Soumen Basak, Sukannya Bhattacharya, Mayukh R. Gangopadhyay, Nur Jaman, Raghavan Rangarajan, M. Sami
In this paper, we consider a scenario of spontaneous baryogenesis in a framework of warm quintessential inflation where the residual inflaton field, left out after warm inflation, plays the role of quintessence field at late times and is coupled to a non-conserved baryonic current. Assuming a four fermion $(B-L)$ violating effective interaction, we have demonstrated that the required baryon asymmetry can be produced successfully in this case. We show that the post-inflationary evolution, with the underlying scalar field potential, $V(φ)=V^4_0 \exp{(-αφ^n/M_{\rm Pl}^4 ) }$, $n>1$ well suited to warm inflation, exhibits scaling behaviour soon after a brief kinetic regime. We show that the coupling of the scalar field to massive neutrino matter can give rise to exit from the scaling regime to cosmic acceleration at late times as massive neutrinos turn non-relativistic. The proposed model is shown to successfully describe the cosmic history from inflation to late-time acceleration, with the evolution independent of initial conditions, along with the generation of baryon asymmetry during the post-inflationary era. A brief analysis of relic gravity waves produced in the scenario is presented.
Shahnawaz A. Adil, Mayukh R. Gangopadhyay, M. Sami, Mohit K. Sharma
We consider a scenario of modified gravity, which is generic to late-time acceleration, namely, acceleration in the Jordan frame and no acceleration in the Einstein frame. The possibility is realized by assuming an interaction between dark matter and the baryonic component in the Einstein frame which is removed by going to the Jordan frame using a disformal transformation giving rise to an exotic effective fluid responsible for causing phantom crossing at late times. In this scenario, past evolution is not distinguished from $Λ$CDM but late time dynamics is generically different due to the presence of phantom crossing that causes a monotonous increase in the expansion rate giving rise to distinctive late-time cosmic feature. The latter can play a crucial role in addressing the tension between the observed value of Hubble parameter by CMB (Cosmic Microwave Background) measurements and the local observations. We demonstrate that the Hubble tension significantly reduces in the scenario under consideration for the chosen scale factor parametrizations. The estimated age of the universe in the model is well within the observational bounds in the low and high red-shift regimes.
Mayukh R. Gangopadhyay, Grant J. Mathews, Kiyotomo Ichiki, Toshitaka Kajino
We explore the possibility that both the suppression of the $\ell = 2$ multipole moment of the power spectrum of cosmic microwave background temperature fluctuations and the possible dip for $\ell = 10-30$ can be explained as well as a possible new dip for $\ell \approx 60$ as the result of the resonant creation of sequential excitations of a fermionic (or bosonic) closed superstring that couples to the inflaton field. We consider a D=26 closed bosonic string with one toroidal compact dimension as an illustration of how string excitations might imprint themselves on the CMB. We analyze the existence of successive momentum states, winding states or oscillations on the string as the source of the three possible dips in the power spectrum. Although the evidence of these dips are of marginal statistical significance, this might constitute the first observational evidence of successive superstring excitations in Nature.
Sukannya Bhattacharya, Koushik Dutta, Mayukh R. Gangopadhyay, Anshuman Maharana
Dec 27, 2022·astro-ph.CO·PDF The $α$-attractor models are some of the most interesting models of inflation from the point of view of upcoming observations in cosmology and also attractive from the point of view of supergravity. We confront representative models of exponential and polynomial $α$-attractors with the latest cosmological data (Planck'18+BICEP2/Keck array) to obtain predictions and best fit values of model parameters. The analysis is done by making use of ModeChord and CosmoMC plugged together via PolyChord.
Yogesh, Bao-Fei Li, Mayukh R. Gangopadhyay, Anzhong Wang
In loop quantum cosmology (LQC), the initial singularity is replaced by a quantum bounce, leading to a universal post-bounce evolution characterized by three distinct epochs: bouncing, transition, and slow-roll inflation, before the hot big-bang universe starts. While the generic nature of inflation in LQC is well-established, the subsequent reheating phase-the process that thermalizes the universe and marks the beginning of the hot big bang has remained unexplored in this quantum gravitational framework. This paper presents the first comprehensive integration of the (generalized) reheating mechanism into the LQC paradigm. Using the Power Law Plateau potential and comparing predictions with the latest Planck 2018 and ACT 2025 data, we demonstrate that the inclusion of a reheating phase with a generic equation of state is fully consistent with the cosmological constraints. In addition, using the observational data for the amplitude and spectral index of the scalar perturbations and the tensor-to-scalar ratio, we also constrain the total number of e-folds from the bounce to the present day and find a lower bound, which is less constrained than that obtained previously from the fitting of the high-$l$ CMB temperature power spectrum (TT), the polarization data (TT, TE, EE) and the low-$l$ polarization data (lowP).
Yogesh, Imtiyaz Ahmad Bhat, Mayukh R. Gangopadhyay, M. Sami
Apr 16, 2026·astro-ph.CO·PDF Recent results from the Atacama Cosmology Telescope (ACT), indicating a higher and more tightly constrained scalar spectral index, $n_s = 0.9743 \pm 0.0034$, place several inflationary models under tension, with quintessential inflation pushed close to or beyond the $2σ$ boundary in the $r$--$n_s$ plane. In this work, we revisit quintessential inflation within the framework of Einstein--Gauss--Bonnet (EGB) gravity, where a scalar field non-minimally coupled to the Gauss--Bonnet invariant modifies the inflationary dynamics. We consider three representative coupling functions -- exponential, hyperbolic secant, and hyperbolic tangent -- and show that the exponential and sech-type couplings can shift the predicted values of $r$ and $n_s$ into the $1σ$ region allowed by ACT, thereby restoring consistency with observations. In contrast, the tanh-type coupling remains disfavored, underscoring the sensitivity of inflationary observables to the coupling structure. We further investigate the reheating phase using a model-independent parametrization and demonstrate that viable thermal histories can be realized even in the absence of a potential minimum, with reheating temperatures consistent with Big Bang nucleosynthesis bounds. Overall, our analysis shows that EGB corrections provide a viable and robust extension that reconciles quintessential inflation with current precision cosmological data, and we identify the corresponding allowed parameter space.
Sukannya Bhattacharya, Kumar Das, Mayukh R. Gangopadhyay
We analyse the epoch of reheating after an inflationary phase in the Randal Sundrum(RS) Type-$\rm II$ braneworld, where we did not consider any particular model of inflation, but rather reconstructed the inflationary potential solving the flow equations using Monte Carlo (MC) approach. It is shown numerically that a potential conceived through the MC reconstruction technique can be represented by an effective potential as a function of the number of e-foldings($N$). Then, the epoch of reheating is studied for this reconstructed potential. The relation between the reheating temperature ($T_{\rm reh}$) and the 5-dimensional Planck mass($M_5$) is established. Moreover, it is argued that there is a stringent bound on the critical reheating temperature that also translates to a tight bound on $M_5$ .
Jiwon Park, Sourav Mridha, Dukjae Jang, Mayukh R. Gangopadhyay, Myung-Ki Cheoun
Feb 28, 2025·astro-ph.CO·PDF The isotropy and homogeneity of our Universe are the cardinal principles of modern cosmology built on the definition of metric through the prescription by Friedmann-Lema$\hat{i}$tre-Robertson-Walker (FLRW). From the aspects of geometry, the presence of anisotropy, inhomogeneity, or both are allowed in the metrics defined as the Bianchi type I and V metrics. In this letter, the Big Bang Nucleosynthesis (BBN) formalism, and the latest observational constraints on nuclear abundances are being used to put bounds on the global anisotropy offered in the Bianchi type I metrics, providing a new path to explore in the background of global anisotropy.
Mayukh R. Gangopadhyay, Jayesh C. Jain, Devanshu Sharma, Yogesh
Aug 31, 2021·astro-ph.CO·PDF In a class of single field models of inflation, the idea of Primordial Black holes(PBHs) production is studied. In this case, the dynamics on small cosmological scales differs significantly from that of the large scales probed by the observations of cosmic microwave background(CMB). This difference becomes a virtue in producing correct physical ambiance for the seeds required to produce PBHs. Thus, once the perturbed scales renter the horizon of our Universe during the later epochs of radiation domination and subsequent matter domination, these seeds collapses to produce PBHs. We have shown, in this class of model, depending on the model parameters and the class defining set parameters, one can have PBHs formed for a vast mass ranges from $10^{-18}$ to $10^{-6}$ solar mass(\(\textup{M}_\odot\)). We have also shown, for a particular class of model, the total dark matter density today can be attributed to the PBHs density. The vast range of the mass depending on the class parameter, gives ample opportunity to study enriched phenomenological implications associated with this model to probe the nascent Universe dynamics.
Mayukh R. Gangopadhyay, Hussain Ahmed Khan, Yogesh
May 30, 2022·astro-ph.CO·PDF We study two of the most theoretically promising models of inflation, namely the Natural inflation and the Mutated Hilltop inflation, in the Einstein-Gauss Bonnet(EGB) gravity framework. In this work, we try to explore these models in EGB framework, keeping the observations from $GW170817$ on the speed of gravitational wave to be equal to the speed of light. This has direct implication on the non-minimal coupling to the Gauss-Bonnet invariant in the action. Thus, the effective potential gets new features. We have not only analysed the inflationary dynamics, but also the reheating dynamics and finally the corresponding energy spectrum of the gravitational wave.
Mayukh R. Gangopadhyay, Shibesh K. Jas Pacif, M. Sami, Mohit K. Sharma
We consider a scenario of large-scale modification of gravity that does not invoke extra degrees of freedom but includes coupling between baryonic matter and dark matter in the Einstein frame. The total matter energy density follows the standard conservation, and evolution has the character of deceleration in this frame. The model exhibits interesting features in the Jordan frame realized by virtue of a disformal transformation where individual matter components adhere to standard conservation but gravity is modified. A generic parametrization of disformal transformation leaves thermal history intact. It gives rise to late time acceleration in the Jordan frame, which necessarily includes phantom crossing, which, in the standard framework, can be realized using at least two scalar fields. This scenario is embodied by two distinguishing features, namely, acceleration in the Jordan frame and deceleration in the Einstein frame, and the possibility of resolution of the Hubble tension thanks to the emergence of the phantom phase at late times.
Miguel Correa, Mayukh R. Gangopadhyay, Nur Jaman, Grant J. Mathews
We report on a study of the natural warm inflationary paradigm (WNI). We show two important new results arise in this model. One is that the observational constraints on the primordial power spectrum from the cosmic microwave background (CMB) can be satisfied without going beyond the Planck scale of the effective field theory. The second is that WNI can inevitably provide perfect conditions for the production of primordial black holes (PBHs) in the golden window of black-hole mass range ($10^{-16} -10^{-11}M_{\odot}$) where it can account for all of the the dark matter content of the universe while satisfying observational constraints.
Mayukh R. Gangopadhyay, Grant J. Mathews
Nov 16, 2016·astro-ph.CO·PDF We analyze the Randal Sundrum brane-world inflation scenario in the context of the latest CMB constraints from Planck. We summarize constraints on the most popular classes of models and explore some more realistic inflaton effective potentials. The constraint on standard inflationary parameters changes in the brane-world scenario. We confirm that in general the brane-world scenario increases the tensor-to-scalar ratio, thus making this paradigm less consistent with the Planck constraints. Indeed, when the BICEP2/Keck constraints are included, all monomial potentials in the brane-world scenario become disfavored compared to the standard scenario. However, for natural inflation the brane-world scenario fits the constraints better due to larger allowed values of the number of e-foldings N before the end of inflation in the brane-world.
Mayukh R. Gangopadhyay, Nilanjana Kumar, Ankan Mukherjee, Mohit K. Sharma
May 30, 2022·astro-ph.CO·PDF A pseudo-Nambu Goldstone Boson (pNGB) arising from the breaking of a global symmetry ($G\rightarrow H$) can be one of the most promising candidates for the quintessence model, to explain the late-time acceleration of our universe. Motivated from the Composite Higgs scenario, we have investigated the case where the pNGB associated with $SO(N)/ SO(N-1)$ develops a potential through its couplings with the particles that do not form the complete representations of $G$. The Coleman Weinberg (CW) potential is generated via the external particles in the loop which are linked with the strongly interacting dynamics and can be computed predicatively. The model of Dark Energy (DE) is tested against several latest cosmological observations such as supernovae data of Pantheon, Baryon Acoustic Oscillation (BAO), Redshift-space distortion (RSD) data, etc. We have found that the fit prefers the sub-Planckian value of the pNGB field decay constant. Moreover, we have found that the model predicts cosmological parameters well within the allowed range of the observation and thus gives a well-motivated model of quintessence.
Sukannya Bhattacharya, Mayukh R. Gangopadhyay
Dec 19, 2018·astro-ph.CO·PDF Recent observations of the cosmic microwave background (CMB) indicate that a successful theory of cosmological inflation needs to have flat potential of the inflaton scalar field. Realizing the inflaton to be a pseudo-Nambu Goldstone boson (pNGB) could ensure the flatness and the sub-Planckian scales related to the dynamics of the paradigm. In this work, we have taken the most general form of such a scenario: Goldstone inflation, and studied the model in the noncanonical domain. Natural inflation is a limiting case of this model, which is also studied here in the noncanonical regime. Our result is compared with the recent release by Planck collaboration and it is shown that for some combination of the model parameters, a Goldstone inflationary model in the noncanonical realisation obeys the current observational bounds. Then, we studied the era of reheating after the end of inflation. For different choice of model parameters, constraints on the reheating temperature ($T_{\rm re}$) and number of e-folds during reheating($N_{\rm re}$) for the allowed inflationary observables (e.g. scalar spectral index($n_s$) and tensor to scalar ratio($r$)) are predicted for this model.
Sayantan Choudhury, Mayukh R. Gangopadhyay, M. Sami
Jan 24, 2023·astro-ph.CO·PDF We examine the possibility of Primordial Black Holes (PBHs) formation in single-field models of inflation. Using the adiabatic or wave function renormalization scheme in the short-range modes, we show that one-loop correction to the power spectrum is free from quadratic UV divergence. We consider a framework in which PBHs are produced during the transition from Slow Roll (SR) to Ultra Slow Roll (USR) followed by the end of inflation. We demonstrate that the renormalized power spectrum softens the contribution of the logarithmic IR divergence and severely restricts the possible mass range of produced PBHs in the said transition, namely, $M_{\rm PBH}\sim 10^{2}{\rm gm}$ ala a no-go theorem. In particular, we find that the produced PBHs are short-lived ($t^{\rm evap}_{\rm PBH}\sim 10^{-20}{\rm sec}$) and the corresponding number of e-folds in the USR region is restricted to $ΔN_{\rm USR}\approx 2$.
Mayukh R. Gangopadhyay, M. Sami, Mohit K. Sharma
Mar 13, 2023·astro-ph.CO·PDF We study the late-time cosmological tensions using the low-redshift background and redshift-space distortion data by employing a machine learning (ML) technique. By comparing the generated observables with the standard cosmological scenario, our findings indicate support for the phantom nature of dark energy, which ultimately leads to a reduction in the existing tensions. The model-independent approach also enables us to examine the combined background and perturbative history, where tensions are reduced. Moreover, from a statistical perspective, we have shown that our results exhibit a better fit to the data when compared to the $Λ$CDM model.
Nishanth Sasankan, Mayukh. R. Gangopadhyay, Grant. J. Mathews, Motohiko Kusakabe
The term dark radiation is used both to describe a noninteracting neutrino species and as a correction to the Friedmann Equation in the simplest five-dimensional RS-II brane-world cosmology. In this paper we consider the constraints on both meanings of dark radiation based upon the newest results for light-element nuclear reaction rates, observed light-element abundances and the power spectrum of the Cosmic Microwave Background (CMB). Adding dark radiation during big bang nucleosynthesis (BBN) alters the Friedmann expansion rate causing the nuclear reactions to freeze out at a different temperature. This changes the final light element abundances at the end of BBN. Its influence on the CMB is to change the effective expansion rate at the surface of last scattering. We find that the BBN constraint reduces the allowed range for both types of dark radiation at 10 Mev to between $-12.1\%$ and $+6.2\%$ of the {\bf total} background energy density at 10 Mev. Combining this result with fits to the CMB power spectrum, produces different results for particle vs. brane-world dark radiation. In the brane-world, the range decreases to $-6.0\%$ to $+6.2\%$. Thus, we find, that the ratio of dark radiation to the background total relativistic mass energy density $ρ_{\rm DR}/ρ$ is consistent with zero although there remains a very slight preference for a positive (rather than negative) contribution.
Nishanth Sasankan, Mayukh R. Gangopadhyay, Grant J. Mathews, Motohiko Kusakabe
Jul 22, 2016·astro-ph.CO·PDF A dark radiation term arises as a correction to the energy momentum tensor in the simplest five-dimensional RS-II brane-world cosmology. In this paper we revisit the constraints on dark radiation based upon the newest results for light-element nuclear reaction rates, observed light-element abundances and the power spectrum of the Cosmic Microwave Background (CMB). Adding dark radiation during big bang nucleosynthesis alters the Friedmann expansion rate causing the nuclear reactions to freeze out at a different temperature. This changes the final light element abundances at the end of BBN. Its influence on the CMB is to change the effective expansion rate at the surface of last scattering. We find that our adopted BBN constraints reduce the allowed range for dark radiation to between $-12.1\%$ and $+6.2\%$ of the ambient background energy density. Combining this result with fits to the CMB power spectrum, the range decreases to $-6.0\%$ to $+6.2\%$. Thus, we find, that the ratio of dark radiation to the background total relativistic mass energy density $ρ_{\rm DR}/ρ$ is consistent with zero although in the BBN analysis there could be a slight preference for a negative contribution. However, the BBN constraint depends strongly upon the adopted primordial helium abundance.
Rathin Adhikari, Mayukh R. Gangopadhyay, Yogesh
Sep 16, 2019·astro-ph.CO·PDF A scalar potential obtained from the $D$-term in the Supergravity models, which dominates over $F$ term and is mainly responsible for the inflationary phase in the early universe, is studied. The potential with canonical kinetic terms for scalar fields in the Lagrangian, has a very slow roll feature in comparison to various other plateau type inflationary potentials. In this case, a much lower tensor-to-scalar ratio ($r$) of $\mathcal{O}(10^{-3})$ is achievable. The requirement of slow roll condition for the inflation potential implies that the up type neutral scalar and the down type neutral scalar in Supergravity models are with equal field strength at the time of inflation. If this relationship holds down to the electroweak scale for the corresponding $vev$ values of these fields, then it will indicate a higher SUSY breaking scale around 100 TeV. The predicted values of the inflationary observables are well within the 1-$σ$ bounds of the recent constraints from {\it Planck'18} observations. The era of reheating after the inflationary phase, is also studied and the bounds on the reheating temperature ($T_{re}$) is calculated for a different equation of states during reheating ($w_{re}$) for the {\it Planck'18} allowed values of the scalar spectral index ($n_s$). For our model with $w_{re}=2/3$ and $w_{re}=1$, after satisfying all the bounds due to gravitino overproduction, we can have big parameter space for $T_{re}$ which is well inside {\it Planck'18} 1-$σ$ bound on $n_s$.