arXiv subjects

Supriya Pan

Publications and source records attributed to Supriya Pan.

At least 19 recordsLinked to original sources

arXiv2026

Late-Time Emergence of Dark Energy and Its Interaction with Dark Matter

We present an interacting scenario between dark energy (DE) and dark matter (DM), where DE has an emergent nature, that means, DE was absent in the early universe but it becomes effective only at late times. We consider two specific emergent DE models, one with no free parameters and the other featuring two parameters describing the speed and epoch of the transition. We constrain both scenarios using the cosmic microwave background (CMB) measurements from the Planck 2018 release, baryon acoustic oscillations from DESI DR2, and three different compilations of Type Ia supernovae (PantheonPlus, DES-Dovekie, and Union3). Our analysis indicates that current cosmological probes are not able to tightly constrain the speed of the transition. For both scenarios, the posterior distribution of the interaction parameter is shifted away from zero at more than 95\% CL whenever the CMB data are combined with any of these additional probes, with the preferred direction corresponding to a transfer of energy from DE to DM. While CMB alone yields a high value of $H_0$, in agreement with local determinations, this effect is reduced when DESI is added and disappears once supernova data are included. In contrast, the clustering parameter $S_8$ is consistently shifted toward lower values in the combined datasets, and it is correlated with the preference for a negative interaction. However, according to the $\Delta \chi^2_{\rm min}$ and Bayesian evidence, none of the interacting models is favored over $\Lambda$CDM or $w_0w_a$CDM, indicating that the interaction does not rescue these emergent DE models. Our results therefore highlight the limitations of these scenarios in addressing current cosmological tensions, while pointing to the crucial role of future data in further assessing their viability.

astro-ph.CO↗

arXiv2026

Do DESI-DR2 BAO data imply a coupling of dark matter and dark energy?

We revisit an interacting dark matter (DM) -- dark energy (DE) model characterized by the interaction function $Q = \Gamma \rho_x$, where $\Gamma$ is a constant coupling parameter and $\rho_x$ is the energy density of DE. This type of interaction is independent of the Hubble rate or other external parameters, but depends only on the fundamental properties of DE, such as its equation of state (EoS), $w_x$. We pay special attention to $w_x$ and study three distinct interacting scenarios distinguished by the nature of $w_x$, i.e. $w_x =-1$ (when DE corresponds to the vacuum energy), $w_{x} < -1$ (when DE has a phantom behavior), and $w_x > -1$ (quintessential DE). We constrain all of them using the most recent cosmological datasets, including CMB from Planck 2018, BAO from DESI DR2, and three compilations of SNIa (PantheonPlus, Union3, and DESY5). Our analyses reveal that evidence of interaction is supported in scenarios with $w_x =-1$ and $w_x < -1$ when all three datasets are combined, but from the Bayesian evidence analysis, $\Lambda$CDM remains favored over these interacting scenarios. Regarding the $S_8$ parameter, when $w_x > -1$, this interacting scenario leads to mildly lower estimates across all datasets.

astro-ph.CO↗

arXiv2026

Beyond dynamical dark energy: the role of dark sector interactions after DESI DR2

Recent DESI DR2 observations have renewed interest in extensions of the $\Lambda$CDM cosmological model, particularly through indications of a time-varying dark energy equation of state. In this work, we investigate whether such deviations may also involve interactions within the dark sector. We consider an interacting dark energy scenario in which the dark matter density evolves as $\rho_{\rm dm}\propto a^{-3+\delta}$, with the constant $\delta$ quantifying the interaction strength, and allow the dark energy equation of state to be either constant but different from $-1$, or dynamically evolving through the CPL parametrization. The models are constrained using Planck CMB data, DESI DR2 BAO measurements, and three Type Ia supernova compilations: PantheonPlus, Union3, and DES-Dovekie. For the constant equation-of-state case, the inclusion of DESI and supernova data leads to a preference for a small negative interaction parameter, with a significance above $2\sigma$. When dynamical dark energy is allowed, the evidence for interaction becomes weak, while the data favor a quintessence-like evolving dark energy component. In both scenarios, Bayesian model comparison still favors $\Lambda$CDM. Our results show that the inferred role of dark-sector interactions depends strongly on the nature of dark energy, highlighting the importance of jointly testing dark energy dynamics and interactions in the DESI era.

astro-ph.CO↗

arXiv2026

Accelerating scaling solutions from dark matter particle creation

This article opens new window to obtain accelerating scaling attractors without any need of dark energy. We study cosmological dynamics in a two-fluid system where pressureless dark matter (DM) undergoes adiabatic particle creation and exchanges energy with a barotropic fluid. Considering six widely used interaction prescriptions, we formulate the corresponding autonomous systems in a compact phase space and perform a unified dynamical analysis. We find that accelerating scaling attractors, namely late-time states where both fluids coexist with fixed energy fractions, arise only when the interaction is controlled by the DM density and energy flows from DM to the second fluid. Such attractors appear in the global and local DM-based interactions, and in the global mixed case, but are entirely absent when the interaction depends on the second fluid or on local mixed terms, which instead drive the universe to a DM-dominated accelerating phase. These results clarify the unique conditions under which matter creation can mimic dark-energy-like behaviour without introducing a dark-energy component.

gr-qc↗

arXiv2026

When One-Parameter Dark Energy Makes Neutrinos Physical Again

A puzzling implication of current data interpreted in the $\Lambda$CDM cosmology is the preference for a negative sum of neutrino masses. Moving to $w_0w_a$CDM brings an appreciable fraction of the neutrino mass posterior back to positive values, while the constant equation-of-state dark energy case $w$CDM does not. We investigate a variety of one-parameter dark energy equations of state (DE EoS), each variation with particular physical properties, to understand whether a two-parameter DE EoS is required to bring the neutrino mass positive. The conclusion is that certain one-parameter DE EoS can suffice, implying that the data are pointing toward physical characteristics rather than a broad degeneracy. The required characteristics are identified as phantom dark energy at high redshift, crossing $w=-1$ at lower redshift.

astro-ph.CO↗

arXiv2026

When Dark Energy Turns On: Constraints on a Critical Emergence Model

We investigate a specific emergent dark energy scenario, known as critically emergent dark energy (CEDE), in which dark energy is effectively absent in the early Universe and becomes dynamically relevant only after a critical cosmic epoch through a phase transition. We constrain this model using recent cosmological observations, including cosmic microwave background (CMB) data from \emph{Planck} 2018, baryon acoustic oscillation (BAO) measurements from SDSS and DESI DR2, and two independent Type Ia supernova compilations, PantheonPlus and Union3. Our results show that within the CEDE framework a dark energy phase transition is not ruled out. In particular, CMB-only, CMB+SDSS, and CMB+DESI datasets provide evidence for a nonzero transition scale factor and, according to standard statistical indicators such as $\Delta\chi^2$ and Bayesian evidence, can favor CEDE over the $\Lambda$CDM model. At the same time, we find that CEDE does not fully resolve the Hubble constant tension. Overall, our analysis indicates that dark energy models featuring a phase transition remain a viable and phenomenologically interesting extension of the standard cosmological framework. Upcoming high-precision cosmological surveys will be essential to further assess whether such emergent dark energy scenarios represent a genuine departure from $\Lambda$CDM or an effective description of current data.

astro-ph.CO↗

arXiv2026

Joint Constraints on Neutrinos and Dynamical Dark Energy in Minimally Modified Gravity

The $w_{\dagger}$VCDM framework provides a theoretically well-controlled extension of $\Lambda$CDM within the class of minimally modified gravity theories, allowing for flexible cosmological background evolution and linear perturbation dynamics while remaining free of pathological instabilities. In this work, we have shown that this scenario remains robust when confronted with current cosmological observations, even in the presence of an extended neutrino sector. Combining \textit{Planck} CMB data with DESI DR2 BAO and DESY5 supernovae, we obtain stringent constraints on neutrino physics, including $\sum m_\nu < 0.11~\mathrm{eV}$ (95\% CL) and $N_{\rm eff} = 2.98^{+0.13}_{-0.14}$, fully consistent with Standard Model expectations. Crucially, the data exhibit a statistically significant preference for a late-time dark-energy transition, characterized by a robust quintessence--phantom crossing that remains stable across all dataset combinations and neutrino-sector extensions, including the presence of a sterile neutrino. The combined effects of modified late-time expansion and additional relativistic degrees of freedom systematically raise the inferred Hubble constant, substantially alleviating the $H_0$ tension without invoking early dark energy or introducing theoretical instabilities. Overall, the $w_{\dagger}$VCDM scenario emerges as a compelling phenomenological framework that simultaneously accommodates current constraints on neutrino physics, provides an excellent fit to recent BAO and supernovae data, and offers a viable pathway toward resolving persistent tensions in the standard cosmological model.

astro-ph.CO↗

arXiv2025

JUNO's Impact on the Neutrino Mass Ordering from Lorentz Invariance Violation

We explore the potential of the Jiangmen Underground Neutrino Observatory (JUNO) to probe new physics by searching for Lorentz-invariance violation (LIV). Using the 59.1-day dataset recently released by this experiment, we analyze neutrino oscillations to place new constraints on the LIV parameters in the CPT-even ($c_{ee} - c_{e\mu}$, $c_{ee} - c_{e\tau}$) and CPT-odd ($a_{ee} - a_{e\mu}$, $a_{ee} - a_{e\tau}$) sectors. Our analysis reveals a significant shift in the oscillation parameter space of $\sin^2\theta_{12}-\Delta m^2_{21}$ when LIV is included; with the best-fit point for normal ordering moving to the higher values of the solar angle $\theta_{12}$, a strong preference emerges for inverted mass ordering. In particular, the $c_{ee} - c_{e\tau}$ and $a_{ee} - a_{e\tau}$ sectors show the most pronounced effects. We report the most stringent bounds from JUNO to date on these LIV parameters, showcasing the detector's unique sensitivity to physics beyond the Standard Model.

hep-ph↗

arXiv2025

Beyond Two Parameters: Revisiting Dark Energy with the Latest Cosmic Probes

Dark energy (DE) models with many free parameters are often considered excessive, as constraining all parameters poses a significant challenge. While such models offer greater flexibility to probe the DE sector in more detail. With the rapid advancement of astronomical surveys and the availability of diverse datasets, it is timely to examine whether current combined observations can effectively constrain an extended parameter space in DE models. This article investigates a four-parameter dynamical DE model that spans a broad region of the universe's expansion history through four key parameters: present-day value of the DE equation of state ($w_0$), its initial value ($w_m$), scale factor depicting transition from $w_m$ to $w_0$ ($a_t$), and steepness of this transition ($\Delta_{\rm de}$). We constrain the model using cosmic microwave background data from Planck, BAO from DESI DR2, and three distinct compilations of Type Ia Supernovae: PantheonPlus, DESY5, and Union3. Our results show that constraining all four parameters remains challenging: $a_t$ is not constrained by any dataset, constraints on $w_m$ and $\Delta_{\rm de}$ remain weak, only $w_0$ is well constrained across all datasets. The results further show that $w_0 > -1$, while $w_m$ is negative, indicating a phantom-like behaviour at early times. Interestingly, despite its larger parameter space, the proposed model shows a preference over the $\Lambda$CDM and $w_0w_a$CDM scenarios for certain combined datasets, according to both $\Delta \chi^2$ and Bayesian evidence, although this preference is not strong.

astro-ph.CO↗

arXiv2025

Phantom cosmology with arbitrary potential: New accelerating scaling attractors

In this article, we investigate the existence of accelerating scaling solutions in coupled phantom cosmology without assuming any specific potential for the phantom scalar field. The coupling between phantom dark energy and dark matter is motivated by the warm inflationary paradigm, with the dissipation coefficient assumed to be either constant or variable. The evolution equations are written in the form of autonomous systems, whose stability is studied using methods of qualitative analysis of dynamical systems. For this analysis, the only requirement imposed on the otherwise arbitrary phantom potential is that a particular dynamical variable, defined in terms of the potential and its derivative, must be invertible. For such a generic potential, we show that accelerated scaling solutions do exist, for both constant and variable dissipation coefficients. Although there is a limitation to these scaling solutions -- specifically, the current stage of accelerated expansion is not preceded by a long enough matter-dominated era -- our results show that the existence of a direct coupling between phantom dark energy and dark matter yields great potential for addressing the cosmic coincidence problem.

gr-qc↗

arXiv2025

Is Dark Energy Changing? Probing the Universe's Expansion with present and future astronomical probes

This study explores the possibility of a time-varying dark energy (DE) equation of state (EoS) deviating from -1. We employ a comprehensive dataset of usual astronomical probes (Type Ia supernovae, baryon acoustic oscillations, Big Bang nucleosynthesis, Hubble data, and Planck 2018 CMB) alongside future mock gravitational wave (GW) distance measurements from the Einstein Telescope. We utilize the Pad'e approximation, a versatile framework encompassing well-known DE models like constant EoS, Chevallier-Polarski-Linder parametrization and other time-evolving DE parametrizations. Within Pad'e parametrization, we examine three specific forms (Pad'e-I, SPad'e-I, Pad'e-II) applied to both spatially flat and non-flat universes. Pad'e-II exhibits particularly interesting features in terms of the evidence of dynamical DE at many standard deviations. Our results can be summarized as follows. Flat Universe: When analyzing the combined dataset of standard probes (including CMB) with Pad'e-II in a flat universe, we find a strong preference (6.4{\sigma}) for a dynamical (time-varying) DE EoS. This preference remains significant (4.7{\sigma}) even when incorporating future GW data. Non-Flat Universe: In a non-flat universe, the combined standard datasets (without or with CMB) also indicate dynamical DE EoS at a high confidence level (6.2{\sigma} and 6.4{\sigma}, respectively). The addition of GW data slightly reduces the evidence (3.8{\sigma} and 5.1{\sigma}, respectively), but the preference persists. These results collectively suggest a robust case for dynamical DE in the dark sector. While a non-flat universe is not strongly favored, Pad'e-II hints at a possible closed universe when CMB data is included (with or without GW data).

astro-ph.CO↗

arXiv2025

Dark Energy Is Not That Into You: Variable Couplings after DESI DR2 BAO

In interacting dark energy (DE) and dark matter (DM) scenarios, the interaction function typically includes a coupling parameter $\xi$ that quantifies the strength of energy exchange between the dark sectors. While $\xi$ is often assumed to be constant, there is no fundamental reason to exclude a time-dependent coupling, which could provide a more general and realistic description of dark sector dynamics. In this work, we study two widely used interacting models involving pressureless DM and DE, where the coupling parameter is allowed to vary with the scale factor $a$. Specifically, we consider two parametrizations: $\xi(a) = \xi_0 + \xi_a (1-a)$ and $\xi(a) = \xi_0 \left(1 + \frac{1-a}{a^2 + (1-a)^2} \right)$, and constrain them using the latest cosmological observations, including Planck 2018 CMB data, DESI DR2 BAO measurements, and multiple Type Ia supernovae samples. Our results show that one scenario yields evidence for a non-zero interaction at more than 95\% confidence level, while the remaining cases indicate at most mild or inconclusive signs of interaction. These findings highlight the potential of variable coupling models and the importance of continued investigation into the nature of the dark sectors.

astro-ph.CO↗

arXiv2025

Parametrizing the Hubble function instead of dark energy: Many possibilities

In the present article, we propose a very simple parametrization of the Hubble function without parametrizing the dark components of the Universe. One of the novelties of the parametrization is that it may include a wide variety of the cosmological models, such as dark energy (both noninteracting and interacting fluids), modified gravity, cosmological matter creation and other known scenarios. The model is constrained with the latest astronomical probes from Hubble parameter measurements, three distinct versions of Type Ia Supernovae (Pantheon+, DESY5, Union3) and baryon acoustic oscillations from Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument data releases 1 and 2. Our results suggest a mild deviation from the standard $\Lambda$CDM cosmological model for most of the combined datasets. We also find that our model is thermodynamically consistent and performs well in the model comparison tests.

astro-ph.CO↗

arXiv2025

Is Dark Energy an Effective Manifestation of Non-equilibrium Thermodynamics? -- Insights from DESI

We investigate the background cosmological expansion on the onset of cosmological homogeneous matter creation scenario, a dynamical dark matter approach ($w_{\rm dm} \neq 0$), and an alternative approach to both dark energy and modified gravity theories, after the recent DESI DR2-BAO release. We consider that the total matter sector consists of three independently evolving components, namely, radiation, baryons, and dark matter, with the latter being governed by an adiabatic matter creation process, affects the background homogeneously, leads to a modified continuity equation. Though the total stress-energy tensor is conserved the only violation of the conservation law in the dark matter sector is coming from the creation pressure, and under a proper choice of dark-matter particle creation rate one can obtain the present accelerating phase as well as the past thermal history of the Universe. We study two specific matter creation rates. By applying the dynamical-system analysis we show that both Model I and Model II can mimic a $\Lambda$CDM-like behavior. Furthermore, we perform a detailed observational confrontation using a series of latest observational datasets including Cosmic Chronometers (CC), Supernovae Type Ia (SNIa) (Pantheon+, DESY5 and Union3 samples) and DESI Baryon Acoustic Oscillations (BAO) (DR1 and DR2 samples). In both Model I and Model II we find evidence of matter creation at many standard deviations. Finally, applying the AIC and BIC information criteria we find that Model I is statistically equivalent with $\Lambda$CDM scenario, while Model II shows a mixed picture, namely for most datasets $\Lambda$CDM scenario is favoured, however when DESI data are included matter creation Model II is favoured over $\Lambda$CDM paradigm.

astro-ph.CO↗

arXiv2025

Shape of Dark Energy: Constraining Its Evolution with a General Parametrization

We consider a general dark energy (DE) model parametrized by its equation-of-state (EoS), featuring three free parameters: $w_0$ (the present-day value of the DE EoS), $w_{\beta}$ (quantifying the dynamical nature of the DE EoS), and $\beta$ (governing various dynamical forms of the DE EoS). The key controlling parameter $\beta$ can recover several existing DE models in the literature, such as the Chevallier-Polarski-Linder (CPL) parametrization ($\beta = 1$), the logarithmic parametrization (in the limit $\beta \rightarrow 0$), and the linear parametrization ($\beta = -1$), alongside generate a class of new DE parametrizations for other values of $\beta$. The resulting DE scenario is constrained using a suite of the latest cosmological probes, including Cosmic Microwave Background (CMB) temperature and polarization anisotropies from three different experiments (Planck 2018 and Atacama Cosmology Telescope combined with WMAP), CMB lensing, Baryon Acoustic Oscillations from DESI Year 2, and PantheonPlus from Type Ia supernovae. Our analyses reveal that stringent constraints on the DE parameters are obtained only when all cosmological probes are combined; otherwise, some parameters remain unconstrained. The present-day value of the DE EoS remains in the quintessence regime according to our results, and no significant evidence for a dynamical DE EoS is found. However, based on the $\Delta \chi^2$ and Bayesian evidence analyses, we observe a mild preference for the present three-parameter DE parametrization over the CPL parametrization when all cosmological probes are taken into account. Nonetheless, the Bayesian evidence difference remains below the threshold for statistical significance according to the revised Jeffreys scale, indicating that both models are effectively equally preferred by the data.

astro-ph.CO↗

arXiv2025

Solving an Interacting Quintessence Model with a Sound Horizon Initial Condition and its Observational Constraints

Astronomical observations suggest that the current standard $\Lambda$-Cold Dark Matter model in modern cosmology has some discrepancies when fitting the data during the whole expansion history of the universe. To solve the Hubble constant ($H_0$) tension, usually an unknown mechanism is considered that shifts the sound horizon at the decoupling era. On the other hand, dynamical dark energy models are also considered to resolve the problems of the cosmological constant, and the additional degrees of freedom require initial conditions for a solution. In this article we have considered a coupled quintessence dark energy model with a special focus on its early-time behaviour. In our solution the initial conditions are naturally decided by setting the value of the sound horizon at the recombination time, $\theta^*$. We find that during this process, $H_0$ could be derived and its value rises with the coupling strength of the interaction. We also performed the background and cosmic microwave background power spectrum analysis, and find that the existence of the interaction term affects the energy density during a narrow time interval range and shifts the early cosmic microwave background spectrum. We also constrained the parameter space of the underlying scenario using the markov chain monte carlo analysis. We find that the best-fit values of $H_0$ and $S_8$ are improved slightly for the interacting model, but not enough to release the tensions.

gr-qc↗

arXiv2025

When Dark Matter Heats Up: A Model-Independent Search for Non-Cold Behavior

This article questions the common assumption of cold dark matter (DM) by exploring the possibility of a non-zero equation of state (EoS) without relying on any parametric approach. In standard cosmological analyses, DM is typically modeled as pressureless dust with $w_{\rm DM} = 0$, an assumption that aligns with large-scale structure formation, supports the empirical success of the $\Lambda$CDM model, and simplifies cosmological modeling. However, there is no fundamental reason to exclude a non-zero $w_{\rm DM}$ from the cosmological framework. In this work, we explore this possibility through non-parametric and parametric reconstructions based on Gaussian Process Regression. The reconstructions use Hubble parameter measurements from Cosmic Chronometers (CC), the Pantheon+ sample of Type Ia supernovae, and Baryon Acoustic Oscillation (BAO) data from DESI DR1 and DR2. Our findings suggest that a dynamical EoS for DM, although only mildly supported statistically, cannot be conclusively ruled out. Notably, we observe a mild tendency ($\sim 1\sigma$) toward a negative $w_{\rm DM}$ at the present epoch, which is most likely due to inconsistencies between the BAO data from DESI and other datasets.

astro-ph.CO↗

arXiv2025

In search of an interaction in the dark sector through Gaussian Process and ANN approaches

Whether the current observational data indicate any evidence of interaction between the dark sector is a matter of supreme interest at the present moment. This article searched for an interaction in the dark sector between a pressure-less dark matter and a dark energy fluid with constant equation of state, $w_{\rm DE}$. For this purpose, two non-parametric approaches, namely, the Gaussian Process (GP) and the Artificial Neural Networks (ANN) have been employed and using the Hubble data from Cosmic Chronometers (CC), Pantheon+ from Supernovae Type Ia and their combination we have reconstructed the interaction function. We find that for $w_{\rm DE} =-1$, the interaction in the dark sector is not prominent while for $w_{\rm DE} \neq -1$, evidence of interaction is found depending on the value of $w_{\rm DE}$. In particularly, we find that if we start deviating from $w_{\rm DE} = -1$ either in the quintessence ($w_{\rm DE} > -1$) or phantom ($w_{\rm DE} < -1$) direction, an emergence of dark interaction is observed from both GP and ANN reconstructions. We further note that ANN which is applied for the first time in this context seems to play a very efficient role compared to GP.

astro-ph.CO↗