184 research outputs found
Analytic self-gravitating Skyrmions, cosmological bounces and AdS wormholes
We present a self-gravitating, analytic and globally regular Skyrmion
solution of the Einstein-Skyrme system with winding number w = 1, in presence
of a cosmological constant. The static spacetime metric is the direct product
RxS3 and the Skyrmion is the self-gravitating generalization of the static
hedgehog solution of Manton and Ruback with unit topological charge. This
solution can be promoted to a dynamical one in which the spacetime is a
cosmology of the Bianchi type-IX with time-dependent scale and squashing
coefficients. Remarkably, the Skyrme equations are still identically satisfied
for all values of these parameters. Thus, the complete set of field equations
for the Einstein-Skyrme-Lambda system in the topological sector reduces to a
pair of coupled, autonomous, nonlinear differential equations for the scale
factor and a squashing coefficient. These equations admit analytic bouncing
cosmological solutions in which the universe contracts to a minimum
non-vanishing size, and then expands. A non-trivial byproduct of this solution
is that a minor modification of the construction gives rise to a family of
stationary, regular configurations in General Relativity with negative
cosmological constant supported by an SU(2) nonlinear sigma model. These
solutions represent traversable AdS wormholes with NUT parameter in which the
only "exotic matter" required for their construction is a negative cosmological
constant.Comment: 8 pages, no figures. References added. Title slightly changed.
Clarifying comments about both the dynamical squashing and the wormhole have
been included. Version accepted for publication on PHYSICS LETTERS
Tensor to scalar ratio of perturbation amplitudes and inflaton dynamics
For the inflaton perturbations it is shown that the evolution of the
difference between the spectral indices can be translated into information on
the scale dependence of the tensor to scalar amplitudes ratio, , and how the
scalar field potential can be derived from that information. Examples are given
where converges to a constant value during inflation but dynamics are
rather different from the power--law model. Cases are presented where a
constant is not characteristic of the inflationary dynamics though the
resulting perturbation spectra are consistent with the CMB and LSS data.
The inflaton potential corresponding to given by a n--th order polynomial
of the e--folds number is derived in quadratures expressions. Since the
observable difference between the spectral indices evaluated at a pivot scale
yields information about the linear term of that polynomial, the first order
case is explicitly written down. The solutions show features beyond the
exponential form corresponding to power--law inflation and can be matched with
current observational data.Comment: 5 two-columns pages, two figures, RevTex4. Minor modifications. Two
references adde
Non-Gravitating Scalar Field in the FRW Background
We study interacting scalar field theory non-minimally coupled to gravity in
the FRW background. We show that for a specific choice of interaction terms,
the energy-momentum tensor of the scalar field vanishes, and as a result the
scalar field does not gravitate. The naive space dependent solution to
equations of motion gives rise to singular field profile. We carefully analyze
the energy-momentum tensor for such a solution and show that the singularity of
the solution gives a subtle contribution to the energy-momentum tensor. The
space dependent solution therefore is not non-gravitating. Our conclusion is
applicable to other space-time dependent non-gravitating solutions as well. We
study hybrid inflation scenario in this model when purely time dependent
non-gravitating field is coupled to another scalar field.Comment: 7 Pages, 2 figures, RevTeX4, v2:added a section on regularized
energy-momentum tensor, references and conclusions modifie
Tricritical gravity waves in the four-dimensional generalized massive gravity
We construct a generalized massive gravity by combining quadratic curvature
gravity with the Chern-Simons term in four dimensions. This may be a candidate
for the parity-odd tricritical gravity theory. Considering the AdS vacuum
solution, we derive the linearized Einstein equation, which is not similar to
that of the three dimensional (3D) generalized massive gravity. When a
perturbed metric tensor is chosen to be the Kerr-Schild form, the linearized
equation reduces to a single massive scalar equation. At the tricritical points
where two masses are equal to -1 and 2, we obtain a log-square wave solution to
the massive scalar equation. This is compared to the 3D tricritical generalized
massive gravity whose dual is a rank-3 logarithmic conformal field theory.Comment: 17 pages, 1 figure, version to appear in EPJ
The geometry of Schr\"odinger symmetry in non-relativistic CFT
The non-relativistic conformal "Schroedinger" symmetry of some gravity
backgrounds proposed recently in the AdS/CFT context, is explained in the
"Bargmann framework". The formalism incorporates the Equivalence Principle.
Newton-Hooke conformal symmetries, which are analogs of those of Schroedinger
in the presence of a negative cosmological constant, are discussed in a similar
way. Further examples include topologically massive gravity with negative
cosmological constant and the Madelung hydrodynamical description.Comment: RevTex, 7 pages, no figures. Presentation rearranged, minor
corrections, some more references adde
Regular black holes in UV self-complete quantum gravity
In this letter we investigate the role of regular (curvature
singularity-free) black holes in the framework of UV self-complete quantum
gravity. The existence of a minimal length, shielding the trans-Planckian
regime to any physical probe, is self-consistently included into the black hole
probe itself. In this way we obtain to slightly shift the barrier below the
Planck Length, with the UV self-complete scenario self-consistently confirmed.Comment: 11 pages, 3 figures, new comments and references, final version
accepted for publication in PL
Lovelock-Lifshitz Black Holes
In this paper, we investigate the existence of Lifshitz solutions in Lovelock
gravity, both in vacuum and in the presence of a massive vector field. We show
that the Lovelock terms can support the Lifshitz solution provided the
constants of the theory are suitably chosen. We obtain an exact black hole
solution with Lifshitz asymptotics of any scaling parameter in both
Gauss-Bonnet and in pure 3rd order Lovelock gravity. If matter is added in the
form of a massive vector field, we also show that Lifshitz solutions in
Lovelock gravity exist; these can be regarded as corrections to Einstein
gravity coupled to this form of matter. For this form of matter we numerically
obtain a broad range of charged black hole solutions with Lifshitz asymptotics,
for either sign of the cosmological constant. We find that these asymptotic
Lifshitz solutions are more sensitive to corrections induced by Lovelock
gravity than are their asymptotic AdS counterparts. We also consider the
thermodynamics of the black hole solutions and show that the temperature of
large black holes with curved horizons is proportional to where is
the critical exponent; this relationship holds for black branes of any size. As
is the case for asymptotic AdS black holes, we find that an extreme black hole
exists only for the case of horizons with negative curvature. We also find that
these Lovelock-Lifshitz black holes have no unstable phase, in contrast to the
Lovelock-AdS case. We also present a class of rotating Lovelock-Lifshitz black
holes with Ricci-flat horizons.Comment: 26 pages, 10 figures, a few references added, typo fixed and some
comments have been adde
Renormalizability of Massive Gravity in Three Dimensions
We discuss renormalizability of a recently established, massive gravity
theory with particular higher derivative terms in three space-time dimensions.
It is shown that this massive gravity is certainly renormalizable as well as
unitary, so it gives us a physically interesting toy model of perturbative
quantum gravity in three dimensions.Comment: 13 pages, no figure
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