515 research outputs found
The recovery of General Relativity in massive gravity via the Vainshtein mechanism
We study in detail static spherically symmetric solutions of non linear
Pauli-Fierz theory. We obtain a numerical solution with a constant density
source. This solution shows a recovery of the corresponding solution of General
Relativity via the Vainshtein mechanism. This result has already been presented
by us in a recent letter, and we give here more detailed information on it as
well as on the procedure used to obtain it. We give new analytic insights upon
this problem, in particular for what concerns the question of the number of
solutions at infinity. We also present a weak field limit which allows to
capture all the salient features of the numerical solution, including the
Vainshtein crossover and the Yukawa decay.Comment: 38 pages, 9 Figs, revtex
Ghosts, Strong Coupling and Accidental Symmetries in Massive Gravity
We show that the strong self-interaction of the scalar polarization of a
massive graviton can be understood in terms of the propagation of an extra
ghost-like degree of freedom, thus relating strong coupling to the sixth degree
of freedom discussed by Boulware and Deser in their Hamiltonian analysis of
massive gravity. This enables one to understand the Vainshtein recovery of
solutions of massless gravity as being due to the effect of the exchange of
this ghost which gets frozen at distances larger than the Vainshtein radius.
Inside this region, we can trust the two-field Lagrangian perturbatively, while
at larger distances one can use the higher derivative formulation. We also
compare massive gravity with other models, namely deconstructed theories of
gravity, as well as DGP model. In the latter case we argue that the Vainshtein
recovery process is of different nature, not involving a ghost degree of
freedom.Comment: 21 page
Matrix Gravity and Massive Colored Gravitons
We formulate a theory of gravity with a matrix-valued complex vierbein based
on the SL(2N,C)xSL(2N,C) gauge symmetry. The theory is metric independent, and
before symmetry breaking all fields are massless. The symmetry is broken
spontaneously and all gravitons corresponding to the broken generators acquire
masses. If the symmetry is broken to SL(2,C) then the spectrum would correspond
to one massless graviton coupled to massive gravitons. A novel
feature is the way the fields corresponding to non-compact generators acquire
kinetic energies with correct signs. Equally surprising is the way Yang-Mills
gauge fields acquire their correct kinetic energies through the coupling to the
non-dynamical antisymmetric components of the vierbeins.Comment: One reference adde
A note on the uniqueness of D=4 N=1 Supergravity
We investigate in 4 spacetime dimensions, all the consistent deformations of
the lagrangian , which is the sum of the
Pauli-Fierz lagrangian for a free massless spin 2 field and the
Rarita-Schwinger lagrangian for a free massless spin 3/2
field. Using BRST cohomogical techniques, we show, under the assumptions of
locality, Poincar\'e invariance, conservation of the number of gauge symmetries
and the number of derivatives on each fields, that N=1 D=4 supergravity is the
only consistent interaction between a massless spin 2 and a massless spin 3/2
field. We do not assume general covariance. This follows automatically, as does
supersymmetry invariance. Various cohomologies related to conservations laws
are also given.Comment: 22+1 pages, LaTeX. References adde
Einstein and Jordan frames reconciled: a frame-invariant approach to scalar-tensor cosmology
Scalar-Tensor theories of gravity can be formulated in different frames, most
notably, the Einstein and the Jordan one. While some debate still persists in
the literature on the physical status of the different frames, a frame
transformation in Scalar-Tensor theories amounts to a local redefinition of the
metric, and then should not affect physical results. We analyze the issue in a
cosmological context. In particular, we define all the relevant observables
(redshift, distances, cross-sections, ...) in terms of frame-independent
quantities. Then, we give a frame-independent formulation of the Boltzmann
equation, and outline its use in relevant examples such as particle freeze-out
and the evolution of the CMB photon distribution function. Finally, we derive
the gravitational equations for the frame-independent quantities at first order
in perturbation theory. From a practical point of view, the present approach
allows the simultaneous implementation of the good aspects of the two frames in
a clear and straightforward way.Comment: 15 pages, matches version to be published on Phys. Rev.
Generation of Entanglement Outside of the Light Cone
The Feynman propagator has nonzero values outside of the forward light cone.
That does not allow messages to be transmitted faster than the speed of light,
but it is shown here that it does allow entanglement and mutual information to
be generated at space-like separated points. These effects can be interpreted
as being due to the propagation of virtual photons outside of the light cone or
as a transfer of pre-existing entanglement from the quantum vacuum. The
differences between these two interpretations are discussed.Comment: 25 pages, 7 figures. Additional references and figur
Finite Size Effects in Thermal Field Theory
We consider a neutral self-interacting massive scalar field defined in a
d-dimensional Euclidean space. Assuming thermal equilibrium, we discuss the
one-loop perturbative renormalization of this theory in the presence of rigid
boundary surfaces (two parallel hyperplanes), which break translational
symmetry. In order to identify the singular parts of the one-loop two-point and
four-point Schwinger functions, we use a combination of dimensional and
zeta-function analytic regularization procedures. The infinities which occur in
both the regularized one-loop two-point and four-point Schwinger functions fall
into two distinct classes: local divergences that could be renormalized with
the introduction of the usual bulk counterterms, and surface divergences that
demand countertems concentrated on the boundaries. We present the detailed form
of the surface divergences and discuss different strategies that one can assume
to solve the problem of the surface divergences. We also briefly mention how to
overcome the difficulties generated by infrared divergences in the case of
Neumann-Neumann boundary conditions.Comment: 31 pages, latex, to appear in J. Math. Phy
Microscopic theory of the Casimir force at thermal equilibrium: large-separation asymptotics
We present an entirely microscopic calculation of the Casimir force
between two metallic plates in the limit of large separation . The models of
metals consist of mobile quantum charges in thermal equilibrium with the photon
field at positive temperature . Fluctuations of all degrees of freedom,
matter and field, are treated according to the principles of quantum
electrodynamics and statistical physics without recourse to approximations or
intermediate assumptions. Our main result is the correctness of the asymptotic
universal formula f(d) \sim -\frac{\zeta(3) \kB T}{8\pi d^3}, .
This supports the fact that, in the framework of Lifshitz' theory of
electromagnetic fluctuations, transverse electric modes do not contribute in
this regime. Moreover the microscopic origin of universality is seen to rely on
perfect screening sum rules that hold in great generality for conducting media.Comment: 34 pages, 0 figures. New version includes restructured intro and
minor typos correcte
On the Energy-Momentum Tensor of the Scalar Field in Scalar--Tensor Theories of Gravity
We study the dynamical description of gravity, the appropriate definition of
the scalar field energy-momentum tensor, and the interrelation between them in
scalar-tensor theories of gravity. We show that the quantity which one would
naively identify as the energy-momentum tensor of the scalar field is not
appropriate because it is spoiled by a part of the dynamical description of
gravity. A new connection can be defined in terms of which the full dynamical
description of gravity is explicit, and the correct scalar field
energy-momentum tensor can be immediately identified. Certain inequalities must
be imposed on the two free functions (the coupling function and the potential)
that define a particular scalar-tensor theory, to ensure that the scalar field
energy density never becomes negative. The correct dynamical description leads
naturally to the Einstein frame formulation of scalar-tensor gravity which is
also studied in detail.Comment: Submitted to Phys. Rev D15, 10 pages. Uses ReVTeX macro
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