arXiv subjects

Muhammad Ali Paracha

Publications and source records attributed to Muhammad Ali Paracha.

3 recordsLinked to original sources

arXiv2026

Optical Signatures of Sgr A* and M87* with Dark Matter Halos

The event horizon telescope (EHT) has opened a new window onto the strong-field regime by imaging the shadows of the supermassive black holes (SMBHs) Sgr A* and M87*. These observations provide a unique laboratory for probing the dark matter (DM) distribution around black holes. In this work we systematically investigate the imprints of two distinct DM halo models, the cold DM (CDM), and the cored scalar field DM (SFDM) profiles on the gravitational lensing signatures of Sgr A* and M87*. We compute the photon spheres, shadows, weak and strong lensing observables, and caustic structures for both models. We then compared the obtained values of the shadow diameters with the EHT data, using $\chi^2$ statistics. We found that all the models are within $1.2\sigma$ of the measured shadow diameters with the small $\chi^2$ differences, $\Delta\chi^2 \lesssim 1.2$. The caustic analysis reveals distinct topological regimes, Sgr A* retains both tangential and radial critical curves, while M87* may show only tangential critical curves due to its larger mass. This topological difference provides a clear observational signature for future observations.

astro-ph.CO↗

arXiv2019

Testing Leptoquark and $Z^{\prime}$ Models via $B\to K_{1}(1270,1400)μ^{+}μ^{-}$ Decays

The measurements of $R_{K^{(*)}}=\mathcal B(B\to K^{(*)}μ^{+}μ^{-})/\mathcal B(B\to K^{(*)}e^{+}e^{-})$ in recent years have hinted lepton flavor non-universality and thus drawn widespread attentions. If these anomalies are induced by new physics (NP), deviations from the SM predictions may also be found in other channels via the same process at the quark level. In this work, we study in $B\to K_{1}(1270,1400)μ^{+}μ^{-}$ decays the effects of two popular classes of NP models which can address the $b\to s$ anomalies, i.e. the leptoquark models and the $Z^{\prime}$ models. By assuming that NP only affects the $b\to sμ^+μ^-$ transition, we find that the unpolarized and polarized lepton flavor universality (LFU) ratios $R_{K_1^{(L,T)}(1270)}$ are useful to distinguish among the NP models (scenarios) and the SM because they are sensitive to the NP effects and insensitive to the mixing angle $θ_{K_1}$, while the $R_{K_1^{(L,T)}(1400)}$ are sensitive to both NP and $θ_{K_1}$. Another ratio $R_μ(K_1)=\mathcal B(B\to K_1(1400)μ^+μ^-)/\mathcal B(B\to K_1(1270)μ^+μ^-)$ is shown to depend weekly on the effects from the NP models (scenarios) under consideration, and thus can be used to determine the $θ_{K_1}$ and complement the $R_{K_1^{(L,T)}}$ in the probe for NP.

hep-ph↗

arXiv2017

Constraints on Two Higgs Doublet Model Parameters in the light of rare $B$-Decays

We established the allowed parameters of two-Higgs doublet model(2HDM) from flavor physics observables, precisely from rare $B$ meson decays. In our analysis most formidable constraints on the 2HDM parameters arise from the branching ratio of rare radiative $B$ meson decay i.e., $B\to X_{s}γ$. However, the constraints arising from the branching ratio of $B_{s}\toμ^{+}μ^{-}$ decay in $m_{H^{\pm}}-\tanβ$ plane give $m_{H^{\pm}} >$ 80 GeV for the value of $\tanβ\sim 2$, that is in agreement with large electron-positron collider (LEP) data. Furthermore, we also investigate the bounds on the $CP$-even $m_{H}$ and $CP$-odd $m_{A^{0}}$ Higgs boson not only from above mentioned physical observables, but also from the zero crossing of the forward-backward asymmetry of $B\to K^{\ast}μ^{+}μ^{-}$ decay. Therefore, these bounds on parameters of the 2HDM will provides a fertile ground to test the 2HDM at current and future $B$-physics experiments.

hep-ph↗