Related papers: Superluminal censorship
A non-singular cosmological bounce in the Einstein frame can only take place if the Null Energy Condition (NEC) is violated. We explore situations where a single scalar field drives the NEC violation and derive the constraints imposed by…
Using Finsler brane solutions [see details and methods in: S. Vacaru, Class. Quant. Grav. 28 (2011) 215001], we show that neutrinos may surpass the speed of light in vacuum which can be explained by trapping effects from gravity theories on…
We revisit the model building challenges that one faces when trying to reconcile the OPERA claim of neutrino superluminality with other observational constraints. The severity of the supernova bound and of the kinematical constraints of…
We study the Null Energy Condition (NEC) arising from the Virasoro constraint on the string worldsheet. We then analyze how the NEC in the external spacetime directions emerges under general time-dependent string compactifications. Finally,…
If Einstein's equations are to describe a field theory of gravity in Minkowski spacetime, then causality requires that the effective curved metric must respect the flat background metric's null cone. The kinematical problem is solved using…
The null energy condition (NEC) is a cornerstone of general relativity, and its violation could leave observable imprints in the cosmic gravitational wave spectrum. Theoretical models suggest that NEC violations during inflation can amplify…
The superluminal behaviors of neutrinos were reported by the OPERA collaboration recently. It was also noticed by Cohen and Glashow that, in standard quantum field theory, the superluminal neutrinos would lose their energy via the…
Eternal inflation is shown to require violations of the Null Energy Condition (NEC) on superhorizon scales. With light scalar fields as the matter sources in a de Sitter background, there can be no classical or semiclassical violations of…
The velocity anomaly recently reported by the OPERA collaboration appears strikingly at odds with the theory of special relativity. I offer a reinterpretation which removes this conflict, to wit that neutrinos yield a truer measurement of…
While special relativity imposes an absolute speed limit at the speed of light, our Universe is not empty Minkowski spacetime. The constituents that fill the interstellar/intergalactic vacuum, including the cosmic microwave background…
We study whether a violation of the null energy condition necessarily implies the presence of instabilities. We prove that this is the case in a large class of situations, including isotropic solids and fluids relevant for cosmology. On the…
We study the simplest concrete theory for spontaneous Lorentz violation, the ``New Aether Theory'' of Jacobson and Mattingly, which is a vector-tensor gravitational theory with a fixed-modulus condition on the vector field. We show that the…
The Ernst spacetime is a solution of the Einstein-Maxwell equations describing two charged black holes accelerating apart in a uniform electric (or magnetic) field. As the field approaches a critical value, the black hole horizon appears to…
The null energy or null convergence condition (NEC) is one of the fundamental assumptions necessary for many celebrated results from Lorentzian Geometry and Mathematical General Relativity. As such there have been several recent efforts to…
I investigate the possibility of the propagation of neutrino with superluminal speed through matter in the context of the relation between gravity, spin and torsion. Using a lemma of Penrose and earlier works on the relation between spin,…
We consider how accelerated expansion, whether due to inflation or dark energy, imposes strong constraints on fundamental theories obtained by compactification from higher dimensions. For theories that obey the null energy condition (NEC),…
General relativity provides an appropriate framework for addressing the issue of sub- or superluminality as an apparent effect. Even though a massless particle travels on the light cone, its average velocity over a finite path measured by…
The classic singularity theorems of General Relativity rely on energy conditions that can be violated in semiclassical gravity. Here, we provide motivation for an energy condition obeyed by semiclassical gravity: the smeared null energy…
Field theories which violate the null energy condition (NEC) are of interest for the solution of the cosmological singularity problem and for models of cosmological dark energy with the equation of state parameter $w<-1$. We discuss the…
The OPERA collaboration has announced to have observed superluminal neutrinos with a mean energy 17.5 GeV, but afterward the superluminal interpretation of the OPERA results has been refuted theoretically by Cherenkov-like radiation and…