47 research outputs found
The Noise of Gravitons
We show that when the gravitational field is treated quantum-mechanically, it
induces fluctuations -- noise -- in the lengths of the arms of gravitational
wave detectors. The characteristics of the noise depend on the quantum state of
the gravitational field, and can be calculated exactly in several interesting
cases. For coherent states the noise is very small, but it can be greatly
enhanced in thermal and (especially) squeezed states. Detection of this
fundamental noise would constitute direct evidence for the quantization of
gravity and the existence of gravitons.Comment: First prize in the Gravity Research Foundation Essay Competition. 6
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Covariant constraints for generic massive gravity and analysis of its characteristics
We perform a covariant constraint analysis of massive gravity valid for its
entire parameter space, demonstrating that the model generically propagates
five degrees of freedom; this is also verified by a new and streamlined
Hamiltonian description. The constraint's covariant expression permits
computation of the model's caustics. Although new features such as the
dynamical Riemann tensor appear in the characteristic matrix, the model still
exhibits the pathologies uncovered in earlier work: superluminality and likely
acausalities.Comment: 26 pages LaTeX, references added, version to appear in Phys. Rev.
From k-essence to generalised Galileons
We determine the most general scalar field theories which have an action that
depends on derivatives of order two or less, and have equations of motion that
stay second order and lower on flat space-time. We show that those theories can
all be obtained from linear combinations of Lagrangians made by multiplying a
particular form of the Galileon Lagrangian by an arbitrary scalar function of
the scalar field and its first derivatives. We also obtain curved space-time
extensions of those theories which have second order field equations for both
the metric and the scalar field. This provide the most general extension, under
the condition that field equations stay second order, of k-essence, Galileons,
k-Mouflage as well as of the kinetically braided scalars. It also gives the
most general action for a scalar classicalizer, which has second order field
equations. We discuss the relation between our construction and the Euler
hierachies of Fairlie et al, showing in particular that Euler hierachies allow
one to obtain the most general theory when the latter is shift symmetric. As a
simple application of our formalism, we give the covariantized version of the
conformal Galileon.Comment: 25 page