Ted Jacobson
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View article: On the viability of minimal Hořava gravity
On the viability of minimal Hořava gravity Open
Hořava gravity is a Lorentz-violating modification of general relativity (GR) with a preferred spacelike foliation. Observational evidence has put strong constraints on the parameter values in this model, so that the remaining viable secto…
View article: Guiding-centre Lagrangian and quasi-symmetry
Guiding-centre Lagrangian and quasi-symmetry Open
A charged particle in a suitably strong magnetic field spirals along the field lines while slowly drifting transversely. This note provides a brief derivation of an effective Lagrangian formulation for the guiding-centre approximation that…
View article: On the lapse contour in the gravitational path integral
On the lapse contour in the gravitational path integral Open
The gravitational path integral is usually implemented with a covariant action by analogy with other gauge field theories, but the gravitational case is different in important ways. A key difference is that the integrand has an essential s…
View article: The enigmatic gravitational partition function
The enigmatic gravitational partition function Open
The saddle point approximation to formal quantum gravitational partition functions has yielded plausible computations of horizon entropy in various settings, but it stands on shaky ground. In this paper we visit some of that shaky ground, …
View article: Pulsar Nulling and Vacuum Radio Emission from Axion Clouds
Pulsar Nulling and Vacuum Radio Emission from Axion Clouds Open
Nonrelativistic axions can be efficiently produced in the polar caps of pulsars, resulting in the formation of a dense cloud of gravitationally bound axions. Here, we investigate the interplay between such an axion cloud and the electrodyn…
View article: Feynman 1947 letter on path integral for the Dirac equation
Feynman 1947 letter on path integral for the Dirac equation Open
In 1947, four months before the famous Shelter Island conference, Richard Feynman wrote a lengthy letter to his former MIT classmate Theodore Welton, reporting on his efforts to develop a path integral describing the propagation of a Dirac…
View article: Guiding-centre Lagrangian and quasi-symmetry
Guiding-centre Lagrangian and quasi-symmetry Open
A charged particle in a suitably strong magnetic field spirals along the field lines while slowly drifting transversely. This note provides a brief derivation of an effective Lagrangian formulation for the guiding-centre approximation that…
View article: de Sitter horizon entropy from a simplicial Lorentzian path integral
de Sitter horizon entropy from a simplicial Lorentzian path integral Open
The dimension of the Hilbert space of a quantum gravitational system can be written formally as a path integral partition function over Lorentzian metrics. We implement this in a 2+1 dimensional simplicial minisuperspace model in which the…
View article: On the lapse contour in the gravitational path integral
On the lapse contour in the gravitational path integral Open
The gravitational path integral is usually implemented with a covariant action by analogy with other gauge field theories, but the gravitational case is different in important ways. A key difference is that the integrand has an essential s…
View article: Pulsar Nulling and Vacuum Radio Emission from Axion Clouds
Pulsar Nulling and Vacuum Radio Emission from Axion Clouds Open
Non-relativistic axions can be efficiently produced in in the polar caps of pulsars, resulting in the formation of a dense cloud of gravitationally bound axions. Here, we investigate the interplay between such an axion cloud and the electr…
View article: Entropy of causal diamond ensembles
Entropy of causal diamond ensembles Open
We define a canonical ensemble for a gravitational causal diamond by introducing an artificial York boundary inside the diamond with a fixed induced metric and temperature, and evaluate the partition function using a saddle point approxima…
View article: Partition Function for a Volume of Space
Partition Function for a Volume of Space Open
We consider the quantum gravity partition function that counts the dimension of the Hilbert space of a spatial region with topology of a ball and fixed proper volume, and evaluate it in the leading order saddle point approximation. The res…
View article: Report on scipost_202303_00042v1
Report on scipost_202303_00042v1 Open
We define a canonical ensemble for a gravitational causal diamond by introducing an artificial York boundary inside the diamond with a fixed induced metric and temperature, and evaluate the partition function using a saddle point approxima…
View article: Report on 2212.10608v3
Report on 2212.10608v3 Open
We define a canonical ensemble for a gravitational causal diamond by introducing an artificial York boundary inside the diamond with a fixed induced metric and temperature, and evaluate the partition function using a saddle point approxima…
View article: Partition function for a volume of space
Partition function for a volume of space Open
We consider the quantum gravity partition function that counts the dimension of the Hilbert space of a spatial region with topology of a ball and fixed proper volume, and evaluate it in the leading order saddle point approximation. The res…
View article: Entropy of causal diamond ensembles
Entropy of causal diamond ensembles Open
We define a canonical ensemble for a gravitational causal diamond by introducing an artificial York boundary inside the diamond with a fixed induced metric and temperature, and evaluate the partition function using a saddle point approxima…
View article: The minus sign in the first law of de Sitter horizons
The minus sign in the first law of de Sitter horizons Open
Due to a well-known, but curious, minus sign in the Gibbons-Hawking first law for the static patch of de Sitter space, the entropy of the cosmological horizon is reduced by the addition of Killing energy. This minus sign raises the puzzlin…
View article: Causal diamonds in 2+1 dimensional quantum gravity
Causal diamonds in 2+1 dimensional quantum gravity Open
We develop the reduced phase space quantization of causal diamonds in pure 2+1 dimensional gravity with a non-positive cosmological constant. The system is defined as the domain of dependence of a topological disc with fixed boundary metri…
View article: Rotating black holes in Einstein-aether theory
Rotating black holes in Einstein-aether theory Open
We introduce new methods to numerically construct for the first time stationary axisymmetric black hole solutions in Einstein-aether theory and study their properties. The key technical challenge is to impose regularity at the spin-2, 1, a…
View article: Scrambling and the black hole atmosphere
Scrambling and the black hole atmosphere Open
We argue that the scrambling time is the same, up to a numerical factor in three or more spacetime dimensions, as the time for the atmosphere to fall across the horizon or escape, to be replaced by new atmosphere. We propose that these tim…
View article: Report on 2009.04512v3
Report on 2009.04512v3 Open
We revisit the theoretical analysis of an expanding ring-shaped Bose-Einstein condensate.Starting from the action and integrating over dimensions orthogonal to the phonon's direction of travel, we derive an effective one-dimensional wave e…
View article: Report on 2009.04512v2
Report on 2009.04512v2 Open
We revisit the theoretical analysis of an expanding ring-shaped Bose-Einstein condensate.Starting from the action and integrating over dimensions orthogonal to the phonon's direction of travel, we derive an effective one-dimensional wave e…
View article: Report on 2009.04512v2
Report on 2009.04512v2 Open
We revisit the theoretical analysis of an expanding ring-shaped Bose-Einstein condensate.Starting from the action and integrating over dimensions orthogonal to the phonon's direction of travel, we derive an effective one-dimensional wave e…
View article: Report on 1812.01596v2
Report on 1812.01596v2 Open
A maximally symmetric causal diamond is a solution to Einstein's equation with a cosmological constant.We establish a Smarr formula for such diamonds and a "first law" for variations to nearby solutions.The latter relates the variations of…
View article: Diffeomorphism invariance and the black hole information paradox
Diffeomorphism invariance and the black hole information paradox Open
We argue that the resolution to the black hole information paradox lies in a\nproper accounting of the implications of diffeomorphism invariance for the\nHilbert space and observables of quantum gravity. The setting of asymptotically\nAnti…
View article: Blandford-Znajek process <i>in vacuo</i> and its holographic dual
Blandford-Znajek process <i>in vacuo</i> and its holographic dual Open
Blandford and Znajek discovered a process by which a spinning black hole can transfer rotational energy to a plasma, offering a mechanism for energy and jet emissions from quasars. Here we describe a version of this mechanism that operates…