The Generation of Particles by Quantum Loops
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Macroscopic Quantum Phenomena in Interacting Bosonic Systems: Josephson flow in Liquid 4He and Multimode Schr¨Odingercat States
Macroscopic quantum phenomena in interacting bosonic systems: Josephson flow in liquid 4He and multimode Schr¨odingercat states by Tyler James Volkoff A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate Division of the University of California, Berkeley Committee in charge: Professor K. Birgitta Whaley, Chair Professor Philip L. Geissler Professor Richard E. Packard Fall 2014 Macroscopic quantum phenomena in interacting bosonic systems: Josephson flow in liquid 4He and multimode Schr¨odingercat states Copyright 2014 by Tyler James Volkoff 1 Abstract Macroscopic quantum phenomena in interacting bosonic systems: Josephson flow in liquid 4He and multimode Schr¨odingercat states by Tyler James Volkoff Doctor of Philosophy in Chemistry University of California, Berkeley Professor K. Birgitta Whaley, Chair In this dissertation, I analyze certain problems in the following areas: 1) quantum dynam- ical phenomena in macroscopic systems of interacting, degenerate bosons (Parts II, III, and V), and 2) measures of macroscopicity for a large class of two-branch superposition states in separable Hilbert space (Part IV). Part I serves as an introduction to important concepts recurring in the later Parts. In Part II, a microscopic derivation of the effective action for the relative phase of driven, aperture-coupled reservoirs of weakly-interacting condensed bosons from a (3 + 1)D microscopic model with local U(1) gauge symmetry is presented. The effec- tive theory is applied to the transition from linear to sinusoidal current vs. phase behavior observed in recent experiments on liquid 4He driven through nanoaperture arrays. Part III discusses path-integral Monte Carlo (PIMC) numerical simulations of quantum hydrody- namic properties of reservoirs of He II communicating through simple nanoaperture arrays. -
The Mechanics of the Fermionic and Bosonic Fields: an Introduction to the Standard Model and Particle Physics
The Mechanics of the Fermionic and Bosonic Fields: An Introduction to the Standard Model and Particle Physics Evan McCarthy Phys. 460: Seminar in Physics, Spring 2014 Aug. 27,! 2014 1.Introduction 2.The Standard Model of Particle Physics 2.1.The Standard Model Lagrangian 2.2.Gauge Invariance 3.Mechanics of the Fermionic Field 3.1.Fermi-Dirac Statistics 3.2.Fermion Spinor Field 4.Mechanics of the Bosonic Field 4.1.Spin-Statistics Theorem 4.2.Bose Einstein Statistics !5.Conclusion ! 1. Introduction While Quantum Field Theory (QFT) is a remarkably successful tool of quantum particle physics, it is not used as a strictly predictive model. Rather, it is used as a framework within which predictive models - such as the Standard Model of particle physics (SM) - may operate. The overarching success of QFT lends it the ability to mathematically unify three of the four forces of nature, namely, the strong and weak nuclear forces, and electromagnetism. Recently substantiated further by the prediction and discovery of the Higgs boson, the SM has proven to be an extraordinarily proficient predictive model for all the subatomic particles and forces. The question remains, what is to be done with gravity - the fourth force of nature? Within the framework of QFT theoreticians have predicted the existence of yet another boson called the graviton. For this reason QFT has a very attractive allure, despite its limitations. According to !1 QFT the gravitational force is attributed to the interaction between two gravitons, however when applying the equations of General Relativity (GR) the force between two gravitons becomes infinite! Results like this are nonsensical and must be resolved for the theory to stand. -
Loop Quantum Cosmology, Modified Gravity and Extra Dimensions
universe Review Loop Quantum Cosmology, Modified Gravity and Extra Dimensions Xiangdong Zhang Department of Physics, South China University of Technology, Guangzhou 510641, China; [email protected] Academic Editor: Jaume Haro Received: 24 May 2016; Accepted: 2 August 2016; Published: 10 August 2016 Abstract: Loop quantum cosmology (LQC) is a framework of quantum cosmology based on the quantization of symmetry reduced models following the quantization techniques of loop quantum gravity (LQG). This paper is devoted to reviewing LQC as well as its various extensions including modified gravity and higher dimensions. For simplicity considerations, we mainly focus on the effective theory, which captures main quantum corrections at the cosmological level. We set up the basic structure of Brans–Dicke (BD) and higher dimensional LQC. The effective dynamical equations of these theories are also obtained, which lay a foundation for the future phenomenological investigations to probe possible quantum gravity effects in cosmology. Some outlooks and future extensions are also discussed. Keywords: loop quantum cosmology; singularity resolution; effective equation 1. Introduction Loop quantum gravity (LQG) is a quantum gravity scheme that tries to quantize general relativity (GR) with the nonperturbative techniques consistently [1–4]. Many issues of LQG have been carried out in the past thirty years. In particular, among these issues, loop quantum cosmology (LQC), which is the cosmological sector of LQG has received increasing interest and has become one of the most thriving and fruitful directions of LQG [5–9]. It is well known that GR suffers singularity problems and this, in turn, implies that our universe also has an infinitely dense singularity point that is highly unphysical. -
Quantum Vacuum Energy Density and Unifying Perspectives Between Gravity and Quantum Behaviour of Matter
Annales de la Fondation Louis de Broglie, Volume 42, numéro 2, 2017 251 Quantum vacuum energy density and unifying perspectives between gravity and quantum behaviour of matter Davide Fiscalettia, Amrit Sorlib aSpaceLife Institute, S. Lorenzo in Campo (PU), Italy corresponding author, email: [email protected] bSpaceLife Institute, S. Lorenzo in Campo (PU), Italy Foundations of Physics Institute, Idrija, Slovenia email: [email protected] ABSTRACT. A model of a three-dimensional quantum vacuum based on Planck energy density as a universal property of a granular space is suggested. This model introduces the possibility to interpret gravity and the quantum behaviour of matter as two different aspects of the same origin. The change of the quantum vacuum energy density can be considered as the fundamental medium which determines a bridge between gravity and the quantum behaviour, leading to new interest- ing perspectives about the problem of unifying gravity with quantum theory. PACS numbers: 04. ; 04.20-q ; 04.50.Kd ; 04.60.-m. Key words: general relativity, three-dimensional space, quantum vac- uum energy density, quantum mechanics, generalized Klein-Gordon equation for the quantum vacuum energy density, generalized Dirac equation for the quantum vacuum energy density. 1 Introduction The standard interpretation of phenomena in gravitational fields is in terms of a fundamentally curved space-time. However, this approach leads to well known problems if one aims to find a unifying picture which takes into account some basic aspects of the quantum theory. For this reason, several authors advocated different ways in order to treat gravitational interaction, in which the space-time manifold can be considered as an emergence of the deepest processes situated at the fundamental level of quantum gravity. -
Aspects of Loop Quantum Gravity
Aspects of loop quantum gravity Alexander Nagen 23 September 2020 Submitted in partial fulfilment of the requirements for the degree of Master of Science of Imperial College London 1 Contents 1 Introduction 4 2 Classical theory 12 2.1 The ADM / initial-value formulation of GR . 12 2.2 Hamiltonian GR . 14 2.3 Ashtekar variables . 18 2.4 Reality conditions . 22 3 Quantisation 23 3.1 Holonomies . 23 3.2 The connection representation . 25 3.3 The loop representation . 25 3.4 Constraints and Hilbert spaces in canonical quantisation . 27 3.4.1 The kinematical Hilbert space . 27 3.4.2 Imposing the Gauss constraint . 29 3.4.3 Imposing the diffeomorphism constraint . 29 3.4.4 Imposing the Hamiltonian constraint . 31 3.4.5 The master constraint . 32 4 Aspects of canonical loop quantum gravity 35 4.1 Properties of spin networks . 35 4.2 The area operator . 36 4.3 The volume operator . 43 2 4.4 Geometry in loop quantum gravity . 46 5 Spin foams 48 5.1 The nature and origin of spin foams . 48 5.2 Spin foam models . 49 5.3 The BF model . 50 5.4 The Barrett-Crane model . 53 5.5 The EPRL model . 57 5.6 The spin foam - GFT correspondence . 59 6 Applications to black holes 61 6.1 Black hole entropy . 61 6.2 Hawking radiation . 65 7 Current topics 69 7.1 Fractal horizons . 69 7.2 Quantum-corrected black hole . 70 7.3 A model for Hawking radiation . 73 7.4 Effective spin-foam models . -
Introduction to Loop Quantum Gravity
Introduction to Loop Quantum Gravity Abhay Ashtekar Institute for Gravitation and the Cosmos, Penn State A broad perspective on the challenges, structure and successes of loop quantum gravity. Addressed to Young Researchers: From Beginning Students to Senior Post-docs. Organization: 1. Historical & Conceptual Setting 2. Structure of Loop Quantum Gravity 3. Outlook: Challenges and Opportunities – p. 1. Historical and Conceptual Setting Einstein’s resistance to accept quantum mechanics as a fundamental theory is well known. However, he had a deep respect for quantum mechanics and was the first to raise the problem of unifying general relativity with quantum theory. “Nevertheless, due to the inner-atomic movement of electrons, atoms would have to radiate not only electro-magnetic but also gravitational energy, if only in tiny amounts. As this is hardly true in Nature, it appears that quantum theory would have to modify not only Maxwellian electrodynamics, but also the new theory of gravitation.” (Albert Einstein, Preussische Akademie Sitzungsberichte, 1916) – p. • Physics has advanced tremendously in the last 90 years but the the problem of unification of general relativity and quantum physics still open. Why? ⋆ No experimental data with direct ramifications on the quantum nature of Gravity. – p. • Physics has advanced tremendously in the last nine decades but the the problem of unification of general relativity and quantum physics is still open. Why? ⋆ No experimental data with direct ramifications on the quantum nature of Gravity. ⋆ But then this should be a theorist’s haven! Why isn’t there a plethora of theories? – p. ⋆ No experimental data with direct ramifications on quantum Gravity. -
Physics of Three-Dimensional Bosonic Topological Insulators: Surface-Deconfined Criticality and Quantized Magnetoelectric Effect
PHYSICAL REVIEW X 3, 011016 (2013) Physics of Three-Dimensional Bosonic Topological Insulators: Surface-Deconfined Criticality and Quantized Magnetoelectric Effect Ashvin Vishwanath Department of Physics, University of California, Berkeley, California 94720, USA Materials Science Division, Lawrence Berkeley National Laboratories, Berkeley, California 94720, USA T. Senthil Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (Received 4 October 2012; revised manuscript received 31 December 2012; published 28 February 2013) We discuss physical properties of ‘‘integer’’ topological phases of bosons in D ¼ 3 þ 1 dimensions, protected by internal symmetries like time reversal and/or charge conservation. These phases invoke interactions in a fundamental way but do not possess topological order; they are bosonic analogs of free- fermion topological insulators and superconductors. While a formal cohomology-based classification of such states was recently discovered, their physical properties remain mysterious. Here, we develop a field-theoretic description of several of these states and show that they possess unusual surface states, which, if gapped, must either break the underlying symmetry or develop topological order. In the latter case, symmetries are implemented in a way that is forbidden in a strictly two-dimensional theory. While these phases are the usual fate of the surface states, exotic gapless states can also be realized. For example, tuning parameters can naturally lead to a deconfined quantum critical point or, in other situations, to a fully symmetric vortex metal phase. We discuss cases where the topological phases are characterized by a quantized magnetoelectric response , which, somewhat surprisingly, is an odd multiple of 2.Two different surface theories are shown to capture these phenomena: The first is a nonlinear sigma model with a topological term. -
Clifford Algebras, Multipartite Systems and Gauge Theory Gravity
Mathematical Phyiscs Clifford Algebras, Multipartite Systems and Gauge Theory Gravity Marco A. S. Trindadea Eric Pintob Sergio Floquetc aColegiado de Física Departamento de Ciências Exatas e da Terra Universidade do Estado da Bahia, Salvador, BA, Brazil bInstituto de Física Universidade Federal da Bahia Salvador, BA, Brazil cColegiado de Engenharia Civil Universidade Federal do Vale do São Francisco Juazeiro, BA, Brazil. E-mail: [email protected], [email protected], [email protected] Abstract: In this paper we present a multipartite formulation of gauge theory gravity based on the formalism of space-time algebra for gravitation developed by Lasenby and Do- ran (Lasenby, A. N., Doran, C. J. L, and Gull, S.F.: Gravity, gauge theories and geometric algebra. Phil. Trans. R. Soc. Lond. A, 582, 356:487 (1998)). We associate the gauge fields with description of fermionic and bosonic states using the generalized graded tensor product. Einstein’s equations are deduced from the graded projections and an algebraic Hopf-like structure naturally emerges from formalism. A connection with the theory of the quantum information is performed through the minimal left ideals and entangled qubits are derived. In addition applications to black holes physics and standard model are outlined. arXiv:1807.09587v2 [physics.gen-ph] 16 Nov 2018 1Corresponding author. Contents 1 Introduction1 2 General formulation and Einstein field equations3 3 Qubits 9 4 Black holes background 10 5 Standard model 11 6 Conclusions 15 7 Acknowledgements 16 1 Introduction This work is dedicated to the memory of professor Waldyr Alves Rodrigues Jr., whose contributions in the field of mathematical physics were of great prominence, especially in the study of clifford algebras and their applications to physics [1]. -
Loop Quantum Gravity Alejandro Perez, Centre De Physique Théorique and Université Aix-Marseille II • Campus De Luminy, Case 907 • 13288 Marseille • France
features Loop quantum gravity Alejandro Perez, Centre de Physique Théorique and Université Aix-Marseille II • Campus de Luminy, case 907 • 13288 Marseille • France. he revolution brought by Einstein’s theory of gravity lies more the notion of particle, Fourier modes, vacuum, Poincaré invariance Tin the discovery of the principle of general covariance than in are essential tools that can only be constructed on a given space- the form of the dynamical equations of general relativity. General time geometry.This is a strong limitation when it comes to quantum covariance brings the relational character of nature into our descrip- gravity since the very notion of space-time geometry is most likely tion of physics as an essential ingredient for the understanding of not defined in the deep quantum regime. Secondly, quantum field the gravitational force. In general relativity the gravitational field is theory is plagued by singularities too (UV divergences) coming encoded in the dynamical geometry of space-time, implying a from the contribution of arbitrary high energy quantum processes. strong form of universality that precludes the existence of any non- This limitation of standard QFT’s is expected to disappear once the dynamical reference system—or non-dynamical background—on quantum fluctuations of the gravitational field, involving the dynam- top of which things occur. This leaves no room for the old view ical treatment of spacetime geometry, are appropriately taken into where fields evolve on a rigid preestablished space-time geometry account. But because of its intrinsically background dependent (e.g. Minkowski space-time): to understand gravity one must definition, standard QFT cannot be used to shed light on this issue. -
Keference International Centre for Theoretical
KEFERENCE INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS IC/86/342 INTERNATIONAL THE REGULAR EFFECTIVE ACTION OF GAUGE FIELD THEORY AND QUANTUM GRAVITY ATOMIC ENERGY AGENCY Nazir S. Baaklini UNITED NATIONS EDUCATIONAL, SCIENTIFIC AND CULTURAL ORGANIZATION IC/86/342 International Atomic Energy Agency 0. INTRODUCTION and The effective action of quantum field theory, defined by the functional United Nations Educational Scientific and Cultural Organization integral , is an elegant and potentially, very powerful framework for compu- INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS ting quantum effects, in a manner that preserves underlying fundamental symmetries. However, this framework had been utilized mainly in computing effective potentials, and in certain discussions of the divergent counter-terms needed in gauge field THE REGULAR EFFECTIVE ACTION OF GAUGE FIELD THEORY theory and quantum gravity. Whereas it should ~ae very fruitful fo develop expre- AND QUANTUM GRAVITY ssions for the effective action which could have general applicability, computa- tions are still performed using conventional Feynman rules. What is needed is a perturbative formalism for the effective action vhicii applies to a general field Nazir S. Baaklini theory containing Bosonic as well as Fermionic fields, and vhich could be used to International Centre for Theoretical Physics, Trieste, Italy address fundamental issues of quantum field theory and quantum gravity. and Dahr el Chir Science Centre, Dhour el Choueir, Lebanon. On the other hand, our study of the effective action makes impact on two fundamental issues. One of these concerns the treatment of gauge field theory and other singular systems. The other concerns the ultraviolet divergences of quantum field theory and quantum gravity. -
An Introduction to Loop Quantum Gravity with Application to Cosmology
DEPARTMENT OF PHYSICS IMPERIAL COLLEGE LONDON MSC DISSERTATION An Introduction to Loop Quantum Gravity with Application to Cosmology Author: Supervisor: Wan Mohamad Husni Wan Mokhtar Prof. Jo~ao Magueijo September 2014 Submitted in partial fulfilment of the requirements for the degree of Master of Science of Imperial College London Abstract The development of a quantum theory of gravity has been ongoing in the theoretical physics community for about 80 years, yet it remains unsolved. In this dissertation, we review the loop quantum gravity approach and its application to cosmology, better known as loop quantum cosmology. In particular, we present the background formalism of the full theory together with its main result, namely the discreteness of space on the Planck scale. For its application to cosmology, we focus on the homogeneous isotropic universe with free massless scalar field. We present the kinematical structure and the features it shares with the full theory. Also, we review the way in which classical Big Bang singularity is avoided in this model. Specifically, the spectrum of the operator corresponding to the classical inverse scale factor is bounded from above, the quantum evolution is governed by a difference rather than a differential equation and the Big Bang is replaced by a Big Bounce. i Acknowledgement In the name of Allah, the Most Gracious, the Most Merciful. All praise be to Allah for giving me the opportunity to pursue my study of the fundamentals of nature. In particular, I am very grateful for the opportunity to explore loop quantum gravity and its application to cosmology for my MSc dissertation. -
Emergence of Time in Loop Quantum Gravity∗
Emergence of time in Loop Quantum Gravity∗ Suddhasattwa Brahma,1y 1 Center for Field Theory and Particle Physics, Fudan University, 200433 Shanghai, China Abstract Loop quantum gravity has formalized a robust scheme in resolving classical singu- larities in a variety of symmetry-reduced models of gravity. In this essay, we demon- strate that the same quantum correction which is crucial for singularity resolution is also responsible for the phenomenon of signature change in these models, whereby one effectively transitions from a `fuzzy' Euclidean space to a Lorentzian space-time in deep quantum regimes. As long as one uses a quantization scheme which re- spects covariance, holonomy corrections from loop quantum gravity generically leads to non-singular signature change, thereby giving an emergent notion of time in the theory. Robustness of this mechanism is established by comparison across large class of midisuperspace models and allowing for diverse quantization ambiguities. Con- ceptual and mathematical consequences of such an underlying quantum-deformed space-time are briefly discussed. 1 Introduction It is not difficult to imagine a mind to which the sequence of things happens not in space but only in time like the sequence of notes in music. For such a mind such conception of reality is akin to the musical reality in which Pythagorean geometry can have no meaning. | Tagore to Einstein, 1920. We are yet to come up with a formal theory of quantum gravity which is mathematically consistent and allows us to draw phenomenological predictions from it. Yet, there are widespread beliefs among physicists working in fundamental theory regarding some aspects of such a theory, once realized.