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Tapomoy Guha Sarkar

Publications and source records attributed to Tapomoy Guha Sarkar.

At least 19 recordsLinked to original sources
arXiv2026

Padé semi-cosmographic reconstruction of residual dark energy in decaying dark matter cosmology: DESI DR2 BAO constraints and mock 21 cm forecasts

Pure cosmographic reconstructions provide a model-agnostic approach towards constraining cosmic evolution.We develop a hybrid phenomenological semi-cosmographic framework that adopts a Padé-rational fraction parametrization of the luminosity distance, and incorporates a phenomenologically motivated two-body decaying dark matter (DDM) sector. In this framework, the effective residual dark-energy equation of state is obtained by subtracting the contributions of DDM, baryons, and radiation from the Padé approximation to the expansion history under the assumptions of flat FLRW cosmology and the standard Friedmann equations. Cosmological observables computed from these semi-cosmographic quantities are fitted to the data to reconstruct cosmological evolution. We present two separate analyses. First, we perform a data fit to the current DESI DR2 BAO measurements. Second, we report a forecast based on an optimistic mock 21\,cm intensity-mapping power spectrum at $z\simeq 1.75$ for a SKA1-MID-like instrument, used jointly with the DESI DR2 BAO data. The forecast serves as proof of concept to demonstrate a possible improvement in model constraints when measurements of the 21\,cm power spectrum complement the BAO background observables. Posterior constraints on the Padé and DDM parameters are obtained using Markov Chain Monte Carlo (MCMC) analysis, and we present the corresponding equations of state of the massive daughter and the effective reconstructed dark energy.

astro-ph.CO↗
arXiv2026

Spherical Collapse and Halo Formation in a Cosmology with Decaying Dark Matter and a Semi-Cosmographic Dark Energy

We investigate nonlinear structure formation in a cosmological model combining one-body decaying dark matter (DDM) with a semi-cosmographic reconstruction of dark energy. In this scenario, a nonrelativistic dark-matter component decays into relativistic dark radiation with decay rate $Γ=τ_{\rm ddm}^{-1}$, while the dark-energy sector is reconstructed directly from the expansion history rather than being fixed to a cosmological constant. Using DESI DR1 BAO and compressed ShapeFit measurements, we constrain the background evolution and propagate the resulting posterior into the nonlinear regime through spherical collapse and halo abundance calculations. This provides a unified framework connecting a reconstructed dark-energy sector and decaying dark matter (DDM) to the nonlinear formation of cosmic structures. We find that the reconstructed dark-energy equation of state can deviate from the $Λ$CDM value, $w=-1$, while the critical density threshold for collapse remains close to its standard prediction. The most pronounced signatures emerge in the abundance of massive halos, reflecting modifications to the growth of structure driven by both dark-matter decay and dynamical dark energy. By combining DESI DR1 clustering constraints with halo mass function measurements from the DESI Legacy Imaging Surveys DR9, we obtain joint constraints on the DDM lifetime and dark-energy parameters, demonstrating that halo abundances provide a powerful complementary probe of non-standard dark-sector physics.

astro-ph.CO↗
arXiv2026

The dynamics of background evolution and structure formation in phase space: a semi-cosmographic reconstruction

The Baryon Acoustic Oscillation (BAO) feature, imprinted in the transverse and radial clustering of dark matter tracers, enables the simultaneous measurement of the angular diameter distance $D_A(z)$ and the Hubble parameter $H(z)$ at a given redshift. Further, measuring the redshift space anisotropy (RSD) allows us to measure the combination $f_8(z)\equiv fσ_8(z)$. Motivated by this, we simultaneously study the dynamics of background evolution and structure formation in an abstract phase space of dynamical quantities: $ x = H_0 D_A/c$, $p = dx/dz$, and $f_8$. We adopt a semi-cosmographic approach, whereby we do not pre-assume any specific dark energy model to integrate the dynamical system. The Luminosity distance is expanded as a Padé rational approximation in the variable $(1+z)^{1/2}$. The dynamical system is solved by using a semi-cosmographic equation of state, which incorporates the dark matter density parameter along with the parameters of the Padé expansion. The semi-cosmographic $D_A(z), H(z)$ and $fσ_8(z)$, thus obtained, are fitted with BAO and RSD data from the SDSS IV. The reconstructed phase trajectories in the $3D$ $(x,p,f_8)$ space are used to reconstruct some diagnostics of background cosmology and structure formation. At low redshifts, a discernible departure from the $Λ$CDM model is observed. The geometry of the phase trajectories in the projected spaces allows us to identify three key redshifts where future observations may be directed for a better understanding of cosmic tensions and anomalies.

astro-ph.CO↗
arXiv2025

Probing Decaying Dark Matter Using the Post-EoR HI 21-cm signal

We propose the HI 21-cm power spectrum from the post-reionization epoch as a probe of a cosmological model with decaying dark matter particles. The unstable particles are assumed to undergo a 2-body decay into a massless and massive daughter. We assume that a fraction $f$ of the total dark matter budget to be unstable and quantify the decay using the life time $Γ^{-1}$ and the relative mass splitting $ε$ between the parent and the massive daughter. The redshift space anisotropic power spectrum of the post-reionization 21-cm signal brightness temperature, as a tracer of the dark matter clustering, imprints the decaying dark matter model through its effect on background evolution and the suppression of power on small scales. We find that with an idealized futuristic intensity mapping experiment with a SKA1-Mid like radio-array, $ε$ and $Γ$ can be measured at $3.37\%$ and $6.86\%$ around their fiducial values of $ε= 0.012$ and $Γ= 0.008 {\rm Gyr}^{-1}$ respectively. When only the foreground-free window is considered in the $k-$ space, these percentage errors in $ε$ and $Γ$ degrade to $9.91\%$ and $12.03\%$ respectively.The forecasts under identical assumptions for a second, literature-anchored benchmark ($ε=1.14\times10^{-4}$, $Γ=1.04\times10^{-3}\,\mathrm{Gyr}^{-1}$) yields projected uncertainties of $6.16\%$ on $ε$ and $8.29\%$ on $Γ$ while, restricting to the foreground-free window increases these to $18.77\%$ and $14.22\%$, respectively.

astro-ph.CO↗
arXiv2025

Disentangling the growth rate of perturbations from the HI bias using only clustering data from galaxy surveys

This work serves two-fold purpose. Firstly, we provide an alternative to the traditional method of determining the growth rate of density perturbations $f(z)$. In usual practice, $f(z)$ can not be directly measured from tracer clustering at some redshift without knowledge of the bias. While the bayron acoustic oscillation (BAO) imprint allows the determination of $(D_A(z), H(z))$, redshift space anisotropy (RSD) allows the measurement of a quantity $f_8(z) = f(z) σ_{8,0} D_{+}(z)$. To extract $f(z)$ from $f_8(z)$, one usually requires some other data set. We show that precise BAO and RSD measurements in and around some key redshifts themselves can solely reconstruct $f(z)$ without requiring any other data sets. Secondly, we extend this approach to another tracer, namely the post-reionization 21-cm brightness temperature intensity maps. We demonstrate that the measured $f(z)$ from purely redshift space clustering allows us to measure the 21-cm bias, which is a largely unknown quantity. This may help interpret the observed intensity mapping signal in the future.

astro-ph.CO↗
arXiv2025

A semi-cosmographic approach to study cosmological evolution in phase space

The signature of Baryon Acoustic Oscillation in the clustering of dark-matter tracers allows us to measure $(D_A(z), H(z))$ independently. Treating these as conjugate variables, we are motivated to study cosmological evolution in the phase space of dimensionless variables $x = H_0 D_A/c$ and $p = dx/dz$. The dynamical variables $(x(z),p(z))$ can be integrated for a known set of equation of state parameters for different matter/energy components. However, to avoid any preference for specific dark energy models, we adopt a cosmographic approach. We consider two scenarios where the Luminosity distance is expanded as Padé rational approximants using expansion in terms of $z$ and $(1+z)^{1/2}$ respectively. However, instead of directly using the Padé ratios to fit kinematic quantities with data, we adopt an alternative approach where the evolution of the cold dark matter sector is incorporated in our analysis through a semi-cosmographic equation of state, which is then, used to solve the dynamical problem in the phase space. The semi-cosmographic $(D_A(z), H(z))$, thus obtained, is fitted with BAO data from DESI DR1, cosmic chronometer (CC) data and SNIa data from Pantheon+ respectively. We also consider a futuristic 21-cm intensity mapping experiment for error projections. We further use the semi-cosmographic fitting to reconstruct some diagnostics of background cosmology and compare our results for the two scenarios of Padé expansions.

astro-ph.CO↗
arXiv2025

Adiabatic modulation of driving protocols in periodically driven quantum systems

We consider a periodically driven system where the high-frequency driving protocol consists of a sequence of potentials switched on and off at different instants within a period. We explore the possibility of introducing an adiabatic modulation of the driving protocol by considering a slow evolution of the instants when the sequence of potentials is switched on/off. We examine how this influences the long-term dynamics of periodically driven quantum systems. By assuming that the slow and fast timescales in the problem can be decoupled, we derive the stroboscopic (effective) Hamiltonian for a four-step driving sequence up to the first order in perturbation theory. We then apply this approach to a spin-$1/2$ system, where the adiabatic modulation of the driving protocol is chosen to produce an evolving emergent magnetic field that interacts with the spin. We study the emergence of diabolical points and diabolical loci in the parameter space of the effective Hamiltonian. Further, we study the topological properties of the maps of the adiabatic paths in the parameter space to the eigenspace of the effective Hamiltonian. In effect, we obtain a technique for tuning the topological properties of the eigenstates by selecting different adiabatic evolutions of the driving protocol, characterized by distinct paths in parameter space. This technique can be applied to any periodic driving protocol to achieve desirable topological effects.

quant-ph↗
arXiv2024

X-ray emission spectrum for axion-photon conversion in magnetospheres of strongly magnetized neutron stars

Detecting axionic dark matter (DM) could be possible in an X-ray spectrum from strongly magnetized neutron stars (NSs). We examine the possibility of axion-photon conversion in the magnetospheres of strongly magnetized NSs. In the current work, we investigate how the modified Tolman Oppenheimer Volkoff (TOV) system of equations (in the presence of a magnetic field) affects the energy spectrum of axions and axions-converted-photon flux. We have considered the distance-dependent magnetic field in the modified TOV system of equations. We employ three different equations of states (EoSs), namely APR, FPS, and SLY, to solve these equations. We obtain the axions emission rate by including the Cooper-pair-breaking formation process and Bremsstrahlung process in the core of NSs using the NSCool code. We primarily focus on Magnificient seven (M7) star RXJ 1856.5-3754. We further investigate the impact of the magnetic field on the actual observables, such as axion energy spectrum and axion-converted-photon flux at an axion mass in meV range by assuming mass $M_{NS} \sim 1.4M_{\odot}$. We compare our calculated axion-converted-photon flux from all available archival data sets from PN+MOS+Chandra. We also study the variation of the energy spectrum at a fixed energy with varying central magnetic fields. Our predicted axion-converted-photon flux values as a function of axion energy closely follow the experimentally archival data, which allows us to put bounds on the axion mass for the three EoS.

astro-ph.HE↗
arXiv2024

Probing dark energy using anisotropies in the clustering of post-EoR HI distribution

We propose an anisotropy quantifier of the HI 21-cm signal traditionally used to clock the astrophysics of the reionization era as a post-reionization dark energy diagnostic. We find that the anisotropy probe can be measured at SNR $\sim 10$ in both auto-correlation and in cross-correlation with the Ly-$α$ forest over a wide $z$ and $k-$range. We propose to use the BAO signature on the anisotropy signal to measure $( H(z), D_A(z))$. Subsequently, we put constraints on a dark energy model involving a negative cosmological constant on top of a quintessence scalar field and find that such a model is consistent with futuristic observations.

astro-ph.CO↗
arXiv2024

Thermal Evolution and Axion Emission Properties of Strongly Magnetized Neutron Stars

Emission properties of compact astrophysical objects such as Neutron stars (NSs) are associated with crucial astronomical observables. In the current work, we obtain the mass, pressure profiles of the non-rotating NSs using the modified Tolman Oppenheimer Volkoff (TOV) system of equations in the presence of intense magnetic field. We obtain the profiles by using a specific distance-dependent magnetic field in the modified TOV equations. We employ three different equations of states (EoS) to solve the TOV equations by assuming the core of NSs comprises a hadronic matter. Employing the above profiles, we determine the cooling rates of spherically symmetric NSs as a function of time with and without including the magnetic field using the NSCool code. We have also determined the cooling rates as a function of radius for three different NSs. Furthermore, we determine the luminosity of neutrinos, axions, and photons emitting from the NSs in the presence and absence of a magnetic field for an axion mass $16$ meV and three different EoS. Our comparative study indicates that the cooling rate and luminosities of neutrinos, axions, and photons change significantly due to the impact of the strong magnetic field. We also find that due to the magnetic field, the axion mass bound increases slightly compared to without a magnetic field..

astro-ph.HE↗
arXiv2024

Conversion of Emitted Axionic Dark Matter to Photons for Non-Rotating Magnetized Neutron Stars

We attempt to find the impact of a modified Tolman Oppenheimer Volkoff (TOV) system of equations on the luminosities of direct photons, neutrinos and axions for a particular axion mass in the presence of a magnetic field. We employ two different equation of states (EoSs) namely APR and FPS to generate the profiles of mass and pressure for spherically symmetric and non-rotating Neutron stars (NSs). We then compute the axions and neutrino emission rates by employing the Cooper-pair-breaking and formation process (PBF) in the core using the NSCool code. We also examine the possibility of axion to photon conversion in the magnetosphere of NSs. Furthermore, we investigate the impact of the magnetic field on the actual observables, such as the energy spectrum of axions and axion-converted photon flux for three different NSs. Our comparative study indicates that axions energy spectrum and axion-converted photon flux changes significantly due to an intense magnetic field.

hep-ph↗
arXiv2023

Post-reionization HI 21-cm signal: A probe of negative cosmological constant

In this study, we investigate a cosmological model involving a negative cosmological constant (AdS vacua in the dark energy sector). We consider a quintessence field on top of a negative cosmological constant and study its impact on cosmological evolution and structure formation. We use the power spectrum of the redshifted HI 21 cm brightness temperature maps from the post-reionization epoch as a cosmological probe. The signature of baryon acoustic oscillations (BAO) on the multipoles of the power spectrum is used to extract measurements of the angular diameter distance $D_A(z)$ and the Hubble parameter $H(z)$. The projected errors on these are then subsequently employed to forecast the constraints on the model parameters ($Ω_Λ, w_0, w_a$) using Markov Chain Monte Carlo techniques. We find that a negative cosmological constant with a phantom dark energy equation of state (EoS) and a higher value of $H_0$ is viable from BAO distance measurements data derived from galaxy samples. We also find that BAO imprints on the 21cm power spectrum obtained from a futuristic SKA-mid like experiment yield a $1-σ$ error on a negative cosmological constant and the quintessence dark energy EoS parameters to be $Ω_Λ=-1.030^{0.589}_{-1.712}$ and $w_0=-1.023^{0.043}_{-0.060}$, $w_a=-0.141^{0.478}_{-0.409}$ respectively.

astro-ph.CO↗
arXiv2022

Intensity mapping of post-reionization 21-cm signal and its cross-correlations as a probe of $f(R)$ gravity

We propose the intensity mapping of the redshifted HI 21-cm signal from the post-reionization epoch as a cosmological probe of $f(R)$ gravity. We consider the Hu-Sawicki class of $f(R)$ gravity models characterized by a single parameter $f_{,R0}$. The $f(R)$ modification to gravity affects the post-reionization $21$-cm power spectrum through the change in the growth rate of density fluctuations. We find that a radio interferometric observation with a SKA1-Mid like radio telescope in both auto-correlation and cross-correlation with galaxy weak-lensing and Ly-$α$ forest may distinguish $f(R)$ models from $LCDM$ cosmology at a precision which is competitive with other probes of $f(R)$ gravity.

astro-ph.CO↗
arXiv2022

Probing Quintessence using BAO imprint on the cross-correlation of weak lensing and post-reionization HI 21 cm signal

In this work we investigate the possibility of constraining a thawing Quintessence scalar field model for dark energy. We propose using the imprint of baryon acoustic oscillation (BAO) on the cross-correlation of post-reionization 21-cm signal and galaxy weak lensing convergence field to tomographically measure the angular diameter distance $D_A(z)$ and the Hubble parameter $H(z)$. The projected errors in these quantities are then used to constrain the Quintessence model parameters. We find that independent $600$hrs radio interferometric observation at four observing frequencies $916 $MHz, $650$ MHz, $520$ MHz and $430 $MHz with a SKA-1-Mid like radio telescope in cross-correlation with a deep weak lensing survey covering half the sky may measure the binned $D_A$ and $H$ at a few percent level of sensitivity. The Monte Carlo analysis for a power law thawing Quintessence model gives the $1-σ$ marginalized bounds on the initial slope $λ_i$,dark energy density parameter $Ω_{ϕ0}$ and the shape of the potential $Γ$ at 8.63%, 10.08% and 9.75% respectively. The constraints improve to 7.66%, 4.39% and 5.86% respectively when a joint analysis with SN and other probes is performed.

astro-ph.CO↗
arXiv2021

Constraining dark energy using the cross correlations of weak lensing with post-reionization probes of neutral hydrogen

We investigate the prospects of detecting the cross correlation of CMBR weak-lensing convergence field with the large scale tracers of the underlying dark matter distribution in the post-reionization epoch. The cross-correlation is then used to make error projections for dark energy equation of state (EoS)for models with a time evolving dark energy. We study the cross-correlation angular power spectrum of the weak-lensing field with the Lyman-$α$ forest and the redshifted HI 21 cm signal from the post reionization epoch. The angular power spectra is expressed as a line of sight average over the tomographic slices. We find that on using multiple $400$ hrs observation with an extended uGMRT like instrument or with a BOSS like survey with quasar (QSO) density of $16 {\rm deg}^{-2}$ the cross-correlation with weak-lensing convergence field covering half the sky can be detected at a very high SNR ($>20$). The cross-correlation of weak-lensing with Lyman-$α$ forest allows the $1-σ$ errors on the dark energy EoS parameters for different parametrizations to be constrained at a level of precision comparable to combined Planck+SNIa+BAO+HST projections. The 21-cm weak-lensing cross-correlation is found to provide strong constraints on the present value of the dark energy EoS parameter at $4\%$ for the 7CPL model. The constraints on $w_a$ is comparable ($\sim 12\%$) for models other than the 7CPL model. We also find that the CPL parametrization may not be the best constrained parametrization for dark energy evolution. The cross-correlation of CMBR weak-lensing with the post-reionization probes of neutral hydrogen thus holds the potential to give us valuable understanding about the nature of evolving dark energy.

astro-ph.CO↗
arXiv2019

Constraining warm dark matter power spectrum using the cross-correlation of HI 21 cm signal and the Lyman-$α$ forest

We have considered the prospects for measuring the cross Warm Dark Matter (WDM) power spectrum of the redshifted HI 21-cm signal and the Lyman-$α$ forest and thereby constraining WDM mass using observations with upcoming radio-interferometers - the Ooty Wide Field Array (OWFA) and SKA1-mid, and a spectroscopic survey of the quasars. We have considered a quasar survey with a mean observed quasar number density of $\bar{\rm n}_{\rm Q} = 48$ deg$^{-2}$ over a collecting area of 14455 deg$^{2}$, and a mean spectroscopic SNR = 5. Our analysis with OWFA shows that it is possible to measure the WDM power spectrum in several $k$-bins at $k < 0.4$ Mpc$^{-1}$ with ${\rm SNR} > 5$ using an observation of 200 hours each in 100 different fields-of-view for $m_{\rm WDM} = 0.25$ keV. Considering the possibility of the joint measurement of the parameters, the warm dark matter density parameter $Ω_{\rm WDM}$, and the dark energy density parameter $Ω_{\Lambda0}$, we find that the relative error on the $1-σ$ measurement of the parameter $Ω_{\rm WDM}$ is $\sim 0.8$ for a fiducial $m_{\rm WDM} = 0.25$ keV. We further find that it is possible to have a measurement of the suppression of power from the Cold Dark Matter (CDM) power spectrum at a confidence level of $\sim 7.2-σ$ and $\sim 2.7-σ$ in two different $k$-bins over the $k$-range $0.1 \leq k \leq 3.13$ Mpc$^{-1}$ for $m_{\rm WDM} = 0.15$ keV. Considering the analysis with SKA1-mid, we find that for a fiducial $m_{\rm WDM}= 0.25$ keV, the suppression in the cross power spectrum can be measured at $\sim 10 - σ$ around $k \sim 0.2 \rm{Mpc}^{-1}$ for a total observing time of $20000$ hrs distributed uniformly over $50$ independent pointings where the available $k$-range is binned as $Δk = k/5$.

astro-ph.CO↗
arXiv2018

Predictions for measuring the cross power spectrum of the HI 21-cm signal and the Lyman-$α$ forest using OWFA

We have studied the possibility of measuring the cross-correlation of the redshifted HI 21-cm signal and the Lyman-$α$ forest using an upcoming radio-interferometric array OWFA and an spectroscopic observation like SDSS-IV. Our results shows that it is possible to have a $6 σ$ detection of the cross-correlation signal with OWFA PII using an observing time of $200$ hrs each in $N_p = 25$ independent fields-of-view. However, not much can be done beyond this using the cross-correlation signal for $z_c = 3.35$ and $B = 30 \, {\rm MHz}$. Apart from this, we have also envisaged a situation where observations are carried out at $z_c = 3.05$ and $2.55$ which lie closer to the peak of the quasar distribution at $z = 2.25$ and with a larger bandwidth of $B = 60 \, {\rm MHz}$. We see that the SNR of the cross-correlation detection can be significantly enhanced to $\sim 17$ for $z_c = 2.55$ and $B = 60 \, {\rm MHz}$. It is then possible to measure $β_T$ and $β_F$ individually with an ${\rm SNR} \ge 5$ by combining the cross-correlation with the HI 21-cm auto-correlation measurements. We further find that a measurement of the binned cross-correlation power spectrum with ${\rm SNR} \ge 5$ is also possible in several bins at $k \le 0.3 \, {\rm Mpc}^{-1}$.

astro-ph.CO↗
arXiv2018

Floquet topological phase transitions in a kicked Haldane-Chern insulator

We consider a periodically $δ$-kicked Haldane type Chern insulator with the kicking applied in the $\hat{z}$ direction. This is known to behave as an inversion symmetry breaking perturbation, since it introduces a time-dependent staggered sub-lattice potential. We study here the effects of such driving on the topological phase diagram of the original Haldane model of a Hall effect in the absence of a net magnetic field. The resultant Floquet band topology is again that of a Chern insulator with the driving parameters, frequency and amplitude, influencing the inversion breaking mass $M$ of the undriven Haldane model. A family of such, periodically related, `Semenoff masses' is observed to occur which support a periodic repetition of Haldane like phase diagrams along the inversion breaking axis of the phase plots. Out of these it is possible to identify two in-equivalent masses in the reduced zone scheme of the Floquet quasienergies, which form the centres of two inequivalent phase diagrams. Further, variation in the driving amplitude's magnitude alone is shown to effect the topological properties by linearly shifting the phase diagram of the driven model about the position of the undriven case. A phenomenon that allows the study of Floquet topological phase transitions in the system. Finally, we also discuss some issues regarding the modifications to Haldane's condition for preventing band overlaps at the Dirac point touchings in the Brillouin zone, in the presence of kicking.

cond-mat.mes-hall↗