17 research outputs found
Discussing Quantum Aspects of Higher-Derivative 3D-Gravity in the First-Order Formalism
In this paper, we reassess the issue of deriving the propagators and
identifying the spectrum of excitations associated to the vielbein and spin
connection of (1+2)-D gravity in the presence of dynamical torsion, while
working in the first-order formulation. A number of peculiarities is pointed
out whenever the Chern-Simons term is taken into account along with a
combination of bilinear terms in the torsion tensor. We present a procedure to
derive the full set of propagators, based on an algebra of enlarged spin-type
operators, and we discuss under which conditions the poles of the tree-level
2-point functions correspond to physical excitations that do not conflict with
causality and unitarity
Big bounce from spin and torsion
The Einstein-Cartan-Sciama-Kibble theory of gravity naturally extends general
relativity to account for the intrinsic spin of matter. Spacetime torsion,
generated by spin of Dirac fields, induces gravitational repulsion in fermionic
matter at extremely high densities and prevents the formation of singularities.
Accordingly, the big bang is replaced by a bounce that occurred when the energy
density was on the order of (in
natural units), where is the fermion number density and is
the number of thermal degrees of freedom. If the early Universe contained only
the known standard-model particles (), then the energy density at
the big bounce was about 15 times larger than the Planck energy. The minimum
scale factor of the Universe (at the bounce) was about times smaller
than its present value, giving \approx 50 \mum. If more fermions existed in
the early Universe, then the spin-torsion coupling causes a bounce at a lower
energy and larger scale factor. Recent observations of high-energy photons from
gamma-ray bursts indicate that spacetime may behave classically even at scales
below the Planck length, supporting the classical spin-torsion mechanism of the
big bounce. Such a classical bounce prevents the matter in the contracting
Universe from reaching the conditions at which a quantum bounce could possibly
occur.Comment: 6 pages; published versio
Four-fermion interaction from torsion as dark energy
The observed small, positive cosmological constant may originate from a
four-fermion interaction generated by the spin-torsion coupling in the
Einstein-Cartan-Sciama-Kibble gravity if the fermions are condensing. In
particular, such a condensation occurs for quark fields during the
quark-gluon/hadron phase transition in the early Universe. We study how the
torsion-induced four-fermion interaction is affected by adding two terms to the
Dirac Lagrangian density: the parity-violating pseudoscalar density dual to the
curvature tensor and a spinor-bilinear scalar density which measures the
nonminimal coupling of fermions to torsion.Comment: 6 pages; published versio
Gravitational Energy of Kerr and Kerr Anti-de Sitter Space-times in the Teleparallel Geometry
In the context of the Hamiltonian formulation of the teleparallel equivalent
of general relativity we compute the gravitational energy of Kerr and Kerr
Anti-de Sitter (Kerr-AdS) space-times. The present calculation is carried out
by means of an expression for the energy of the gravitational field that
naturally arises from the integral form of the constraint equations of the
formalism. In each case, the energy is exactly computed for finite and
arbitrary spacelike two-spheres, without any restriction on the metric
parameters. In particular, we evaluate the energy at the outer event horizon of
the black holes.Comment: 11 pages, 1 figure, to appear in JHEP11(2003)00
Gravitation and inertia; a rearrangement of vacuum in gravity
We address the gravitation and inertia in the framework of 'general gauge
principle', which accounts for 'gravitation gauge group' generated by hidden
local internal symmetry implemented on the flat space. We connect this group to
nonlinear realization of the Lie group of 'distortion' of local internal
properties of six-dimensional flat space, which is assumed as a toy model
underlying four-dimensional Minkowski space. The agreement between proposed
gravitational theory and available observational verifications is satisfactory.
We construct relativistic field theory of inertia and derive the relativistic
law of inertia. This theory furnishes justification for introduction of the
Principle of Equivalence. We address the rearrangement of vacuum state in
gravity resulting from these ideas.Comment: 17 pages, no figures, revtex4, Accepted for publication in Astrophys.
Space Sc
Quadratic Curvature Gravity with Second Order Trace and Massive Gravity Models in Three Dimensions
The quadratic curvature lagrangians having metric field equations with second
order trace are constructed relative to an orthonormal coframe. In
dimensions, pure quadratic curvature lagrangian having second order trace
constructed contains three free parameters in the most general case. The fourth
order field equations of some of these models, in arbitrary dimensions, are
cast in a particular form using the Schouten tensor. As a consequence, the
field equations for the New massive gravity theory are related to those of the
Topologically massive gravity. In particular, the conditions under which the
latter is "square root" of the former are presented.Comment: 24 pages, to appear in GR
Deriving the mass of particles from Extended Theories of Gravity in LHC era
We derive a geometrical approach to produce the mass of particles that could
be suitably tested at LHC. Starting from a 5D unification scheme, we show that
all the known interactions could be suitably deduced as an induced symmetry
breaking of the non-unitary GL(4)-group of diffeomorphisms. The deformations
inducing such a breaking act as vector bosons that, depending on the
gravitational mass states, can assume the role of interaction bosons like
gluons, electroweak bosons or photon. The further gravitational degrees of
freedom, emerging from the reduction mechanism in 4D, eliminate the hierarchy
problem since generate a cut-off comparable with electroweak one at TeV scales.
In this "economic" scheme, gravity should induce the other interactions in a
non-perturbative way.Comment: 30 pages, 1 figur
Torsion Constraints in the Randall--Sundrum Scenario
Torsion appears due to fermions coupled to gravity and leads to the strongest
particle physics bounds on flat extra dimensions. In this work, we consider
torsion constraints in the case of a warped extra dimension with brane and bulk
fermions. From current data we obtain a 3-sigma bound on the TeV--brane mass
scale scale \Lambda_\pi > 2.2 (10) TeV for the AdS curvature k=1 (0.01) in
(reduced) Planck units. If Dirac or light sterile neutrinos reside on the
brane, the bound increases to 17 (78) TeV.Comment: typos corrected, matches the Phys. Rev. D versio
A Review about the Invariance Induced Gravity:Gravity and Spin from Local Conformal-Affine Symmetry
In this review paper, we discuss how gravity and spin can be obtained as the
realization of the local Conformal-Affine group of symmetry transformations. In
particular, we show how gravitation is a gauge theory which can be obtained
starting from local invariance as the Poincar\'{e} local symmetry.Comment: 23 pages, to appear in Foundations of Physic