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Deepak Jain

Publications and source records attributed to Deepak Jain.

At least 19 recordsLinked to original sources
arXiv2026

A cosmographic analysis using DESI-DR2 and strong lensing: II. Distance Ratio measurements

The distance ratios derived from strong lensing systems, combined with complementary cosmological observations, allow for the study of cosmic expansion and curvature without assuming a fixed background cosmological model. In this work, we perform an analysis of cosmic expansion using the latest Type Ia supernova samples, including PantheonPlus, Union3, and DES Y5, combined with baryon acoustic oscillation dataset from DESI DR2 and strong-lensing distance ratios. The cosmic expansion is carried out to fourth order in the variable $y = z/(1+z)$, which allows constraints on the present-day deceleration, jerk, and snap parameters $(q_0, j_0, s_0)$. The analysis utilizes the distance sum rule to provide an independent determination of the spatial curvature parameter $Ω_{k0}$ without assuming any specific cosmological dynamics. Our results from combining strong lensing distance ratios with each supernova dataset indicate that a flat Universe remains consistent at the 95\% confidence level, and the inclusion of DESI-DR2 measurements tightens the parameter intervals while preserving agreement with flat geometry at the 68\% confidence level, in line with standard cosmology. The inferred values of $q_0$ and $j_0$ are compatible with $Λ$CDM predictions for all dataset combinations. The constraints on $s_0$ remain weak, although modest improvement appears after DESI DR2 data are included. This work represents the second and final paper in the two-part cosmography study.

astro-ph.CO↗
arXiv2026

Quantitative study of Silicon Waveguides for the Generation of Quantum Correlated Photon Pairs Bridging Mid-Infrared and Telecom Bands

Sources of quantum correlated photons pairs bridging the 3um-4um Mid-infrared (MIR) band and Telecom/Near-Infrared/Visible band are of high importance for quantum technologies. Spontaneous Parametric Down Conversion is generally used for realizing such sources, but requires costly implementation platforms with reduced versatility. Here, we explore the potentialities of Spontaneous Four-Wave Mixing (SFWM) in all-solid Silicon On Insulator (SOI) waveguides thanks to an experimentally validated model and propose designs ensuring the production of correlated photon pairs bridging the 3um-4um Mid-infrared band and Telecom C-band. Choosing a pump with a wavelength in the range 2100nm-2210nm and a pulse duration of 5ps, we quantitatively performed simulations targeting a probability of photon pair generation per pulse of 0.05, and we found realistic conditions of utilization (2cm-length straight waveguides, intra-modal Four Wave Mixing with the fundamental TE00 mode) with a pump peak power in between 9.2mW and 32mW. A first design (wCOM) reaches a signal wavelength as high as 3.905um, which is situated in an atmospheric transparency window, while maintaining an idler in the Telecom C-band, making it of high interest for atmospheric Quantum Key Distribution. Two other designs wCH4 and wNO2 aim precise CH4 and NO2 gas sensing with a signal wavelength of 3265nm and 3461nm respectively. In terms of signal/idler wavelength separation, wCOM attains the value of 2364nm which is well above the current record of ~1125nm obtained in quantum regime with SFWM in all-solid SOI waveguides.

quant-ph↗
arXiv2025

A cosmographic analysis using DESI-DR2 and strong lensing: I. Time-Delay measurements

Strong gravitational lensing time-delay measurements, together with the distance sum rule (DSR), offer a model-independent approach to probe the geometry and expansion of the universe without relying on a fiducial cosmological model. In this work, we perform a cosmographic analysis by combining the latest Type Ia supernova datasets (PantheonPlus, DESY5, and Union3), baryon acoustic oscillation data from DESI-DR2, and updated time-delay distances from strong lensing systems. The analyses using SGL with individual SNIa datasets (SGL+PantheonPlus, SGL+DESY5, and SGL+Union3) indicate a preference for an open universe, though they remain consistent with spatially flat universe at the $95%$ confidence level. When DESI-DR2 data is included in each combination, the constraints tighten and shift slightly toward a closed universe, while flatness remains supported at the $68%$ confidence level. The best-fit values of $q_0$ and $j_0$ agree with $Λ$CDM expectations within $95%$ or $99%$ confidence depending on the dataset, whereas $s_0$ remains weakly constrained in all cases. This work is the first in a series of two companion papers on cosmography with DESI-DR2 and strong lensing.

astro-ph.CO↗
arXiv2025

Study of Various Dark Matter Halo Profiles in Milky Way and M31 Galaxies within the Standard Cosmology Framework

In this paper, we study the rotation curves of the Milky Way galaxy (MW) and Andromeda galaxy (M31) by considering their bulge, disk, and halo components. We model the bulge region by the widely accepted de Vaucouleur's law and the disk region by the well-established exponential profile. In order to understand the distribution of dark matter in the halo region, we consider three different dark matter profiles in the framework of the standard $Λ$CDM model, namely, Navarro-Frenk-White (NFW), Hernquist, and Einasto profiles. We use recent datasets of rotation curves of the Milky Way and Andromeda galaxies. The data consist of rotation velocities of the stars and gas in the galaxy as a function of the radial distance from the center. Using Bayesian statistics, we perform an overall fit including all the components, i.e., bulge, disk, and halo, with the data. Our results indicate that the NFW and Hernquist profiles are in concordance with the observational data points. However, the Einasto profile poorly explains the behavior of dark matter in both the galaxies.

astro-ph.GA↗
arXiv2024

Some positive thoughts about Negative Absolute Temperature

It is now widely accepted that the concept of negative absolute temperature is real one and not just theoretical curiosity. In this brief report, by combining the formalism used in the statistical mechanics and thermodynamics, we have explained some aspects of negative temperature ( both mathematically and graphically ) in the two level system. We believe that these simple calculations may give useful and concrete insights about the negative absolute temperature to the undergraduate students.

cond-mat.stat-mech↗
arXiv2023

Constraints on the transition redshift from the calibrated Gamma-ray Burst $E_{\rm p}$-$E_{\rm iso}$ correlation

We constrain the deceleration-acceleration epoch, namely the transition redshift $z_{tr}$, adopting model-independent techniques that utilize a calibrated $E_{\rm p}$-$E_{\rm iso}$ correlation for gamma-ray bursts (GRBs). To do so, in addition to real data points, we employ up to $1000$ simulated observational Hubble data (OHD) points. We then calibrate the $E_{\rm p}$-$E_{\rm iso}$ correlation by means of the well-consolidate Bézier polynomial technique, interpolating OHD up to the second order. Once GRB data have been calibrated, we consider two strategies of cosmographic expansions, i.e., first we take a direct Hubble rate expansion around $z_{tr}$, and second the expansion of the deceleration parameter around the same redshift, but with a different order. Employing type Ia supernovae, baryonic acoustic oscillations and GRB data sets, from Monte Carlo analyses we infer tight constraints on $z_{tr}$ and the jerk parameters at $z=z_{tr}$, namely $j_{tr}$. Our results are extremely compatible with previous outcomes and confirm the $Λ$CDM predictions, being slightly different in terms of the jerk parameter. In this respect, we conjecture which extensions of the concordance paradigm are possible and we compare our findings with expectations provided by generic dark energy models.

astro-ph.CO↗
arXiv2023

Gamma Rays Bursts: A Viable Cosmological Probe?

In this work, our focus is on exploring the potential of current GRB measurements to provide reliable constraints on cosmological model parameters at high redshift. This work is divided into two parts. First, we calibrate the Amati relation in a model-independent way by using Hubble parameter measurements obtained from the differential ages of the galaxies. We further check if the Amati relation parameters evolve with the GRBs' redshift or not, using the data of Old Astrophysical Objects. The results indicate that GRBs do seem to evolve with redshift. In the second part, we test different cosmological models with the calibrated GRB data obtained by using constant and dynamical Amati relation. Our results indicate that the present quality of GRB data is not good enough to put tight constraints on the cosmological parameters. Hence we perform a joint analysis with the combined data of GRBs and Type Ia Supernovae (SNe) and find that this can considerably enhance cosmological constraints in contrast to solely relying on GRBs.

astro-ph.CO↗
arXiv2023

Revisiting the epoch of cosmic acceleration

We revisit the epoch of cosmic speed-up characterized by the redshift of transition from a decelerated to an accelerated phase. This redshift is termed the transition redshift ($z_t$). We use the spatially Flat and Non-Flat variants of the most common $Λ$CDM and XCDM models to put constraints on the transition redshift along with the other model parameters. The data for this analysis comes from the recent and updated Pantheon+ Supernova dataset and the Hubble parameter measurements obtained from Cosmic Chronometers. We consider both datasets with their respective covariance matrices incorporating all kinds of statistical and systematic uncertainties. We observe that using the combined datasets of H(z) and SNe, the best fit value of transition redshift lies in the range $0.61 < z_t < 0.82$ for all four dark energy models. Incidentally, we observe a positive curvature for the Non-Flat models and correlations between several model parameters.

astro-ph.CO↗
arXiv2023

Double roton-minima in bosonic fractional quantum Hall states

We have studied the collective spin-conserving collective excitation spectra in rotating diluted ultra-cold Bose atoms. Double roton-minima have been observed in the fractional quantum Hall (FQH) states for the two filling fractions ($ν$) of the first series of Jain's composite fermion sequences. The obtained roton-minima for $ν$ = 1/4 are at the wave-vectors 1.26 and 2.38 and the roton-minima for $ν$ = 1/6 have been shifted to 1.08 and 2.06. Such shift of roton-minima is attributed due to strong correlation between the particles in bosonic FQH-system. Moreover, the number of roton minima observed depends upon number of attached fluxes as well as the ranges of interaction between the particles.

cond-mat.mes-hall↗
arXiv2023

Constraints on the Transition Redshift using Hubble Phase Space Portrait

One of the most significant discoveries in modern cosmology is that the universe is currently in a phase of accelerated expansion after a switch from a decelerated expansion. The redshift corresponding to this epoch is referred to as the transition redshift $z_t$. In this work we put constraints on the $z_t$ with both model-independent and model-dependent approaches. We consider 32 Hubble parameter measurements and the Pantheon sample of Type Ia Supernovae (SNe). In order to include the possible systematic effects in this analysis, we use the full covariance matrix of systematic uncertainties for the Hubble parameter measurements. We plot a Hubble Phase Space Portrait (HPSP) between $\dot{H}(z)$ and $H(z)$ in a model-independent way. From this HPSP diagram, we estimate the transition redshift as well as the current value of the equation of state parameter $ω_0$ in a model-independent way. By considering H(z) measurements, we find the best fit value of $z_t=0.591^{+0.332}_{-0.332}$ and $ω_0=-0.677^{+0.238}_{-0.238}$. We obtain the best fit value of $z_t=0.849^{+0.117}_{-0.117}$ and $ω_0=-0.870^{+0.013}_{-0.013}$ using the Pantheon database. Further, we also use a model dependent approach to determine $z_t$. Here, we consider a non-flat $Λ$CDM model as a background cosmological model. We reconstruct the cosmic triangle plot among $\log(Ω_{m0})$, $-\log(2Ω_{\Lambda0})$ and $3\log(1+z_t)$ where the constraints of each parameter are determined by the location in this triangle plot. Using $Ω_{m0}$ and $Ω_{\Lambda0}$ values, we find the best value of the transition redshift $z_t=0.619^{+0.580}_{-0.758}$, which is in good agreement with the Planck 2018 results at $1σ$ confidence level. We also simulate the observed Hubble parameter measurements in the redshift range $0<z<2$ and perform the same analysis to estimate the transition redshift.

astro-ph.CO↗
arXiv2022

A non-parametric test of variability of Type Ia supernovae luminosity and CDDR

The first observational evidence for cosmic acceleration appeared from Type Ia supernovae (SNe Type Ia) Hubble diagram from two different groups. However, the empirical treatment of SNe Type Ia and their ability to show cosmic acceleration have been the subject of some debate in the literature. In this work we probe the assumption of redshift-independent absolute magnitude $(M_{\mathrm{B}})$ of SNe along with its correlation with spatial curvature ($Ω_{k0}$) and cosmic distance duality relation (CDDR) parameter ($η(z)$). This work is divided into two parts. Firstly, we check the validity of CDDR which relates the luminosity distance ($d_L$) and angular diameter distance ($d_A$) via redshift. We use the Pantheon SNe Ia dataset combined with the $H(z)$ measurements derived from the cosmic chronometers. Further, four different redshift-dependent parametrizations of the distance duality parameter $(η(z))$ are used. The CDDR is fairly consistent for almost every parametrization within a $2σ$ confidence level in both flat and a non-flat universe. In the second part, we assume the validity of CDDR and emphasize on the variability of $M_{\mathrm{B}}$ and its correlation with $Ω_{k0}$. We choose four different redshift-dependent parametrizations of $M_{\mathrm{B}}$. The results indicate no evolution of $M_{\mathrm{B}}$ within $2σ$ confidence level. For all parametrizations, the best fit value of $Ω_{k0}$ indicates a flat universe at $2σ$ confidence level. However a mild inclination towards a non flat universe is also observed. We have also examined the dependence of the results on the choice of different priors for $H_0$.

astro-ph.CO↗
arXiv2022

Strong lensing systems and galaxy cluster observations as probe to the cosmic distance duality relation

{In this paper, we use large scale structure observations to test the redshift dependence of cosmic distance duality relation (CDDR), $D_{\rm L}(1+z)^{-2}/D_{\rm A}=η(z)$}, with $D_{\rm L}$ and $D_{\rm A}$, being the luminosity and angular diameter distances, respectively. In order to perform the test, the following data set are considered: strong lensing systems and galaxy cluster measurements (gas mass fractions). No specific cosmological model is adopted, only a flat universe is assumed. { By considering two $η(z)$ parametrizations, It is observed that the CDDR remain redshift independent within $1.5σ$ which is in full agreement with other recent tests involving cosmological data}. It is worth to comment that our results are independent of the baryon budget of galaxy clusters.

astro-ph.CO↗
arXiv2021

Constraining Cosmological and Galaxy Parameters using Strong Gravitational Lensing Systems

Strong gravitational lensing along with the distance sum rule method can constrain both cosmological parameters as well as density profiles of galaxies without assuming any fiducial cosmological model. To constrain galaxy parameters and cosmic curvature $(Ω_{k0})$, we use the distance ratio data from a recently compiled database of $161$ galactic scale strong lensing systems. We use databases of supernovae type-Ia (Pantheon) and Gamma Ray Bursts (GRBs) for calculating the luminosity distance. To study the model of the lens galaxy, we consider a general lens model namely, the Extended Power-Law model. Further, we take into account two different parametrisations of the mass density power-law index $(γ)$ to study the dependence of $γ$ on redshift. The best value of $Ω_{k0}$ suggests a closed universe, though a flat universe is accommodated at $68\%$ confidence level. We find that parametrisations of $γ$ have a negligible impact on the best fit value of the cosmic curvature parameter. Furthermore, measurement of time delay can be a promising cosmographic probe via "time delay distance" that includes the ratio of distances between the observer, the lens and the source. We again use the distance sum rule method with time-delay distance dataset of H0LiCOW to put constraints on the Cosmic Distance Duality Relation (CDDR) and the cosmic curvature parameter $(Ω_{k0})$. For this we consider two different redshift-dependent parametrisations of the distance duality parameter $(η)$. The best fit value of $Ω_{k0}$ clearly indicates an open universe. However, a flat universe can be accommodated at $95\%$ confidence level. Further, at $95\%$ confidence level, no violation of CDDR is observed. We believe that a larger sample of strong gravitational lensing systems is needed in order to improve the constraints on the cosmic curvature and distance duality parameter.

astro-ph.CO↗
arXiv2020

Impact of magnetic field on the gas mass fraction of galaxy clusters

Magnetic fields have been observed in galaxy clusters with strengths of the order of $\sim μ$G. The non-thermal pressure exerted by magnetic fields also contributes to the total pressure in galaxy clusters and can in turn affect the estimates of the gas mass fraction, $f_{gas}$. In this paper, we have considered a central magnetic field strength of $5μ$G, motivated by observations and simulations of galaxy clusters. The profile of the magnetic field has also been taken from the results obtained from simulations and observations. The role of magnetic field has been taken into account in inferring the gas density distribution through the hydrostatic equilibrium condition (HSE) by including the magnetic pressure. We have found that the resultant gas mass fraction is smaller with magnetic field as compared to that without magnetic field. However, this decrease is dependent on the strength and the profile of the magnetic field. We have also determined the total mass using the NFW profile to check for the dependency of $f_{gas}$ estimates on total mass estimators. From our analysis, we conclude that for the magnetic field strength that galaxy clusters seem to possess, the non-thermal pressure from magnetic fields has an impact of $\approx 1~\%$ on the gas mass fraction of galaxy clusters. However, with upcoming facilities like Square Kilometre Array (SKA), it can be further expected to improve with more precise observations of the magnetic field strength and profile in galaxy clusters, particularly in the interior region.

astro-ph.CO↗
arXiv2019

Real-time High-Resolution Mid-infrared Optical Coherence Tomography

The potential for improving the penetration depth of optical coherence tomography systems by using increasingly longer wavelength light sources has been known since the inception of the technique in the early 1990s. Nevertheless, the development of mid-infrared optical coherence tomography has long been challenged by the maturity and fidelity of optical components in this spectral region, resulting in slow acquisition, low sensitivity, and poor axial resolution. In this work, a mid-infrared spectral-domain optical coherence tomography system operating at 4 micron central wavelength with an axial resolution of 8.6 microns is demonstrated. The system produces 2D cross-sectional images in real-time enabled by a high-brightness 0.9-4.7 micron mid-infrared supercontinuum source with 1 MHz pulse repetition rate for illumination and broadband upconversion of more than 1 micron bandwidth from 3.58-4.63 microns to 820-865 nm, where a standard 800 nm spectrometer can be used for fast detection. Images produced by the mid-infrared system are compared with those delivered by a state-of-the-art ultra-high-resolution near-infrared optical coherence tomography system operating at 1.3 μm, and the potential applications and samples suited for this technology are discussed. In doing so, the first practical mid-infrared optical coherence tomography system is demonstrated, with immediate applications in real-time non-destructive testing for the inspection of defects and thickness measurements in samples that are too highly scattering at shorter wavelengths.

physics.optics↗
arXiv2018

Bounds on graviton mass using weak lensing and SZ effect in galaxy clusters

In General Relativity (GR), the graviton is massless. However, a common feature in several theoretical alternatives of GR is a non-zero mass for the graviton. These theories can be described as massive gravity theories. Despite many theoretical complexities in these theories, on phenomenological grounds, the implications of massive gravity have been widely used to put bounds on graviton mass. One of the generic implications of giving a mass to the graviton is that the gravitational potential will follow a Yukawa-like fall off. We use this feature of massive gravity theories to probe the mass of graviton by using the largest gravitationally bound objects, namely galaxy clusters. In this work, we use the mass estimates of galaxy clusters measured at various cosmologically defined radial distances measured via weak lensing (WL) and Sunyaev-Zel'dovich (SZ) effect. We also use the model independent values of Hubble parameter $H(z)$ smoothed by a non-parametric method, Gaussian process. Within $1σ$ confidence region, we obtain the mass of graviton $m_g < 5.9 \times 10^{-30}$ eV with the corresponding Compton length scale $λ_g > 6.82$ Mpc from weak lensing and $m_g < 8.31 \times 10^{-30}$ eV with $λ_g > 5.012$ Mpc from SZ effect. This analysis improves the upper bound on graviton mass obtained earlier from galaxy clusters.

astro-ph.CO↗
arXiv2018

Cosmic transparency and acceleration

In this paper, by considering an absorption probability independent of photon wavelength, we show that current type Ia supernovae (SNe Ia) and gamma ray burst (GRBs) observations plus high-redshift measurements of the cosmic microwave background (CMB) radiation temperature support cosmic acceleration regardless of the transparent-universe assumption. Two flat scenarios are considered in our analyses: the $Λ$CDM model and a kinematic model. We consider $τ(z)=2\ln(1+z)^{\varepsilon}$, where $τ(z)$ denotes the opacity between an observer at $z=0$ and a source at $z$. This choice is equivalent to deforming the cosmic distance duality relation as $D_LD^{-1}_A = (1 + z)^{2+\varepsilon}$ and, if the absorption probability is independent of photon wavelength, the CMB temperature evolution law is $T_{CMB}(z)=T_0(1+z)^{1+2\varepsilon/3 }$. By marginalizing on the $\varepsilon$ parameter, our analyses rule out a decelerating universe at 99.99 \% c.l. for all scenarios considered. Interestingly, by considering only SNe Ia and GRBs observations, we obtain that a decelerated universe indicated by $Ω_Λ \leq 0.33$ and $q_0 > 0$ is ruled out around 1.5$σ$ c.l. and 2$σ$ c.l., respectively, regardless of the transparent-universe assumption.

astro-ph.CO↗