In this article, we study the implications of the coupling between Axion-Like-Particles (ALPs) and Leptons to cosmology in particular, the Big Bang Nucleosynthesis (BBN). We show that the BBN, through the constraint on the effective number of relativistic neutrino species, provides the most stringent bound on the ALP-electron interaction strength for the mass of axion between 20 keV and 1 MeV. For other values of the mass, the BBN bound complements the stellar-evolution and laboratory bounds.

Recent results from several direct detection experiments have imposed severe constraints on the multi-GeV mass window for various dark matter (DM) models. However, many of these experiments are not sensitive to MeV scale DM as the corresponding recoil energies are, largely, lower than the detector thresholds. We reexamine the light scalar DM in a model-independent approach. In this first of a two-part work, we develop an appropriate methodology to determine the effective coupling of such a DM to hadrons, thereby allowing for the determination of the corresponding annihilation rates. We find that while the parameter space can be constrained using cosmological and astrophysical observations, a significantly large fraction is still viable. In the companion paper, we study the sensitivity of both direct detection experiments as well as colliders to such a DM.

Adopting a model independent approach, we constrain the various effective interactions of leptophilic DM particles with the visible world from the WMAP and Planck data. The thermally averaged indirect DM annihilation cross section and the DM-electron direct-detection cross section for such a DM candidate are observed to be consistent with the respective experimental data. We study the production of cosmologically allowed leptophilic DM in association with Z (Z → ff ), f ≡ q, e − , μ − at the ILC. We perform the χ 2 analysis and compute the 99% C.L. acceptance contours in the m χ and Λ plane from the two-dimensional differential distributions of various kinematic observables obtained after employing parton showering and hadronisation to the simulated data. We observe that the dominant hadronic channel provides the best kinematic reach of 2.62 TeV (m χ = 25 GeV), which further improves to ∼3 TeV for polarised beams at √ s = 1 TeV and an integrated luminosity of 1 ab −1 .

Ultralight dark photons predicted in several Standard Model extensions can trigger the superradiant instability around rotating black holes if their Compton wavelength is comparable to the Blackhole radius. Consequently, the angular momentum of the black hole is reduced to a value which depends upon the mass and spin of the black hole as well as the mass of the dark photon. We use the mass and spin measurements of the primary black holes in two recently observed binary black hole systems: GW190517 and GW190426 152155 to constrain dark photon mass in the ranges 1.7 × 10 −14 eV < m A < 7.6 × 10 −13 eV and 1.3 × 10 −13 eV < m A < 4.2 × 10 −12 eV respectively, assuming a timescale of a few million years from the time of formation of the binary black hole system to the time of their merger. We also discuss an interesting X-ray binary system, MAXI J1820 070, albeit with a relatively small value of the spin parameter.

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