Null energy condition and superluminal propagation
Sergei Dubovsky,Sergei Dubovsky,Thomas Gregoire,Thomas Gregoire,Alberto Nicolis,Riccardo Rattazzi +5 more
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In this paper, the null energy condition is violated in a large class of situations, including isotropic solids and fluids relevant for cosmology, and the existence of superluminal modes is shown to imply the presence of instabilities.Abstract:
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 other hand we present several counter-examples of consistent effective field theories possessing a stable background where the null energy condition is violated. Two necessary features of these counter-examples are the lack of isotropy of the background and the presence of superluminal modes. We argue that many of the properties of massive gravity can be understood by associating it to a solid at the edge of violating the null energy condition. We briefly analyze the difficulties of mimicking u H > 0 in scalar tensor theories of gravity.read more
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The effective field theory of multi-component fluids
Guillermo Ballesteros,Guillermo Ballesteros,Brando Bellazzini,Brando Bellazzini,Lorenzo Mercolli +4 more
TL;DR: In this article, the effective Lagrangian at leading order in derivatives has been studied for cosmological applications and it has been shown that interactions lead to anisotropic stresses that depend on the mixing terms in the quadratic action for perturbations.
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Reconstructing the History of Energy Condition Violation from Observational Data
TL;DR: In this article, the authors study the likelihood of energy condition violations in the history of the universe and find that the data suggest a history of strong energy condition violation, but the null and dominant energy conditions are likely to be fulfilled.
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Higher derivative scalar-tensor theory through a non-dynamical scalar field
TL;DR: In this paper, a non-dynamical scalar field with spacelike gradient is proposed to fix a scalar mode in the gravity sector, which preserves only spatial covariance.
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Note on scalars, perfect fluids, constrained field theories, and all that
TL;DR: In this article, the Lagrangian density for the velocitypotential can be read directly from the expression relating the pressure with the Taub charge and the entropy per particle in the fluid, whereas the other quantities of interest can be obtained from the thermodynamic relations.
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Aspects of Galileon Non-Renormalization
TL;DR: In this paper, non-renormalization theorems applying to Galileon field theories and their generalizations are discussed and compared to other derivatively coupled effective field theories, including general relativity and $P(X)$ theories.
References
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The Large Scale Structure of Space-Time
TL;DR: In this paper, the authors discuss the General Theory of Relativity in the large and discuss the significance of space-time curvature and the global properties of a number of exact solutions of Einstein's field equations.
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Type Ia supernova discoveries at z > 1 from the Hubble Space Telescope: Evidence for past deceleration and constraints on dark energy evolution
Adam G. Riess,Louis-Gregory Strolger,John L. Tonry,Stefano Casertano,Henry C. Ferguson,Bahram Mobasher,Peter Challis,Alexei V. Filippenko,Saurabh Jha,Weidong Li,Ryan Chornock,Robert P. Kirshner,Bruno Leibundgut,Mark Dickinson,Mario Livio,Mauro Giavalisco,Charles C. Steidel,Txitxo Benítez,Zlatan Tsvetanov +18 more
TL;DR: For a flat universe with a cosmological constant, the transition between the two epochs is constrained to be at z = 0.46 ± 0.13 as mentioned in this paper, and w = -1.02 ± (and w < -0.76 at the 95% confidence level) for an assumed static equation of state of dark energy.
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Type Ia Supernova Discoveries at z>1 From the Hubble Space Telescope: Evidence for Past Deceleration and Constraints on Dark Energy Evolution
Adam G. Riess,Louis-Gregory Strolger,John L. Tonry,Stefano Casertano,Henry C. Ferguson,Bahram Mobasher,Peter Challis,Alexei V. Filippenko,Saurabh Jha,Weidong Li,Ryan Chornock,Robert P. Kirshner,Bruno Leibundgut,Mark Dickinson,Mario Livio,Mauro Giavalisco,Charles C. Steidel,Narciso Benítez,Zlatan Tsvetanov +18 more
TL;DR: In this article, the first conclusive evidence for cosmic deceleration that preceded the current epoch of cosmic acceleration was provided by the discovery of 16 Type Ia supernovae with the Hubble Space Telescope (HST).
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4D Gravity on a Brane in 5D Minkowski Space
TL;DR: In this article, the authors propose a mechanism by which four-dimensional Newtonian gravity emerges on a 3-brane in 5D Minkowski space with an infinite size extra dimension.