1,718 research outputs found
Gauge Symmetry and Consistent Spin-Two Theories
We study Lagrangians with the minimal amount of gauge symmetry required to
propagate spin-two particles without ghosts or tachyons. In general, these
Lagrangians also have a scalar mode in their spectrum. We find that, in two
cases, the symmetry can be enhanced to a larger group: the whole group of
diffeomorphisms or a enhancement involving a Weyl symmetry. We consider the
non-linear completions of these theories. The intuitive completions yield the
usual scalar-tensor theories except for the pure spin-two cases, which
correspond to two inequivalent Lagrangians giving rise to Einstein's equations.
A more constructive self-consistent approach yields a background dependent
Lagrangian.Comment: 7 pages, proceedings of IRGAC'06; typo correcte
Bigravity and Lorentz-violating Massive Gravity
Bigravity is a natural arena where a non-linear theory of massive gravity can
be formulated. If the interaction between the metrics and is
non-derivative, spherically symmetric exact solutions can be found. At large
distances from the origin, these are generically Lorentz-breaking bi-flat
solutions (provided that the corresponding vacuum energies are adjusted
appropriately). The spectrum of linearized perturbations around such
backgrounds contains a massless as well as a massive graviton, with {\em two}
physical polarizations each. There are no propagating vectors or scalars, and
the theory is ghost free (as happens with certain massive gravities with
explicit breaking of Lorentz invariance). At the linearized level, corrections
to GR are proportional to the square of the graviton mass, and so there is no
vDVZ discontinuity. Surprisingly, the solution of linear theory for a static
spherically symmetric source does {\em not} agree with the linearization of any
of the known exact solutions. The latter coincide with the standard
Schwarzschild-(A)dS solutions of General Relativity, with no corrections at
all. Another interesting class of solutions is obtained where and are
proportional to each other. The case of bi-de Sitter solutions is analyzed in
some detail.Comment: 25 pages. v3 Typos corrected, references added. v4 Introduction
extende
Note About Hamiltonian Formalism of Healthy Extended Horava-Lifshitz Gravity
In this paper we continue the study of the Hamiltonian formalism of the
healthy extended Horava-Lifshitz gravity. We find the constraint structure of
given theory and argue that this is the theory with the second class
constraints. Then we discuss physical consequence of this result. We also apply
the Batalin-Tyutin formalism of the conversion of the system with the second
class constraints to the system with the first class constraints to the case of
the healthy extended Horava-Lifshitz theory. As a result we find new theory of
gravity with structure that is different from the standard formulation of
Horava-Lifshitz gravity or General Relativity.Comment: 17 pages, v.2. references added, v.3. typos corrected, references
adde
On the consistency of the Horava Theory
With the goal of giving evidence for the theoretical consistency of the
Horava Theory, we perform a Hamiltonian analysis on a classical model suitable
for analyzing its effective dynamics at large distances. The model is the
lowest-order truncation of the Horava Theory with the detailed-balance
condition. We consider the pure gravitational theory without matter sources.
The model has the same potential term of general relativity, but the kinetic
term is modified by the inclusion of an arbitrary coupling constant lambda.
Since this constant breaks the general covariance under space-time
diffeomorphisms, it is believed that arbitrary values of lambda deviate the
model from general relativity. We show that this model is not a deviation at
all, instead it is completely equivalent to general relativity in a particular
partial gauge fixing for it. In doing this, we clarify the role of a
second-class constraint of the model.Comment: The wording has been revised in general, specially in abstract,
introduction and conclusions. No changes in results. Version published in
IJMP
Counterterms in semiclassical Horava-Lifshitz gravity
We analyze the semiclassical Ho\v{r}ava-Lifshitz gravity for quantum scalar
fields in 3+1 dimensions. The renormalizability of the theory requires that the
action of the scalar field contains terms with six spatial derivatives of the
field, i.e. in the UV, the classical action of the scalar field should preserve
the anisotropic scaling symmetry ( ,
with ) of the gravitational action. We discuss the renormalization
procedure based on adiabatic subtraction and dimensional regularization in the
weak field approximation. We verify that the divergent terms in the adiabatic
expansion of the expectation value of the energy-momentum tensor of the scalar
field contain up to six spatial derivatives, but do not contain more than two
time derivatives. We compute explicitly the counterterms needed for the
renormalization of the theory up to second adiabatic order and evaluate the
associated functions in the minimal subtraction scheme.Comment: 8 page
Cosmological perturbations in a healthy extension of Horava gravity
In Horava's theory of gravity, Lorentz symmetry is broken in exchange for
renormalizability, but the original theory has been argued to be plagued with
problems associated with a new scalar mode stemming from the very breaking of
Lorentz symmetry. Recently, Blas, Pujolas, and Sibiryakov have proposed a
healthy extension of Horava gravity, in which the behavior of the scalar mode
is improved. In this paper, we study scalar modes of cosmological perturbations
in extended Horava gravity. The evolution of metric and density perturbations
is addressed analytically and numerically. It is shown that for vanishing
non-adiabatic pressure of matter the large scale evolution of cosmological
perturbations converges to that described by a single constant, , which
is an analog of a curvature perturbation on the uniform-density slicing
commonly used in usual gravitational theories. The subsequent evolution is thus
determined completely by the value of .Comment: 10 pages, 4 figures; v2: published versio
Horava-Lifshitz gravity: tighter constraints for the Kehagias-Sfetsos solution from new solar system data
We analytically work out the perturbation induced by the Kehagias-Sfetsos
(KS) space-time solution of the Horava-Lifshitz (HL) modified gravity at long
distances on the two-body range for a pair of test particles A and B orbiting
the same mass M. We apply our results to the most recently obtained
range-residuals \delta\rho for some planets of the solar system (Mercury, Mars,
Saturn) ranged from the Earth to effectively constrain the dimensionsless KS
parameter \psi_0 for the Sun. We obtain \psi_0 >= 7.2 x 10^-10 (Mercury),
\psi_0 >= 9 x 10^-12 (Mars), \psi_0 >= 1.7 x 10^-12 (Saturn). Such lower bounds
are tighter than other ones existing in literature by several orders of
magnitude. We also preliminarily obtain \psi_0 >= 8 x 10^-10 for the system
constituted by the S2 star orbiting the Supermassive Black Hole (SBH) in the
center of the Galaxy.Comment: LaTex2e, 15 pages, 1 table, 3 figures, 31 references. Version
matching the one at press in International Journal of Modern Physics D
(IJMPD
Horava-Lifshitz gravity: a status report
This is intended to be a brief introduction and overview of Horava-Lifshitz
gravity. The motivation and all of the various version of the theory (to date)
are presented. The dynamics of the theory are discussed in some detail, with a
focus on low energy viability and consistency, as these have been the issues
that attracted most of the attention in the literature so far. Other properties
of the theory and developments within its framework are also covered, such as:
its relation to Einstein-aether theory, cosmology, and future perspectives.Comment: 17 pages, no figures, based on talk given at the 14th Conference on
Recent Developments in Gravity (NEBXIV), Ioannina, Greece, 8-11 Jun 2010; v2:
minor changes to match published version, references adde
Perceived value of advanced mobile messaging services: A cross-cultural comparison of Greek and Spanish users
Purpose
The purpose of this paper is to analyse the role of perceived value on post-acceptance behaviour for users of advanced mobile messaging services (AMMS). The paper also compares differences in the influence of perceived value on satisfaction and of satisfaction on loyalty to AMMS in Spain and Greece, to test the moderating effect of culture.
Design/methodology/approach
Partial least squares path modelling is used to test the model. Perceived value is modelled as a multidimensional reflective construct with four dimensions. Culture is studied at a national level. Differences between countries are tested using the multigroup analysis approach proposed by Henseler et al. (2009).
Findings
Perceived value contributes significantly to satisfaction. Satisfaction also has a significant effect on loyalty. Regarding the moderating effect of culture, the influence of perceived value on satisfaction is higher in Greece than in Spain. The authors report similar findings for the effect of satisfaction on loyalty, demonstrating the relevant moderating role of cultures with different degrees of masculinity, uncertainty avoidance and collectivism.
Practical implications
This cross-cultural comparison enables mobile phone companies to understand how to provide the greatest value with AMMS in each country in order to increase user satisfaction and loyalty to the service.
Originality/value
This is one of the first studies that develops cross-cultural research to analyse the post-acceptance of mobile services. It analyses the effect of perceived value and satisfaction, making an original comparison of two countries generally considered too similar to be compared
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