5 research outputs found
Problems and hopes in nonsymmetric gravity
We consider the linearized nonsymmetric theory of gravitation (NGT) within
the background of an expanding universe and near a Schwarzschild mass. We show
that the theory always develops instabilities unless the linearized
nonsymmetric lagrangian reduces to a particular simple form. This form contains
a gauge invariant kinetic term, a mass term for the antisymmetric metric-field
and a coupling with the Ricci curvature scalar. This form cannot be obtained
within NGT. Based on the linearized lagrangian we know to be stable, we
consider the generation and evolution of quantum fluctuations of the
antisymmetric gravitational field (B-field) from inflation up to the present
day. We find that a B-field with a mass m ~ 0.03(H_I/10^(13)GeV)^4 eV is an
excellent dark matter candidate.Comment: 9 pages, 1 figure. Based on two talks by the authors at the 2nd
International Conference on Quantum Theories and Renormalization Group in
Gravity and Cosmology (IRGAC) 2006, Barcelon
Instabilities in the nonsymmetric theory of gravitation
We consider the linearized nonsymmetric theory of gravitation (NGT) within
the background of an expanding universe and near a Schwarzschild metric. We
show that the theory always develops instabilities unless the linearized
nonsymmetric lagrangian reduces to a particular simple form. This theory
contains a gauge invariant kinetic term, a mass term for the antisymmetric
metric-field and a coupling with the Ricci curvature scalar. This form cannot
be obtained within NGT. Next we discuss NGT beyond linearized level and
conjecture that the instabilities are not a relic of the linearization, but are
a general feature of the full theory. Finally we show that one cannot add
ad-hoc constraints to remove the instabilities as is possible with the
instabilities found in NGT by Clayton.Comment: 29 page
Vacuum properties of nonsymmetric gravity in de Sitter space
We consider quantum effects of a massive antisymmetric tensor field on the
dynamics of de Sitter space-time. Our starting point is the most general,
stable, linearized Lagrangian arising in nonsymmetric gravitational theories
(NGTs), where part of the antisymmetric field mass is generated by the
cosmological term. We construct a renormalization group (RG) improved effective
action by integrating out one loop vacuum fluctuations of the antisymmetric
tensor field and show that, in the limit when the RG scale goes to zero, the
Hubble parameter -- and thus the effective cosmological constant -- relaxes
rapidly to zero. We thus conclude that quantum loop effects in de Sitter space
can dramatically change the infrared sector of the on-shell gravity, making the
expansion rate insensitive to the original (bare) cosmological constant.Comment: 32 pages, 2 eps figure
Scalar cosmological perturbations from inflationary black holes
We study the correction to the scale invariant power spectrum of a scalar
field on de Sitter space from small black holes that formed during a
pre-inflationary matter dominated era. The formation probability of such black
holes is estimated from primordial Gaussian density fluctuations. We determine
the correction to the spectrum by first deriving the Keldysh propagator for a
massless scalar field on Schwarzschild-de Sitter space. Our results suggest
that the effect is strong enough to be tested -- and possibly even ruled out --
by observations.Comment: 41 pages, 11 figures, published versio