No abstract

We investigated the scenario of time-dependent diffusive interaction between dark matter and dark energy and showed that such a model can be accommodated within the observations of luminosity distance -redshift data in Supernova Ia (SNe Ia) observations. We obtain constrains on different relevant parameters of this model from the observational data. We consider a homogeneous scalar field φ(t) driven by a k−essence Lagrangian of the from L = V (φ)F (X) with constant potential V (φ) = V , to describe the dynamics of dark energy in this model. Using the temporal behaviour of the FRW scale factor, the equation of state and total energy density of the dark fluid, extracted from the analysis of SNe Ia (JLA) data, we have obtained the timedependence of the k−essence scalar field and also reconstructed form of the function F (X) in the k−essence Lagrangian.

We consider a unified model of interacting dark matter and dark energy to account for coincidence of present day dark energy and dark matter densities. We assume dark energy to be represented by a homogeneous scalar field φ whose dynamics is driven by a (noncanonical) k-essence Lagrangian with constant potential and the particles of dark matter fluid undergoing velocity diffusion in background medium of the k−essence scalar field φ. This results in a transfer of energy from the fluid of dark matter to that of dark energy. This effect shows up as a source term in the continuity equation for dark matter and dark energy fluids. The source term involves a diffusion coefficient which is a measure of average energy transferred per unit time due to diffusion. We use time evolutions of the scale factor of background FRW spacetime, energy density and pressure of the dark fluid obtained from analysis of Supernova Ia data to obtain bounds on the diffusion parameter. For a constant potential in the k-essence Lagrangian, the temporal behaviour of a homogeneous k-essence field φ is obtained for different values of the diffusion parameter. The obtained temporal behaviour may be expressed as φ(t/t 0 ) = φ 0 + ε 1 (t/t 0 − 1) + ε 2 (t/t 0 − 1) 2 , where t 0 is the time corresponding to present epoch. The coefficients ε 1 and ε 2 have been found and obtained as linear functions of diffusion parameter. 1

We study portal interactions connecting visible and dark sectors, and involving local interactions of a photon, a dark photon and a axion-like particle (ALP) at future e + e − colliders. These interactions, mediated by higher-dimensional effective operators, may arise at one-loop by kinetic mixing between dark and ordinary photons, or, for massless dark photons, by direct short-distance contributions. We explore these portal interactions for a heavy ALP with masses between about 10 GeV and 230 GeV by investigating the sensitivity of the production e + e − → γγγ to the effective couplings, where the dark photonγ gives rise to missing momentum in the final state. We will show how an appropriate choice of missing-energy and missing-mass cuts can optimize the signal to standardmodel background ratio. Exclusion regions for the effective photon-dark-photon-ALP couplings versus the ALP mass are worked out for a few representative values of the collision energy and integrated luminosity, as presently envisaged by future e + e − projects. * sanjoy.biswas@rkmvu.ac.in † anirban.chatterjee@rkmvu.ac.in