arXiv subjects

Koushik Dutta

Publications and source records attributed to Koushik Dutta.

At least 19 recordsLinked to original sources

arXiv2026

Distinguishing Coupled Dark Matter Dark Energy from Kinematic Phantom Crossing

Recent measurements of cosmic expansion have renewed interest in dark-energy scenarios in which the effective equation of state exhibits phantom-like evolution and may cross $w=-1$. Such behavior, however, does not require a fundamental phantom field: in coupled dark-energy-dark-matter~(CDEDM) models, energy exchange between a canonical scalar field and cold dark matter, happens Lagrangian labels, can reproduce the same effective equation of state evolution as that of phenomenological $w_0w_a$CDM model. We show that this microscopic interaction leaves distinctive, testable signatures in structure growth by forming a two-fluid system in which only cold dark matter feels the scalar-mediated fifth force (and an associated drag term), while baryons remain uncoupled. When combined with neutrino-free streaming, this setup generates a characteristic coupling, neutrino-mass degeneracy, whose leading scaling $\sum m_ν\propto f_c^2 α^2$ follows analytically from the two-fluid growth equations. Using DESI DR2 BAO, CMB distance information, ACT DR6 lensing, redshift-space distortions, and three supernova compilations, we find that this scaling is recovered for both exponential and inverse-power-law potentials. We further show that the dominant contribution to the growth response arises from the coupling-induced modification of the background evolution, with the fifth force enhancing growth and the drag partially counteracting it. Finally, the interaction induces a running dark-matter mass, changing it at recombination by $4.3\%$--$5.5\%$, so CMB distance calculations must account for the evolving dark-matter density. These correlated growth and recombination effects provide a route to distinguish interaction-driven phantom crossing from purely kinematic dark-energy parametrizations.

astro-ph.CO↗

arXiv2026

Scalaron dark matter dynamics: effects of Higgs non-minimal coupling to gravity

One of the key features of the $R^2$-gravity is the embedding of a scalar field, scalaron, into the gravity sector. The scalaron interacts with the Standard Model (SM) matter fields through Planck-suppressed couplings. If the scalaron serves as a viable dark matter (DM) candidate, it can account for the lack of evidence of DM interactions beyond gravity in experimental and observational probes to date. The realization of the scalaron, as a cold DM candidate, depends on an induced trilinear interaction with the SM Higgs via its quartic self coupling. Here, we introduce a Higgs non-minimal coupling to gravity that additionally contributes to the induced trilinear interaction with its existing competing part, originated from the $R^2$-gravity. We study the interplay between these two contributions in the early universe, which determines both the initial conditions and evolution of the scalaron, leading to cold DM behavior at a later epoch. The trilinear interaction vanishes at the leading order for certain combinations of the Higgs non-minimal coupling ($ξ$) and the scalaron mass ($m$), thereby setting the scalaron density through misalignment mechanism, as in axions. In this case, the scalaron DM mass is obtained as, $2.7 ~{\rm meV} \lesssim m \lesssim 0.7 ~\rm{MeV}$. The lower limit on the mass is set by the fifth force constraints, whereas the upper bound arises from INTEGRAL/SPI limits on the excess gamma-ray flux due to scalaron decaying into two photons. On the other hand, when the trilinear interaction is non-zero and dominated by the Higgs quartic self coupling, the DM relic density is satisfied with $m \simeq 3.6$ meV. When the Higgs non-minimal coupling dominates, the mass lies within 10-770 meV. We also obtain, for the first time within the scalaron-Higgs mixed model, an upper bound on $|ξm|$ of $1.5\times 10^{17}$ GeV, from Higgs mass measurement at the LHC.

hep-ph↗

arXiv2025

Production of Gravitational Waves from Preheating and Tachyonic Instabilities

We analyze GW production during preheating for an $α$-attractor potential terminating in the positive-curvature regime, with energy transfer via $ϕχ^{2}$. Linear Floquet analysis and nonlinear simulations show that $ϕ$ fluctuations grow by parametric resonance, while $χ$ undergoes tachyonic bursts. The GW spectrum features two peaks: a dominant low-frequency peak from the parametric channel and a subdominant high-frequency peak from the tachyonic channel. Redshifted to today, the peak reaches $h^{2}Ω_{\rm GW}^{(0)} \sim 10^{-11}$ at $f^{(0)}_{p} \sim 10^{7}$ Hz. This multi-peak structure is a characteristic imprint of trilinear preheating in $α$-attractors.

astro-ph.CO↗

arXiv2025

DESI results: Hint towards coupled dark matter and dark energy

We investigate a scenario where a dark energy quintessence field $ϕ$ with positive kinetic energy is coupled with dark matter. With two different self-interaction potentials for the field and a particular choice of the coupling function, we show explicitly how the observable effective equation of state parameter $w_{\rm eff}$ for the dark energy field crosses the phantom barrier ($w_{\rm eff} = -1$) while keeping the equation of state of the quintessence field $w_ϕ> -1$. With appropriate choices of parameters, $w_{\rm eff}$ crosses the phantom divide around redshift $z\sim 0.5$, transitioning from $w_{\rm eff} <-1$ in the past to $w_{\rm eff}>-1$ today. This explains DESI observations well. Our analysis reveals that the model remains consistent within the $2σ$ confidence intervals provided by DESI for several combinations of the scalar field parameters, highlighting its potential in explaining the dynamics of dark energy arising from a simple Yukawa-type long-range interaction in the dark sector. While the current findings offer a promising framework for interpreting DESI observations, future work, including a comprehensive Markov Chain Monte Carlo (MCMC) analysis, is necessary to constrain the parameter space further and strengthen the statistical significance of the results.

astro-ph.CO↗

arXiv2024

CMB Constraints on Natural Inflation with Gauge Field Production

The natural inflation model with a periodic cosine potential is ruled out by recent Planck 2018 data for the decay constant $f \lesssim 5.5~M_{\rm Pl}$. If the Planck data is combined with the BICEP Keck array and BAO data, the model is excluded (at $2$-$σ$) for all values of $f$. In this context, we revisit the model when the pseudoscalar inflation $ϕ$ is coupled with a gauge field via a coupling of the form $\fracα{f} ϕF \tilde{F}$, where $F (\tilde F)$ denotes the gauge field (dual) strength tensor, and $α$ is the coupling constant. The back-reactions associated with the gauge field production during the later stages of inflation extend the duration of inflation. We numerically evaluate the dynamics of the fields while neglecting the effects due to the perturbations in the inflaton field. It allows us to determine the scalar and tensor power spectra leading to the calculations of observables at the Cosmic Microwave Background (CMB) scales. We find that the natural inflation model survives the test of the latest data only for a certain range of the coupling constant $α$. Our analysis shows that the latest constraints coming from the scalar spectral index are more stringent than the ones arising from the non-gaussianities and the running of the scalar spectrum. This leads to lower and upper bounds on $ξ_*$, the parameter that controls the growth of the gauge field.

astro-ph.CO↗

arXiv2024

Improved Treatment of Bosonic Dark Matter Dynamics in Neutron Stars: Consequences and Constraints

It is conceivable that a bosonic dark matter (DM) with non-gravitational interactions with SM particles will be accumulated at the center of a neutron star (NS) and can lead to black hole formation. In contrast to previous works with a fixed NS temperature, we dynamically determine the formation of Bose-Einstein condensate (BEC) for a given set of DM parameters, namely the DM-neutron scattering cross-section ($σ_{χn}$), the thermal average of DM annihilation cross-section ($\langleσv\rangle$) and the DM mass ($m_χ$). For both non-annihilating and annihilating DM with $\langleσv \rangle \lesssim 10^{-26}{~\rm cm^3~ s^{-1}}$, the BEC forms for $m_χ\lesssim 10$ TeV. In case of non-annihilating DM, observations of old NS allows $σ_{χn}\lesssim 10^{-52}~{\rm cm^2}$ for $10 {~\rm MeV} \leq m_χ \lesssim 10 {~\rm GeV}$ (with BEC) and $σ_{χn}\lesssim 10^{-47}~{\rm cm^2}$ for $5 {~\rm TeV} \lesssim m_χ\lesssim 30 {~\rm PeV} $ (without BEC). This analysis shows that the electroweak mass window, $10 {~\rm GeV} \lesssim m_χ\lesssim 5 {~\rm TeV}$ is essentially unconstrained by NS observations and therefore is subject only to direct detection experiments. In the annihilating DM scenario, the exclusion limits on DM parameters become weaker and even vanish for typical WIMP annihilation cross-section. However, the late-time heating of the NS enables us to probe the region with $σ_{χn}\gtrsim 10^{-47}~{\rm cm^2}$, using the James Webb Space Telescope in the foreseeable future. When our results are viewed in the context of indirect searches of DM, it provides a lower limit on the $\langleσv\rangle$, which is sensitive to the DM thermal state.

hep-ph↗

arXiv2023

Non-thermal moduli production during preheating in $α$-attractor inflation models

Production of gravitationally coupled light moduli fields must be suppressed in the early universe, so that its decay products do not alter Big Bang Nucleosynthesis (BBN) predictions for light elements. On the other hand, the moduli quanta can be copiously produced non-thermally during preheating after the end of inflation. In this work, we study the production of moduli in the $α$-attractor inflationary model through parametric resonances. For our case, where the inflationary potential at its minimum is quartic, the inflaton field self-resonates, and subsequently induces large production of moduli particles. We find that this production is suppressed for small values of $α$. Combining semi-analytical estimation and numerical lattice simulations, we infer the parametric dependence on $α$ and learn that $α$ needs to be $\lesssim 10^{-8}\,m_{\rm Pl}^2$ to be consistent with BBN. This in turn predicts an upper bound on the energy scale of inflation and on the reheating temperature.

astro-ph.CO↗

arXiv2023

MeV to multi-TeV thermal WIMPs: most conservative limits

We consider a weakly interacting massive particle (WIMP) dark matter (DM) annihilating into all possible Standard Model (SM) particle pairs, including the SM neutrinos, via $s$-wave processes and derive the branching ratio independent upper limit on the total annihilation cross-section $\langle σv \rangle$ using the data of CMB, gamma-ray, cosmic-ray and several neutrino observations. For conservative choices of all relevant astrophysical parameters, we obtain upper limits of $10^{-23}-10^{-25}\,{\rm cm}^3{\rm s}^{-1}$ on the total $\langle σv \rangle$ for the WIMP mass range $10\,{\rm MeV}-100\,{\rm TeV}$, thus making the entire mass range consistent with the observed relic density. An important input that goes into our analysis is the assumption that thermal WIMPs can have significant coupling to the SM neutrinos.

hep-ph↗

arXiv2023

$α$-attractor inflation: Models and predictions

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.

astro-ph.CO↗

arXiv2022

Constraints on the mass and self-coupling of Ultra-Light Scalar Field Dark Matter using observational limits on galactic central mass

It is well known that Ultra-Light Dark Matter (ULDM), usually scalar fields of mass $m \sim 10^{-22}~{\rm eV}$, can solve some of the outstanding problems of the Cold Dark Matter (CDM) paradigm. Such a scalar field could have non-negligible self-coupling $λ$. In this work, using the known observational upper limit on the amount of centrally concentrated dark matter in a galaxy, we arrive at the observational constraints in the $λ- m$ (self coupling $-$ mass) parameter space. It is found that the observational limit on the mass $m$ of the ULDM depends upon the sign and strength of the self-interactions. We demonstrate that, for $m \sim 10^{-22}~{\rm eV}$, self-coupling values of ${\cal O}(10^{-96})$ (corresponding to a scattering length of $a_s \sim 10^{-82}~{\rm m}$) can be probed using limits on the dark matter mass within 10 pc of the centre of M87 galaxy. Our analysis suggests that if Ultra Light Axions (ULAs) form all of dark matter, its mass has to be less than $\sim 6 \times 10^{-23}$ eV.

astro-ph.CO↗

arXiv2022

A general study of decaying scalar dark matter: existing limits and projected radio signals at the SKA

We consider a decaying scalar dark matter (DM) with mass $m_χ$ in the range 10 GeV - 10 TeV and vary the branching ratios of all possible two-body SM final states (excluding and including $ν\barν$) in the range $0\%-100\%$ to derive constraints on the total decay width $Γ$ using the data collected by several astrophysical and cosmological observations. We find that, $Γ\lesssim 10^{-26} - 10^{-27}\,{\rm s}^{-1}$ (excluding $ν\barν$) and $Γ\lesssim 10^{-24} - 10^{-26}\,{\rm s}^{-1}$ (including $ν\barν$) are allowed, depending on the values of $m_χ$, which are most robust upper limits on $Γ$ for a generic decaying scalar DM. We then investigate the prospect of the upcoming Square Kilometre Array (SKA) radio telescope in detecting the DM decay induced radio signals originating inside the dwarf spheroidal (dSph) galaxies. We have classified the DM parameter space, allowed by the existing observations, independently of the branching ratio of each individual two-body SM final state, based on the detectability at the SKA. Excluding the $ν\barν$ decay mode, we find that, throughout the DM mass range considered, $Γ\gtrsim 10^{-30}\,{\rm s}^{-1} - 10^{-29}\,{\rm s}^{-1}$ is detectable for all possible branching ratio combinations at the SKA (assuming 100 hours of observation time), with conservative choices for the relevant astrophysical parameters. On the other hand, when arbitrary branching ratios are allowed also for the $ν\barν$ decay mode, DM decays can be probed independently of the branching ratio of each SM final state for $Γ\gtrsim 2 \times 10^{-29}\,{\rm s}^{-1}$, provided DM masses are greater than a few hundreds of GeV.

hep-ph↗

arXiv2022

Observational Constraints on Axion(s) Dark Energy with a Cosmological Constant

The present work deals with a dark energy model that has an oscillating scalar field potential along with a cosmological constant (CC). The oscillating part of the potential represents the contribution of a light axion field in the dark energy that has its origin in the String-Axiverse scenario. The model has been confronted with the latest cosmological observations. The results show that a sub-Planckian value of the axion field decay constant is consistent with observational data. Furthermore, in terms of the observational data considered in this work, the axion model is preferred over the $Λ$CDM model in terms of AIC, BIC information criteria as well as in terms of Bayesian evidence. The oscillating feature in the scalar field evolution and in the equation of state for the dark energy can be observed for the allowed parameters space. It is also observed that cluster number counts in this axion model are suppressed compared to the $Λ$CDM and this suppression is enhanced for the sub-Planckian values for the axion decay constant.

astro-ph.CO↗

arXiv2022

Effects of Reheating on Moduli Stabilization

Moduli potential loses its minima due to external energy sources of inflaton energy density or radiation produced at the end of inflation. But, the non-existence of minima does not necessarily mean destabilization of moduli. In fact, the destabilization of moduli is always dependent on the initial field values of the fields. In this work, we study carefully how the effects of reheating ease the problem of moduli destabilization. The associated time scale to produce the thermal bath allows a larger initial field range to stabilize the field. Contrary to the usual notion, the allowed initial field range is larger for higher temperatures when the effective potential is of a run-away nature. This eases the moduli destabilization problem for heavy mass moduli. For low mass moduli ($\lesssim$ 30 TeV), the allowed field range still causes the cosmological moduli problem by violating the BBN constraints unless its initial abundance is suppressed.

hep-ph↗

arXiv2022

Screening Mechanism and Late-time Cosmology: Role of a Chameleon-Brans-Dicke Scalar Field

We discuss a way in which the geometric scalar field in a Brans-Dicke theory can evade local astronomical tests and act as a driver of the late-time cosmic acceleration. This requires a self-interaction of the Brans-Dicke scalar as well as an interaction with ordinary matter. The scalar field in this construct acquires a density-dependent effective mass much like a Chameleon field. We discuss the viability of this setup in the context of the Equivalence Principle, Fifth Force, and Solar System tests. The cosmological consistency is adjudged in comparison with observational data from recalibrated light curves of type Ia supernova (JLA), the Hubble parameter measurements (OHD), and the Baryon Acoustic Oscillation (BAO). We deduct that the astrophysical constraints indeed favor the existence of a mild scalar-matter interaction in the Jordan Frame.

gr-qc↗

arXiv2021

Solar Mass Primordial Black Holes in Moduli Dominated Universe

We explore the prospect of producing primordial black holes around the solar mass region during an early matter domination epoch. The early matter-dominated epoch can arise when a moduli field comes to dominate the energy density of the Universe prior to big bang nucleosynthesis. The absence of radiation pressure during a matter-dominated epoch enhances primordial black hole formation from the gravitational collapse of primordial density fluctuations. In particular, we find that primordial black holes are produced in the $0.1-10~M_{\odot}$ mass range with a favorable choice of parameters in the theory. However, they cannot explain all of the merger events detected by the LIGO/Virgo gravitational wave search. In such a case, primordial black holes form about $4\%$ of the total dark matter abundance, of which $95\%$ belongs to the LIGO/Virgo consistent mass range. The rest of the dark matter could be in the form of particles that are produced from the decay of the moduli field during reheating.

astro-ph.CO↗

arXiv2021

Decaying fermionic warm dark matter and XENON1T electronic recoil excess

In the light of the recently observed XENON1T electronic recoil (ER) data, we investigate the possibility of constraining the parameter space of a generic fermionic warm dark matter (WDM), decaying into a standard model (SM) neutrino and a photon. The photon as a decay product, when produced inside the XENON1T chamber, interacts with an electron of a xenon (Xe) atom, leading to a contribution in the observed ER data. We add this dark matter (DM) induced signal over the standard background ($\rm B_0$) considered by the XENON1T collaboration and perform a $χ^2$ fit against the XENON1T data to obtain the best-fit values of the DM decay width and the associated $95\%$ confidence level (C.L.) band for DM mass ($m_χ$) varied in the range $2 - 60$ keV. Additionally, we have extended our analysis by including two other background models available in the literature and in each case, the corresponding limits on the DM decay width are estimated for DM mass ($m_χ$) in the domain $2 - 18$ keV. By comparing the constraints, obtained by fitting the XENON1T data, with the upper limits arising from various existing astrophysical and cosmological observations, we find that, for the background model $\rm B_0$, a fair amount of the DM parameter space is allowed at $95\%$ C.L. for DM masses outside the range $3.5\,{\rm keV} \lesssim m_χ\lesssim 8.5\,{\rm keV}$. However, in case of other two background models, reasonable parts of the DM parameter space are favoured at $95\%$ C.L. by all astrophysical data for all DM masses in the range $2 - 18$ keV.

hep-ph↗

arXiv2020

Fibre inflation and precision CMB data

Generic features of models of inflation obtained from string compactifications are the correlations between the model parameters and the postinflationary evolution of the universe. Thus, the postinflationary evolution depends on the inflationary model parameters and accurate inflationary predictions require that this be incorporated in the evolution of the primordial spectrum. The fibre inflation model is a promising model of inflation constructed in type IIB string theory. This model has two interesting features in its postinflationary evolution. The reheating temperature of the model is directly correlated with the model parameters. The model also necessarily predicts some dark radiation, which can be sizable for certain choices of discrete parameters in the model. We analyze this model in detail using publicly available codes - ModeChord and CosmoMC with the latest Planck+BICEP2/Keck array data to constrain the model parameters and $N_{\rm pivot}$ (the number of $e$-foldings between horizon exit of the CMB pivot mode and the end of inflation). We also carry out the same analysis using the publicly available code Cobaya. We find the results of both the analysis to be in agreement. Our analysis provides the basic methods necessary to extract precise inflationary prediction in string models incorporating correlations between model parameters and postinflationary evolution.

astro-ph.CO↗

arXiv2020

Non-thermal Hot Dark Matter from Inflaton/Moduli Decay: The Momentum Distribution and Relaxing the Cosmological Mass Bound

Decay of the inflaton or moduli which dominated the energy density of the universe at early times leads to a matter to radiation transition epoch. We consider non-thermal sterile dark matter particles produced as decay product during such transitions. The particles have a characteristic energy distribution - that associated with decays taking place in a matter dominated universe evolving to radiation domination. We primarily focus on the case when the particles are hot dark matter, and study their effects on the Cosmic Microwave Background (CMB) and Large Scale Structure (LSS), explicitly taking into account their non-thermal momentum distribution. Our results for CMB angular power and linear matter power spectra reveal interesting features - such as an order of magnitude higher values of hot dark matter mass in comparison to the thermal case being consistent with the present data. We observe that this is related to the fact that $ΔN_{\rm eff}$ and the hot DM energy density can be independent of each other unlike the case of thermal or non-resonantly produced sterile hot DM. We also find features in the CMB at low $\ell$ angular power potentially related to supersonic transmission of hot dark matter through the photon-baryon plasma.

astro-ph.CO↗