1,708 research outputs found
Gravity and Scalar Fields
Gravity theories with non-minimally coupled scalar fields are used as
characteristic examples in order to demonstrate the challenges, pitfalls and
future perspectives of considering alternatives to general relativity. These
lecture notes can be seen as an illustration of concepts, subtleties and
techniques present in all alternative theories, but they also provide a brief
review of generalised scalar-tensor theories.Comment: 21 pages, based on a lecture given at the Seventh Aegean Summer
School "Beyond Einstein's Theory of Gravity
Geodesic properties in terms of multipole moments in scalar-tensor theories of gravity
The formalism for describing a metric and the corresponding scalar in terms
of multipole moments has recently been developed for scalar-tensor theories. We
take advantage of this formalism in order to obtain expressions for the
observables that characterise geodesics in terms of the moments. These
expressions provide some insight into how the structure of a scalarized compact
object affects observables. They can also be used to understand how deviations
from general relativity are imprinted on the observables.Comment: 16 page
Strong coupling in extended Horava-Lifshitz gravity
An extension of Horava-Lifshitz gravity was recently proposed in order to
address the pathological behavior of the scalar mode all previous versions of
the theory exhibit. We show that even in this new extension the strong coupling
persists, casting doubts on whether such a model can constitute an interesting
alternative to general relativity (GR).Comment: 4 pages; v2: minor changes and references added; v3: clarification
regarding the strong coupling scale added; v4: version accepted for
publication in PLB, addresses issues raised in arXiv:0912.055
Horava-Lifshitz gravity with detailed balance
Horava-Lifshitz gravity with "detailed balance" but without the
projectability assumption is discussed. It is shown that detailed balance is
quite efficient in limiting the proliferation of couplings in Horava-Lifshitz
gravity, and that its implementation without the projectability assumption
leads to a theory with sensible dynamics. However, the (bare) cosmological
constant is restricted to be large and negative.Comment: Contribution to the proceedings of NEB 15 conference, Chania, 20-23
June 2012 (talk given by D.V.
Surface singularities in Eddington-inspired Born-Infeld gravity
Eddington-inspired Born-Infeld gravity was recently proposed as an
alternative to general relativity that offers a resolution of spacetime
singularities. The theory differs from Einstein's gravity only inside matter
due to nondynamical degrees of freedom, and it is compatible with all current
observations. We show that the theory is reminiscent of Palatini f(R) gravity
and that it shares the same pathologies, such as curvature singularities at the
surface of polytropic stars and unacceptable Newtonian limit. This casts
serious doubts on its viability.Comment: 5 pages. v2: minor corrections to match published versio
Perturbed Kerr Black Holes can probe deviations from General Relativity
Although the Kerr solution is common to many gravity theories, its
perturbations are different in different theories. Hence, perturbed Kerr black
holes can probe deviations from General Relativity.Comment: minor changes to match version published in Phys. Rev. Let
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