arXiv subjects

Suresh Kumar

Publications and source records attributed to Suresh Kumar.

At least 55 records · Page 3Linked to original sources

arXiv2019

Testing the warmness of dark matter

Dark matter (DM) as a pressureless perfect fluid provides a good fit of the standard $Λ$CDM model to the astrophysical and cosmological data. In this paper, we investigate two extended properties of DM: a possible time dependence of the equation of state of DM via Chevallier-Polarski-Linder parametrization, $w_{\rm dm} = w_{\rm dm 0} + w_{\rm dm 1}(1-a)$, and the constant non-null sound speed $\hat{c}^2_{\rm s,dm}$. We analyze these DM properties on top of the base $Λ$CDM model by using the data from Planck cosmic microwave background (CMB) temperature and polarization anisotropy, baryonic acoustic oscillations (BAO) and the local value of the Hubble constant from the Hubble Space Telescope (HST). We find new and robust constraints on the extended free parameters of DM. The most tight constraints are imposed by CMB + BAO data where the three parameters $w_{\rm dm0}$, $w_{\rm dm1}$ and $\hat{c}^2_{\rm s,dm}$ are respectively constrained to be less than $1.43\times 10^{-3}$, $1.44\times 10^{-3}$ and $1.79\times 10^{-6}$ at 95\% CL. All the extended parameters of DM show consistency with zero at 95\% CL, indicating no evidence beyond the CDM paradigm. We notice that the extended properties of DM significantly affect several parameters of the base $Λ$CDM model. In particular, in all the analyses performed here, we find significantly larger mean values of $H_0$ and lower mean values of $σ_8$ in comparison to the base $Λ$CDM model. Thus, the well-known $H_0$ and $σ_8$ tensions might be reconciled in the presence of extended DM parameters within the $Λ$CDM framework. Also, we estimate the warmness of DM particles as well as its mass scale and find a lower bound: $\sim$ 500 eV from our analyses.

astro-ph.CO↗

arXiv2019

Constraints on a Bianchi type I spacetime extension of the standard $Λ$CDM model

We consider the simplest anisotropic generalization, as a correction, to the standard $Λ$CDM model, by replacing the spatially flat Robertson-Walker metric by the Bianchi type-I metric, which brings in a new term $Ω_{σ0}a^{-6}$ (mimicking the stiff fluid) in the average expansion rate $H(a)$ of the Universe. From Hubble and Pantheon data, relevant to the late Universe ($z\lesssim 2.4$), we obtain the constraint $Ω_{\sigma0}\lesssim10^{-3}$, in line with the model-independent constraints. When the baryonic acoustic oscillations and cosmic microwave background (CMB) data are included, the constraint improves by 12 orders of magnitude, i.e., $Ω_{\sigma0}\lesssim10^{-15}$. We find that this constraint could alter neither the matter-radiation equality redshift nor the peak of the matter perturbations. Demanding that the expansion anisotropy has no significant effect on the standard big bang nucleosynthesis (BBN), we find the constraint $Ω_{\sigma0}\lesssim10^{-23}$. We show explicitly that the constraint from BBN renders the expansion anisotropy irrelevant to make a significant change in the CMB quadrupole temperature, whereas the constraint from the cosmological data in our model provides the temperature change up to $\sim11\, \rm mK$, though it is much beyond the CMB quadrupole temperature.

astro-ph.CO↗

arXiv2019

Dark sector interaction: a remedy of the tensions between CMB and LSS data

The well-known tensions on the cosmological parameters $H_0$ and $σ_8$ within the $Λ$CDM cosmology shown by the Planck-CMB and LSS data are possibly due to the systematics in the data or our ignorance of some new physics beyond the $Λ$CDM model. In this letter, we focus on the second possibility, and investigate a minimal extension of the $Λ$CDM model by allowing a coupling between its dark sector components (dark energy and dark matter). We analyze this scenario with Planck-CMB, KiDS and HST data, and find that the $H_0$ and $σ_8$ tensions disappear at 68\% CL. In the joint analyzes with Planck, HST and KiDS data, we find non-zero coupling in the dark sector up to 99\% CL. Thus, we find a strong statistical support from the observational data for an interaction in the dark sector of the Universe while solving the $H_0$ and $σ_8$ tensions simultaneously.

astro-ph.CO↗

arXiv2018

Cosmological implications of scale-independent energy-momentum squared gravity: Pseudo nonminimal interactions in dark matter and relativistic relics

In this paper, we introduce a scale-independent energy-momentum squared gravity (EMSG) that allows different gravitational couplings for different types of sources, which may lead to scenarios with many interesting applications/implications in cosmology. In the present study, to begin with, we study a modification of the $Λ$ cold dark matter ($Λ$CDM) model, where photons and baryons couple to the spacetime as in general relativity, while the cold dark matter and relativistic relics (neutrinos and any other relativistic relics) couple to the spacetime in accordance with EMSG. This scenario induces pseudo nonminimal interactions on these components, leading to modification at both the background and perturbative levels. A consequence of this scenario is that the dimensionless free parameter of the theory may induce direct changes on the effective number of the relativistic species, without the need to introduce new extra species. In order to quantify the observational consequences of the cosmological scenario, we use the cosmic microwave background Planck data (temperature, polarization, and lensing power spectrum) and baryonic acoustic oscillations data. We find that the free model parameter is too small to induce statistically significant corrections on the $Λ$CDM model due to EMSG. We deduce that the model presented here is quite rich with promising cosmological applications/implications that deserve further investigations.

gr-qc↗

arXiv2018

Cosmological bounds on dark matter-photon coupling

We investigate an extension of the $Λ$CDM model where the dark matter (DM) is coupled to photons, inducing a nonconservation of the numbers of particles for both species, where the DM particles are allowed to dilute throughout the cosmic history with a small deviation from the standard evolution decaying into photons, while the associated scattering processes are assumed to be negligible. In addition, we consider the presence of massive neutrinos with the effective number of species $N_{\rm eff}$ as a free parameter. The effects of the DM-photon coupling on the cosmic microwave background (CMB) and matter power spectra are analyzed. We derive the observational constraints on the model parameters by using the data from CMB, baryonic acoustic oscillation (BAO) measurements, the recently measured new local value of the Hubble constant from the Hubble Space Telescope, and large scale structure (LSS) information from the abundance of galaxy clusters. The DM-photon coupling parameter $Γ_{γ}$ is constrained to $Γ_{γ} \leq 1.3 \times10^{-5}$ (at 95\% C.L.) from the joint analysis carried out by using all the mentioned data sets. The neutrino mass scale $\sum m_ν$ upper bounds at 95\% C.L. are obtained as $\sum m_ν \sim 0.9$ eV and $\sum m_ν \sim 0.4$ eV with and without the LSS data, respectively. We observe that the DM-photon coupling cause significant changes in the best fit value of $N_{\rm eff}$ but yields statistical ranges of $N_{\rm eff}$ compatible with the standard predictions, and we do not find any evidence of dark radiation. Due to nonconservation of photons in our model, we also evaluate and analyze the effects on the BAO acoustic scale at the drag epoch. The DM-photon coupling model yields high values of Hubble constant consistent with the local measurement, and thus alleviates the tension on this parameter.

astro-ph.CO↗

arXiv2018

Cosmic acceleration in dust only Universe via energy-momentum powered gravity

We propose a modified theory of gravitation constructed by the addition of the term $f(T_{μν}T^{μν})$ to the Einstein-Hilbert action, and elaborate a particular case $f(T_{μν}T^{μν})=α(T_{μν}T^{μν})^η$, where $α$ and $η$ are real constants, dubbed as energy-momentum powered gravity (EMPG). We search for viable cosmologies arising from EMPG especially in the context of the late-time accelerated expansion of the Universe. We investigate the ranges of the EMPG parameters $(α,η)$ on theoretical as well as observational grounds leading to the late-time acceleration of the Universe with pressureless matter only, while keeping the successes of standard general relativity at early times. We find that $η=0$ corresponds to the $Λ$CDM model, whereas $η\neq 0$ leads to a $w$CDM-type model. However, the underlying physics of the EMPG model is entirely different in the sense that the energy in the EMPG Universe is sourced by pressureless matter only. Moreover, the energy of the pressureless matter is not conserved, namely, in general it does not dilute as $ρ\propto a^{-3}$ with the expansion of the Universe. Finally, we constrain the parameters of an EMPG-based cosmology with a recent compilation of 28 Hubble parameter measurements, and find that this model describes an evolution of the Universe similar to that in the $Λ$CDM model. We briefly discuss that EMPG can be unified with Starobinsky gravity to describe the complete history of the Universe including the inflationary era.

gr-qc↗

arXiv2017

Echo of interactions in the dark sector

We investigate the observational constraints on an interacting vacuum energy scenario with two different neutrino schemes (with and without a sterile neutrino) using the most recent data from CMB temperature and polarization anisotropy, baryon acoustic oscillations (BAO), type Ia supernovae from JLA sample and structure growth inferred from cluster counts. We find that inclusion of the galaxy clusters data with the minimal data combination CMB + BAO + JLA suggests an interaction in the dark sector, implying the decay of dark matter particles into dark energy, since the constraints obtained by including the galaxy clusters data yield a non-null and negative coupling parameter between the dark components at 99\% confidence level. We deduce that the current tensions on the parameters $H_0$ and $σ_8$ can be alleviated within the framework of the interacting as well as non-interacting vacuum energy models with sterile neutrinos.

astro-ph.CO↗

arXiv2017

Observational constraints on dark matter-dark energy scattering cross section

In this letter, we report precise and robust observational constraints on dark matter-dark energy scattering cross section, using the latest data from cosmic microwave background (CMB) Planck temperature and polarization, baryon acoustic oscillations (BAO) measurements and weak gravitational lensing data from Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). The scattering scenario consists of a pure momentum exchange between the dark components, and we find $σ_d < 10^{-29} \, {\rm cm^2}$ at 95\% CL from the joint analysis (CMB + BAO + CFHTLenS), for typical dark matter particle mass of the order 1-10 ${\rm GeV}/c^2$. We notice that the scattering among the dark components may influence the growth of large scale structure in the Universe, leaving the background cosmology unaltered.

astro-ph.CO↗

arXiv2017

A CsI(Tl) detector array for the measurement of light charged particles in heavy-ion reactions

An array of eight CsI(Tl) detectors has been set up to measure the light charged particles in nuclear reactions using heavy ions from the Pelletron Linac Facility, Mumbai. The energy response of CsI(Tl) detector to $α$-particles from 5 to 40 MeV is measured using radioactive sources and the $^{12}$C($^{12}$C, $α$) reaction populating discrete states in $^{20}$Ne. The energy non-linearity and the count rate effect on the pulse shape discrimination property have also been measured and observed the deterioration of pulse shape discrimination with higher count rate.

physics.ins-det↗

arXiv2017

Measurement of the response of a liquid scintillation detector to monoenergetic electrons and neutrons

The response of the liquid scintillator (EJ-301 equivalent to NE-213) to the monoenergetic electrons produced in Compton scattered $γ$-ray tagging has been carried out for various radioactive $γ$-ray sources. The measured electron response is found to be linear up to $\sim$4~MeVee and the resolution of the liquid scintillator at 1~MeVee is observed to be $\sim$~11\%. The pulse shape discrimination and pulse height response of the liquid scintillator for neutrons has been measured using $^7$Li(p,n$_1$)$^7$Be*(0.429 MeV) reaction. Non linear response to mono-energetic neutrons for the liquid scintillator is observed at E$_n$=5.3, 9.0 and 12.7 MeV. The measured response of the liquid scintillator for electrons and neutrons have been compared with Geant4 simulation.

physics.ins-det↗

arXiv2017

Comparison between the Logotropic and $Λ$CDM models at the cosmological scale

We perform a detailed comparison between the Logotropic model [P.H. Chavanis, Eur. Phys. J. Plus 130 (2015) 130] and the $Λ$CDM model. These two models behave similarly at large (cosmological) scales up to the present. Differences will appear only in the far future, in about $25\, {\rm Gyrs}$, when the Logotropic Universe becomes phantom while the $Λ$CDM Universe enters in the de Sitter era. However, the Logotropic model differs from the $Λ$CDM model at small (galactic) scales, where the latter encounters serious problems. Having a nonvanishing pressure, the Logotropic model can solve the cusp problem and the missing satellite problem of the $Λ$CDM model. In addition, it leads to dark matter halos with a constant surface density $Σ_0=ρ_0 r_h$, and can explain its observed value $Σ_0=141 \, M_{\odot}/{\rm pc}^2$ without adjustable parameter. This makes the logotropic model rather unique among all the models attempting to unify dark matter and dark energy. In this paper, we compare the Logotropic and $Λ$CDM models at the cosmological scale where they are very close to each other in order to determine quantitatively how much they differ. This comparison is facilitated by the fact that these models depend on only two parameters, the Hubble constant $H_0$ and the present fraction of dark matter $Ω_{\rm m0}$. Using the latest observational data from Planck 2015+Lensing+BAO+JLA+HST, we find that the best fit values of $H_0$ and $Ω_{\rm m0}$ are $H_0=68.30\, {\rm km}\, {\rm s}^{-1}\,{\rm Mpc}^{-1}$ and $Ω_{\rm m0}=0.3014$ for the Logotropic model, and $H_0=68.02\, {\rm km}\, {\rm s}^{-1}\,{\rm Mpc}^{-1}$ and $Ω_{\rm m0}=0.3049$ for the $Λ$CDM model. The difference between the two models appears at the percent level.

astro-ph.CO↗

arXiv2016

Determining the Hubble constant from Hubble parameter measurements

We use 28 Hubble parameter, $H(z)$, measurements at intermediate redshifts $0.07 \leq z \leq 2.3$ to determine the present-day Hubble constant $H_0$ in four cosmological models. We measure $H_0 = 68.3^{ +2.7}_{ -2.6 }, 68.4^{ +2.9 }_{ -3.3 }, 65.0^{ +6.5 }_{ -6.6 }$ and $ 67.9^{ +2.4}_{-2.4}$ km s${}^{-1}$ Mpc${}^{-1}$ (1$σ$ errors) in the $Λ$CDM (spatially flat and non-flat), $ω$CDM and $ϕ$CDM models, respectively. These measured $H_0$ values are more consistent with the lower values determined from recent cosmic microwave background and baryon acoustic oscillation data, as well as with that found from a median statistics analysis of Huchra's compilation of $H_0$ measurements,but include the higher local measurements of $H_0$ within the 2$σ$ confidence limits.

astro-ph.CO↗

arXiv2016

Probing the interaction between dark matter and dark energy in the presence of massive neutrinos

We consider the possibility of an interaction in the dark sector in the presence of massive neutrinos, and study the observational constraints on three different scenarios of massive neutrinos using the most recent CMB anisotropy data in combination with type Ia supernovae, baryon acoustic oscillations, and Hubble parameter measurements. When a sterile neutrino is introduced in the interacting dark sector scenario in addition to the standard model prediction of neutrinos, we find that the coupling parameter, characterizing the interaction between dark matter and dark energy, is non-zero at 2$σ$ confidence level. The interaction model with sterile neutrino is also found to be a promising one to alleviate the current tension on Hubble constant. We do not find the evidence for a coupling in the dark sector when the possibility of a sterile neutrino is discarded.

astro-ph.CO↗

arXiv2016

Characterization of PARIS LaBr$_3$(Ce)-NaI(Tl) phoswich detectors upto $E_γ$ $\sim$ 22 MeV

In order to understand the performance of the PARIS (Photon Array for the studies with Radioactive Ion and Stable beams) detector, detailed characterization of two individual phoswich (LaBr$_3$(Ce)-NaI(Tl)) elements has been carried out. The detector response is investigated over a wide range of $E_γ$ = 0.6 to 22.6 MeV using radioactive sources and employing $^{11}B(p,γ)$ reaction at $E_p$ = 163 keV and $E_p$ = 7.2 MeV. The linearity of energy response of the LaBr$_3$(Ce) detector is tested upto 22.6 MeV using three different voltage dividers. The data acquisition system using CAEN digitizers is set up and optimized to get the best energy and time resolution. The energy resolution of $\sim$ 2.1% at $E_γ$ = 22.6~MeV is measured for the configuration giving best linearity upto high energy. Time resolution of the phoswich detector is measured with a $^{60}$Co source after implementing CFD algorithm for the digitized pulses and is found to be excellent (FWHM $\sim$ 315~ps). In order to study the effect of count rate on detectors, the centroid position and width of the $E_γ$ = 835~keV peak were measured upto 220 kHz count rate. The measured efficiency data with radioactive sources are in good agreement with GEANT4 based simulations. The total energy spectrum after the add-back of energy signals in phoswich components is also presented.

physics.ins-det↗

arXiv2015

Consistency of the nonflat $Λ$CDM model with the new result from BOSS

Using 137,562 quasars in the redshift range $2.1\leq z\leq3.5$ from the Data Release 11 (DR11) of the Baryon Oscillation Spectroscopic Survey (BOSS) of Sloan Digital Sky Survey (SDSS)-III, the BOSS-SDSS collaboration estimated the expansion rate $H(z=2.34)=222\pm7$ km/s/Mpc of Universe, and reported that this value is in tension with the predictions of flat $Λ$CDM model at around 2.5$σ$ level. In this paper, we briefly describe some attempts made in the literature to relieve the tension, and show that the tension can naturally be alleviated in non-flat $Λ$CDM model with positive curvature. We also perform the observational consistency check by considering the constraints on the non-flat $Λ$CDM model from Planck,WP and BAO data. We find that the non-flat $Λ$CDM model constrained with Planck+WP data fits better to the line of sight measurement $H(z=2.34)=222\pm7$ km/s/Mpc, but only at the expense of still having a poor fit to the BAO transverse measurements.

gr-qc↗

arXiv2014

Observational constraints on variable equation of state parameters of dark matter and dark energy after Planck

In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann-Robertson-Walker space-time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier-Polarski-Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck+WMAP9+WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.

gr-qc↗

arXiv2014

Probing the matter and dark energy sources in a viable Big Rip model of the Universe

Chevallier-Polarski-Linder (CPL) parametrization for the equation of state of dark energy in terms of cosmic redshift or scale factor have been frequently studied in the literature. In this study, we consider cosmic time based CPL parametrization for the equation of state parameter of the effective cosmic fluid that fills the fabric of spatially flat and homogeneous Robertson-Walker spacetime in general relativity. The model exhibits two worthy features: (i) It fits the observational data from the latest $H(z)$ and Union 2.1 SN Ia compilations matching the success of $Λ$CDM model. (ii) It describes the evolution of the Universe from the matter-dominated phase to the recent accelerating phase similar to the $Λ$CDM model but leads to Big Rip end of the Universe contrary to the everlasting de Sitter expansion in the $Λ$CDM model. We investigate the matter and dark energy sources in the model, in particular, behavior of the dynamical dark energy responsible for the Big Rip end of Universe.

gr-qc↗

arXiv2014

Probing kinematics and fate of the Universe with linearly time-varying deceleration parameter

The parametrizations $q=q_0+q_1 z$ and $q=q_0+q_1 (1-a/a_0)$ (Chevallier-Polarski-Linder parametrization) of deceleration parameter, which are linear in cosmic redshift $z$ and scale factor $a$, have been frequently utilized in the literature to study kinematics of Universe. In this paper, we follow a strategy that leads to these two well known parametrizations of deceleration parameter as well as an additional new parametrization $q=q_0+q_1(1-t/t_0)$, which is linear in cosmic time $t$. We study the features of this linearly time-varying deceleration parameter in contrast with the other two linear parametrizations. We investigate in detail the kinematics of the Universe by confronting the three models with the latest observational data. We further study the dynamics of the Universe by considering the linearly time-varying deceleration parameter model in comparison with the standard $Λ$CDM model. We also discuss future of the Universe in the context of the models under consideration.

gr-qc↗