No abstract

The evaporations of Primordial Black Holes (PBH) (via Hawking radiation) can produce electrons/positrons (e − /e + ) in the Galactic Centre (GC) region which under the influence of the magnetic field of Centre region can emit synchrotron radiation. These e − /e + can also induce Inverse Compton radiation due to the scattering with ambient photons. In this work three different PBH mass distributions namely, monochromatic, power law and lognormal distributions are considered to calculate such radiation fluxes. On the other hand, annihilation or decay of dark matter in the Galactic Centre region can also yield e − /e + as the end product which again may emit synchrotron radiation in the Galactic magnetic field and also induce Inverse Compton scattering. In this work a comparative study is made for these radiation fluxes from both PBH evaporations and from dark matter origins and their detectabilities are addressed in various ongoing and other telescopes as well as in upcoming telescopes such as SKA. The variations of these radiation fluxes with the distance from the Galactic Centre are also computed and it is found that such variations could be a useful probe to determine the mass of PBH or the mass of dark matter.

We explore in this work whether the 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 as 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 (∇V ) is small and |∇V | V ∼ 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 |∇V |/V > c ∼ 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.

We consider a simple extension of Standard Model by adding two complex singlet scalars with a U (1) symmetry. A discrete Z 2 ×Z 2 symmetry is imposed in the model and the added scalars acquire a non zero vacuum expectation value (VEV) when the imposed symmetry is broken spontaneously. The real (CP even) parts of the complex scalars mix with the SM Higgs and give three physical mass eigenstates. One of these physical mass eigenstates is attributed to the SM like Higgs boson with mass 125.09 GeV. In the present scenario, domain walls are formed in the early Universe due to the breaking of discrete Z 2 × Z 2 symmetry. In order to ensure the unstability of the domain wall this discrete symmetry is also explicitly broken by adding a bias potential to the Lagrangian. The unstable annihilating domain walls produce a significant amount of gravitational waves (GWs). In addition, we also explore the possibility of the production of GW emission from the strong first-order phase transition. We calculate the intensities and frequencies of each of such gravitational waves originating from two different phenomena of the early Universe namely annihilating domain walls and strong first-order phase transition. Finally, we investigate the observational signatures from these GWs at the future GW detectors such as ALIA, BBO, DECIGO, LISA, TianQin, Taiji, aLIGO, aLIGO+ and pulsar timing arrays such as SKA, IPTA, EPTA, PPTA, NANOGrav11 and NANOGrav12.5.

We consider a simple extension of Standard Model by adding two complex singlet scalars with a U(1) symmetry. A discrete $$ {\mathcal{Z}}_2\times {\mathcal{Z}}_2^{\prime } $$ Z 2 × Z 2 ′ symmetry is imposed in the model and the added scalars acquire a non zero vacuum expectation value (VEV) when the imposed symmetry is broken spontaneously. The real (CP even) parts of the complex scalars mix with the SM Higgs and give three physical mass eigenstates. One of these physical mass eigenstates is attributed to the SM like Higgs boson with mass 125.09 GeV. In the present scenario, domain walls are formed in the early Universe due to the breaking of discrete $$ {\mathcal{Z}}_2\times {\mathcal{Z}}_2^{\prime } $$ Z 2 × Z 2 ′ symmetry. In order to ensure the unstability of the domain wall this discrete symmetry is also explicitly broken by adding a bias potential to the Lagrangian. The unstable annihilating domain walls produce a significant amount of gravitational waves (GWs). In addition, we also explore the possibility of the production of GW emission from the strong first-order phase transition. We calculate the intensities and frequencies of each of such gravitational waves originating from two different phenomena of the early Universe namely annihilating domain walls and strong first-order phase transition. Finally, we investigate the observational signatures from these GWs at the future GW detectors such as ALIA, BBO, DECIGO, LISA, TianQin, Taiji, aLIGO, aLIGO+ and pulsar timing arrays such as SKA, IPTA, EPTA, PPTA, NANOGrav11 and NANOGrav12.5.