scholarly journals Scalar-torsion theories of gravity. I. General formalism and conformal transformations

2018 ◽  
Vol 98 (6) ◽  
Author(s):  
Manuel Hohmann
Keyword(s):  
Conformal Transformations ◽  
Theories Of Gravity ◽  
Torsion Theories

scholarly journals Conformal mapping of the Misner–Sharp mass from gravitational collapse

2016 ◽  
Vol 25 (07) ◽  
pp. 1650081 ◽  
Author(s):  
Fayçal Hammad
Keyword(s):  
Conformal Mapping ◽  
Gravitational Collapse ◽  
Conformal Transformation ◽  
Conformal Mappings ◽  
Conformal Transformations ◽  
Theories Of Gravity ◽  
Definition Of ◽  
Geometric Definition

The conformal transformation of the Misner–Sharp mass is reexamined. It has recently been found that this mass does not transform like usual masses do under conformal mappings of spacetime. We show that when it comes to conformal transformations, the widely used geometric definition of the Misner–Sharp mass is fundamentally different from the original conception of the latter. Indeed, when working within the full hydrodynamic setup that gave rise to that mass, i.e. the physics of gravitational collapse, the familiar conformal transformation of a usual mass is recovered. The case of scalar–tensor theories of gravity is also examined.

scholarly journals Light propagation and optical scalars in torsion theories of gravity

2019 ◽  
Vol 34 (04) ◽  
pp. 1950029
Author(s):  
Siamak Akhshabi
Keyword(s):  
Gravitational Lensing ◽  
Light Propagation ◽  
Raychaudhuri Equation ◽  
Angular Diameter Distance ◽  
Propagation Of Light ◽  
Light Rays ◽  
Theories Of Gravity ◽  
Torsion Theories ◽  
Basic Equations ◽  
Gauge Theory Of Gravity

We investigate the propagation of light rays and evolution of optical scalars in gauge theories of gravity where torsion is present. Recently, the modified Raychaudhuri equation in the presence of torsion has been derived. We use this result to derive the basic equations of geometric optics for several different interesting solutions of the Poincaré gauge theory of gravity. The results show that the focusing effects for neighboring light rays will be different than general relativity. This in turn has practical consequences in the study of gravitational lensing effects and also in determining the angular diameter distance for cosmological objects.

scholarly journals ON BOUNDARY TERMS AND CONFORMAL TRANSFORMATIONS IN CURVED SPACETIMES

2002 ◽  
Vol 11 (05) ◽  
pp. 703-714 ◽  
Author(s):  
R. CASADIO ◽  
A. GRUPPUSO
Keyword(s):  
Hamiltonian Formalism ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Conformal Transformations ◽  
Five Dimensions ◽  
Four Dimensions ◽  
Boundary Terms ◽  
Pure Gravity ◽  
Theories Of Gravity ◽  
Flat Spacetimes

We intend to clarify the interplay between boundary terms and conformal transformations in scalar-tensor theories of gravity. We first consider the action for pure gravity in five dimensions and show that, on compactifing a la Kaluza–Klein to four dimensions, one obtains the correct boundary terms in the Jordan (or String) Frame form of the Brans–Dicke action. Further, we analyze how the boundary terms change under the conformal transformations which lead to the Pauli (or Einstein) frame and to the nonminimally coupled massless scalar field. In particular, we study the behaviour of the total energy in asymptotically flat spacetimes as it results from surface terms in the Hamiltonian formalism.

scholarly journals An issue with the classification of the scalar–tensor theories of gravity

2020 ◽  
Vol 29 (07) ◽  
pp. 2050047
Author(s):  
Israel Quiros ◽  
Roberto De Arcia ◽  
Ricardo García-Salcedo ◽  
Tame Gonzalez ◽  
Francisco Antonio Horta-Rangel
Keyword(s):  
Conformal Transformations ◽  
Scalar Tensor Theory ◽  
Specific Criterion ◽  
Tensor Theory ◽  
Gravitational Theories ◽  
Higher Derivatives ◽  
Theories Of Gravity ◽  
Conformal Frames ◽  
Incorrect Classification

In the bibliography, a certain confusion arises in what regards to the classification of the gravitational theories into scalar–tensor theories (STT) and general relativity with a scalar field either minimally or nonminimally coupled to matter. Higher-derivatives Horndeski and beyond Horndeski theories that at first sight do not look like STT only add to the confusion. To further complicate things, the discussion on the physical equivalence of the different conformal frames in which a given scalar–tensor theory may be formulated, makes even harder to achieve a correct classification. In this paper, we propose a specific criterion for an unambiguous identification of STT and discuss its impact on the conformal transformations issue. The present discussion carries not only pedagogical but also scientific interest since an incorrect classification of a given theory as a scalar–tensor theory of gravity may lead to conceptual issues and to the consequent misunderstanding of its physical implications.

scholarly journals CURVATURE QUINTESSENCE

2002 ◽  
Vol 11 (04) ◽  
pp. 483-491 ◽  
Author(s):  
SALVATORE CAPOZZIELLO
Keyword(s):  
Scalar Field ◽  
Fourth Order ◽  
Order Theory ◽  
Cosmic Acceleration ◽  
Accelerated Expansion ◽  
Conformal Transformations ◽  
Effective Pressure ◽  
Alternative Scheme ◽  
Theories Of Gravity ◽  
Jordan And Einstein Frames

The issues of quintessence and cosmic acceleration can be discussed in the framework of higher order theories of gravity. We can define effective pressure and energy density directly connected to the Ricci scalar of curvature of a generic fourth order theory and then ask for the conditions to get an accelerated expansion. Exact accelerated expanding solutions can be achieved for several fourth order theories so that we get an alternative scheme to the standard quintessence scalar field, minimally coupled to gravity, usually adopted. We discuss also conformal transformations in order to see the links of quintessence between the Jordan and Einstein frames.

scholarly journals THE CAUCHY PROBLEM FOR f(R)-GRAVITY: AN OVERVIEW

2012 ◽  
Vol 09 (01) ◽  
pp. 1250006 ◽  
Author(s):  
S. CAPOZZIELLO ◽  
S. VIGNOLO
Keyword(s):  
Cauchy Problem ◽  
General Relativity ◽  
Scalar Fields ◽  
Conformal Transformations ◽  
Field Equations ◽  
The Cauchy Problem ◽  
Theories Of Gravity ◽  
Matter Fields

We review the Cauchy problem for f(R) theories of gravity, in metric and metric-affine formulations, pointing out analogies and differences with respect to General Relativity. The role of conformal transformations, effective scalar fields and sources in the field equations is discussed in view of the well-formulation and the well-position of the problem. Finally, criteria of viability of the f(R)-models are considered according to the various matter fields acting as sources.

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