73 research outputs found

### Generalised nonminimally gravity-matter coupled theory

In this paper, a new generalised gravity-matter coupled theory of gravity is
presented. This theory is constructed by assuming an action with an arbitrary
function $f(T,B,L_m)$ which depends on the scalar torsion $T$, the boundary
term $B=\nabla_{\mu}T^{\mu}$ and the matter Lagrangian $L_m$. Since the
function depends on $B$ which appears in $R=-T+B$, it is possible to also
reproduce curvature-matter coupled models such as $f(R,L_m)$ gravity.
Additionally, the full theory also contains some interesting new teleparallel
gravity-matter coupled theories of gravities such as $f(T,L_m)$ or $C_1 T+
f(B,L_m)$. The complete dynamical system for flat FLRW cosmology is presented
and for some specific cases of the function, the corresponding cosmological
model is studied. When it is necessary, the connection of our theory and the
dynamical system of other well-known theories is discussed.Comment: Matches published version in EPJ

### Is Gravity Actually the Curvature of Spacetime?

The Einstein equations, apart from being the classical field equations of
General Relativity, are also the classical field equations of two other
theories of gravity. As the experimental tests of General Relativity are done
using the Einstein equations, we do not really know, if gravity is the
curvature of a torsionless spacetime, or torsion of a curvatureless spacetime,
or if it occurs due to the non-metricity of a curvatureless and torsionless
spacetime. However, as the classical actions of all these theories differ from
each other by boundary terms, and the Casimir effect is a boundary effect, we
propose that a novel gravitational Casimir effect between superconductors can
be used to test which of these theories actually describe gravity.Comment: Essay received an honorable mention in the Gravity Research
Foundation Essay Competition 2019. 7 page

### Noether Symmetry Approach in $f(T,B)$ teleparallel cosmology

We consider the cosmology derived from $f(T,B)$ gravity where $T$ is the
torsion scalar and $B=\frac{2}{e}\partial_{\mu}(e T^{\mu})$ a boundary term. In
particular we discuss how it is possible to recover, under the same standard,
the teleparallel $f(T)$ gravity, the curvature $f(R)$ gravity and the
teleparallel-curvature $f(R,T)$ gravity, which are particular cases of
$f(T,B)$. We adopt the Noether Symmetry Approach to study the related dynamical
systems and to find out cosmological solutions.Comment: 21 page

### Stability of a $d$-dimensional thin-shell wormhole surrounded by quintessence

We study the stability of different higher dimensional thin--shell wormholes
(HDTSW) in general relativity with a cosmological constant. We show that a
$d$--dimensional thin--shell wormhole surrounded by quintessence can have three
different throat geometries: spherical, planar and hyperbolic. Unlike the
spherical geometry, the planar and hyperbolic geometries allow different
topologies that can be interpreted as higher-dimensional domain walls or branes
connecting two universes. To construct these geometries, we use the
cut-and-paste procedure by joining two identical vacuum spacetime solutions.
Properties such as the null energy condition and geodesics are also studied. A
linear stability analysis around the static solutions is carried out. Our
stability analysis takes into account a more general HDTSW geometry than
previous works so it is possible to recover other well-known stability HDTSW
conditions.Comment: 10 pages; 3 figures; matches the accepted version, to appear in
Gravitation and Cosmolog

### (N+1)-dimensional Lorentzian evolving wormholes supported by polytropic matter

In this paper we study $(N+1)$-dimensional evolving wormholes supported by
energy satisfying a polytropic equation of state. The considered evolving
wormhole models are described by a constant redshift function and generalizes
the standard flat Friedmann-Robertson-Walker spacetime. The polytropic equation
of state allows us to consider in $(3+1)$-dimensions generalizations of the
phantom energy and the generalized Chaplygin gas sources.Comment: 6 pages, 2 figures, accepted for publication in European Physical
Journal

### Geometrically nonlinear Cosserat elasticity in the plane: applications to chirality

Modelling two-dimensional chiral materials is a challenging problem in
continuum mechanics because three-dimensional theories reduced to isotropic
two-dimensional problems become non-chiral. Various approaches have been
suggested to overcome this problem. We propose a new approach to this problem
by formulating an intrinsically two-dimensional model which does not require
references to a higher dimensional one. We are able to model planar chiral
materials starting from a geometrically non-linear Cosserat type elasticity
theory. Our results are in agreement with previously derived equations of
motion but can contain additional terms due to our non-linear approach. Plane
wave solutions are briefly discussed within this model.Comment: 22 pages, 1 figure; v2 updated versio

### New classes of modified teleparallel gravity models

New classes of modified teleparallel theories of gravity are introduced. The
action of this theory is constructed to be a function of the irreducible parts
of torsion $f(T_{\rm ax},T_{\rm ten},T_{\rm vec})$, where $T_{\rm ax},T_{\rm
ten}$ and $T_{\rm vec}$ are squares of the axial, tensor and vector components
of torsion, respectively. This is the most general (well-motivated) second
order teleparallel theory of gravity that can be constructed from the torsion
tensor. Different particular second order theories can be recovered from this
theory such as new general relativity, conformal teleparallel gravity or $f(T)$
gravity. Additionally, the boundary term $B$ which connects the Ricci scalar
with the torsion scalar via $R=-T+B$ can also be incorporated into the action.
By performing a conformal transformation, it is shown that the two unique
theories which have an Einstein frame are either the teleparallel equivalent of
general relativity or $f(-T+B)=f(R)$ gravity, as expected.Comment: v2: 10 pages, accepted for publication in PLB; for a detailed
derivation of the field equations see Appendix A in v

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