Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session D13: Quantum Aspects of Gravitation - I |
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Sponsoring Units: DGRAV Chair: Steven Carlip, University of California, Davis Room: A224-225 |
Saturday, April 14, 2018 3:30PM - 3:42PM |
D13.00001: Gravitational thermodynamics of causal diamonds Ted Jacobson, Manus Visser A maximally symmetric causal diamond is a solution to Einstein's equation with a cosmological constant. We establish a ``first law", analogous to the first law of black hole mechanics, for variations to nearby solutions. It relates the variations of the bounding area, spatial volume of the maximal slice, matter Hamiltonian, and cosmological constant. The Hamiltonian is the generator of evolution along the conformal Killing flow that preserves the diamond. It is the same as the generator of York time (mean curvature) flow orthogonal to the maximal foliation, and its gravitational part is the spatial volume of the maximal slice. To interpret this first law as a Clausius relation, $\delta S = \delta Q/T$, it appears necessary to assign a negative temperature to the diamond, as has been suggested previously for the special case of the static patch of de Sitter spacetime. We discuss arguments pro and con for this negative temperature. [Preview Abstract] |
Saturday, April 14, 2018 3:42PM - 3:54PM |
D13.00002: Blurry Einstein Equation Batoul Banihashemi, Ted Jacobson The derivation of Einstein's equation from entanglement equilibrium (arxiv:1505.04753) has a limited resolution. It is inherently blurred by terms suppressed by the ratio of the Planck length to the curvature length scale. We explore the potential influence of such blurring on solutions, using both generally covariant and non-covariant models. We find indications that in the non-covariant case large deviations from the predictions of the Einstein equation might be inherited today from the early universe, whereas in the covariant case the deviation remains suppressed. [Preview Abstract] |
Saturday, April 14, 2018 3:54PM - 4:06PM |
D13.00003: Entanglement and curvature perturbations in the pre-inflationary universe Eugenio Bianchi In the approach to a classical cosmological singularity, metric perturbations at space-like separation decouple. In this talk I discuss a quantum version of this property of classical general relativity. I consider states of the quantum geometry of space which have Planckian curvature and vanishing correlations at space-like separation. These states arise naturally in loop quantum gravity. When taken as initial states for cosmological perturbations, these states lead to a new cosmological scenario in which the entanglement entropy of a region of space grows from zero to an area law during a pre-inflationary phase of the universe. I discuss imprints that these initial states can leave in the primordial power spectrum of scalar and tensor modes. [Preview Abstract] |
Saturday, April 14, 2018 4:06PM - 4:18PM |
D13.00004: Adiabatic vacua from linear complex structures Lucas Hackl, Eugenio Bianchi, Miguel Fernandez, Monica Rincon Ramirez Adiabatic vacua play an important role as initial quantum states of gravitational perturbations on a dynamical spacetime. Adiabaticity requires that the vacuum evolves slowly under the background dynamics and the standard method requires a WKB approximation to find the vacuum order by order. In this talk, I present an alternative approach that utilizes the concept of a linear complex structure to label field theory vacua and allows one to find the adiabatic vacua from a simple recursion relation. I will do this explicitly for FLRW spacetimes and comment on its relation to the adiabatically renormalized energy-momentum tensor. [Preview Abstract] |
Saturday, April 14, 2018 4:18PM - 4:30PM |
D13.00005: Pre-inflationary Dynamics of the Universe in Loop Quantum Cosmology Anzhong Wang ~Loop quantum cosmology (LQC) provides an elegant resolution of the big bang singularity by a quantum bounce in the deep Planck era. In this talk, we shall first give a brief review on LQC, and then present our recent results on the investigations of the pre-inflationary dynamics of the universe from inflation down to deep Planck regime. In particular, I shall show that the evolutions of both the flat FLRW background and its linear (scalar and tensor) perturbations are universal during the pre-inflationary phase and can be given analytically, provided that the universe was initially dominated by the kinetic energy of the inflaton at the quantum bounce. We calculate the corresponding Bogoliubov coefficients at the onset of the slow-roll inflation, which are valid for any inflationary models with a single scalar field, and show that particles are generically created during the pre-inflationary period. Matching them to those in the slow-roll inflationary phase, we investigate the effects of the quantum bounce on the power spectra and find features that can be tested by current and forthcoming observations. In particular, to be consistent with the Planck 2015 data, we find the constraints of the theory. [Preview Abstract] |
Saturday, April 14, 2018 4:30PM - 4:42PM |
D13.00006: Inflationary secular loop corrections are real Shinjini Basu, Richard Woodard The existence of secular loop corrections due to inflationary gravitons is currently a matter of great debate. It is a widespread belief among the skeptics that secular loop corrections due to quantum gravity can be subsumed into a coordinate redefinition. This is certainly true for the infrared divergences caused by modes which are initially super-horizon, but there is no reason to assume it is true for the secular dependence arising from the continual passage of initially sub-horizon modes into the super-horizon regime. Assuming it in any case would make the apparent infrared logarithm corrections to any quantity simply the result of taking the expectation value of the tree order quantity at the transformed coordinates in the graviton vacuum. We call this belief the transformation ansatz and, in arXiv:1606.02417, we have compared its predictions against explicit one loop computations in Maxwell + Einstein and Dirac + Einstein on de Sitter background. In each case the ansatz fails. [Preview Abstract] |
Saturday, April 14, 2018 4:42PM - 4:54PM |
D13.00007: Local graviton two-point function in a dressed background Jordan Moxon, Eanna Flanagan In quantum field theories, one can construct states, such as squeezed states, that source local negative expectation values of the energy density. This local violation of classical energy conditions is of interest for gravitational theories, in which negative energy densities may produce distinctive signatures in nearby metric perturbations. Semiclassical gravity is invalid for such states, due to their high variance, so we evaluate gravitational effects using an effective field theory obtained from the Einstein action coupled to a scalar. We present a detailed computation of the local two-point function of the metric perturbation sourced by a squeezed state to tree level. We canonically quantize the metric perturbation using Dirac quantization techniques, and compute the dressed state via the resulting first-class constraints. The calculation method is motivated by prior work by Donoghue and by Ford, who have explored other observables in similar theories. [Preview Abstract] |
Saturday, April 14, 2018 4:54PM - 5:06PM |
D13.00008: Local Operator Product Relations for Quantum Field Theory in Curved Spacetime Mark Klehfoth Pointwise products of quantum field operators are not well-defined. Nevertheless, products of field operators evaluated at separate spacetime points are known to satisfy asymptotic relations called operator product expansions (OPEs) in the coincidence limit. Hollands and Wald have argued interacting quantum field theories in curved spacetime are determined by the coefficients appearing in their OPEs. For interacting $\lambda\phi^4$-theory in flat Euclidean spacetime, Holland and Hollands have derived flow equations for all OPE coefficients with respect to the interaction parameter, $\lambda$. An obstacle to generalizing their result to curved spacetime is the flow equations involve an integration of OPE coefficients over all spacetime, but OPE coefficients in curved spacetime are only defined in a small neighborhood of the expansion point. Here we consider flow equations for free Klein-Gordon theory, where the mass parameter, $m^2$, will now be viewed as the interaction parameter. For this theory, the renormalization ambiguities for defining OPE coefficients are well known and tightly constrained. This enables us to determine whether renormalization ambiguities are sufficient to transform the flow equations into local relations which can then be generalized to curved spacetime. [Preview Abstract] |
Saturday, April 14, 2018 5:06PM - 5:18PM |
D13.00009: Operator mixing in deformed D1D5 CFT and the OPE on the cover Benjamin Burrington, Ian Jardine, Amanda Peet AdS/CFT is a very fruitful way to study aspects of quantum gravity. Of particular interest is the D1D5 CFT, which becomes a free orbifold CFT at a certain point in moduli space. The deformation of the theory towards the gravitational description is accomplished by a twist operator, and thus efficient techniques for computing correlation functions involving twist operators are invaluable. Using covering space techniques, operators are lifted from the base space to the covering surface and, along with information about the twist sector of the operators, the correlation function on the base space can be constructed from the correlation function on the cover. A natural question is whether the OPE on the covering surface leads to the OPE in the base space. This would yield an extremely efficient way to read off the structure constants of the orbifold CFT. We present some evidence that this is the case by exploring the correlation functions of some example operators in the D1D5 CFT at the free orbifold point using covering space techniques. [Preview Abstract] |
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