergravity with a cosmological constant can be expressed as constrained topological field theory based on the supergroup $Osp(1|4)$. The theory is then extended to include timelike boundaries with finite spatial area. Consistent ... More

Generalized Lorentz invariance with an invariant energy scaleJul 22 2002The hypothesis that the Lorentz transformations may be modified at Planck scale energies is further explored. We present a general formalism for theories which preserve the relativity of inertial frames with a non-linear action of the Lorentz transformations ... More

The Maldacena Conjecture and Rehren DualityJun 08 2001We analyse the implications of the fact that there are two claims for a dual to \N=4 superconformal SU(N) Yang-Mills theory (SCYM), the Maldacena conjecture and the theorem of Rehren. While the Maldacena dual is conjectured to be a non-perturbative string ... More

The Chern-Simons Invariant as the Natural Time Variable for Classical and Quantum CosmologyMay 06 1994Oct 30 1994We propose that the Chern-Simons invariant of the Ashtekar-Sen connection is the natural internal time coordinate for classical and quantum cosmology. The reasons for this are a number of interesting properties of this functional, which we describe here. ... More

The physical hamiltonian in nonperturbative quantum gravityAug 05 1993A quantum hamiltonian which evolves the gravitational field according to time as measured by constant surfaces of a scalar field is defined through a regularization procedure based on the loop representation, and is shown to be finite and diffeomorphism ... More