137 research outputs found
A Higgs Mechanism for Gravity
In this paper we elaborate on the idea of an emergent spacetime which arises
due to the dynamical breaking of diffeomorphism invariance in the early
universe. In preparation for an explicit symmetry breaking scenario, we
consider nonlinear realizations of the group of analytical diffeomorphisms
which provide a unified description of spacetime structures. We find that
gravitational fields, such as the affine connection, metric and coordinates,
can all be interpreted as Goldstone fields of the diffeomorphism group. We then
construct a Higgs mechanism for gravity in which an affine spacetime evolves
into a Riemannian one by the condensation of a metric. The symmetry breaking
potential is identical to that of hybrid inflation but with the non-inflaton
scalar extended to a symmetric second rank tensor. This tensor is required for
the realization of the metric as a Higgs field. We finally comment on the role
of Goldstone coordinates as a dynamical fluid of reference.Comment: 15 pages, 2 figures, 3 tables, appendix C on on-shell d.o.f. added,
references adde
A class of colliding waves in metric-affine gravity, nonmetricity and torsion shock waves
By using our recent generalization of the colliding waves concept to
metric-affine gravity theories, and also our generalization of the advanced and
retarded time coordinate representation in terms of Jacobi functions, we find a
general class of colliding wave solutions with fourth degree polynomials in
metric-affine gravity. We show that our general approach contains the standard
second degree polynomials colliding wave solutions as a particular case.Comment: 13 pages, latex, to appear in J.Math.Phy
Generalized Gauge Theories and Weinberg-Salam Model with Dirac-K\"ahler Fermions
We extend previously proposed generalized gauge theory formulation of
Chern-Simons type and topological Yang-Mills type actions into Yang-Mills type
actions. We formulate gauge fields and Dirac-K\"ahler matter fermions by all
degrees of differential forms. The simplest version of the model which includes
only zero and one form gauge fields accommodated with the graded Lie algebra of
supergroup leads Weinberg-Salam model. Thus the Weinberg-Salam model
formulated by noncommutative geometry is a particular example of the present
formulation.Comment: 33 pages, LaTe
Superrelativity as a unification of quantum theory and relativity(II)
A underlying dynamical structure for both relativity and quantum
theory-``superrelativity'' has been proposed in order to overcome the well
known incompatibility between these theories. The relationship between
curvature of spacetime (gravity) and curvature of the projective Hilbert space
of pure quantum states is established as well.Comment: 6 pages,LaTeX,In the Abstract ``proposed on order'' should be read as
``proposed in order'
BRST-antifield-treatment of metric-affine gravity
The metric-affine gauge theory of gravity provides a broad framework in which
gauge theories of gravity can be formulated. In this article we fit
metric-affine gravity into the covariant BRST--antifield formalism in order to
obtain gauge fixed quantum actions. As an example the gauge fixing of a general
two-dimensional model of metric-affine gravity is worked out explicitly. The
result is shown to contain the gauge fixed action of the bosonic string in
conformal gauge as a special case.Comment: 19 pages LATEX, to appear in Phys. Rev.
Dynamical measure and field theory models free of the cosmological constant problem
Summary of abstract Field theory models including gauge theories with SSB are
presented where the energy density of the true vacuum state (TVS) is zero
without fine tuning. The above models are constructed in the gravitational
theory where a measure of integration \Phi in the action is not necessarily
\sqrt{-g} but it is determined dynamically through additional degrees of
freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in
terms of the matter degrees of freedom due to the existence of a constraint. We
study a few explicit field theory models where it is possible to combine the
solution of the cosmological constant problem with: 1) possibility for
inflationary scenario for the early universe; 2) spontaneously broken gauge
unified theories (including fermions). The models are free from the well known
problem of the usual scalar-tensor theories in what is concerned with the
classical GR tests. The only difference of the field equations in the Einstein
frame from the canonical equations of the selfconsistent system of Einstein's
gravity and matter fields, is the appearance of the effective scalar field
potential which vanishes in TVS without fine tuning.Comment: Extended version of the contribution to the fourth Alexander
Friedmann International Seminar on Gravitation and Cosmology; accepted for
publication in Phys. Rev. D; 31 page
de Sitter gravity from lattice gauge theory
We investigate a lattice model for Euclidean quantum gravity based on
discretization of the Palatini formulation of General Relativity. Using Monte
Carlo simulation we show that while a naive approach fails to lead to a vacuum
state consistent with the emergence of classical spacetime, this problem may be
evaded if the lattice action is supplemented by an appropriate counter term. In
this new model we find regions of the parameter space which admit a ground
state which can be interpreted as (Euclidean) de Sitter space.Comment: 16 pages, 11 figures. email address update
Volume elements of spacetime and a quartet of scalar fields
Starting with a `bare' 4-dimensional differential manifold as a model of
spacetime, we discuss the options one has for defining a volume element which
can be used for physical theories. We show that one has to prescribe a scalar
density \sigma. Whereas conventionally \sqrt{|\det g_{ij}|} is used for that
purpose, with g_{ij} as the components of the metric, we point out other
possibilities, namely \sigma as a `dilaton' field or as a derived quantity from
either a linear connection or a quartet of scalar fields, as suggested by
Guendelman and Kaganovich.Comment: 7 pages RevTEX, submitted to Phys. Rev.
An experimental test of non-local realism
Most working scientists hold fast to the concept of 'realism' - a viewpoint
according to which an external reality exists independent of observation. But
quantum physics has shattered some of our cornerstone beliefs. According to
Bell's theorem, any theory that is based on the joint assumption of realism and
locality (meaning that local events cannot be affected by actions in space-like
separated regions) is at variance with certain quantum predictions. Experiments
with entangled pairs of particles have amply confirmed these quantum
predictions, thus rendering local realistic theories untenable. Maintaining
realism as a fundamental concept would therefore necessitate the introduction
of 'spooky' actions that defy locality. Here we show by both theory and
experiment that a broad and rather reasonable class of such non-local realistic
theories is incompatible with experimentally observable quantum correlations.
In the experiment, we measure previously untested correlations between two
entangled photons, and show that these correlations violate an inequality
proposed by Leggett for non-local realistic theories. Our result suggests that
giving up the concept of locality is not sufficient to be consistent with
quantum experiments, unless certain intuitive features of realism are
abandoned.Comment: Minor corrections to the manuscript, the final inequality and all its
conclusions do not change; description of corrections (Corrigendum) added as
new Appendix III; Appendix II replaced by a shorter derivatio
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