Narrow Results

In this paper we consider the Gauss-Bonnet action in Weyl-Cartan geometry. The role of Gauss-Bonnet action in Weyl and also Cartan gravity is known for decades and we know that this combinations lead to a gravity theory plus some gauge fields. We first show that the Weyl-Cartan theory gives rise to a gravitational theory minimally coupled to two vector fields, one of which is massless and the other is massive. The parameters will be then constraint to have a healthy theory. By generalizing the action through introducing a scalar filed coupled to Gauss-Bonnet action we will show that the axion inflation model can be produced in this model. The theory predicts a coupling between the axion field and the canonical vector kinetic term as well as the usual axion-vector field coupling. We will also consider the cosmological implications of the axion model.

Very light axions represent an excellent dark matter candidate, and may be detected by their resonant conversion to photons in a microwave cavity within a strong magnetic field. Current experiments are commencing searches for cosmic axions in the 1–100 μeV range constituting our galactic halo. The sensitivity of these experiments largely results from the development of quantum-limited amplifiers, such as SQUIDs and Josephson Parametric Amplifiers; future experiments may achieve even greater sensitivity by evading the standard quantum limit on noise temperature altogether.

The propagation of very high energy gamma-rays (E > 100 GeV) over cosmological distances is limited by pair-production processes with the ubiquitous extra-galactic soft photon background in the optical to near infra-red. The detailed spectroscopy of gamma-ray emitting blazars has revealed the signature of this absorption process leading to a meaningful measurement of the background photon field which is linked to the star forming history of the universe. Deviations from the expected absorption have been claimed in the past. Here the status of the observations is summarized, an update on the search for anomalous transparency is given and discussed.

Current proposed photon rocket designs include the Nuclear Photonic Rocket and the Antimatter Photonic Rocket (proposed by Eugen Sanger in the 1950s, as reported by Ref. 1). This paper examines the feasibility of improving the thrust of photon-driven ramjet propulsion by using DM rocket propulsion. The open question is: would a heavy WIMP, if converted to photons, upgrade the power (thrust) of a photon rocket drive, to make interstellar travel a feasible proposition?

Pseudoscalar-photon interactions were proposed in the study of the relations among equivalence principles. The interaction of pseudoscalar axion with gluons was proposed as a way to solve the strong CP problem. Subsequent proposal of axion as a dark matter candidate has been a focus of search. Motivation from superstring theories add to its importance. After a brief introduction and historical review, we present (i) the current status of our optical experiment using high-finesse Fabry-Perot resonant cavity — Q & A experiment — to detect pseudoscalar-photon interactions, (ii) the constraints on pseudoscalar-photon interactions from astrophysical and cosmological observations on cosmic polarization rotation, and (iii) theoretical models of non-minimal interactions of gravitational, electromagnetic and pseudoscalar (axion) fields, and their relevance to cosmology.