arXiv subjects

Atrideb Chatterjee

Publications and source records attributed to Atrideb Chatterjee.

14 recordsLinked to original sources

arXiv2026

Impact of Primordial Black Hole population on 21 cm observables at high redshift

The 21-centimetre (21-cm) signal is one of the most promising probes of the high-redshift Universe. It has typically been modelled without accounting for the effects of active galactic nuclei (AGNs) in the pre-JWST era, primarily due to the lack of observational evidence for AGNs at z > 6. However, following the discovery of several AGNs at redshifts as high as z~ 10 by JWST, it has become imperative to incorporate the impact of these early AGNs when predicting the 21-cm signal. Based on the assumption that these AGNs are seeded by primordial black holes (PBHs), we studied their impact with a semi-numerical model setup. Specifically, we extended the explicitly photon-conserving reionisation framework, SCRIPT, including essential cosmic dawn physics and PBH contributions. This enabled us to compute both the global signal and the power spectrum of the 21-cm line over the redshift range z ~ 30 - 5 within a self-consistent framework. Building on this set-up, we investigated the impact of different PBH mass functions (obeying current observational constraints) on the resulting signal. We find the X-ray heating from PBHs can substantially make the global 21-cm signal shallower and suppress the expected power spectrum amplitude during cosmic dawn. We also find that the choice of mass function plays a crucial role in shaping the 21-cm signal, and can, in fact, lead to significantly different predictions.

astro-ph.CO↗

arXiv2026

Effect of Primordial Black Holes on the global 21-cm signal

The 21-cm global signal, a treasure trove of information about the nature of the first luminous sources of the Universe, has traditionally been modelled assuming that these early sources were predominantly star-forming galaxies. However, recent observations by the James Webb Space Telescope (JWST) have revealed several AGNs as early as z ~ 10 - 10.4 . In light of this, it is important to investigate the contribution of such AGNs to the 21-cm signal. Assuming that these AGNs are seeded by Primordial Black Holes (PBHs) and employing an analytical PBH model, consistent with existing cosmological and astrophysical constraints, we show that these exotic objects can have a significant impact on the redshift evolution of the global signal.

astro-ph.CO↗

arXiv2025

Learning Cosmology from Nearest Neighbour Statistics

Extracting cosmological parameters from galaxy/halo catalogues with sub-percent level accuracy is an important aspect of modern cosmology, especially in view of ongoing and upcoming surveys such as Euclid, DESI, and LSST. While traditional two-point statistics have been known to be suboptimal for this task, recently proposed k-Nearest Neighbour (kNN) based summary statistics have demonstrated tighter constraining power. Building on the kNN statistics, we introduce a new field-level representation of discrete halo catalogues - NN distance maps. We employ this technique on the halo catalogues obtained from Quijote N-body simulation suites. By combining these maps with kNN-based summary statistics, we train a hybrid neural network to infer cosmological parameters, showing that the resulting constraints achieve state-of-the-art, if not the best, accuracy. In addition, our hybrid framework is 5-10 times more computationally efficient than some of the existing point-cloud-based ML methods.

astro-ph.CO↗

arXiv2025

Exploring the BSM parameter space with Neural Network aided Simulation-Based Inference

Some of the issues that make sampling parameter spaces of various beyond the Standard Model (BSM) scenarios computationally expensive are the high dimensionality of the input parameter space, complex likelihoods, and stringent experimental constraints. In this work, we explore likelihood-free approaches, leveraging neural network-aided Simulation-Based Inference (SBI) to alleviate this issue. We focus on three amortized SBI methods: Neural Posterior Estimation (NPE), Neural Likelihood Estimation (NLE), and Neural Ratio Estimation (NRE) and perform a comparative analysis through the validation test known as the \textit{ Test of Accuracy with Random Points} (TARP), as well as through posterior sample efficiency and computational time. As an example, we focus on the scalar sector of the phenomenological minimal supersymmetric SM (pMSSM) and observe that the NPE method outperforms the others and generates correct posterior distributions of the parameters with a minimal number of samples. The efficacy of this framework is tested on 5 parameter pMSSM with Higgs and flavor physics data and its performance is compared with the MCMC method. We further add dark matter (DM) observables to make the task more challenging and consider a 9 parameter pMSSM. We observe that even though the efficiency factor drops, the amortized SBI method still produces faithful posterior distributions. SBI predicted points satisfying DM constraints are mostly bino-dominated upto $\sim$ 1.5 TeV, and are mostly wino-dominated within the 1.5 - 2 TeV range.

hep-ph↗

arXiv2024

Cosmology from Point Clouds with Dark Matter Halos from the Quijote Simulations

We train a novel deep learning architecture to perform likelihood-free inference on the value of the cosmological parameters from halo catalogs of the Quijote N-body simulations. Our model takes as input a halo catalog where each halo is characterized by its position, mass, and velocity modulus. By construction, our model is E(3) invariant and is designed to extract information hierarchically. Unlike graph neural networks, it does not require the transformation of the input halo (or galaxy) catalog into a graph. Given its simplicity, our model can process point clouds with large numbers of points. We discuss the advantages of this class of methods but also point out their limitations and potential ways to improve them for cosmological data.

astro-ph.CO↗

arXiv2023

Ruling out Strongly Interacting Dark Matter-Dark Radiation Models from Joint Observations of Cosmic Microwave Background and Quasar Absorption Spectra

The cold dark matter (CDM) paradigm provides a remarkably good description of the Universe's large-scale structure. However, some discrepancies exist between its predictions and observations at very small sub-galactic scales. To address these issues, the consideration of a strong interaction between dark matter particles and dark radiation emerges as an intriguing alternative. In this study, we explore the constraints on those models using joint observations of Cosmic Microwave Background (CMB) and Quasars absorption spectra with our previously built parameter estimation package CosmoReionMC. At 2-$\sigma$ confidence limits, this analysis rules out the strongly interacting Dark Matter - Dark Radiation models within the recently proposed ETHOS framework, representing the most stringent constraint on those models to the best of our knowledge. Future research using a 21-cm experiment holds the potential to reveal stronger constraints or uncover hidden interactions within the dark sector.

astro-ph.CO↗

arXiv2023

Predictions of the 21cm global signal in the JWST and ALMA era

We calculate the redshift evolution of the global 21cm signal in the first billion years using a semi-analytic galaxy formation model, DELPHI, that jointly tracks the assembly of dark matter halos and their constituent baryons including the impact of supernova feedback and dust enrichment. Employing only two redshift- and mass-independent free parameters, our model predicts galaxy populations in accord with data from both the James Webb Space Telescope (JWST) and the Atacama Large Millimetre Array (ALMA) at $z \sim 5-12$. In addition to this ``fiducial" model, which fully incorporates the impact of dust attenuation, we also explore an unphysical ``maximal" model wherein galaxies can convert a 100\% of their gas into stars instantaneously (and supernova feedback is ignored) required to explain JWST data at $z >=13$. We also explore a wide range of values for our {\it 21cm} parameters that include the impact of X-ray heating ($f_{\rm X,h} =0.02-2.0$) and the escape fraction of Lyman Alpha photons ($f_\alpha = 0.01-1.0$). Our key findings are: (i) the fiducial model predicts a global 21cm signal which reaches a minimum brightness temperature of $ T_{\rm b, min}\sim -215$ mK at a redshift $z_{\rm min} \sim 14$; (ii) since the impact of dust on galaxy properties (such as the star formation rate density) only becomes relevant at $z <= 8$, dust does not have a sensible impact on the global 21cm signal; (iii) the ``maximal" model predicts $T_{\rm b, min}= -210$ mK as early as $z_{\rm min} \sim 18$; (iv) galaxy formation and 21cm parameters have a degenerate impact on the global 21cm signal. A combination of the minimum temperature and its redshift will therefore be crucial in constraining galaxy formation parameters and their coupling to the 21cm signal at these early epochs.

astro-ph.CO↗

arXiv2023

Warm Dark Matter constraints from the joint analysis of CMB, Lyman-$\alpha$, and global 21 cm data

With the help of our previously built MCMC-based parameter estimation package \texttt{CosmoReionMC}, we investigate in detail the potential of 21 cm global signal, when combined with CMB and observations related to the QSO absorption spectra, to constraint the mass of Warm Dark Matter (WDM) particle. For the first time, we simultaneously vary all the free parameters (mass of WDM particle, cosmological parameters, and astrophysical parameters) in a joint analysis with CMB, observations related to the QSO absorption spectra and 21 cm global signal, to address the long-overlooked issue of the possible degeneracies between the Dark Matter particle mass $m_X$ and cosmological/astrophysical parameters. From the existing CMB and QSO absorption spectra data, we can rule out $m_X < 2.8$ keV at 95\% confidence level. Including a mock 21~cm global signal in the redshift range $z = 25 - 5$ expected to be observed with upcoming instruments designed for global signal, the forecasted constraint is found to be much tighter $m_X > 7.7$ keV, assuming that the true dark matter model is the usual cold dark matter. In case the mock 21 cm signal is constructed for dark matter particles having $m_X = 7$ keV, our forecasts indicate that $\left(m_X / \text{keV}\right)^{-1}$ is in the range $[0.1, 0.2]$ ($95\%$ confidence level). This implies that the future 21 cm data should allow detection of the WDM particle mass if $m_X \sim 7$ keV.

astro-ph.CO↗

arXiv2023

Non-parametric Reconstruction of Photon Escape Fraction from Reionization

One of the most crucial yet poorly constrained parameters in modelling the ionizing emissivity is the escape fraction of photons from star-forming galaxies. Several theoretical and observational studies have been conducted over the past few years, but consensus regarding its redshift evolution has yet to be achieved. We present here the first non-parametric reconstruction of this parameter as a function of redshift from a data-driven reionization model using a Gaussian Process Regression method. Our finding suggests a mild redshift evolution of escape fraction with a mean value of $4\%,7\%,\sim10\%$ at $z=2,6,12$. However, a constant escape fraction of $6-10\%$ at $z\gtrsim 6$ is still allowed by current data and also matches other reionization-related observations. With the detection of fainter high redshift galaxies from upcoming observations of JWST, the approach presented here will be a robust tool to put the most stringent constraint on escape fraction as well as reionization histories.

astro-ph.CO↗

arXiv2022

Studying Cosmic Dawn using redshifted HI 21-cm signal: A brief review

In this review article, we briefly outline our current understanding of the physics associated with the HI 21-cm signal from cosmic dawn. We discuss different phases of cosmic dawn as the ambient gas and the background radiations evolve with the redshift. We address the consequences of several possible heating sources and radiation background on the global 21-cm signal. We further review our present perspective of other important aspects of the HI 21-cm signal such as the power spectrum and imaging. Finally, we highlight the future key measurements of the Square Kilometre Array and other ongoing/upcoming experiments that will enlighten our understanding of the early Universe.

astro-ph.CO↗

arXiv2021

CosmoReionMC: A package for estimating cosmological and astrophysical parameters using CMB, Lyman-{\alpha} absorption and global 21 cm data

We present a Markov Chain Monte Carlo (MCMC)-based parameter estimation package, CosmoReionMC, to jointly constrain cosmological parameters of the $\Lambda$CDM model and the astrophysical parameters related to hydrogen reionization. The package is based on a previously developed physically motivated semi-analytical model for reionization, a similar semi-analytical model for computing the global 21~cm signal during the cosmic dawn and using an appropriately modified version of the publicly available CAMB for computing the CMB anisotropies. These calculations are then coupled to an MCMC ensemble sampler \texttt{emcee} to compute the posterior distributions of the model parameter. The model has twelve free parameters in total: five cosmological and seven related to the stellar populations. We constrain the parameters by matching the theoretical predictions with CMB data from Planck, observations related to the quasar absorption spectra and, for the first time, the global 21~cm signal from EDGES. We find that incorporating the quasar spectra data in the analysis tightens the bounds on the electron scattering optical depth $\tau$ and consequently the normalization $A_s$ of the primordial matter power spectrum (or equivalently $\sigma_8$). Furthermore, when we include the EDGES data in the analysis, we find that an early population of metal-free stars with efficient radio emission is necessary to match the absorption amplitude. The CosmoReionMC package should have interesting future applications, e.g., probing non-standard extensions to the $\Lambda$CDM model.

astro-ph.CO↗

arXiv2020

Using Artificial Neural Networks to extract the 21-cm Global Signal from the EDGES data

The redshifted 21-cm signal of neutral Hydrogen is a promising probe into the period of evolution of our Universe when the first stars were formed (Cosmic Dawn), to the period where the entire Universe changed its state from being completely neutral to completely ionized (Reionization). The most striking feature of this line of neutral Hydrogen is that it can be observed across an entire frequency range as a sky-averaged continuous signature, or its fluctuations can be measured using an interferometer. However, the 21-cm signal is very faint and is dominated by a much brighter Galactic and extra-galactic foregrounds, making it an observational challenge. We have used different physical models to simulate various realizations of the 21-cm Global signals, including an excess radio background to match the amplitude of the EDGES 21-cm signal. First, we have used an artificial neural network (ANN) to extract the astrophysical parameters from these simulated datasets. Then, mock observations were generated by adding a physically motivated foreground model and an ANN was used to extract the astrophysical parameters from such data. The $R^2$ score of our predictions from the mock-observations is in the range of 0.65-0.89. We have used this ANN to predict the signal parameters giving the EDGES data as the input. We find that the reconstructed signal closely mimics the amplitude of the reported detection. The recovered parameters can be used to infer the physical state of the gas at high redshifts.

astro-ph.CO↗

arXiv2020

A hint on the metal-free star formation rate density from 21cm-EDGES data

We aim to provide the first data-constrained estimate of the metal-free (Population III; Pop III) star formation rate density $\dotρ_{*}^{III}$ required at high-redshifts ($z \gtrsim 16$) in order to reproduce both the amplitude and the redshift of the EDGES 21-cm global signal. Our model accounts for the Lyman Alpha (Ly$α$), radio and X-ray backgrounds from both Pop III and metal-enriched Population II (Pop II) stars. For the latter, we use the star formation rate density estimates (and the Ly$α$ background) from the {\it Delphi} semi-analytic model that has been shown to reproduce all key observables for galaxies at $z \gtrsim 5$; the radio and X-ray backgrounds are fixed using low-$z$ values. The constraints on the free parameters characterizing the properties of the Pop III stars are obtained using a Markov Chain Monte Carlo analysis. Our results yield a $\dotρ_{*}^{III}$ that whilst increasing from $z \sim 21-16$ thereafter shows a sharp decline which is in excellent agreement with the results found by \citet{valiante2016} to simulate the growth of $z \sim 6 - 7$ quasars and their host galaxies, suggesting that the bulk of Pop III star formation occurs in the rarest and most massive metal-poor halos at $z \lesssim 20$. This allows Pop III stars to produce a rapidly growing Ly$α$ background between $z \sim 21-15$. Further, Pop III stars are required to provide a radio background that is about $3-4$ orders of magnitude higher than that provided by Pop II stars although Pop II stars dominate the X-ray background.

astro-ph.CO↗

arXiv2019

Ruling out 3 keV warm dark matter using 21 cm-EDGES data

Weakly interacting cold dark matter (CDM) particles, which are otherwise extremely successful in explaining various cosmological observations, exhibit a number of problems on small scales. One possible way of solving these problems is to invoke (so-called) warm dark matter (WDM) particles with masses $m_x \sim$ keV. Since the formation of structure is delayed in such WDM models, it is natural to expect that they can be constrained using observations related to the first stars, e.g., the 21 cm signal from cosmic dawn. In this work, we use a detailed galaxy formation model, Delphi, to calculate the 21 cm signal at high-redshifts and compare this to the recent EDGES observations. We find that while CDM and 5 keV WDM models can obtain a 21 cm signal within the observed redshift range, reproducing the amplitude of the observations requires the introduction of an excess radio background. On the other hand, WDM models with $m_x \leq 3$ keV can be ruled out since they are unable to match either the redshift range or the amplitude of the EDGES signal, irrespective of the parameters used. Comparable to values obtained from the low-redshift Lyman Alpha forest, our results extend constraints on the WDM particle to an era inaccessible by any other means; additional forthcoming 21 cm data from the era of cosmic dawn will be crucial in refining such constraints.

astro-ph.CO↗