Loop-and-allied QG bibliography

[marcus]

http://arxiv.org/abs/1004.2504
Primordial Gravitational Waves and Cosmology
Lawrence Krauss (1), Scott Dodelson (2,3) Stephan Meyer (3), ((1) Arizona State University, (2)Fermi National Laboratory, (3) University of Chicago)
12 pages. 4 figures
(Submitted on 14 Apr 2010)
"The observation of primordial gravitational waves could provide a new and unique window on the earliest moments in the history of the universe, and on possible new physics at energies many orders of magnitude beyond those accessible at particle accelerators. Such waves might be detectable soon in current or planned satellite experiments that will probe for characteristic imprints in the polarization of the cosmic microwave background (CMB), or later with direct space-based interferometers. A positive detection could provide definitive evidence for Inflation in the early universe, and would constrain new physics from the Grand Unification scale to the Planck scale."

http://arxiv.org/abs/1004.2586
Emergent Horizons in the Laboratory
Ralf Schützhold
7 pages, 4 figures
(Submitted on 15 Apr 2010)
"The concept of a horizon known from general relativity describes the loss of causal connection and can be applied to non-gravitational scenarios such as out-of-equilibrium condensed-matter systems in the laboratory. This analogy facilitates the identification and theoretical study (e.g., regarding the trans-Planckian problem) and possibly the experimental verification of 'exotic' effects known from gravity and cosmology, such as Hawking radiation. Furthermore, it yields a unified description and better understanding of non-equilibrium phenomena in condensed matter systems and their universal features. By means of several examples including general fluid flows, expanding Bose-Einstein condensates, and dynamical quantum phase transitions, the concepts of event, particle, and apparent horizons will be discussed together with the resulting quantum effects."

http://pirsa.org/10040067/
Neil Turok video lecture on Cosmology Basics

 

[MTd2]

http://arxiv.org/abs/1004.2552

Massive graviton propagation of the deformed Hořava-Lifgarbagez gravity without projectability condition

Yun Soo Myung
(Submitted on 15 Apr 2010)
We study graviton propagations of scalar, vector, and tensor modes in the deformed Ho\v{r}ava-Lifgarbagez gravity ($\lambda R$-model) without projectability condition. The quadratic Lagrangian is invariant under diffeomorphism only for $\lambda=1$ case, which contradicts to the fact that $\lambda$ is irrelevant to a consistent Hamiltonian approach to the $\lambda R$ model. In this case, as far as scalar propagations are concerned, there is no essential difference between deformed Ho\v{r}ava-Lifgarbagez gravity ($\lambda R$-model) and general relativity. This implies that there are two degrees of freedom for a massless graviton without Ho\v{r}ava scalar, and five degrees of freedom appear for a massive graviton when introducing Lorentz-violating and Fierz-Pauli mass terms. Finally, it is shown that for $\lambda=1$, the vDVZ discontinuity is absent in the massless limit of Lorentz-violating mass terms by considering external source terms.

http://arxiv.org/abs/1004.2632

Gravity and a Geometrization of Turbulence

Christopher Eling, Itzhak Fouxon, Yaron Oz
(Submitted on 15 Apr 2010)
The dynamics of fluids is a long standing challenge that remained as an unsolved problem for centuries. Understanding its main features, chaos and turbulence, is likely to provide an understanding of the principles and non-linear dynamics of a large class of systems far from equilibrium. We consider a conceptually new viewpoint to study these features using black hole dynamics. Since the gravitational field is characterized by a curved geometry, the gravity variables provide a geometrical framework for studying the dynamics of fluids: A geometrization of turbulence.

http://arxiv.org/abs/1004.2260

The new vertices and canonical quantization

Sergei Alexandrov
(Submitted on 13 Apr 2010)
We present two results on the recently proposed new spin foam models. First, we show how a (slightly modified) restriction on representations in the EPRL model leads to the appearance of the Ashtekar-Barbero connection, thus bringing this model even closer to LQG. As our second result, we however demonstrate that the quantization leading to the new models is completely inconsistent since it relies on the symplectic structure of the unconstraint BF theory.

 

[MTd2]

http://motls.blogspot.com/2010/04/d...sReferenceFrame+(Lubos+Motl's+reference+frame)

Dark energy, the holographic principle, and IPMUBy Paul Frampton, Professor of Physics and Astronomy at Chapel Hill, NC

It is a high honor to be invited, by Lubos, to write about dark energy. I first met Lubos, when he was an assistant professor, at Harvard University, and found him extremely intelligent and charming in person, quite different from the aggressively strident blogger. I confess to joking that Lubos is afflicted by "blog-rage", when he sits at his keyboard, by analogy with the road-rage suffered by drivers in California when they shoot dead the other driver, after a minor fender-bender.

 

[MTd2]

http://arxiv.org/abs/1004.2879

Quantizing Geometry or Geometrizing the Quantum?

Bejamin Koch
(Submitted on 16 Apr 2010)
The unsatisfactory status of the search for a consistent and predictive quantization of gravity is taken as motivation to study the question whether geometrical laws could be more fundamental than quantization procedures. In such an approach the quantum mechanical laws should emerge from the geometrical theory. A toy model that incorporates the idea is presented and its necessary formulation in configuration space is emphasized.

 

[marcus]

http://arxiv.org/abs/1004.2834
Abelian Chern-Simons theory, Stokes' Theorem, and generalized connections
Hanno Sahlmann, Thomas Thiemann
13 pages, 4 figures
(Submitted on 16 Apr 2010)
"Generalized connections and their calculus have been developed in the context of quantum gravity. Here we apply them to abelian Chern-Simons theory. We derive the expectation values of holonomies in U(1) Chern-Simons theory using Stokes' Theorem, flux operators and generalized connections. A framing of the holonomy loops arises in our construction, and we show how, by choosing natural framings, the resulting expectation values nevertheless define a functional over gauge invariant cylindrical functions.
The abelian theory considered in the present article is test case for our method. It can also be applied to the non-abelian theory. Results for that case will be reported elsewhere."

brief mention:
http://arxiv.org/abs/1004.2794
Revisiting the Entropic corrections to Newton's law
M. R. Setare, D. Momeni
6 pages
(Submitted on 16 Apr 2010)
"In this short letter we calculate separately the GUP and self gravitational corrections to the Newton's gravitational formula. We show that for a complete description of the GUP and self-gravity effects both temperature and the entropy must be modified."

http://arxiv.org/abs/1004.2901
Reviving Gravity's Aether in Einstein's Universe
Niayesh Afshordi (Perimeter Institute/ University of Waterloo)
4 pages, 1 figure, to appear in Physics in Canada
(Submitted on 16 Apr 2010)
"Einstein's theory of general relativity describes gravity as the interaction of particles with space-time geometry, as opposed to interacting with a physical fluid, as in the old gravitational aether theories. Moreover, any theoretical physicist would tell you that, despite its counter-intuitive structure, general relativity is one of the simplest, most beautiful, and successful theories in physics, that has withstood a diverse battery of precision tests over the past century. So, is there any motivation to relax its fundamental principle, and re-introduce a gravitational aether? Here, I give a short and non-technical account of why quantum gravity and cosmological constant problems provide this motivation."

 

[marcus]

http://arxiv.org/abs/1004.2952
Lectures on LQG/LQC
Ghanashyam Date
72 pages
(Submitted on 17 Apr 2010)
"A School on Loop Quantum Gravity was held at the IMSc during Sept 8 -- 18, 2009. In the first week a basic introduction to LQG was provided while in the second week the focus was on the two main application, to cosmology (LQC) and to the black hole entropy. These notes are an expanded written account of the lectures that I gave. These are primarily meant for beginning researchers."

 

[MTd2]

http://arxiv.org/abs/1004.2954

Influence on the entropic force by the virtual degree of freedom on the holographic screen

Qiyuan Pan, Bin Wang
(Submitted on 17 Apr 2010)
We generalize the study of entropic force to a general static spherical spacetime and examine the acceleration, temperature, equation of gravity and the energy associated with the holographic screen in this general background. We show that the virtual degree of freedom on the holographic screen plays a crucial role in interpreting field equations of gravity based on thermodynamical perspective.

 

[marcus]

http://arxiv.org/abs/1004.3450
Non-commutative flux representation for loop quantum gravity
Aristide Baratin, Bianca Dittrich, Daniele Oriti, Johannes Tambornino
21 pages, 1 figure
(Submitted on 20 Apr 2010)
"The Hilbert space of loop quantum gravity is usually described in terms of cylindrical functionals of the gauge connection, the electric fluxes acting as non-commuting derivation operators. Here we introduce a dual description of this space, by means of a Fourier transform mapping the usual loop gravity states to non-commutative functions on Lie algebras. We show that the Fourier transform defines a unitary equivalence of representations for loop quantum gravity. In the dual representation, flux operators act by star-multiplication and holonomy operators act by translation. We describe the gauge invariant dual states and discuss their geometrical meaning. Finally, we apply the construction to the simpler case of a U(1) gauge group and compare the resulting flux representation with the triad representation used in loop quantum cosmology."

 

[John86]

http://arxiv.org/abs/1004.3564

Topos Methods in the Foundations of Physics
Authors: Chris J. Isham
(Submitted on 20 Apr 2010)

Abstract: This article gives a conceptual introduction to the topos approach to the formulation of physical theories.

Comments: 24 pages; to appear in "Deep Beauty", ed. Hans Halvorson, Cambridge University Press (2010)
Subjects: Quantum Physics (quant-ph); General Relativity and Quantum Cosmology (gr-qc); Mathematical Physics (math-ph)
Cite as: arXiv:1004.3564v1 [quant-ph]

http://arxiv.org/abs/1004.3573

The physical interpretation of daseinisation
Authors: Andreas Doering
(Submitted on 20 Apr 2010)

Abstract: We provide a conceptual discussion and physical interpretation of some of the quite abstract constructions in the topos approach to physics. In particular, the daseinisation process for projection operators and for self-adjoint operators is motivated and explained from a physical point of view. Daseinisation provides the bridge between the standard Hilbert space formalism of quantum theory and the new topos-based approach to quantum theory. As an illustration, we will show all constructions explicitly for a three-dimensional Hilbert space and the spin-z operator of a spin-1 particle. This article is a companion to the article by Isham in the same volume.

http://arxiv.org/abs/1004.3561

Topos Quantum Logic and Mixed States
Authors: Andreas Doering
(Submitted on 20 Apr 2010)

Abstract: The topos approach to the formulation of physical theories includes a new form of quantum logic. We present this topos quantum logic, including some new results, and compare it to standard quantum logic, all with an eye to conceptual issues. In particular, we show that topos quantum logic is distributive, multi-valued, contextual and intuitionistic. It incorporates superposition without being based on linear structures, has a built-in form of coarse-graining which automatically avoids interpretational problems usually associated with the conjunction of propositions about incompatible physical quantities, and provides a material implication that is lacking from standard quantum logic. Importantly, topos quantum logic comes with a clear geometrical underpinning. The representation of pure states and truth-value assignments are discussed. It is briefly shown how mixed states fit into this approach.

 

[marcus]

http://arxiv.org/abs/1004.3979
The high-density regime of kinetic-dominated loop quantum cosmology
Martin Bojowald, David Mulryne, William Nelson, Reza Tavakol
26 pages, 7 figures
(Submitted on 22 Apr 2010)
"We study the dynamics of states perturbatively expanded about a harmonic system of loop quantum cosmology, exhibiting a bounce. In particular, the evolution equations for the first and second order moments of the system are analyzed. These moments back-react on the trajectories of the expectation values of the state and hence alter the energy density at the bounce. This analysis is performed for isotropic loop quantum cosmology coupled to a scalar field with a small but non-zero constant potential, hence in a regime in which the kinetic energy of matter dominates. Analytic restrictions on the existence of dynamical coherent states and the meaning of semi-classicality within these systems are discussed. A numerical investigation of the trajectories of states that remain semi-classical across the bounce demonstrates that, at least for such states, the bounce persists and that its properties are similar to the standard case, in which the moments of the states are entirely neglected. However the bounce density does change, implying that a quantum bounce may not be guaranteed to happen when the potential is no longer negligible."

 

[MTd2]

http://arxiv.org/abs/1004.4550

Spinfoams in the holomorphic representation

Eugenio Bianchi, Elena Magliaro, Claudio Perini
(Submitted on 26 Apr 2010)
We study a holomorphic representation for spinfoams. The representation is obtained via the Ashtekar-Lewandowski-Marolf-Mour\~ao-Thiemann coherent state transform. We derive the expression of the 4d spinfoam vertex for Euclidean and for Lorentzian gravity in the holomorphic representation. The advantage of this representation rests on the fact that the variables used have a clear interpretation in terms of a classical intrinsic and extrinsic geometry of space. We show how the peakedness on the extrinsic geometry selects a single exponential of the Regge action in the semiclassical large-scale asymptotics of the spinfoam vertex.

 

[marcus]

http://arxiv.org/abs/1004.4866
Unification of gravity, gauge fields, and Higgs bosons
A. Garrett Lisi, Lee Smolin, Simone Speziale
12 pages
(Submitted on 27 Apr 2010)
"We consider a diffeomorphism invariant theory of a gauge field valued in a Lie algebra that breaks spontaneously to the direct sum of the spacetime Lorentz algebra, a Yang-Mills algebra, and their complement. Beginning with a fully gauge invariant action -- an extension of the Plebanski action for general relativity -- we recover the action for gravity, Yang-Mills, and Higgs fields. The low-energy coupling constants, obtained after symmetry breaking, are all functions of the single parameter present in the initial action and the vacuum expectation value of the Higgs."

http://arxiv.org/abs/1004.4681
Entropy in Spin Foam Models: The Statistical Calculation
J.Manuel Garcia-Islas
11 pages, 1 figure
(Submitted on 26 Apr 2010)
"Recently an idea for computing the entropy of black holes in the spin foam formalism has been introduced. Particularly complete calculations for the three dimensional euclidean BTZ black hole were done. The whole calculation is based on observables living at the horizon of the black hole universe. Departing from this idea of observables living at the horizon, we now go further and compute the entropy of BTZ black hole in the spirit of statistical mechanics. We compare both calculations and show that they are very interrelated and equally valid. This latter behaviour is certainly due to the importance of the observables."

 

[marcus]

http://arxiv.org/abs/1004.5196
Bubble divergences from cellular homology
Valentin Bonzom (CPT), Matteo Smerlak (CPT)
5 pages
(Submitted on 29 Apr 2010)
"We consider a class of lattice topological field theories, among which are the weak-coupling limit of 2d Yang-Mills theory, the Ponzano-Regge model of 3d quantum gravity and discrete BF theory, whose dynamical variables are flat discrete connections with compact structure group on a cell 2-complex. In these models, it is known that the path integral measure is ill-defined in general, because of a phenomenon called `bubble divergences'. A common expectation is that the degree of these divergences is given by the number of `bubbles' of the 2-complex. In this note, we show that this expectation, although not realistic in general, is met in some special cases: when the 2-complex is simply connected, or when the structure group is Abelian -- in both cases, the divergence degree is given by the second Betti number of the 2-complex."


http://arxiv.org/abs/1004.5371
Classical general relativity as BF-Plebanski theory with linear constraints
Steffen Gielen, Daniele Oriti
15 pages, revtex, to be submitted to Class. Quant. Grav.
(Submitted on 29 Apr 2010)
"We investigate a formulation of continuum 4d gravity in terms of a constrained BF theory, in the spirit of the Plebanski formulation, but involving only linear constraints, of the type used recently in the spin foam approach to quantum gravity. We identify both the continuum version of the linear simplicity constraints used in the quantum discrete context and a linear version of the quadratic volume constraints that are necessary to complete the reduction from the topological theory to gravity. We illustrate and discuss also the discrete counterpart of the same continuum linear constraints. Moreover, we show under which additional conditions the discrete volume constraints follow from the simplicity constraints, thus playing the role of secondary constraints."

 

[MTd2]

http://arxiv.org/abs/1004.4016

On Dark Matter, Spiral Galaxies, and the Axioms of General Relativity

Hubert L. Bray
(Submitted on 22 Apr 2010)
Beginning with a geometric motivation for dark matter going back to the axioms of general relativity, we show how scalar field dark matter, which naturally forms dark matter density waves due to its wave nature, may cause the observed barred spiral pattern density waves in many disk galaxies and triaxial shapes with plausible brightness profiles in many elliptical galaxies. If correct, this would provide a unified explanation for spirals and bars in spiral galaxies and for the brightness profiles of elliptical galaxies. We compare the results of preliminary computer simulations with photos of actual galaxies.

******

There are things that might prove fundamental to quantum gravity here.

 

[marcus]

http://arxiv.org/abs/1005.0535
Comments on Nonlocality in Deformed Special Relativity, in reply to arXiv:1004.0664 by Lee Smolin and arXiv:1004.0575 by Jacob et al
Sabine Hossenfelder
(Submitted on 4 May 2010)
"It was previously shown that models with deformations of special relativity that have an energy-dependent yet observer-independent speed of light suffer from nonlocal effects that are in conflict with observation to very high precision. In a recent paper it has been proposed that these paradoxa arise only in the classical limit and can be prevented by an ad-hoc introduction of a quantum uncertainty that would serve to hide the nonlocality. We will show here that the proposed ansatz for this resolution is inconsistent with observer-independence and, when corrected, is in agreement with the earlier argument that revealed the troublesome nonlocality. We further offer an alternative derivation for the energy-dependent speed of light in the model used."

 

[MTd2]

http://arxiv.org/abs/1005.0475

The universal viscosity to entropy density ratio from entanglement

Goffredo Chirco, Christopher Eling, Stefano Liberati
(Submitted on 4 May 2010)
We present evidence that the universal Kovtun-Son-Starinets shear viscosity to entropy density ratio of 1/4\pi can be associated with a Rindler causal horizon in flat spacetime. Since there is no known holographic (gauge/gravity) duality for this spacetime, a natural microscopic explanation for this viscosity is in the peculiar properties of quantum entanglement. In particular, it is well-known that the Minkowski vacuum state is a thermal state and carries an area entanglement entropy density in the Rindler spacetime. Based on the fluctuation-dissipation theorem, we expect a similar notion of viscosity arising from vacuum fluctuations. Therefore, we propose a holographic Kubo formula in terms of a two-point function of the stress tensor of matter fields in the bulk. We calculate this viscosity assuming a minimally coupled scalar field theory and find that the ratio with respect to the entanglement entropy density is exactly 1/4\pi in four dimensions. The issues that arise in extending this result to non-minimally coupled scalar fields, higher spins, and higher dimensions provide interesting hints about the relationship between entanglement entropy and black hole entropy.

 

[MTd2]

http://arxiv.org/abs/1005.0619

Holography in Action

Sanved Kolekar, T. Padmanabhan
(Submitted on 4 May 2010)
Einstein-Hilbert action and its natural generalizations to higher dimensions (like the Lanczos-Lovelock action) have certain peculiar features. All of them can be separated into a bulk and a surface term, with a specific ("holographic") relationship between the two, so that either term can be used to extract information about the other. Further, the surface term leads to entropy of the horizons on-shell. It has been argued in the past that these features are impossible to understand in the conventional approach but find a natural explanation if we consider gravity as an emergent phenomenon. We provide further support for this point of view in this paper. We describe an alternative decomposition of the Einstein-Hilbert action and Lanczos-Lovelock action into a new pair of surface and bulk terms, such that the surface term becomes Wald entropy on a horizon and the bulk term is the energy density (which is the ADM Hamiltonian density for Einstein gravity). We show that this new pair also obeys a holographic relationship and give a thermodynamic interpretation to this relation in this context. Since the bulk and surface terms, in this decomposition, are related to energy and entropy, the holographic condition can be thought of as analogous to inverting the expression for entropy given as a function of energy S = S(E,V) to obtain the energy E = E(S,V) in terms of the entropy in a normal thermodynamic system. Thus the holographic nature of the action allows us to relate the descriptions of the same system in terms of two different thermodynamic potentials. Some further possible generalizations and implications are discussed.

http://arxiv.org/abs/1005.0764

Face amplitude of spinfoam quantum gravity

Eugenio Bianchi, Daniele Regoli, Carlo Rovelli
(Submitted on 5 May 2010)
The structure of the boundary Hilbert-space and the condition that amplitudes behave appropriately under compositions determine the face amplitude of a spinfoam theory. In quantum gravity the face amplitude turns out to be simpler than originally thought.

 

[marcus]

http://arxiv.org/abs/1005.0814
Observational hints on the Big Bounce
Jakub Mielczarek, Michal Kamionka, Aleksandra Kurek, Marek Szydlowski
25 pages, 8 figures
(Submitted on 5 May 2010)
"In this paper we study possible observational consequences of the bouncing cosmology. We consider a model where a phase of inflation is preceded by a cosmic bounce. While we consider in this paper only that the bounce is due to loop quantum gravity, most of the results presented here can be applied for different bouncing cosmologies. We concentrate on the scenario where the scalar field, as the result of contraction of the universe, is driven from the bottom of the potential well. The field is amplified, and finally the phase of the standard slow-roll inflation is realized. Such an evolution modifies the standard inflationary spectrum of perturbations by the additional oscillations and damping on the large scales. We extract the parameters of the model from the observations of the cosmic microwave background radiation. In particular, the value of inflaton mass is equal to $$m=(2.6 \pm 0.6) \cdot 10^{13}$$ GeV. In our considerations we base on the seven years of observations made by the WMAP satellite. We propose the new observational consistency check for the phase of slow-roll inflation. We investigate the conditions which have to be fulfilled to make the observations of the Big Bounce effects possible. We translate them to the requirements on the parameters of the model and then put the observational constraints on the model. Based on assumption usually made in loop quantum cosmology, the Barbero-Immirzi parameter was shown to be constrained by $$\gamma<1100$$ from the cosmological observations. We have compared the Big Bounce model with the standard Big Bang scenario and showed that the present observational data is not informative enough to distinguish these models."

http://arxiv.org/abs/1005.0817
A regularization of the hamiltonian constraint compatible with the spinfoam dynamics
Emanuele Alesci, Carlo Rovelli
24 pages
(Submitted on 5 May 2010)
"We introduce a new regularization for Thiemann's Hamiltonian constraint. The resulting constraint can generate the 1-4 Pachner moves and is therefore more compatible with the dynamics defined by the spinfoam formalism. We calculate its matrix elements and observe the appearence of the 15j Wigner symbol in these."

 

[John86]

http://arxiv.org/abs/1005.0790

CMB acoustic scale in the entropic accelerating universe
Authors: Roberto Casadio, Alessandro Gruppuso
(Submitted on 5 May 2010)
Abstract: We show that the entropic accelerating universe recently proposed by Easson et al [4,5] is equivalent to a model with a dark energy component with constant parameter of state w_X = -1 + 2gamma/3, where gamma is related to the coefficients of the new terms in the Friedman equations. After discussing all the Friedman equations for an arbitrary gamma, we show how to recover the standard scalings for dust and radiation. The acoustic scale l_A, related to the peak positions in the pattern of the angular power spectrum of the Cosmic Microwave Background anisotropies, is also computed and yields the stringent bound gamma<<1, which implies that the correction proportional to dH/dt must be negligible with respect to that proportional to H^2. We then argue that future data might be able to distinguish this model from pure LambdaCDM (corresponding to gamma=0).

http://arxiv.org/abs/1005.0499

Schwarzschild Geometry Emerging from Matrix Models
Authors: Daniel N. Blaschke, Harold Steinacker
(Submitted on 4 May 2010)
Abstract: We demonstrate how various geometries can emerge from Yang-Mills type matrix models with branes, and consider the examples of Schwarzschild and Reissner-Nordstroem geometry. We provide an explicit embedding of these branes in R^{2,5} and R^{4,6}, as well as an appropriate Poisson resp. symplectic structure which determines the non-commutativity of space-time. The embedding is asymptotically flat with asymptotically constant \theta^{\mu\nu} for large r, and therefore suitable for a generalization to many-body configurations. This is an illustration of our previous work arXiv:1003.4132, where we have shown how the Einstein-Hilbert action can be realized within such matrix models.

http://arxiv.org/abs/0911.3397

Surprising phenomena in a rich new class of inflationary models
Authors: Pascal M. Vaudrevange, Dmitry I. Podolsky, Glenn D. Starkman
(Submitted on 18 Nov 2009 (v1), last revised 29 Apr 2010 (this version, v2))
Abstract: We report on a new class of fast-roll inflationary models. In a huge part of its parameter space, inflationary perturbations exhibit quite unusual phenomena such as scalar and tensor modes freezing out at widely different times, as well as scalar modes reentering the horizon during inflation. In another, narrower range of parameters, this class of models agrees with observations. One specific point in parameter space is characterized by extraordinary behavior of the scalar perturbations. Freeze-out of scalar perturbations as well as particle production at horizon crossing are absent. Also the behavior of the perturbations around this quasi-de Sitter background is dual to a quantum field theory in flat space-time. Finally, the form of the primordial power spectrum is determined by the interaction between different modes of scalar perturbations.

 

[ensabah6]

arXiv:1005.0380
http://arxiv.org/abs/1005.0838
First Dark Matter Results from the XENON100 Experimen
Authors: E. Aprile, K. Arisaka, F. Arneodo, A. Askin, L. Baudis, A. Behrens, E. Brown, J. M. R. Cardoso, B. Choi, D. B. Cline, S. Fattori, A. D. Ferella, K.-L. Giboni, K. Hugenberg, A. Kish, C. W. Lam, J. Lamblin, R. F. Lang, K. E. Lim, J. A. M. Lopes, T. Marrodán Undagoitia, Y. Mei, A. J. Melgarejo Fernandez, K. Ni, U. Oberlack, S. E. A. Orrigo, E. Pantic, G. Plante, A. C. C. Ribeiro, R. Santorelli, J. M. F. dos Santos, M. Schumann, P. Shagin, A. Teymourian, D. Thers, E. Tziaferi, H. Wang, C. Weinheimer (XENON100 Collaboration)
(Submitted on 3 May 2010)

Abstract: The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso in Italy, is designed to search for dark matter WIMPs scattering off 62 kg of liquid xenon in an ultra-low background dual-phase time projection chamber. In this letter, we present first dark matter results from the analysis of 11.17 live days of non-blind data, acquired in October and November 2009. In the selected fiducial target of 40 kg, and within the pre-defined signal region, we observe no events and hence exclude spin-independent WIMP-nucleon elastic scattering cross-sections above 3 x 10^-44 cm^2 for 50 GeV/c^2 WIMPs at 90% confidence level. Below 20 GeV/c^2, this result challenges the interpretation of the CoGeNT or DAMA signals as being due to spin-independent, elastic, light mass WIMP interactions.

 

[marcus]

http://arxiv.org/abs/1005.1057
Spin Foams and Noncommutative Geometry
Domenic Denicola (Caltech), Matilde Marcolli (Caltech), Ahmad Zainy al-Yasry (ICTP)
48 pages, 30 figures
(Submitted on 6 May 2010)
"We extend the formalism of embedded spin networks and spin foams to include topological data that encode the underlying three-manifold or four-manifold as a branched cover. These data are expressed as monodromies, in a way similar to the encoding of the gravitational field via holonomies. We then describe convolution algebras of spin networks and spin foams, based on the different ways in which the same topology can be realized as a branched covering via covering moves, and on possible composition operations on spin foams. We illustrate the case of the groupoid algebra of the equivalence relation determined by covering moves and a 2-semigroupoid algebra arising from a 2-category of spin foams with composition operations corresponding to a fibered product of the branched coverings and the gluing of cobordisms. The spin foam amplitudes then give rise to dynamical flows on these algebras, and the existence of low temperature equilibrium states of Gibbs form is related to questions on the existence of topological invariants of embedded graphs and embedded two-complexes with given properties. We end by sketching a possible approach to combining the spin network and spin foam formalism with matter within the framework of spectral triples in noncommutative geometry."

http://pirsa.org/10050002/
Deformations of General Relativity
Kirill Krasnov
2010-05-05
"I will describe a very special (infinite-parameter) family of gravity
theories that all describe, exactly like General Relativity, just two
propagating degrees of freedom. The theories are obtained by generalizing
Plebanski's self-dual (chiral) formulation of GR. I will argue that this
class of gravity theories provides a potentially powerful new framework for
testing the asymptotic safety conjecture in quantum gravity."

 

[John86]

http://arxiv.org/abs/1003.5179

Gauge fields in graphene
Authors: M. A. H. Vozmediano, M. I. Katsnelson, F. Guinea
(Submitted on 26 Mar 2010)
Abstract: The physics of graphene is acting as a bridge between quantum field theory and condensed matter physics due to the special quality of the graphene quasiparticles behaving as massless two dimensional Dirac fermions. Moreover, the particular structure of the 2D crystal lattice sets the arena to study and unify concepts from elasticity, topology and cosmology. In this paper we analyze these connections combining a pedagogical, intuitive approach with a more rigorous formalism when required.

 

[MTd2]

http://arxiv.org/abs/1005.1132

Tolman mass, generalized surface gravity, and entropy bounds

Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 7 May 2010)
In any static spacetime the quasi-local Tolman mass contained within a volume can be reduced to a Gauss-like surface integral involving the flux of a suitably defined generalized surface gravity. By introducing some basic thermodynamics and invoking the Unruh effect one can then develop elementary bounds on the quasi-local entropy that are very similar in spirit to the holographic bound, and closely related to entanglement entropy.

http://arxiv.org/abs/1005.1169

Debye entropic force and modified Newtonian dynamics

Xin Li, Zhe Chang
(Submitted on 7 May 2010)
Verlinde has suggested that the gravity has an entropic origin, and a gravitational system could be regarded as a thermodynamical system. It is well-known that the equipartition law of energy is invalid at very low temperature. Therefore, entropic force should be modified while the temperature of the holographic screen is very low. It is shown that the modified entropic force is proportional to the square of the acceleration, while the temperature of the holographic screen is much lower than the Debye temperature $T_D$. The modified entropic force returns to the Newton's law of gravitation while the temperature of the holographic screen is much higher than the Debye temperature. The modified entropic force is connected with modified Newtonian dynamics (MOND). The constant $a_0$ involved in MOND is linear in the Debye frequency $\omega_D$, which can be regarded as the largest frequency of the bits in screen. We find that there do have a strong connection between MOND and cosmology in the framework of Verlinde's entropic force, if the holographic screen is taken to be bound of the Universe. The Debye frequency is linear in the Hubble constant $H_0$.http://arxiv.org/abs/1005.1174

Notes on "quantum gravity" and non-commutative geometry

Jose M. Gracia-Bondia
(Submitted on 7 May 2010)
I hesitated for a long time before giving shape to these notes, originally intended for preliminary reading by the attendees to the Summer School "New paths towards quantum gravity" (Holbaek Bay, Denmark, May 2008). At the end, I decide against just selling my mathematical wares, and for a survey, necessarily very selective, but taking a global phenomenological approach to its subject matter. After all, non-commutative geometry does not purport yet to solve the riddle of quantum gravity; it is more of an insurance policy against the probable failure of the other approaches. The plan is as follows: the introduction invites students to the fruitful doubts and conundrums besetting the application of even classical gravity. Next, the first experiments detecting quantum gravitational states inoculate us a healthy dose of skepticism on some of the current ideologies. In Section 3 we look at the action for general relativity as a consequence of gauge theory for quantum tensor fields. Section 4 briefly deals with the unimodular variants. Section 5 arrives at non-commutative geometry. I am convinced that, if this is to play a role in quantum gravity, commutative and non-commutative manifolds must be treated on the same footing; which justifies the place granted to the reconstruction theorem. Together with Section 3, this part constitutes the main body of the notes. Only very summarily at the end of this section we point to some approaches to gravity within the non-commutative realm. The last section delivers a last dose of skepticism. My efforts will have been rewarded if someone from the young generation learns to mistrust current mindsets.

 

[marcus]

http://arxiv.org/abs/1005.1291
The Immirzi Parameter as an Instanton Angle
Simone Mercuri, Andrew Randono
24 pages
(Submitted on 7 May 2010)
"The Barbero-Immirzi parameter is a one parameter quantization ambiguity underpinning the loop approach to quantum gravity that bears tantalizing similarities to the theta parameter of gauge theories such as Yang-Mills and QCD. Despite the apparent semblance, the Barbero-Immirzi field has resisted a direct topological interpretation along the same lines as the theta-parameter. Here we offer such an interpretation. Our approach begins from the perspective of Einstein-Cartan gravity as the symmetry broken phase of a de Sitter gauge theory. From this angle, just as in ordinary gauge theories, a theta-term emerges from the requirement that the vacuum is stable against quantum mechanical tunneling. The Immirzi parameter is then identified as a combination of Newton's constant, the cosmological constant, and the theta-parameter."

http://arxiv.org/abs/1005.1294
Gravity from a fermionic condensate of a gauge theory
Andrew Randono
16 pages
(Submitted on 7 May 2010)
"The most prominent realization of gravity as a gauge theory similar to the gauge theories of the standard model comes from enlarging the gauge group from the Lorentz group to the de Sitter group. To regain ordinary Einstein-Cartan gravity the symmetry must be broken, which can be accomplished by known quasi-dynamic mechanisms. Motivated by symmetry breaking models in particle physics and condensed matter systems, we propose that the symmetry can naturally be broken by a homogenous and isotropic fermionic condensate of ordinary spinors. We demonstrate that the condensate is compatible with the Einstein-Cartan equations and can be imposed in a fully de Sitter invariant manner. This lends support, and provides a physically realistic mechanism for understanding gravity as a gauge theory with a spontaneously broken local de Sitter symmetry."

http://arxiv.org/abs/1005.1488
Non-perturbative QEG Corrections to the Yang-Mills Beta Function
J.-E. Daum, U. Harst, M. Reuter
To appear in the proceedings of CORFU 2009
(Submitted on 10 May 2010)
"We discuss the non-perturbative renormalization group evolution of the gauge coupling constant by using a truncated form of the functional flow equation for the effective average action of the Yang-Mills-gravity system. Our result is consistent with the conjecture that Quantum Einstein Gravity (QEG) is asymptotically safe and has a vanishing gauge coupling constant at the non-trivial fixed point."

 

[MTd2]

http://arxiv.org/abs/1005.1866

Large-spin asymptotics of Euclidean LQG flat-space wavefunctions

Aleksandar Mikovic, Marko Vojinovic
(Submitted on 11 May 2010)
We analyze the large-spin asymptotics of a class of spin-network wavefunctions of Euclidean Loop Quantum Gravity, which corresponds to a flat spacetime. A wavefunction from this class can be represented as a sum over the spins of an amplitude for a spin network whose graph is a composition of the the wavefunction spin network graph with the dual one-complex graph and the tetrahedron graphs for a triangulation of the spatial 3-manifold. This spin-network amplitude can be represented as a product of 6j symbols, which is then used to find the large-spin asymptotics of the wavefunction. By using the Laplace method we show that the large-spin asymptotics is given by a sum of Gaussian functions. However, these Gaussian functions are not of the type which gives the correct graviton propagator.

 

[MTd2]

http://arxiv.org/abs/1005.2130

U(N) Coherent States for Loop Quantum Gravity

Laurent Freidel, Etera R. Livine
(Submitted on 12 May 2010)
We investigate the geometry of the space of N-valent SU(2)-intertwiners. We propose a new set of holomorphic operators acting on this space and a new set of coherent states which are covariant under U(N) transformations. These states are labeled by elements of the Grassmannian Gr(N,2), they possesses a direct geometrical interpretation in terms of framed polyhedra and are shown to be related to the well-known coherent intertwiners.

 

[MTd2]

http://arxiv.org/abs/1005.2256

The spectral action and cosmic topology

Matilde Marcolli (Caltech), Elena Pierpaoli (USC), Kevin Teh (Caltech)
(Submitted on 13 May 2010)
The spectral action functional, considered as a model of gravity coupled to matter, provides, in its non-perturbative form, a slow-roll potential for inflation, whose form and corresponding slow-roll parameters can be sensitive to the underlying cosmic topology. We explicitly compute the non-perturbative spectral action for some of the main candidates for cosmic topologies, namely the quaternionic space, the Poincare' dodecahedral space, and the flat tori. We compute the corresponding slow-roll parameters and see we check that the resulting inflation model behaves in the same way as for a simply-connected spherical topology in the case of the quaternionic space and the Poincare' homology sphere, while it behaves differently in the case of the flat tori. We add an appendix with a discussion of the case of lens spaces.

 

[marcus]

http://arxiv.org/abs/1005.2294
Holographic Principle and the Surface of Last Scatter
Paul Howard Frampton
7 pages
(Submitted on 13 May 2010)
"Using data, provided by WMAP7, I calculate the entropy of the visible universe, where visible refers to electromagnetic radiation, and hence the visible universe is bounded by the Surface of Last Scatter. The dimensionless entropy, S/k, is 8.85 +/- 0.37 times larger than allowed by the holographic principle, that the entropy cannot exceed that of a black hole. The measurement of a shift parameter, introduced by Bond, Efstathiou and Tegmark in 1997, plays an important role in the accuracy of the calculation, which leads to the surprisingly large discrepancy."
Frampton earlier co-authored with Nobelist George Smoot on entropic force cosmology.

http://arxiv.org/abs/1005.2357
Entropic Dynamics, Time and Quantum Theory
Ariel Caticha
24 pages
(Submitted on 13 May 2010)
"A general framework for dynamics based on the method of maximum entropy is applied to non-relativistic quantum mechanics. The basic assumption is that in addition to the particles of interest there exist hidden variables that are subject to an uncertainty of unspecified origin. To each point in the particle configuration space there corresponds a probability distribution and an entropy for the hidden variables. These distributions constitute a curved statistical manifold. The Schroedinger equation is derived from three elements: (a) The method of maximum entropy is used to derive the probability that the particles take an infinitesimally short step. (b) The concept of entropic time is introduced in order to keep track of the accumulation of many successive short steps. A welcome feature of entropic time is that it incorporates a natural distinction between past and future. (c) The statistical manifold participates in the dynamics: the manifold guides the motion of the particles while they, in their turn, react back and affect its evolving geometry. The manifold dynamics is specified by imposing the conservation of a time-reversal invariant energy. The entropic approach to quantum theory provides a natural explanation of its linearity, its unitarity, and of its formulation in terms of complex numbers. The phase of the wave function is related to the entropy of the hidden variables. There is a quantum analogue to the gravitational equivalence principle. Finally, the model is extended to include external electromagnetic fields and the corresponding gauge symmetries."

I think Ariel is at Perimeter, in any case he recently gave a seminar talk about this, which is on video.

MTd2 spotted this paper, but the URL given in post #1181 was wrong. Here is the corrected URL:
http://arxiv.org/abs/1005.2090
U(N) Coherent States for Loop Quantum Gravity
Laurent Freidel, Etera R. Livine
23 pages
(Submitted on 12 May 2010)
"We investigate the geometry of the space of N-valent SU(2)-intertwiners. We propose a new set of holomorphic operators acting on this space and a new set of coherent states which are covariant under U(N) transformations. These states are labeled by elements of the Grassmannian Gr(N,2), they possesses a direct geometrical interpretation in terms of framed polyhedra and are shown to be related to the well-known coherent intertwiners."

http://pirsa.org/10050018/ [VIDEO]
Loop Quantum Cosmology and Spin Foams
Adam Henderson
13/05/2010
"Loop quantum gravity and spin foams are two closely related theories of quantum gravity. There is an expectation that the sum over histories or path integral formulation of LQG will take the form of a spin foam, although a rigorous connection between the two is available only in 2+1 gravity. Understanding the relation between them will resolve many open questions of both theories. We probe the connection through an exactly soluble model of loop quantum cosmology. Beginning from the canonical theory we construct a spin foam like expansion of LQC. This construction reveals a number of insights into spin foams including the nature of the continuum limit."

http://pirsa.org/10050022/
The Emergence of Gravity
Erik Verlinde
12/05/2010
"Theoretical insights originated from the study of black holes combined with developments in string theory indicate that space time and gravity are emergent. A central role in these developments is played by the holographic principle. I will present a heuristic argument that indicates that at a microscopic level gravity is an entropic force caused by changes in the available phase space due to the displacement of material bodies. Refinement of the argument makes clear that this entropic view on gravity is consistent with quantum mechanics and supported by various results in string theory. I end with some thoughts on the possible emergence of the other forces of Nature."

 

[MTd2]

http://arxiv.org/abs/1005.2294

Entropic force and its cosmological implications

Yun Soo Myung
(Submitted on 13 May 2010)
We investigate a possibility of realizing the entropic force into the cosmology. A main issue is how the holographic screen is implemented in the Newtonian cosmology. Contrary to the relativistic realization of Friedmann equations, we do not clarify the connection between Newtonian cosmology and entropic force because there is no way of implementing the holographic screen in the Newtonian cosmology

 

[MTd2]

http://arxiv.org/abs/1005.2471

Quantum cosmology for the 21st century: A debate

Martin Bojowald, Claus Kiefer, Paulo Vargas Moniz
(Submitted on 14 May 2010)
Quantum cosmology from the late sixties into the early twenty-first century is reviewed and appraised in the form of a debate, set up by two presentations on mainly the Wheeler-DeWitt quantization and on loop quantum cosmology, respectively. (Open) questions, encouragement and guiding lines shared with the audience are provided here.

http://arxiv.org/abs/1005.2518

Discretisation parameter and operator ordering in loop quantum cosmology with the cosmological constant

Tomo Tanaka, Fumitoshi Amemiya, Masahiro Shimano, Tomohiro Harada, Takashi Tamaki
(Submitted on 14 May 2010)
In loop quantum cosmology, the Hamiltonian reduces to a finite difference operator. We study the initial singularity and the large volume limit against the ambiguities in the discretisation and the operator ordering within a homogeneous, isotropic and spatially flat model with the cosmological constant. We find that the absence of the singularity strongly depends on the choice of the operator ordering and the requirement for the absence singles out a very small class of orderings. Moreover we find a general ordering rule required for the absence of the singularity. We also find that the large volume limit naturally recovers a smooth wave function in the discretisation where each step corresponds to a fixed volume increment but not in the one where each step corresponds to a fixed area increment. If loop quantum cosmology is to be a phenomenological realisation of full loop quantum gravity, these results are important to fix the theoretical ambiguities.

 

[MTd2]

http://arxiv.org/abs/1005.2739

Quantum mechanics emerges from information theory applied to causal horizons
Jae-Weon Lee
Comments: 7pages, 2 figures
Subjects: High Energy Physics - Theory (hep-th); High Energy Physics - Phenomenology (hep-ph); Quantum Physics (quant-ph)
It is suggested that quantum mechanics is not fundamental but emerges from information theory applied to a causal horizon. The path integral quantization and quantum randomness can be derived by considering information loss of fields or particles crossing Rindler horizons for accelerating observers. This implies that information is one of the fundamental root of all physical phenomena. The connection between this theory and Verlinde's entropic gravity theory is also investigated.

http://arxiv.org/abs/1005.2996

Entropic force, noncommutative gravity and un-gravity

Piero Nicolini
(Submitted on 17 May 2010)
After recalling the basic concepts of gravity as an emergent phenomenon, we analyze the recent derivation of Newton's law in terms of entropic force proposed by Verlinde. By reviewing some points of the procedure, we extend it to the case of a generic quantum gravity entropic correction to get compelling deviations to the Newton's law. More specifically, we study: 1) Noncommutative Geometry deviations; 2) Un-graviton corrections. As a special result in the noncommutative case, we find that the noncommutative character of the manifold would be equivalent to the temperature of a thermodynamic system. Therefore, in analogy to the zero temperature configuration, the description of spacetime in terms of a differential manifold could be obtained only asymptotically. Finally, we extend the Verlinde's derivation to a general case, which includes all possible effects, noncommutativity, un-gravity, electrostatic energy, extradimensions, showing that the procedure is solid versus such modifications.

http://arxiv.org/abs/1005.2927

On the geometry of loop quantum gravity on a graph

Carlo Rovelli, Simone Speziale
(Submitted on 17 May 2010)
We discuss the meaning of geometrical constructions associated to loop quantum gravity states on a graph. In particular, we discuss the "twisted geometries" and derive a simple relation between these and Regge geometries.

http://arxiv.org/abs/1005.2985

Thermal time and the Tolman-Ehrenfest effect: temperature as the "speed of time"

Carlo Rovelli, Matteo Smerlak
(Submitted on 17 May 2010)
The thermal time hypothesis has been introduced as a possible basis for a fully general-relativistic thermodynamics. Here we use the notion of thermal time to study thermal equilibrium on stationary spacetimes. Notably, we show that the Tolman-Ehrenfest effect (the variation of temperature in space so that T\sqrt{g_{00}} remains constant) can be reappraised as a manifestation of this fact: at thermal equilibrium, temperature is locally the rate of flow of thermal time with respect to proper time - pictorially, "the speed of (thermal) time". Our derivation of the Tolman-Ehrenfest effect makes no reference to the physical mechanisms underlying thermalization, thus illustrating the import of the notion of thermal time.

 

[marcus]

http://arxiv.org/abs/1005.3298
Surface terms, Asymptotics and Thermodynamics of the Holst Action
Alejandro Corichi, Edward Wilson-Ewing
16 pages
(Submitted on 18 May 2010)
"We consider a first order formalism for general relativity derived from the Holst action. This action is obtained from the standard Palatini-Hilbert form by adding a topological-like term and can be taken as the starting point for loop quantum gravity and spin foam models. The equations of motion derived from the Holst action are, nevertheless, the same as in the Palatini formulation. Here we study the form of the surface terms of the action for general boundaries as well as the symplectic current in the covariant formulation of the theory. Furthermore, we analyze the behavior of the surface terms in asymptotically flat space-times. We show that the contribution to the symplectic structure from the Holst term vanishes and one obtains the same asymptotic expressions as in the Palatini action. It then follows that the asymptotic Poincare symmetries and conserved quantities such as energy, linear momentum and relativistic angular momentum found here are equivalent to those obtained from the standard Arnowitt, Deser and Misner formalism. Finally, we consider the Euclidean approach to black hole thermodynamics and show that the on-shell Holst action, when evaluated on some static solutions containing horizons, yields the standard thermodynamical relations."

 

[John86]

http://arxiv.org/abs/1005.3293

Minimal Scales from an Extended Hilbert Space
Authors: Martin Kober, Piero Nicolini
(Submitted on 18 May 2010)
Abstract: We consider an extension of the conventional quantum Heisenberg algebra, assuming that coordinates as well as momenta fulfil nontrivial commutation relations. As a consequence, a minimal length and a minimal mass scale are implemented. Our commutators do not depend on positions and momenta and we provide an extension of the coordinate coherent state approach to Noncommutative Geometry. We explore, as toy model, the corresponding quantum field theory in a (2+1)-dimensional spacetime. Then we investigate the more realistic case of a (3+1)-dimensional spacetime, foliated into noncommutative planes. As a result, we obtain propagators, which are finite in the ultraviolet as well as the infrared regime.

 

[marcus]

http://arxiv.org/abs/1005.3310
Testing gravitational parity violation with coincident gravitational waves and short gamma-ray bursts
Nicolas Yunes, Richard O'Shaughnessy, Benjamin J. Owen, Stephon Alexander
21 pages, 2 figures, submitted to Phys. Rev. D
(Submitted on 18 May 2010)
"Gravitational parity violation is a possibility motivated by particle physics, string theory and loop quantum gravity. One effect of it is amplitude birefringence of gravitational waves, whereby left and right circularly-polarized waves propagate at the same speed but with different amplitude evolution. Here we propose a test of this effect through coincident observations of gravitational waves and short gamma-ray bursts from binary mergers involving neutron stars. Such gravitational waves are highly left or right circularly-polarized due to the geometry of the merger. Using localization information from the gamma-ray burst, ground-based gravitational wave detectors can measure the distance to the source with reasonable accuracy. An electromagnetic determination of the redshift from an afterglow or host galaxy yields an independent measure of this distance. Gravitational parity violation would manifest itself as a discrepancy between these two distance measurements. We exemplify such a test by considering one specific effective theory that leads to such gravitational parity-violation, Chern-Simons gravity. We show that the advanced LIGO-Virgo network and all-sky gamma-ray telescopes can be sensitive to the propagating sector of Chern-Simons gravitational parity violation to a level roughly two orders of magnitude better than current stationary constraints from the LAGEOS satellites."

 

[John86]

http://arxiv.org/abs/1005.3767

A Potentiality and Conceptuality Interpretation of Quantum Physics
Authors: Diederik Aerts
(Submitted on 20 May 2010)
Abstract: We elaborate on a new interpretation of quantum mechanics which we introduced recently. The main hypothesis of this new interpretation is that quantum particles are entities interacting with matter conceptually, which means that pieces of matter function as interfaces for the conceptual content carried by the quantum particles. We explain how our interpretation was inspired by our earlier analysis of non-locality as non-spatiality and a specific interpretation of quantum potentiality, which we illustrate by means of the example of two interconnected vessels of water. We show by means of this example that philosophical realism is not in contradiction with the recent findings with respect to Leggett's inequalities and their violations. We explain our recent work on using the quantum formalism to model human concepts and their combinations and how this has given rise to the foundational ideas of our new quantum interpretation. We analyze the equivalence of meaning in the realm of human concepts and coherence in the realm of quantum particles, and how the duality of abstract and concrete leads naturally to a Heisenberg uncertainty relation. We illustrate the role played by interference and entanglement and show how the new interpretation explains the problems related to identity and individuality in quantum mechanics. We put forward a possible scenario for the emergence of the reality of macroscopic objects.