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The evaporation of Primordial Black Hole (PBH) via Hawking radiation influences the evolution of Inter Galactic Medium by heating up the latter and consequently affects the 21cm signal originated from the neutral Hydrogen atoms. In this work, we have considered EDGES observational data of 21cm line corresponding to cosmic dawn era to constrain the mass and the abundance of PBHs. In this context, two different PBH mass distributions namely, power law and lognormal mass distributions are considered to estimate the effects of PBH evaporation on the 21cm brightness temperature $T_{21}$. In addition to these two mass distributions, different monochromatic masses are also considered. The impacts of Dark Matter - baryon interactions on $T_{21}$ are also considered in this work along with the influences of PBH evaporation. Furthermore, adopting different monochromatic masses for PBHs, an attempt has been made to formulate a distribution for PBH masses by associating a probability weightage of the $T_{21}$ values (at $z \sim 17.2$), within the range given by EDGES experiment, with the calculated $T_{21}$ values for each of the PBH mass values. The distribution best suited for the present purpose is found to be a combination of an error function and Owen function. Allowed contours in the parameter space of (initial PBH mass-dark matter mass) are obtained., Comment: 17 pages, 9 figures

The EDGES experiment related to the observant of brightness temperature \(T_{21}\) of 21cm line arising from ground state of neutral Hydrogen atom, has shown an excess absorption feature ( \(− 500^ {+200}_{ − 500}\) mK) in \(T_{21}\) spectrum corresponds to the era of cosmic dawn (\(z \sim 17.2\)). In order to explain the observed excess trough of \(T_{21}\) we consider Interacting Dark Energy scenario (interaction of Dark Matter and Dark Energy) along with the scattering of baryon matter with Dark Matter. Three different Interacting Dark Energy (IDE) models are used and the viability of those models are tested in the context of EDGES experimental results. It is found that Dark Matter-Dark Energy interaction modifies the evolution process of the Universe and hence consequently affects the brightness temperature. Dark Matter-baryon interaction also affects the \(T_{21}\) temperature since baryon fluid would transfer heat to the colder Dark Matter due to the Dark Matter baryon collision. In addition we also give bounds on the model parameters of the IDE models and Dark Matter model from EDGES observational data. It is noted that Dark Matter-Dark Energy interaction enables to explore larger range of Dark Matter mass regimes that would satisfy the EDGES result.

We explore the perturbationsn in Dark Energy by taking the Slotheon field model. The Slotheon field model follows from the extra-dimensional DGP (Dvali, Gabadadze, and Porrati) model and based on the Galileon transformation in curved space time. In this model a scalar field \(\pi \) in DGP theory is subjected to a shift symmetry in such a way that the final theory is invariant under this shift symmetry in curved space time. We consider that the accelerated expansion and Dark Energy are driven by the scalar field \(\pi \) with a potential \(V(\pi )\). Then we explore the Dark Energy perturbations within the framework of this Slotheon model. Using these perturbations we compute the matter power spectrum.

We consider a dark energy scenario driven by a scalar field $\phi$ with a pseudo Nambu Goldstone boson (pNGB) type potential $V(\phi)=\mu^4 \left( 1+ {\rm cos}(\phi/f) \right)$. The pNGB originates out of breaking of spontaneous symmetry at a scale $f$ close to Planck mass $M_{\rm{pl}}$. We consider two cases namely the quintessence dark energy and the other, where the standard pNGB action is modified by the terms related to Slotheon cosmology. We demonstrate that for this pNGB potential, high-$f$ problem is better addressed when interaction between dark matter and dark energy is taken into account and that Slotheon dark energy scenario works even better over quintessence in this respect. To this end, a mass limit for dark matter is also estimated., Comment: 20 pages, 12 figures

The EDGES experiment has observed an excess trough ($-500^{+200}_{-500}$ mK) in the brightness temperature $T_{21}$ of the 21cm absorption line of neutral Hydrogen atom (HI) from the era of cosmic dawn ($z \simeq 17.2$). We consider possible interaction of Dark Matter and Dark Energy fluid along with the cooling off of the baryon matter by its collision with Dark Matter to explain the observed excess trough of $T_{21}$. We make use of three different Dark Matter-Dark Energy (DM-DE) interaction models to taste the viability of those models in explaining the EDGES results. The evolution of Hubble parameter is modified by DM-DE interactions and this is also addressed in this work. This in turn influences the optical depth of HI 21cm as well as the baryon temperature and thus effects the $T_{21}$ brightness temperature. In addition we also find that the DM-DE interaction enables us to explore Dark Matter with varied mass regimes and their viabilities in terms of satisfying the EDGES result., 19 pages, 10 figures

Within the framework of modified gravity model namely Slotheon model, inspired by the theory of extra dimensions, we explore the behaviour of Dark Energy and the perturbations thereof. The Dark Energy and matter perturbations equations are then derived and solved numerically by defining certain dimensionless variables and properly chosen initial conditions. The results are compared with those for standard quintessence model and $\Lambda$CDM model. The matter power spectrum is obtained and also compared with that for $\Lambda$CDM model. It appears that Dark Energy in Slotheon model is more akin to that for $\Lambda$CDM model than the standard quintessence model., Comment: 20 pages LaTeX, 6 figures

We explore in this work whether Slotheon model of Dark Energy obeys the Swampland criteria of string theory. Since de Sitter vacuum is very difficult to construct in string theory the cosmological constant as an explanation of Dark Energy is almost ruled out in string theory since it involves a scalar potential $V$ with positive local minimum that ends up to a stable (or meta stable) de Sitter (ds) vacuum. In quintessence model however if the derivative of the scalar potential $V$ ($\nabla V$) is small and $\frac{|\nabla V|}{V} \sim {\cal {O}}(1)$ then in this situation the potential $V$ can be positive but the scalar field may not be at the minimum. For a consistent quantum theory of gravity the theory should not have any ds or meta stable ds vacua. In this regard the Swampland criterion is proposed which any low energy theory should obey to be consistent with quantum theory of gravity. This criterion is written as $|\nabla V|/V > c \sim {\cal {O}}(1)$. In this work we consider a scalar field model for Dark Energy namely the Slotheon Dark Energy model inspired by the theories of extra dimensions and show that this Dark Energy model agrees better with the Swampland criteria than the quintessence Dark Energy model., 15 pages LaTeX, 5 figures