73 research outputs found
A Proof Of Ghost Freedom In de Rham-Gabadadze-Tolley Massive Gravity
We identify different helicity degrees of freedom of Fierz-Paulian massive
gravity around generic backgrounds. We show that the two-parameter family
proposed by de Rham, Gabadadze, and Tolley always propagates five degrees of
freedom and therefore is free from the Boulware-Deser ghost. The analysis has a
number of byproducts, among which (a) it shows how the original decoupling
limit construction ensures ghost freedom of the full theory, (b) it reveals an
enhanced symmetry of the theory around linearized backgrounds, and (c) it
allows us to give an algorithm for finding dispersion relations. The proof
naturally extends to generalizations of the theory with a reference metric
different from Minkowski.Comment: 34 pages; references added and the presentation improve
Uptunneling to de Sitter
Abstract
We propose a Euclidean preparation of an asymptotically AdS2 spacetime that contains an inflating dS2 bubble. The setup can be embedded in a four dimensional theory with a Minkowski vacuum and a false vacuum. AdS2 approximates the near horizon geometry of a two-sided near-extremal Reissner-Nordström black hole, and the two sides can connect to the same Minkowski asymptotics to form a topologically nontrivial worm- hole geometry. Likewise, in the false vacuum the near-horizon geometry of near-extremal black holes is approximately dS2 times 2-sphere. We interpret the Euclidean solution as describing the decay of an excitation inside the wormhole to a false vacuum bubble. The result is an inflating region inside a non-traversable asymptotically Minkowski wormhole
Double Soft Limits of Cosmological Correlations
Correlation functions of two long-wavelength modes with several
short-wavelength modes are shown to be related to lower order correlation
functions, using the background wave method, and independently, by exploiting
symmetries of the wavefunction of the Universe. These soft identities follow
from the non-linear extension of the adiabatic modes of Weinberg, and their
generalization by Hinterbichler et. al. The extension is shown to be unique. A
few checks of the identities are presented.Comment: 18+16 page
CMB Anisotropies from a Gradient Mode
A linear gradient mode must have no observable dynamical effect on short
distance physics. We confirm this by showing that if there was such a gradient
mode extending across the whole observable Universe, it would not cause any
hemispherical asymmetry in the power of CMB anisotropies, as long as
Maldacena's consistency condition is satisfied. To study the effect of the long
wavelength mode on short wavelength modes, we generalize the existing second
order Sachs-Wolfe formula in the squeezed limit to include a gradient in the
long mode and to account for the change in the location of the last scattering
surface induced by this mode. Next, we consider effects that are of second
order in the long mode. A gradient mode generated in Single-field inflation is shown to induce an observable
quadrupole moment. For instance, in a matter-dominated model it is equal to
. This quadrupole can be canceled
by superposition of a quadratic perturbation. The result is shown to be a
nonlinear extension of Weinberg's adiabatic modes: a long-wavelength physical
mode which looks locally like a coordinate transformation.Comment: 21+8 pages. improved presentatio
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