arXiv subjects

Debarun Paul

Publications and source records attributed to Debarun Paul.

11 recordsLinked to original sources

arXiv2026

Tracing Ultra Light Axions in Post-reionization, Lyman-$\alpha$ and CMB Missions

Ultra-light axions (ULAs) are dark matter candidates proposed to resolve the small scale anomalies of the standard cosmological model. Due to their inherent quantum pressure, ULAs result in a distinct, scale-dependent suppression on the matter power spectrum, which can leave imprints on the upcoming observations. We explore such possibilities by forecasting on the post-reionization large scale structure (LSS) surveys and next-generation cosmic microwave background (CMB) missions. By utilizing the cross-correlation between 21-cm intensity mapping (SKA1-MID and PUMA) and the Lyman-$\alpha$ forest (DESI-like), we explore possible signatures of ULAs in post-reionization surveys while mitigating instrument-specific systematics. The Fisher matrix analysis projects uncertainties on the fractional ULA abundance across a wide ULA mass range of $10^{-30}\text{ eV} \le m_a \le 10^{-20}\text{ eV}$, revealing an optimal detection sensitivity at intermediate masses around $m_a \sim 10^{-25}\text{ eV}$. Furthermore, while next-generation CMB mission alone can yield small projected errors on the ULA fraction compared to future LSS missions, a joint analysis of the DESI-like and PUMA cross-spectrum alongside CMB-S4-like missions estimates an error on the ULA fraction to be $\mathcal{O}(10^{-4})$ for $m_a\lesssim 10^{-28}$ eV, highlighting a significant improvement over standalone LSS and CMB missions.

astro-ph.CO↗

arXiv2026

Prospects of Indirect Detection of Dark Matter via Primordial Black Hole Induced Gravitational Waves

Primordial black holes (PBHs), produced in the early Universe, can source a stochastic background of induced gravitational waves (GWs) and provide a non-thermal origin for dark matter (DM). We investigate DM production in a PBH-dominated cosmological framework, including contributions from PBH evaporation, gravitational production, and thermal freeze-in and freeze-out mechanisms, and determine the regions consistent with the observed DM relic abundance. We find that thermal freeze-in can compensate for the underabundance of PBH-sourced DM, while indirect detection remains largely insensitive due to the feeble interaction strength, making future GW observatories such as LISA and the Einstein Telescope (ET) unique probes of this scenario. For freeze-out DM, indirect detection experiments constrain regions with relatively large annihilation cross-sections, whereas GW observations probe complementary regions with heavier DM masses and smaller interaction strengths. Consequently, the same DM parameter space cannot be simultaneously probed by both indirect detection searches and GW missions. These results establish GW observations as a powerful and independent probe of DM production in PBH-dominated cosmologies, opening a new observational window into DM properties and the thermal history of the pre-BBN Universe.

astro-ph.CO↗

arXiv2025

Exploring the Co-SIMP dark matter model using the 21-cm signal from the dark ages

The redshifted 21-cm signal from the dark ages offers a powerful probe of cosmological models and the underlying dark matter (DM) microphysics. We investigate deviations from the standard $\Lambda$CDM prediction, an absorption trough of approximately $-40.6\,\mathrm{mK}$ at redshift $z\simeq85.6$, in the context of co-SIMP (strongly interacting massive particle) DM. The co-SIMP interaction strength is encoded by the parameter $C_{\rm int}$, incorporating the masses of DM and standard model (SM) particles, the interaction cross-section, and the amount of heat exchange between the two sectors. Increasing $C_{\rm int}$ deepens the absorption feature and shifts the trough to higher redshifts in the global signal. For $C_{\rm int}=1.0$, the minimum brightness temperature reaches $-50.6,\mathrm{mK}$ at $z\simeq86.2$. The 21-cm power spectrum increases with $C_{\rm int}$ in addition to the global signal. We assess the detectability of these signatures using signal-to-noise ratio (SNR) and Fisher forecasts. The maximum SNR reaches $\sim 15.7$ for $C_{\rm int}=1.0$ for the global signal. Fisher forecasts for $1,000$ hours of integration time show that this model can be distinguished from a null-signal at $4.3\sigma$ and a mild 1.6$\sigma$ from $\Lambda$CDM, improving by an order of magnitude for 100,000 hours. For the 21-cm power spectrum, a $5,\mathrm{km}^2$ array with 1,000 hours yields a $4.63\sigma$ detection and mildly separated from the standard scenario at $1.78\sigma$. These findings highlight the potential of the 21-cm cosmology to probe the properties of DM and demonstrate that upcoming dark ages experiments, particularly space-based and lunar observations, can offer a promising avenue to test co-SIMP models.

astro-ph.CO↗

arXiv2025

Primordial Gravitational Waves as Complementary Probe of Dark Matter Indirect Detection

We propose a novel cosmological probe of dark matter (DM) through inflationary primordial gravitational wave (GW) measurements highlighting its complementarity with traditional indirect detection. In scenarios like early matter domination (EMD), the thermal DM relic is diluted and then replenished via non-thermal production, leaving characteristic imprints on the primordial GW spectrum, inducing frequency-dependent suppressions in the GW amplitudes. By analysing signal-to-noise ratio (SNR) and employing Fisher forecast, we show that upcoming GW experiments have good potential to probe the DM parameter space involving its mass and annihilation cross-section. We show, for instance, LISA will be sensitive to DM mass range $[2\times 10^2-10^5]$ GeV. Furthermore, we identify a significant overlap of the GW missions' sensitivity reaches with the projected reach of future indirect searches like CTA with gamma rays, ANTARES, KM3NeT with neutrinos. In those overlapping regions of interests, we forecast on the GW experiments to estimate the precision of measurements. We show, for instance, that DM mass of $10^5$ GeV with an annihilation cross-section of $10^{-24}~{\rm cm}^3{\rm /s}$, and a mass of $10^4$ GeV with an annihilation cross-section of $2\times10^{-25}~{\rm cm}^3{\rm /s}$, lie within the projections of CTA. We find that whilst the former can be probed by ET with $\sim 1\%$ uncertainties, the latter can be probed by $\mu$-ARES with $\sim 7 \%$ uncertainties. Similarly, DM mass of $10^5$ GeV, with cross-section $10^{-23}~{\rm cm}^3{\rm /s}$ lies within the projection of ANTARES and KM3NeT, which can be probed by ET with $\sim 1\%$ uncertainties.

hep-ph↗

arXiv2025

Improved Predictions on Higgs-Starobinsky Inflation and Reheating with ACT DR6 and Primordial Gravitational Waves

We investigate the implications of recent CMB observations for Higgs-Starobinsky inflationary models and their associated reheating dynamics, utilizing data from ACT DR6, Planck 2018, BICEP/Keck 2018, and DESI, collectively referred to as P-ACT-LB-BK18. In addition to direct CMB constraints, we incorporate indirect bounds arising from the potential overproduction of primordial gravitational waves (PGWs), particularly through limits on the effective number of relativistic species, $\Delta N_{\rm eff}$, during Big Bang Nucleosynthesis (BBN). These constraints become especially relevant in scenarios featuring a stiff post-inflationary equation of state $w_{\rm RH}\geq 0.58$. Our analysis shows that, when both P-ACT-LB-BK18 data and $\Delta N_{\rm eff}$ bounds are considered, the viable number of inflationary e-folds is restricted to the range ($57.9$-$62.2$) at the $2\sigma$ confidence level (C.L.). Correspondingly, the reheating temperature is constrained to lie between the BBN energy scale and $10^{12}$ GeV, with the post-inflationary equation-of-state parameter satisfying $w_{\rm RH} > 0.41$. However, no parameter space remains viable at the $1\sigma$ C.L. once $\Delta N_{\rm eff}$ constraints from PGWs are included, rendering the Higgs-Starobinsky model highly restricted.

astro-ph.CO↗

arXiv2025

Axion Dark Matter Archaeology with Primordial Gravitational Waves

We investigate the complementary information to be gained from inflationary gravitational wave (IGW) signals and searches for QCD axion dark matter. We focus on post-inflationary Peccei-Quinn (PQ) breaking axion models that are cosmologically safe. Recent work has shown that a greater number of such models exist. This is because the heavy quarks required for the colour anomaly can provoke a period of heavy quark domination (HQD), which, through decay, dilutes the axion abundance. In this work we show for the first time that the axion dark matter mass can be as low as $m_a\sim10^{-8}\,{\rm eV}$ for models where the heavy quarks decay via dimension 6 terms. This is achieved by allowing the mass of the heavy quarks to differ from the axion decay constant, $m_Q\neq f_a$. Consequently, the observables that would distinguish between pre- and post-inflationary PQ breaking, $m_a$ and the additional relativistic degrees of freedom $\Delta N_{\rm eff}$, now become indiscernible. To solve this, we propose using blue-tilted IGWs to probe HQD. In scenarios where such a blue tilt is present, the enhanced GW signal allows future interferometers to place non-trivial constraints on the parameters $m_Q$ and $f_a$, thereby complementing haloscope searches. While some degeneracies with other parameters such as $m_Q$ remain, detectors such as BBO and ET will be able to optimistically probe $f_a\gtrsim 10^{14}\,{\rm GeV}$.

astro-ph.CO↗

arXiv2025

ACT DR6 Insights on the Inflationary Attractor models and Reheating

We investigate the observational constraints on $\alpha$-attractor inflationary models and their post-inflationary reheating dynamics in light of the latest CMB data from ACT DR6 combined with Planck18, BICEP/$Keck$ 2018, and DESI (P-ACT-LB-BK18). Focusing on both E- and T-type attractor potentials, we analyze how inflationary observables, namely the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$, are indirectly influenced by reheating parameters such as the reheating temperature $T_{\text{RH}}$, the inflaton EoS $w_\phi$, and consequently the inflaton's couplings to SM particles. We incorporate constraints from PGW overproduction via $\Delta N_{\rm eff}$ bounds. Additionally, we include theoretical constraints from CW one-loop radiative corrections, as well as inflaton self-resonance, a non-perturbative effect that can occur even in the absence of inflaton-SM interactions and imposes a strong lower limit, particularly significant for $1/3\lesssim w_\phi\lesssim 0.7$. Our analysis shows that E-models allow a broad range of reheating scenarios, including matter-like reheating ($w_\phi=0$), whereas the T-model yields more restrictive results and remains viable only for $w_\phi>1/2$ for all three non-gravitational interaction channels, $\phi\to\bar{f}f$, $\phi\to bb$, and $\phi\phi \to bb$ are considered. For stiffer EoS, an intermediate coupling window survives, bounded from above by CW corrections or $2\sigma$ observational limits, and from below by the combined PGW and self-resonance constraints. We derive updated bounds on inflaton couplings for both decay and scattering channels and identify parameter regions consistent with successful perturbative reheating. These results establish a robust connection between inflationary dynamics, reheating physics, and particle interactions, and provide concrete targets for upcoming precision CMB observations.

astro-ph.CO↗

arXiv2025

Gravitational Wave Signatures of Primordial Black Hole Reheating in Upcoming Interferometry Missions

We investigate the prospects of detecting a stochastic gravitational wave (GW) background from the primordial black hole (PBH) reheating epoch. If PBHs form during a non-standard cosmological phase prior to the radiation-dominated era, they can dominate the energy density of the Universe before evaporating via Hawking radiation. Such PBHs can generate induced GWs that may fall within the detectable range of future interferometry missions: (i) through isocurvature perturbations arising from the inhomogeneous spatial distribution of PBHs, and (ii) through the amplification of adiabatic perturbations triggered by the abrupt transition from PBH domination to radiation domination. We assess the detection prospects of such GW spectra using the signal-to-noise ratio, Fisher forecast analysis, and Markov chain Monte Carlo analysis with mock data from LISA and ET. Our findings reveal that ET exhibits superior sensitivity to both isocurvature- and adiabatic-induced GWs, covering a wide PBH mass range of $M_{\rm in} \in (0.5-4\times 10^7)$ g. However, we find that the relative uncertainties associated with the parameter of the isocurvature source are quite high. LISA, by contrast, is mostly sensitive to the adiabatic source, with $M_{\rm in} \in (2\times10^4-5\times 10^8)$ g. The combined effect of adiabatic and isocurvature sources on ET and LISA provides a multi-stage window into the post-inflationary Universe by constraining PBH mass, energy fraction, and the background equation of state.

astro-ph.CO↗

arXiv2024

Revisiting primordial magnetic fields through 21-cm physics: Bounds and forecasts

Primordial magnetic fields (PMFs) may significantly influence 21-cm physics via two mechanisms: (i) magnetic heating of the intergalactic medium (IGM) through ambipolar diffusion (AD) and decaying magnetohydrodynamic turbulence (DT), (ii) impact on the star formation rate density (SFRD) through small-scale enhancement of the matter power spectrum. In this analysis, we integrate both of these effects within a unified analytical framework and use it to determine upper bounds on the parameter space of a nearly scale-invariant non-helical PMF in the light of the global 21-cm signal observed by EDGES. Our findings reveal that the joint consideration of both effects furnishes constraints of the order $B_0\lesssim\mathcal{O}(10^{-2})$ nG on the present-day magnetic field strength, which are considerably tighter compared to earlier analyses. We subsequently explore the prospects of detecting such a magnetized 21-cm power spectrum at the upcoming SKA-Low mission. For the relevant parameters of the PMF ($B_0$ and $n_{\!_{B}}$) and the excess radio background ($\xi$), SNR estimation and Fisher forecast analysis indicate that it may be possible to constrain these three parameters with relative $1\sigma$ uncertainties $\lesssim10\%$ and an associated SNR $\gtrsim10$ at SKA-Low. This also leads to possible correlations among these three parameters, thus revealing intriguing trends of interplay among the various physical processes involved.

astro-ph.CO↗

arXiv2024

Primordial Gravitational Waves as Probe of Dark Matter in Interferometer Missions: Fisher Forecast and MCMC

We propose novel inflationary primordial gravitational wave (GW) spectral shapes at interferometer-based current and future GW missions to test dark matter (DM) production via gravity-portal.We consider three right-handed neutrinos (RHNs), the lightest among them is DM candidate while the others participate in baryogenesis via leptogenesis. We find that future GW detectors BBO, DECIGO, ET, for instance, are able to probe DM mass for $5\times 10^6\, {\rm GeV} 10$, along with the observed amount of baryon asymmetry due to gravitational leptogenesis for heavy RHN mass $M_{\cal{N}}$ to be around $8\times 10^{12}$ GeV. Employing Fisher matrix forecast analysis, we identify the parameter space involving non-minimal coupling to gravity $\xi$, reheating temperature of the Universe $T_{\rm rh}$ and DM mass $M_{\rm DM}$ where the GW detector-sensitivities will be the maximum with the least error, along with SNR $>10$. Finally, utilizing mock data for each GW detector, we perform MCMC analysis to find out the combined constraints on the various microphysics parameters. We also explore production of other cosmological relics such as QCD axion relic as DM candidate, produced via gravity-portal in early universe. We find that ET, for instance, can probe the decay constant of such DM candidates ($f_{a}$) as $10^9\,{\rm GeV}\lesssim f_{a}\lesssim 10^{14}\,{\rm GeV}$ for misalignment angle $\theta_i\in[0.1,\pi/\sqrt{3}]$ and $\xi=1$ with SNR $>10$, whereas this range decreases with the increase of non-minimal coupling. Thus the upcoming GW missions will be able to test such non-thermal DM and baryogenesis scenarios involving very high energy scales, which is otherwise impossible to reach in particle physics experiments in laboratories.

hep-ph↗

arXiv2023

Confronting global 21-cm signal with $\mathbb{Z}_3$ symmetric dark matter models

While the $\mathbb{Z}_3$ symmetric dark matter models have shown tremendous prospects in addressing a number of (astro-)particle physics problems, they can leave interesting imprints on cosmological observations as well. We consider two such promising models: semi-annihilating dark matter (SADM) and Co-SIMP $2\rightarrow 3$ interaction, and investigate their effects on the global 21-cm signal. SADM alone cannot address the EDGES dip but can perform better with the aid of an excess radio background, whereas Co-SIMP can naturally explain the EDGES absorption feature by virtue of an intrinsic cooling effect without invoking any such excess radiation. Hence, the latter model turns out to be a rare model within the domain of CDM, that uses leptophilic interaction to achieve the EDGES dip. Further, keeping in mind the ongoing debate between EDGES and SARAS 3 on the global 21-cm signal, we demonstrate that our chosen models can still remain viable in this context, even if the EDGES data requires reassessment in future. We then extend our investigation to possible reflections on the Dark Ages, followed by a consistency check with the CMB and BAO observations via Planck 2018(+BAO) datasets. This work thus presents a compelling case of exploring these interesting particle physics models in the light of different cosmological observations.

astro-ph.CO↗