Front Matter
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Semiclassical Gravity and Quantum De Sitter
Semiclassical gravity and quantum de Sitter Neil Turok Perimeter Institute Work with J. Feldbrugge, J-L. Lehners, A. Di Tucci Credit: Pablo Carlos Budassi astonishing simplicity: just 5 numbers Measurement Error Expansion rate: 67.8±0.9 km s−1 Mpc−1 1% today (Temperature) 2.728 ± 0.004 K .1% (Age) 13.799 ±0.038 bn yrs .3% Baryon-entropy ratio 6±.1x10-10 1% energy Dark matter-baryon ratio 5.4± 0.1 2% Dark energy density 0.69±0.006 x critical 2% Scalar amplitude 4.6±0.006 x 10-5 1% geometry Scalar spectral index -.033±0.004 12% ns (scale invariant = 0) A dns 3 4 gw consistent +m 's; but Ωk , 1+ wDE , d ln k , δ , δ ..,r = A with zero ν s Nature has found a way to create a huge hierarchy of scales, apparently more economically than in any current theory A fascinating situation, demanding new ideas One of the most minimal is to revisit quantum cosmology The simplest of all cosmological models is de Sitter; interesting both for today’s dark energy and for inflation quantum cosmology reconsidered w/ S. Gielen 1510.00699, Phys. Rev. Le+. 117 (2016) 021301, 1612.0279, Phys. Rev. D 95 (2017) 103510. w/ J. Feldbrugge J-L. Lehners, 1703.02076, Phys. Rev. D 95 (2017) 103508, 1705.00192, Phys. Rev. Le+, 119 (2017) 171301, 1708.05104, Phys. Rev. D, in press (2017). w/A. Di Tucci, J. Feldbrugge and J-L. Lehners , in PreParaon (2017) Wheeler, Feynman, Quantum geometrodynamics De Wi, Teitelboim … sum over final 4-geometries 3-geometry (4) Σ1 gµν initial 3-geometry Σ0 fundamental object: Σ Σ ≡ 1 0 Feynman propagator 1 0 Basic object: phase space Lorentzian path integral 2 2 i 2 i (3) i j ADM : ds ≡ (−N + Ni N )dt + 2Nidtdx + hij dx dx Σ1 i (3) (3) i S 1 0 = DN DN Dh Dπ e ! ∫ ∫ ∫ ij ∫ ij Σ0 1 S = dt d 3x(π (3)h!(3) − N H i − NH) ∫0 ∫ ij ij i Basic references: C. -
Notes on Semiclassical Gravity
ANNALS OF PHYSICS 196, 296-M (1989) Notes on Semiclassical Gravity T. P. SINGH AND T. PADMANABHAN Theoretical Astrophvsics Group, Tata Institute of Fundamental Research, Horn; Bhabha Road, Bombay 400005, India Received March 31, 1989; revised July 6, 1989 In this paper we investigate the different possible ways of defining the semiclassical limit of quantum general relativity. We discuss the conditions under which the expectation value of the energy-momentum tensor can act as the source for a semiclassical, c-number, gravitational field. The basic issues can be understood from the study of the semiclassical limit of a toy model, consisting of two interacting particles, which mimics the essential properties of quan- tum general relativity. We define and study the WKB semiclassical approximation and the gaussian semiclassical approximation for this model. We develop rules for Iinding the back- reaction of the quantum mode 4 on the classical mode Q. We argue that the back-reaction can be found using the phase of the wave-function which describes the dynamics of 4. We find that this back-reaction is obtainable from the expectation value of the hamiltonian if the dis- persion in this phase can be neglected. These results on the back-reaction are generalised to the semiclassical limit of the Wheeler-Dewitt equation. We conclude that the back-reaction in semiclassical gravity is ( Tlk) only when the dispersion in the phase of the matter wavefunc- tional can be neglected. This conclusion is highlighted with a minisuperspace example of a massless scalar field in a Robertson-Walker universe. We use the semiclassical theory to show that the minisuperspace approximation in quantum cosmology is valid only if the production of gravitons is negligible. -
Unitarity Condition on Quantum Fields in Semiclassical Gravity Abstract
KNUTH-26,March1995 Unitarity Condition on Quantum Fields in Semiclassical Gravity Sang Pyo Kim ∗ Department of Physics Kunsan National University Kunsan 573-701, Korea Abstract The condition for the unitarity of a quantum field is investigated in semiclas- sical gravity from the Wheeler-DeWitt equation. It is found that the quantum field preserves unitarity asymptotically in the Lorentzian universe, but does not preserve unitarity completely in the Euclidean universe. In particular we obtain a very simple matter field equation in the basis of the generalized invariant of the matter field Hamiltonian whose asymptotic solution is found explicitly. Published in Physics Letters A 205, 359 (1995) Unitarity of quantum field theory in curved space-time has been a problem long debated but sill unsolved. In particular the issue has become an impassioned altercation with the discovery of the Hawking radiation [1] from black hole in relation to the information loss problem. Recently there has been a series of active and intensive investigations of quantum ∗E-mail : [email protected] 1 effects of matter field through dilaton gravity and resumption of unitarity and information loss problem (for a good review and references see [2]). In this letter we approach the unitarity problem and investigate the condition for the unitarity of a quantum field from the point of view of semiclassical gravity based on the Wheeler-DeWitt equation [3]. By developing various methods [4–18] for semiclassical gravity and elaborating further the new asymptotic expansion method [19] for the Wheeler-DeWitt equation, we derive the quantum field theory for a matter field from the Wheeler-DeWittt equation for the gravity coupled to the matter field, which is equivalent to a gravitational field equation and a matrix equation for the matter field through a definition of cosmological time. -
Inflation Without Quantum Gravity
Inflation without quantum gravity Tommi Markkanen, Syksy R¨as¨anen and Pyry Wahlman University of Helsinki, Department of Physics and Helsinki Institute of Physics P.O. Box 64, FIN-00014 University of Helsinki, Finland E-mail: tommi dot markkanen at helsinki dot fi, syksy dot rasanen at iki dot fi, pyry dot wahlman at helsinki dot fi Abstract. It is sometimes argued that observation of tensor modes from inflation would provide the first evidence for quantum gravity. However, in the usual inflationary formalism, also the scalar modes involve quantised metric perturbations. We consider the issue in a semiclassical setup in which only matter is quantised, and spacetime is classical. We assume that the state collapses on a spacelike hypersurface, and find that the spectrum of scalar perturbations depends on the hypersurface. For reasonable choices, we can recover the usual inflationary predictions for scalar perturbations in minimally coupled single-field models. In models where non-minimal coupling to gravity is important and the field value is sub-Planckian, we do not get a nearly scale-invariant spectrum of scalar perturbations. As gravitational waves are only produced at second order, the tensor-to-scalar ratio is negligible. We conclude that detection of inflationary gravitational waves would indeed be needed to have observational evidence of quantisation of gravity. arXiv:1407.4691v2 [astro-ph.CO] 4 May 2015 Contents 1 Introduction 1 2 Semiclassical inflation 3 2.1 Action and equations of motion 3 2.2 From homogeneity and isotropy to perturbations 6 3 Matching across the collapse 7 3.1 Hypersurface of collapse 7 3.2 Inflation models 10 4 Conclusions 13 1 Introduction Inflation and the quantisation of gravity. -
Open Dissertation-Final.Pdf
The Pennsylvania State University The Graduate School The Eberly College of Science CORRELATIONS IN QUANTUM GRAVITY AND COSMOLOGY A Dissertation in Physics by Bekir Baytas © 2018 Bekir Baytas Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2018 The dissertation of Bekir Baytas was reviewed and approved∗ by the following: Sarah Shandera Assistant Professor of Physics Dissertation Advisor, Chair of Committee Eugenio Bianchi Assistant Professor of Physics Martin Bojowald Professor of Physics Donghui Jeong Assistant Professor of Astronomy and Astrophysics Nitin Samarth Professor of Physics Head of the Department of Physics ∗Signatures are on file in the Graduate School. ii Abstract We study what kind of implications and inferences one can deduce by studying correlations which are realized in various physical systems. In particular, this thesis focuses on specific correlations in systems that are considered in quantum gravity (loop quantum gravity) and cosmology. In loop quantum gravity, a spin-network basis state, nodes of the graph describe un-entangled quantum regions of space, quantum polyhedra. We introduce Bell- network states and study correlations of quantum polyhedra in a dipole, a pentagram and a generic graph. We find that vector geometries, structures with neighboring polyhedra having adjacent faces glued back-to-back, arise from Bell-network states. The results present show clearly the role that entanglement plays in the gluing of neighboring quantum regions of space. We introduce a discrete quantum spin system in which canonical effective methods for background independent theories of quantum gravity can be tested with promising results. In particular, features of interacting dynamics are analyzed with an emphasis on homogeneous configurations and the dynamical building- up and stability of long-range correlations. -
What Atheist Steven Hawking Has Discovered at All, If Black Holes Do Not Evaporate?
What atheist Steven Hawking has discovered at all, if Black Holes do not evaporate? Dmitri Martila Tartu University (2004{2011), Estonia∗ (Dated: December 8, 2020) Abstract It is the severe scientific criticism against Hawking's life work. One of the issues is the following. The evaporation of the Black Holes is impossible at first because of Steven Hawking's sentence in his original paper that the Schwarzschild Black Hole does not evaporate. We have no other spherical symmetric Black Hole, which would have an event horizon, and what shrinks despite that. ∗Electronic address: [email protected] 1 I. HISTORY OF MY UNDERSTANDING The evaporation of a Black Hole leads to the Paradox of Information Loss. So maybe Stephen Hawking has made a fatal mistake introducing Hawking Radiation? \Extraordinary claims require extraordinary evidence" (the Sagan standard) was a phrase popularized by Carl Sagan. However, the roots of this phrase are much older, with the French mathematician Pierre-Simon Laplace stating that \. the weight of evidence for an extraordinary claim must be proportioned to its strangeness." The alleged Loss of Information is an absurd consequence of Steven Hawking's extraordinary thesis that \Black Holes do evaporate". Well, I still do not understand how the Black Hole can evaporate. Black Holes are obtained as the end products of a collapse (in other words: gravitational compression) of supernova matter. However, during the collapse, there is no event horizon. According to Hawking, evaporation does not occur at the most final stage of the collapse of a star, but it performs already during the collapse (according to Ref. -
Arxiv:0905.2641V1
TOPICS IN INFLATIONARY COSMOLOGY AND ASTROPHYSICS by Matthew M. Glenz A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Physics at The University of Wisconsin-Milwaukee December 2008 arXiv:0905.2641v1 [hep-th] 16 May 2009 TOPICS IN INFLATIONARY COSMOLOGY AND ASTROPHYSICS by Matthew M. Glenz A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Physics at The University of Wisconsin-Milwaukee December 2008 Major Professor Date Graduate School Approval Date ii ABSTRACT TOPICS IN INFLATIONARY COSMOLOGY AND ASTROPHYSICS by Matthew M. Glenz The University of Wisconsin-Milwaukee, 2008 Under the Supervision of Distinguished Professor Leonard Parker We introduce a general way of modeling inflation in a framework that is indepen- dent of the exact nature of the inflationary potential. Because of the choice of our initial conditions and the continuity of the scale factor in its first two derivatives, we obtain non-divergent results without the need of any renormalization beyond what is required in Minkowski space. In particular, we assume asymptotically flat initial and final values of our scale factor that lead to an unambiguous measure of the number of particles created versus frequency. We find exact solutions to the evolution equation for inflaton perturbations when their effective mass is zero and approximate solutions when their effective mass is non-zero. We obtain results for the scale invariance of the inflaton spectrum and the size of density perturbations. Finally, we show that a substantial contribution to reheating occurs due to gravitational particle production during the exit from the inflationary stage of the universe. -
Classical Simulations of Quantum Field Theory in Curved Spacetime I: Fermionic Hawking-Hartle Vacua from a Staggered Lattice Scheme
Classical Simulations of Quantum Field Theory in Curved Spacetime I: Fermionic Hawking-Hartle Vacua from a Staggered Lattice Scheme Adam G. M. Lewis1 and Guifr´e Vidal1,2 1Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, Ontario, Canada, N2L 2Y5 2X, The Moonshot Factory, Mountain View, CA 94043 We numerically compute renormalized expectation values of quadratic operators in a quantum field theory (QFT) of free Dirac fermions in curved two-dimensional (Lorentzian) spacetime. First, we use a staggered-fermion discretization to gener- ate a sequence of lattice theories yielding the desired QFT in the continuum limit. Numerically-computed lattice correlators are then used to approximate, through ex- trapolation, those in the continuum. Finally, we use so-called point-splitting regular- ization and Hadamard renormalization to remove divergences, and thus obtain finite, renormalized expectation values of quadratic operators in the continuum. As illus- trative applications, we show how to recover the Unruh effect in flat spacetime and how to compute renormalized expectation values in the Hawking-Hartle vacuum of a Schwarzschild black hole and in the Bunch-Davies vacuum of an expanding universe described by de Sitter spacetime. Although here we address a non-interacting QFT us- ing free fermion techniques, the framework described in this paper lays the groundwork for a series of subsequent studies involving simulation of interacting QFTs in curved spacetime by tensor network techniques. 1 Introduction While by now it is generally expected that black holes will radiate and evaporate [12, 27, 52] in the presence of a quantum field, the details remain murky. The specific interplay between gravity and quantum fields during the early Universe's presumed inflationary [2, 24, 36, 48] phase is similarly unclear. -
Arxiv:1702.07132V1 [Physics.Hist-Ph] 23 Feb 2017 Letenti’ Hoyo Eea Eaiiy H Uni- the Relativity, General of Theory Einstein’S Albert Observations New with Creation
Fifty years of cosmological particle creation Leonard Parker1, ∗ and Jos´eNavarro-Salas2, † 1Physics Department, University of Wisconsin-Milwaukee, Kenwood Integrated Research Complex, 3135 North Maryland Avenue, Milwaukee, WI 53211, USA. 2Departamento de Fisica Teorica and IFIC, Centro Mixto Universidad de Valencia-CSIC. Facultad de Fisica, Universidad de Valencia, Burjassot-46100, Valencia, Spain. (Dated: February 24, 2017) In the early sixties Leonard Parker discovered that the expansion of the universe can create particles out of the vacuum, opening a new and fruitfull field in physics. We give a historical review in the form of an interview that took place during the Conference ERE2014 (Valencia 1-5, September, 2014). PACS numbers: 04.62.+v I. PREAMBLE versity of Valencia hosted the Conference ERE2014 (Al- most 100 Years after Einstein’s Revolution) during the Prof. Parker is the pioneer of the theory of quantized first week of September. Prof. Parker delivered a talk on fields in curved spacetime. His breakthrough discovery, the phenomena of gravitational particle creation. J. N-S in the early sixties, that the expansion of the universe can then took the opportunity to interview him about these create particles out of the vacuum opened a new field in topics from a historical and personal perspective. A very physics, with many treasures inside. This surprising re- small fraction of the interview was published in M`etode, sult was stated and analyzed with detail in his Ph.D. the magazine of the University of Valencia. We believe thesis (Harvard University, 1966) and related papers in that it will be of interest for young students and re- Physical Review Letters and Physical Review. -
SEMICLASSICAL GRAVITY and ASTROPHYSICS Arundhati Dasgupta, Lethbridge, CCGRRA-16 WHY PROBE SEMICLASSICAL GRAVITY at ALL
SEMICLASSICAL GRAVITY AND ASTROPHYSICS arundhati dasgupta, lethbridge, CCGRRA-16 WHY PROBE SEMICLASSICAL GRAVITY AT ALL quantum gravity is important at Planck scales Semi classical gravity is important, as Hawking estimated for primordial black holes of radius using coherent states I showed that instabilities can happen due to semi classical corrections for black holes with horizon radius of the order of WHY COHERENT STATES useful semiclassical states in any quantum theory expectation values of the operators are closest to their classical values fluctuations about the classical value are controlled, usually by `standard deviation’ parameter as in a Gaussian, and what can be termed as `semi-classical’ parameter. in SHM coherent states expectation values of operators are exact, but not so in non-abelian coherent states LQG: THE QUANTUM GRAVITY THEORY WHERE COHERENT STATES CAN BE DEFINED based on work by mathematician Hall. coherent states are defined as the Kernel of transformation from real Hilbert space to the Segal-Bergman representation. S e & # 1 h A = Pexp$ Adx! I I −1 e ( ) $ ∫ ! Pe = − Tr[T h e * E h e ] % e " a ∫ EXPECTATION VALUES OF OPERATORS Coherent State in the holonomy representation The expectation values of the momentum operator non-polynomial corrections CORRECTIONS TO THE HOLONOMY GEOMETRIC INTERPRETATION Lemaitre metric does not cancel when corrected The corrected metric does not transform to the Schwarzschild metric WHAT DOES THIS `EXTRA TERM’ MEAN It is a `strain’ on the space-time fabric. Can LIGO detect such changes from the classical metric? This is a linearized perturbation over a Schwarzschild metric, and would contribute to `even’ mode of a spherical gravity wave, though cannot be anticipated in the polynomial linearized mode expansion unstatic-unspherical semiclassical correction THE STRAIN MAGNITUDE A. -
Quantum Extensions of Classically Singular Spacetimes – the CGHS Model
Quantum Extensions of Classically Singular Spacetimes – The CGHS Model Victor Taveras Pennsylvania State University Loops ’07 Morelia, Mexico 6/29/07 Work with Abhay Ashtekar and Madhavan Varadarajan CGHS Model Action: •Free Field Equation for f •Dilaton is completely determined by stress energy due to f. •Field Redefinitions: •Equations of motion Callan, Giddings, Harvey, and Strominger (1992) BH Collapse Solutions in CGHS Black Hole Solutions Physical spacetime has a singularity. True DOFs in f+ and f-. Hawking Effect •Trace anomaly •Conservation Law •Hawking Radiation Giddings and Nelson (1992) Numerical Work •Incorporated the backreaction into an effective term in the action •Equations discretized and solved numerically. Evolution breaks down at the singularity and near the endpoint of evaporation. Lowe (1993), Piran & Strominger (1993) Quantum Theory Operator Equations: + Boundary conditions • For an operator valued distribution and a positive operator • well defined everywhere even though may vanish • Ideally we would like to be able to specify (work in progress) • Even without one can proceed by making successive approximations to the full quantum theory Bootstrapping 0th order – Put Compute in the state This yields the BH background. 1st order – Interpret the vacuum on the of the BH background metric, this is precisely the Hawking effect. 2nd order - Semiclassical gravity (mean field approximation) : Ignore fluctuations in and , but not f. Use determined from the trace anomaly. Agreement with analytic solution near obtained by asymptotic analysis. Asymptotic Analysis •Expand and in inverse powers of x+. •Idea: We should have a decent control of what is going on near since curvatures and fluxes there are small •The Hawking flux and the Bondi mass go to 0 and the physical metric approaches the flat one. -
Approximate Solution to the CGHS Field Equations for Two-Dimensional
Approximate solution to the CGHS field equations for two-dimensional evaporating black holes Amos Ori Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel November 6, 2018 Abstract Callan, Giddings, Harvey and Strominger (CGHS) previously in- troduced a two-dimensional semiclassical model of gravity coupled to a dilaton and to matter fields. Their model yields a system of field equations which may describe the formation of a black hole in gravita- tional collapse as well as its subsequent evaporation. Here we present an approximate analytical solution to the semiclassical CGHS field equations. This solution is constructed using the recently-introduced formalism of flux-conserving hyperbolic systems. We also explore the asymptotic behavior at the horizon of the evaporating black hole. 1 Introduction arXiv:1007.3856v1 [gr-qc] 22 Jul 2010 The semiclassical theory of gravity treats spacetime geometry at the classi- cal level but allows quantum treatment of the various fields which reside in spacetime. This theory asserts that a quantum field living on a black-hole (BH) background will usually be endowed with non-trivial fluxes of energy- momentum. These fluxes, represented by the renormalized stress-Energy ten- ^ sor Tαβ, originate from the field’s quantum fluctuations, and typically they do not vanish even in the (incoming) vacuum state. The Hawking radiation 1 [1], and the consequent black-hole (BH) evaporation, are perhaps the most dramatic manifestations of these quantum fluxes. In the framework of semiclassical gravity the spacetime reacts to the quan- tum fluxes via the Einstein equations, which now receive the extra quantum ^ contribution Tαβ at their right-hand side.