717 citations · 4.8k across the 112 of their papers we have counts for
34 papers · 1 filter
Pure gauge theory for the gravitational spin connection
Stephon Alexander, Tucker Manton
The gravitational spin connection appears in gravity as a non-Abelian gauge field for the Lorentz group , which is non-compact. The action for General Relativity is linear…
An Exact Fermionic Chern-Simons-Kodama State in Quantum Gravity
Stephon Alexander, Tatsuya Daniel, Marcell Howard +1
The Chern-Simons-Kodama (CSK) state is an exact, non-perturbative wave function in the Ashtekar formulation of classical General Relativity. In this work, we find a generalized fer…
Torsion and the Probability of Inflation
Emma Albertini, Stephon Alexander, Gabriel Herczeg +1
We revisit the problem of the "probability of inflation" from the point of view of the Einstein-Cartan theory, where torsion can be present off-shell even in the absence of spinori…
Black Hole Superradiance in Dynamical Chern-Simons Gravity
Stephon Alexander, Gregory Gabadadze, Leah Jenks +1
Black hole superradiance provides a window into the dynamics of light scalar fields and their interactions close to a rotating black hole. Due to the rotation of the black hole, th…
Black hole and cosmological analysis of BF sequestered gravity
Stephon Alexander, Steven J. Clark, Gabriel Herczeg +1
We study a minimal extension of a recently proposed modification of general relativity that draws on concepts from topological field theory to resolve aspects of the cosmological c…
A generalized Hartle-Hawking wavefunction
Stephon Alexander, Gabriel Herczeg, Joao Magueijo
The Hartle-Hawking wave function is known to be the Fourier dual of the Chern-Simons or Kodama state reduced to mini-superspace, using an integration contour covering the whole rea…
Probing Noncommutative Gravity with Gravitational Wave and Binary Pulsar Observations
Leah Jenks, Kent Yagi, Stephon Alexander
Noncommutative gravity is a natural method of quantizing spacetime by promoting the spacetime coordinates themselves to operators which do not commute. This approach is motivated,…
Chiral Symmetry and the Cosmological Constant
Stephon Alexander, Gabriel Herczeg, Jinglong Liu +1
In this work we provide a link between a nearly vanishing cosmological constant and chiral symmetry. This is accomplished with a modification of General Relativity coupled to a top…
Gravity waves in parity-violating Copernican Universes
Stephon Alexander, Leah Jenks, Pavel Jiroušek +2
In recent work minimal theories allowing the variation of the cosmological constant by means of a balancing torsion, have been proposed. It was found that such theories contain par…
The cosmology of minimal varying Lambda theories
Stephon Alexander, Marina Cortês, Andrew R. Liddle +3
Inserting a varying Lambda in Einstein's field equations can be made consistent with the Bianchi identities by allowing for torsion, without the need to add scalar field degrees of…
A Zero-Parameter Extension of General Relativity with Varying Cosmological Constant
Stephon Alexander, Marina Cortês, Andrew R. Liddle +3
We provide a new extension of general relativity (GR) which has the remarkable property of being more constrained than GR plus a cosmological constant, having one less free paramet…
Topological Features of the Quantum Vacuum
Stephon Alexander, Raúl Carballo-Rubio
A central aspect of the cosmological constant problem is to understand why vacuum energy does not gravitate. In order to account for this observation, while allowing for nontrivial…
An Entropy-Area Law for Neutron Stars Near the Black Hole Threshold
Stephon H. Alexander, Kent Yagi, Nicolas Yunes
Neutron stars exhibit a set of universal relations independent of their equation of state that bears semblance to the black hole no hair relations. Motivated by this, we analytical…
Hidden-Sector Modifications to Gravitational Waves From Binary Inspirals
Stephon Alexander, Evan McDonough, Robert Sims +1
Gravitational wave astronomy has placed strong constraints on fundamental physics, and there is every expectation that future observations will continue to do so. In this work we q…
The quantum cosmological constant
Stephon Alexander, Joao Magueijo, Lee Smolin
We present an extension of general relativity in which the cosmological constant becomes dynamical and turns out to be conjugate to the Chern-Simons invariant of the Ashtekar conne…
The Equivalence Principle and the Emergence of Flat Rotation Curves
Stephon Alexander, Lee Smolin
We explain flat rotation curves and the baryonic Tully-Fisher relation by a combination of three hypotheses. The first is a formulation of the equivalence principle for gravitation…
Gravitational Waves Probes of Parity Violation in Compact Binary Coalescence
Stephon H. Alexander, Nicolas Yunes
Is gravity parity violating? Given the recent observations of gravitational waves from coalescing compact binaries, we develop a strategy to find an answer with current and future…
On the Classical and Quantum Stability of a Cosmic Ghost
Stephon Alexander, Sam Cormack, David Lowe +1
Ghost fields have reemerged in a handful of phenomenologically motivated cosmological and particle physics scenarios, and most recently in a cyclic mechanism to address the fine-tu…
On a Relation of Vacuum Energy to the Hierarchy of Forces
Stephon Alexander, Laura Mersini-Houghton
We investigate the relation between vacuum energy and the hierarchy of forces in habitable universes. The hierarchy of forces studied in \cite{fred} was bound by $\frac{α_G}α \le 1…
V-mode Polarization in Axion Inflation and Preheating
Stephon Alexander, Evan McDonough, Robert Sims
We study the production of primordial circular ("V-mode") polarization in axion inflation coupled to fermions and gauge fields, with special attention paid to (p)reheating. We cons…
Dark matter and baryogenesis in the Fermi-bounce curvaton mechanism
Andrea Addazi, Stephon Alexander, Yi-Fu Cai +1
We elaborate on a toy-model of matter bounce, in which the matter content is constituted by two fermion species endowed with four fermion interaction term. We describe the curvaton…
A Unified picture of Dark Matter and Dark Energy from Invisible QCD
Andrea Addazi, Antonino Marciano, Stephon Alexander
It has been shown in a companion paper that the late time acceleration of the universe can be accounted for by an extension of the QCD color to a invisible sector (IQCD). I…
Inflation and the Measurement Problem
Stephon Alexander, Dhrubo Jyoti, Joao Magueijo
We propose a solution to the quantum measurement problem in Inflation. Our model treats Fourier modes of cosmological perturbations as analogous to particles in a weakly-interactin…
Turning on gravity with the Higgs mechanism
Stephon Alexander, John D. Barrow, Joao Magueijo
We investigate how a Higgs mechanism could be responsible for the emergence of gravity in extensions of Einstein theory. In this scenario, at high energies, symmetry restoration co…