String-Inspired Chern-Simons Modified Gravity In 4-Dimensions
Chern-Simons modified gravity models in 4-dimensions are shown to be special cases of low energy effective string models to first order in the string constant.
gr-qc↗
arXiv subjects
M. Adak
Publications and source records attributed to M. Adak.
The Quadratic Symmetric Teleparallel Gravity in Two-Dimensions
A 2D symmetric teleparallel gravity model is given by a generic 4-parameter action that is quadratic in the non-metricity tensor. Variational field equations are derived. A class of conformally flat solutions is given. We also discuss static and cosmological solutions.
hep-th↗
Poisson-sigma model for 2D gravity with non-metricity
We present a Poisson-sigma model describing general 2D dilaton gravity with non-metricity, torsion and curvature. It involves three arbitrary functions of the dilaton field, two of which are well-known from metric compatible theories, while the third one characterizes the local strength of non-metricity. As an example we show that alpha' corrections in 2D string theory can generate (target space) non-metricity.
hep-th↗
The Symmetric Teleparallel Gravity
We study symmetric teleparallel (STP) gravity model, in which only spacetime non-metricity is nonzero. First we obtain STP equivalent Einstein-Hilbert Lagrangian and give an approach for a generic solution in terms of only metric tensor. Then we obtain a spherically symmetric static solution to the Einstein's equation in STP space-time and discuss the singularities. Finally, we study a model given by a Lagrangian 4-form quadratic in non-metricity. Thus, we seek Schwarzschild-type solutions because of its observational success and obtain some sets of solutions. Finally, we discuss physical relevance of the solutions.
gr-qc↗
Possible effects of spacetime non-metricity on neutrino oscillations
The contribution of gravitational neutrino oscillations to the solar neutrino problem is studied by constructing the Dirac Hamiltonian and calculating the corresponding dynamical phase in the vicinity of the Sun in a non-Riemann background Kerr space-time with torsion and non-metricity. We show that certain components of non-metricity and the axial as well as non-axial components of torsion may contribute to neutrino oscillations. We also note that the rotation of the Sun may cause a suppression of transitions among neutrinos. However, the observed solar neutrino deficit could not be explained by any of these effects because they are of the order of Planck scales.
gr-qc↗
Spinor couplings to dilaton gravity induced by the dimensional reduction of topologically massive gravity
A Dirac spinor is coupled to topologically massive gravity and the D=3 dimensional action is reduced to D=2 dimensions with a metric that includes both the electromagnetic potential 1-form A and a dilaton scalar ϕ. The dimensionnaly reduced spinor is made a mass eigenstate with a (local) chiral rotation. The non-trivial interactions thus induced are discussed.
gr-qc↗
Dirac equation in spacetimes with torsion and non-metricity
Dirac equation is written in a non-Riemannian spacetime with torsion and non-metricity by lifting the connection from the tangent bundle to the spinor bundle over spacetime. Foldy-Wouthuysen transformation of the Dirac equation in a Schwarzschild background spacetime is considered and it is shown that both the torsion and non-metricity couples to the momentum and spin of a massive, spinning particle. However, the effects are small to be observationally significant.
gr-qc↗
Neutrino Oscillations Induced by Space-Time Torsion
The gravitational neutrino oscillation problem is studied by considering the Dirac Hamiltonian in a Riemann-Cartan space-time and calculating the dynamical phase. Torsion contributions which depend on the spin direction of the mass eigenstates are found. These effects are of the order of Planck scales.
gr-qc↗