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Defining Gravity: Effective Field Theory, Entanglement, and Cosmology


Remmen, Grant Newton (2017) Defining Gravity: Effective Field Theory, Entanglement, and Cosmology. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z90R9MD1.


Many of the most exciting open problems in high-energy physics are related to the behavior and ultimate nature of gravity and spacetime. In this dissertation, several categories of new results in quantum and classical gravity are presented, with applications to our understanding of both quantum field theory and cosmology.

A fundamental open question in quantum field theory is related to ultraviolet completion: Which low-energy effective field theories can be consistently combined with quantum gravity? A celebrated example of the swampland program---the investigation of this question---is the weak gravity conjecture, which mandates, for a U(1) gauge field coupled consistently to gravity, the existence of a state with charge-to-mass ratio greater than unity. In this thesis, we demonstrate the tension between the weak gravity conjecture and the naturalness principle in quantum field theory, generalize the weak gravity conjecture to multiple gauge fields, and exhibit a model in which the weak gravity conjecture solves the standard model hierarchy problem. Next, we demonstrate that gravitational effective field theories can be constrained by infrared physics principles alone, namely, analyticity, unitarity, and causality. In particular, we derive bounds related to the weak gravity conjecture by placing such infrared constraints on higher-dimension operators in a photon-graviton effective theory. We furthermore place bounds on higher-curvature corrections to the Einstein equations, first using analyticity of graviton scattering amplitudes and later using unitarity of an arbitrary tree-level completion, as well as constrain the couplings in models of massive gravity. Completing our treatment of perturbative quantum gravity, outside of the swampland program, we also reformulate graviton perturbation theory itself, finding a field redefinition and gauge-fixing of the Einstein-Hilbert action that drastically simplifies the Feynman diagram expansion. Furthermore, our reformulation also exhibits a hidden symmetry of general relativity that corresponds to the double copy relations equating gravity amplitudes to sums of squares of gluon amplitudes in Yang-Mills theory, a surprising correspondence that yields insights into the structure of quantum field theories.

Moving beyond perturbation theory into nonperturbative questions in quantum gravity, we consider the deep relation between spacetime geometry and properties of the quantum state. In the context of holography and the anti-de Sitter/conformal field theory correspondence, we test the proposed ER=EPR correspondence equating quantum entanglement with wormholes in spacetime. In particular, we demonstrate that the no-cloning theorem in quantum mechanics and the no-go theorem for topology change of spacetime are dual under the ER=EPR correspondence. Furthermore, we prove that the presence of a wormhole is not an observable in quantum gravity, rescuing ER=EPR from potential violation of linearity of quantum mechanics. Excitingly, we also prove a new area theorem within classical general relativity for arbitrary dynamics of two collections of wormholes and black holes; this area theorem is the ER=EPR analogue of entanglement conservation. We next turn our attention to the emergence of spacetime itself, placing consistency conditions on the proposed correspondence between anti-de Sitter space and the Multiscale Entanglement Renormalization Ansatz, a special tensor network that constitutes a computational tool for finding the ground state of certain quantum systems. Further examining the role of quantum entanglement entropy in the emergence of general relativity, we ask whether there is a consistent microscopic formulation of the entropy in theories of entropic gravity; we find that our results weaken equation-of-state proposals for entropic gravity while strengthening those more akin to holography, guiding future investigation of theories of emergent gravity.

Finally, we examine the consequences of the Hamiltonian constraint in classical gravity for the early universe. The Hamiltonian constraint allows for the Liouville measure on the phase space of cosmological parameters for homogeneous, isotropic universes to be converted into a probability distribution on trajectories, or equivalently, on initial conditions. However, this measure diverges on the set of spacetimes that are spatially flat, like the observable universe. In this thesis, we derive the unique, classical, Hamiltonian-conserved measure for the subset of flat universes. This result allows for distinction between different models of cosmic inflation with similar observable predictions; for example, we find that the measure favors models of large-scale inflation, as such potentials more naturally produce the number of e-folds necessary to match cosmological observations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:general relativity; particle physics; quantum gravity; weak gravity conjecture; effective field theory; swampland program; scattering amplitudes; black holes; graviton; unitarity; analyticity; causality; higher-curvature operators; string theory; massive gravity; double copy; ER=EPR conjecture; AdS/CFT correspondence; holography; qubits; entanglement; wormholes; area theorem; tensor networks; multiscale entanglement renormalization ansatz; entropy; entropic gravity; cosmology; attractor; inflation; scalar field; measure; e-folds
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Awards:John Stager Stemple Memorial Prize in Physics, 2015
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Cheung, Clifford W. (co-advisor)
  • Carroll, Sean M. (co-advisor)
Group:Caltech Theory
Thesis Committee:
  • Cheung, Clifford W. (co-chair)
  • Carroll, Sean M. (co-chair)
  • Wise, Mark B.
  • Weinstein, Alan Jay
Defense Date:17 May 2017
Funding AgencyGrant Number
Hertz FoundationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1144469
Record Number:CaltechTHESIS:04072017-131612641
Persistent URL:
Related URLs:
URLURL TypeDescription appearing in Ch. 2: C. Cheung and G. N. Remmen, “Naturalness and the Weak Gravity Conjecture,” Phys. Rev. Lett. 113 (2014) 051601, arXiv:1402.2287 [hep-ph]. appearing in Ch. 3: C. Cheung and G. N. Remmen, “Infrared Consistency and the Weak Gravity Conjecture,” JHEP 1412 (2014) 087, arXiv:1407.7865 [hep-th]. appearing in Ch. 4: B. Bellazzini, C. Cheung, and G. N. Remmen, “Quantum Gravity Constraints from Unitarity and Analyticity,” Phys. Rev. D93 (2016) 064076, arXiv:1509.00851 [hep-th]. appearing in Ch. 5: C. Cheung and G. N. Remmen, “Positive Signs in Massive Gravity,” JHEP 04 (2016) 002, arXiv:1601.04068 [hep-th]. appearing in Ch. 6: C. Cheung and G. N. Remmen, “Positivity of Curvature-Squared Corrections in Gravity,” Phys. Rev. Lett. 118 (2017) 051601, arXiv:1608.02942 [hep-th]. appearing in Ch. 7: C. Cheung and G. N. Remmen, “Twofold Symmetries of the Pure Gravity Action,” JHEP 01 (2017) 104, arXiv:1612.03927 [hep-th]. appearing in Ch. 8: N. Bao, J. Pollack, and G. N. Remmen, “Splitting Spacetime and Cloning Qubits: Linking No-Go Theorems across the ER=EPR Duality,” Fortsch. Phys. 63 (2015) 705, arXiv:1506.08203 [hep-th]. appearing in Ch. 9: N. Bao, J. Pollack, and G. N. Remmen, “Wormhole and Entanglement (Non-)Detection in the ER=EPR Correspondence,” JHEP 11 (2015) 126, arXiv:1509.05426 [hep-th]. appearing in Ch. 10: G. N. Remmen, N. Bao, and J. Pollack, “Entanglement Conservation, ER=EPR, and a New Classical Area Theorem for Wormholes,” JHEP 07 (2016) 048, arXiv:1604.08217 [hep-th]. appearing in Ch. 11: N. Bao, C. Cao, S. M. Carroll, A. Chatwin-Davies, N. Hunter-Jones, J. Pollack, and G. N. Remmen, “Consistency Conditions for an AdS/MERA Correspondence,” Phys. Rev. D91 (2015) 125036, arXiv:1504.06632 [hep-th]. appearing in Ch. 12: S. M. Carroll and G. N. Remmen, “What is the Entropy in Entropic Gravity?,” Phys. Rev. D93 (2016) 124052, arXiv:1601.07558 [hep-th]. appearing in Ch. 13: G. N. Remmen and S. M. Carroll, “Attractor Solutions in Scalar-Field Cosmology,” Phys.Rev. D88 (2013) 083518, arXiv:1309.2611 [gr-qc]. appearing in Ch. 14: G. N. Remmen and S. M. Carroll, “How Many e-Folds Should We Expect from High-Scale Inflation?,” Phys. Rev. D90 (2014) 063517, arXiv:1405.5538 [hep-th].
Remmen, Grant Newton0000-0001-6569-8866
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ID Code:10132
Deposited By: Grant Remmen
Deposited On:30 May 2017 23:21
Last Modified:26 Oct 2021 16:40

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