3 research outputs found
Conformal transformation in theories
It is well-known that theories are dynamically equivalent to a
particular class of scalar-tensor theories. In analogy to the extension
of the Einstein-Hilbert action of general relativity, theories are
generalizations of the action of teleparallel gravity. The field equations are
always second order, remarkably simpler than theories. It is interesting
to investigate whether theories have the similar conformal features
possessed in theories. It is shown, however, that theories are
not dynamically equivalent to teleparallel action plus a scalar field via
conformal transformation, there appears an additional scalar-torsion coupling
term. We discuss briefly what constraint of this coupling term may be put on
theories from observations of the solar system.Comment: 4 pages, Revision to be publishe
Existence of relativistic stars in f(T) gravity
We examine the existence of relativistic stars in f(T) modified gravity and
explicitly construct several classes of static perfect fluid solutions. We
derive the conservation equation from the complete f(T) gravity field equations
and present the differences with its teleparallel counterpart. Firstly, we
choose the tetrad field in the diagonal gauge and study the resulting field
equations. Some exact solutions are explicitly constructed and it is noted that
these solutions have to give a constant torsion scalar. Next, we choose a non
diagonal tetrad field which results in field equations similar to those of
general relativity. For specific models we are able to construct exact
solutions of these field equations. Among those new classes of solutions, we
find negative pressure solutions, and an interesting class of polynomial
solutions.Comment: 19 pages; substantially revised and extended version, off diagonal
tetrad discussion adde