arXiv subjects

Ashadul Halder

Publications and source records attributed to Ashadul Halder.

At least 19 recordsLinked to original sources

arXiv2025

Viscous Dark Energy and Mass-Varying Dark Matter in Lyra Manifold: Cosmological Dynamics and Observational Constraints

We investigate the cosmological dynamics of a universe described by Lyra's geometry in the presence of dark energy (DE) and dark matter (DM). Dark energy is modeled as a quintessence scalar field with bulk viscosity, while dark matter is allowed to interact with the scalar sector. The displacement vector field, arising naturally in Lyra's manifold, provides an additional geometric contribution. By employing dynamical system techniques, we analyze stability properties and late-time attractors. Our results indicate that viscosity and DE--DM interaction enrich the phase space structure and can help address both the cosmic acceleration and the coincidence problem. Furthermore, by performing a Markov Chain Monte Carlo (MCMC) analysis with recent observational datasets, we derive best-fit values for the model parameters that exhibit good consistency with current data.

astro-ph.CO↗

arXiv2025

Bridging the Gap Between Virtual and Physical Laboratories: A Web-Based Interactive Platform for Undergraduate Physics Practicals

The COVID-19 pandemic highlighted the challenges of maintaining hands-on laboratory instruction in undergraduate physics education. In response, we developed and deployed an interactive online physics laboratory platform designed to closely replicate the experimental setups available and curriculum of St. Xavier's College (Autonomous), Kolkata. The platform is designed to closely replicate real experimental arrangements and is aligned with the curriculum, allowing students to prepare effectively before performing physical experiments. Student feedback revealed that 100% of the respondents rated the platform as beneficial (rating 4 or 5 on a 5-point scale) to improve conceptual understanding and increase confidence in conducting physical experiments. Furthermore, all students agreed that having access to the online prelab simulations is advantageous and recommended its regular use. These findings highlight the effectiveness of web-based simulations as a complementary and sustainable resource for physics education.

physics.ed-ph↗

arXiv2025

IceCube PeV neutrinos from heavy dark matter decay with 12 years HESE data

The decay of superheavy dark matter from the early universe may undergo decay via QCD cascades and electroweak cascade to produce neutrinos as one of the decay products. We consider the neutrino events in and around PeV region reported by IceCube collaboration are due to the decay of such heavy dark matter. The neutrino spectrum could be from the decay processes via hadronic decay modes and/or leptonic decay modes. Using the numerical evolution of QCD cascades as well as electroweak corrections where use has been made of DGLAP equations, the neutrino fluxes from the heavy dark matter decay have been computed. The mass of the decaying superheavy dark matter and its decay lifetime have then been estimated from a $\chi^2$ analysis of the IceCube 12-year data. The fractional contribution ($f_{\rm lep}$) of the leptonic decay channel in such a decay process is also estimated from the same $\chi^2$ analyses. It is seen that to explain the IceCube 12-year ultrahigh energy (UHE) events the mass of a decaying superheavy dark matter would be $\sim9.4\times 10^6$ GeV and decay time $\tau \simeq 4.2 \times 10^{28}$ second. It is also found that the lepton channel contribution is very small, $f_{\rm lep} \sim 0.001$.

hep-ph↗

arXiv2024

Exploring the effects of dark matter - dark energy interaction on cosmic evolution in viscous dark energy scenario

We explore the influence of interactions between dark matter (DM) and dark energy (DE) on the cosmic evolution of the Universe within a viscous dark energy (VDE) framework. Moving beyond traditional interacting dark energy (IDE) models, we propose a generalized IDE model adaptable to diverse IDE scenarios via IDE coupling parameters. In order to investigate deviations from $\Lambda$CDM across cosmic epochs by highlighting how viscous and the interactions between DM and DE impact cosmic density and expansion rates, we consider a model agnostic form of VDE. Eventually we perform a Bayesian analysis using the Union 2.1 Supernova Ia dataset and Markov Chain Monte Carlo (MCMC) sampling to obtain optimal values of model parameters. This comprehensive analysis provides insights about the interplay between viscous and IDE in shaping the Universe's expansion history.

astro-ph.CO↗

arXiv2024

Compact objects and dark matter dynamics in astroparticle physics

The quark star is such an exotic star of our Universe. The limiting mass for quark stars essentially depends on rotational frequency apart from bag constant and other fundamental parameters. The analytical results obtained agree with the results of several relevant numerical estimates as well as observational evidence. Primordial black hole (PBH) is another hypothetical candidate of compact astrophysical objects. We explore the combined effect of PBH evaporation and the baryon-dark matter (DM) interaction in the 21cm scenario. We address both upper and lower bounds on several PBH and DM parameters using the observational excess (-500^{+200}_{-500} mK) of EDGES's experimental results. A similar investigation has been carried out in the framework of interacting dark energy (IDE) models. We consider three IDE models and eventually measure the allowed limits of IDE coupling parameters for individual cases. Keeping in view of the 21cm scenario, we also explore the multimessenger signals from possible rare decay of fundamental Heavy Dark Matters (HDM). HDM can undergo QCD cascade decay to produce leptons or $\gamma$ as end products. One of the multimessenger signals could be the source of ultra high energy neutrino ($\sim$PeV) signals at the IceCube detector whereas the other signal attributes to the cooling/heating of the baryons due to HDM decay and corresponding influences in the global 21cm signal. The consequence of late time decay of such HDMs may also have significant implications on the aspect of matter-antimatter asymmetry. The mass and lifetime of such Dark Matter particles have been obtained by performing a $\chi^2$ analysis with the PeV neutrino data of IceCube and finally, the amount of baryon asymmetry produced in the Universe is estimated if caused by Dark Matter decay.

hep-ph↗

arXiv2023

Analyzing the 21-cm signal brightness temperature in the Universe with inhomogeneities

We explore the 21-cm signal in our Universe containing inhomogeneous matter distribution at considerably large scales. Employing Buchert's averaging procedure in the context of a model of spacetime with multiple inhomogeneous domains, we evaluate the effect of our model parameters on the observable 21-cm signal brightness temperature. Our model parameters are constrained through the Markov Chain Monte Carlo method using the Union 2.1 supernova Ia observational data. We find that a significant dip in the brightness temperature compared to the $\Lambda$CDM prediction could arise as an effect of the inhomogeneities present in the Universe.

astro-ph.CO↗

arXiv2023

Future deceleration due to backreaction in a Universe with multiple inhomogeneous domains

We formulate a model of spacetime with inhomogeneous matter distribution in multiple domains. In the context of the backreaction framework using Buchert's averaging procedure, we evaluate the effect of backreaction due to the inhomogeneities on the late time global evolution of the Universe. Examining the future evolution of this universe, we find that it can transit from the presently accelerating phase to undergo future deceleration. The future deceleration is governed by our model parameters. We constrain the model parameters using observational analysis of the Union 2.1 supernova Ia data employing the Markov Chain Monte Carlo method.

gr-qc↗

arXiv2023

Addressing the self-interaction for ELDER dark matter from the 21-cm signal

The self-interacting dark matter can affect various cosmological processes. Such interactions can be number conserving (\emph{e.g.} $2 \rightarrow 2$) or number violating (\emph{e.g.} $3 \rightarrow 2,\,4 \rightarrow 2$ etc.). The latter processes where three (or more) dark matter particles undergo self-annihilation/scattering to produce less number of dark matter is termed as ``Cannibalism'' process. In this work, the self-interaction of dark matter and the strength of such interactions are investigated in the light of experimental results of the global 21-cm spectrum of neural hydrogen from the era of cosmic dawn. From the present work, it appears that $2\rightarrow 2$ process is much more dominant over the $3\rightarrow 2$ process. It is also found that such interactions affect the dark matter-baryon elastic scattering cross-section. The study also indicates the presence of multi component dark matter of different mass range in the Universe.

astro-ph.CO↗

arXiv2022

Global 21-cm brightness temperature in viscous dark energy models

We investigate the global 21-cm brightness temperature in the context of viscous dark energy (VDE) models. The bulk viscosity of dark energy perturbs the Hubble evolution of the Universe which could cool baryons faster, and hence, alter the 21-cm brightness temperature. An additional amount of entropy is also produced as an outcome of the viscous flow. We study the combined contribution of Hawking radiation from primordial black holes, decay and annihilation of particle dark matter and baryon-dark matter scattering in the backdrop of VDE models towards modification of the 21-cm temperature. We obtain bounds on the VDE model parameters which can account for the observational excess of the EDGES experiment ($-500^{+200}_{-500}$ mK at redshift $14<z<20$) due to the interplay of the above effects. Moreover, our analysis yields modified constraints on the dark matter mass and scattering cross-section compared to the case of the $\Lambda$CDM model.

astro-ph.CO↗

arXiv2022

KM3NeT upper bounds of detection rates of solar neutrinos from annihilations of dark matter at the solar core

The Weakly Interacting Massive Particles (WIMPs) so far remain one of the most popular candidates for dark matter. If captured gravitationally inside the core of the Sun, these WIMPs may produce high energy neutrinos as the end product in case they undergo self annihilations at the solar core. In this work, we address the detectability of such neutrinos at the proposed KM3NeT detector. Upper bounds of the detection rate for such neutrinos at KM3NeT are computed for the case of a generic dark matter scenario and also when specific models for particle dark matter are chosen. In this work, upper bounds of muon event rates for different annihilating dark matter masses are computed for each of the cases of dark matter annihilation channels (e.g. $b\bar{b}~, W^+W^-, Z\bar{Z} $ etc). These upper bounds are also computed by considering the dark matter scattering cross-section using upper bounds obtained from PandaX-4T direct dark matter search experiment.

hep-ph↗

arXiv2022

Constraining PBH mass distributions from 21cm brightness temperature results and an analytical mapping between probability distribution of 21cm signal and PBH masses

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.

astro-ph.CO↗

arXiv2021

Exploring multimessenger signals from heavy dark matter decay with EDGES 21-cm result and IceCube

The primordial heavy or superheavy dark matter that could be created during the reheating or preheating stage of the Universe can undergo QCD cascade decay process to produce leptons or $\gamma$ as end products. Although these could be rare decays, the energy involved in such decay process can influence 21-cm signal of hyperfine transition of neutral hydrogen during the reionization era. We explore in this work, possible multimessenger signals of such heavy dark matter decays. One of which could be the source of ultra high energy neutrino (of $\sim$ PeV energy regime) signals at IceCube detector whereas the other signal attributes to the cooling/heating of the baryons by the exchange of energy involved in this decay process and its consequent influence on 21-cm signal. The effect of evaporation of primordial black holes and baryon scattering with light cold dark matter are also included in relation to the evolution of the 21-cm signal temperature and their influence are also discussed.

astro-ph.CO↗

arXiv2021

Bounds on abundance of primordial black hole and dark matter from EDGES 21-cm signal

The redshifted 21cm radio signal has emerged as an important probe for investigating the dynamics of the dark age Universe (recombination to reionization). In the current analysis, we explore the combined effect of primordial black hole (PBH) evaporation and the baryon-dark matter (DM) interaction in the 21cm scenario. The variation of brightness temperature shows remarkable dependence on the DM masses ($m_{\chi}$) and the baryon-DM cross-sections ($\overline{\sigma}_0$) besides the influences of the PBH parameters (mass $\mathcal{M_{\rm BH}}$ and initial mass fraction $\beta_{\rm BH}$). We address both upper and lower bounds on $\beta_{\rm BH}$ for a wide range of PBH mass in presence of different $m_{\chi}$ and $\overline{\sigma}_0$ by incorporating the observational excess $\left(-500^{+200}_{-500}\: {\rm mK}\right)$ of EDGES's experimental results. Finally, we address similar limits in the $m_{\chi}$ - $\overline{\sigma}_0$ parameter plane for different PBH masses.

astro-ph.CO↗

arXiv2021

Probing the effects of primordial black holes on 21-cm EDGES signal along with interacting dark energy and dark matter - baryon scattering

21-cm radio signal has emerged as an important probe in investigating the dark age of the Universe (recombination to reionization). In the current analysis, we explore the combined effects of primordial black holes (PBH), cooling off of the baryonic matter due to dark matter (DM) - baryon collisions and interaction of dark matter - dark energy (DE) fluid on the 21-cm brightness temperature. The variation of brightness temperature shows remarkable dependence on DM mass ($m_{\chi}$) and the dark matter - baryon scattering cross-section ($\sigma_0$). Bounds in $m_{\chi}$ - $\sigma_0$ parameter space are obtained for different possible PBH masses and for different interacting dark energy (IDE) models. These bounds are estimated based on the observed excess ($-500^{+200}_{-500}$ mK) of 21-cm brightness temperature by EDGES experiment. Eventually, bounds on PBH mass is also obtained for different values of dark matter mass and for different IDE model coupling parameters. The compatibility of the constraints of the IDE models, in the estimated bounds are also addressed.

astro-ph.CO↗

arXiv2020

Chandrasekhar limit for rotating quark stars

The limiting mass is a significant characteristic for compact exotic stars. In the case of quark stars, the limiting mass can be expressed in terms of fundamental constants and the Bag constant. In the present work, using bag model description, the maximum mass of a rotating quark star is found to depend on the rotational frequency apart from other fundamental parameters. The analytical results obtained agree with the results of several relevant numerical estimates as well as observational evidences.

astro-ph.HE↗

arXiv2020

The Violation of Equivalence Principle and Four Neutrino Oscillations for Long Baseline Neutrinos

Violation of equivalence principle predicts that neutrinos of different flavor couple differently with gravity. Such a scenario can give rise to gravity induced flavor oscillations in addition to the usual mass flavor neutrino oscillations during the neutrino propagation. Even if the equivalence principle is indeed violated, their measure will be extremely small. We explore the possibility to probe the violation of equivalence principle (VEP) for the case of long baseline (LBL) neutrinos in a 4-flavor neutrino framework (3 active + 1 sterile) where both mass and gravity induced oscillations are considered. To this end, we have explicitly calculated the oscillation probability in 4-flavor framework that includes in addition to the mass-flavor mixing in matter, the gravity-flavor mixing also. The energy eigenvalues are then obtained by diagonalizing such a 4-flavor mixing matrix. The formalism is then employed to estimate the wrong and right sign muon yields at a far detector for neutrinos produced in a neutrino factory and travel through the Earth matter. These results are compared with the similar estimations when the usual three active neutrinos are considered.

hep-ph↗

arXiv2019

Estimation of Baryon Asymmetry from Dark Matter Decaying into IceCube Neutrinos

The recent results of IceCube Neutrino Observatory include an excess of PeV neutrino events which appear to follow a broken power law different from the other lower energy neutrinos detected by IceCube. The possible astrophysical source of these neutrinos is still unknown. One possible source of such neutrinos could be the decay of non-thermal, long-living heavy mass Dark Matter, whose mass should be $> 10^{6} \rm {GeV}$ and could have produced at the very early Universe. They can undergo cascading decay via both hadronic and leptonic channels to finally produce such high energy neutrinos. This possibility has been explored in this work by studying the decay flux of these Dark Matter candidates. The mass and lifetime of such Dark Matter particles have been obtained by performing a $\chi^2$ fit with the PeV neutrino data of IceCube. We finally estimate the baryon asymmetry produced in the Universe due to such Dark Matter decay.

hep-ph↗

arXiv2019

Addressing $\gamma$-ray emissions from dark matter annihilations in 45 milky way satellite galaxies and in extragalactic sources with particle dark matter models

The mass to luminosity ratio of the dwarf satellite galaxies in the Milky Way suggests that these dwarf galaxies may contain substantial dark matter. The dark matter at the dense region such as within or at the vicinity of the centres of these dwarf galaxies may undergo the process of self annihilation and produce $\gamma$-rays as the end product. The satellite borne $\gamma$-ray telescope such as Fermi-LAT reported the detection of $\gamma$-rays from around 45 Dwarf Spheroidals (dSphs) of Milky Way. In this work, we consider particle dark matter models described in the literature and after studying their phenomenologies, we calculate the $\gamma$-ray fluxes from the self annihilation of the dark matter within the framework of these models in case of each of these 45 dSphs. we then compare the computed results with the observational upper bounds for $\gamma$-ray flux reported by Fermi-LAT and Dark Energy Survey (DES) for each of the 45 dSphs. The fluxes are calculated by adopting different dark matter density profiles. We then extend similar analysis for the observational upper bounds given by Fermi-LAT for the continuum $\gamma$-ray fluxes originating from extragalactic sources.

astro-ph.CO↗