arXiv subjects

Suresh Kumar

Publications and source records attributed to Suresh Kumar.

At least 37 records · Page 2Linked to original sources

arXiv2023

Exploring the $H_0$ tension and the evidence of dark sector interaction from 2D BAO measurements

We explore observational constraints on a cosmological model with an interaction between dark energy (DE) and dark matter (DM), using a compilation of 15 measurements of the 2D BAO (i.e., transversal) scale in combination with Planck-CMB data, to explore the parametric space of a class of interacting DE models. We find that 2D BAO measurements can generate different observational constraints compared to the traditional approach of studying the matter clustering in the 3D BAO measurements. Contrary to the observations for the $Λ$CDM and IDE models when analyzed with Planck-CMB + 3D BAO data, we note that Planck-CMB + 2D BAO data favor high values of the Hubble constant $H_0$. From the joint analysis with Planck-CMB + 2D BAO + Gaussian prior on $H_0$, we find $H_0 = 73.4 \pm 0.88$ km/s/Mpc. We conclude that the $H_0$ tension is solved in the IDE model with strong statistical evidence (more than 3$σ$) for the IDE cosmologies.

astro-ph.CO↗

arXiv2023

New cosmological constraints on $f(T)$ gravity in light of full Planck-CMB and type Ia supernovae data

We investigate two new observational perspectives in the context of torsional gravitational modification of general relativity, i.e., the $f(T)$ gravity: i) We use Pantheon data of type Ia supernovae motivated by a time variation of the Newton's constant on the supernovae distance modulus relation, and find that a joint analysis with Baryon Acoustic Oscillations (BAO) and Big Bang Nucleosynthesis (BBN), i.e., Pantheon+BAO+BBN, provides constraints on the effective free parameter of the theory to be well compatible with the $Λ$CDM prediction; ii) We present the framework of $f(T)$ gravity at the level of linear perturbations with the phenomenological functions, namely the effective gravitational coupling $μ$ and the light deflection parameter $Σ$, which are commonly used to parameterize possible modifications of the Poisson equation relating the matter density contrast to the lensing and the Newtonian potentials, respectively. We use the available Cosmic Microwave Background (CMB) data sets from the Planck 2018 release to constrain the free parameters of the $f(T)$ power-law gravity and $Λ$CDM models. We find that CMB data, and its joint analyses with Pantheon and BAO data constrain the $f(T)$ power-law gravity scenario to be practically indistinguishable from the $Λ$CDM model. We obtain the strongest limits ever reported on $f(T)$ power-law gravity scenario at the cosmological level.

astro-ph.CO↗

arXiv2023

Testing spatial curvature and anisotropic expansion on top of the $Λ$CDM model

We explore the possible advantages of extending the $Λ$CDM model by more realistic backgrounds compared to its spatially flat RW spacetime assumption, while preserving the underpinning physics; in particular, by simultaneously allowing non-zero spatial curvature and anisotropic expansion on top of it, viz., the An-$oΛ$CDM model. This is to test whether the latest data support spatial flatness and/or isotropic expansion, and, if not, to explore the roles of spatial curvature and expansion anisotropy (due to its stiff fluid-like behavior) in addressing some of the cosmological tensions. We first present the theoretical background and explicit mathematical construction of An-$oΛ$CDM; combining the simplest anisotropic generalizations of the RW spacetime, viz., the Bianchi type I, V, and IX spacetimes. Then we constrain this model and its particular cases, viz., An-$Λ$CDM, $oΛ$CDM, and $Λ$CDM, by using the data sets from different probes, viz., Planck CMB(+Lens), BAO, SnIa Pantheon, and CC data, and discuss the results. Ultimately, we conclude that, within the setup under consideration, (i) the data confirm the spatial flatness and isotropic expansion, though a very small amount of present-day expansion anisotropy cannot be excluded, e.g., $Ω_{\sigma0}\lesssim10^{-18}$ (95\% C.L.) for An-$Λ$CDM from CMB+Lens, (ii) the introduction of spatial curvature or anisotropic expansion, or both, on top $Λ$CDM does not offer a possible relaxation to the $H_0$ tension, and (iii) the introduction of anisotropic expansion neither affects the closed space prediction from CMB(+Lens) nor does it improve the drastically reduced value of $H_0$ led by the closed space. We discuss why it is important and indispensable to maintain the geometric generalization work program, especially in models that offer solutions to cosmological tensions. [abridged]

astro-ph.CO↗

arXiv2022

OLGA : An Ontology and LSTM-based approach for generating Arithmetic Word Problems (AWPs) of transfer type

Machine generation of Arithmetic Word Problems (AWPs) is challenging as they express quantities and mathematical relationships and need to be consistent. ML-solvers require a large annotated training set of consistent problems with language variations. Exploiting domain-knowledge is needed for consistency checking whereas LSTM-based approaches are good for producing text with language variations. Combining these we propose a system, OLGA, to generate consistent word problems of TC (Transfer-Case) type, involving object transfers among agents. Though we provide a dataset of consistent 2-agent TC-problems for training, only about 36% of the outputs of an LSTM-based generator are found consistent. We use an extension of TC-Ontology, proposed by us previously, to determine the consistency of problems. Among the remaining 64%, about 40% have minor errors which we repair using the same ontology. To check consistency and for the repair process, we construct an instance-specific representation (ABox) of an auto-generated problem. We use a sentence classifier and BERT models for this task. The training set for these LMs is problem-texts where sentence-parts are annotated with ontology class-names. As three-agent problems are longer, the percentage of consistent problems generated by an LSTM-based approach drops further. Hence, we propose an ontology-based method that extends consistent 2-agent problems into consistent 3-agent problems. Overall, our approach generates a large number of consistent TC-type AWPs involving 2 or 3 agents. As ABox has all the information of a problem, any annotations can also be generated. Adopting the proposed approach to generate other types of AWPs is interesting future work.

cs.CL↗

arXiv2022

Updating non-standard neutrinos properties with Planck-CMB data and full-shape analysis of BOSS and eBOSS galaxies

Using the latest observational data from Planck-CMB and its combination with the pre-reconstructed full-shape (FS) galaxy power spectrum measurements from the BOSS DR12 sample and eBOSS LRG DR16 sample, we report the observational constraints on the cosmic neutrino properties given by the extended $Λ$CDM scenario: $Λ$CDM + $N_{\rm eff}$ + $\sum m_ν$ + $c^2_{\rm eff}$ + $c^2_{\rm vis}$ + $ξ_ν$, and its particular case $Λ$CDM + $c^2_{\rm eff}$ + $c^2_{\rm vis}$ + $ξ_ν$, where $N_{\rm eff}$, $\sum m_ν$, $c^2_{\rm eff}$, $c^2_{\rm vis}$, $ξ_ν$ are the effective number of species, the total neutrino mass, the sound speed in the neutrinos rest frame, the viscosity parameter and the degeneracy parameter quantifying a cosmological leptonic asymmetry, respectively. We observe that the combination of FS power spectrum measurements with the CMB data significantly improves the parametric space of the models compared to the CMB data alone case. We find no evidence for neutrinos properties other than the ones predicted by the standard cosmological theory. Our most robust observational constraints are given by CMB + BOSS analysis. For the generalized extended $Λ$CDM scenario, we find $c^2_{\rm eff}=0.3304^{+0.0064}_{-0.0075}$, $c^2_{\rm vis}=0.301^{+0.037}_{-0.033}$, $ξ_ν < 0.05$, $N_{\rm eff}=2.90 \pm 0.15$ at 68\% CL, with $\sum m_ν < 0.116$ eV at 95\% CL. These are the strongest limits ever reported for these extended $Λ$CDM scenarios.

astro-ph.CO↗

arXiv2022

Report of the Topical Group on Cosmic Probes of Fundamental Physics for for Snowmass 2021

Cosmic Probes of Fundamental Physics take two primary forms: Very high energy particles (cosmic rays, neutrinos, and gamma rays) and gravitational waves. Already today, these probes give access to fundamental physics not available by any other means, helping elucidate the underlying theory that completes the Standard Model. The last decade has witnessed a revolution of exciting discoveries such as the detection of high-energy neutrinos and gravitational waves. The scope for major developments in the next decades is dramatic, as we detail in this report.

hep-ph↗

arXiv2022

New tests of dark sector interactions from the full-shape galaxy power spectrum

We explore the role of redshift-space galaxy clustering data in constraining non-gravitational interactions between dark energy (DE) and dark matter (DM), for which state-of-the-art limits have so far been obtained from late-time background measurements. We use the joint likelihood for pre-reconstruction full-shape (FS) galaxy power spectrum and post-reconstruction Baryon Acoustic Oscillation (BAO) measurements from the BOSS DR12 sample, alongside Cosmic Microwave Background (CMB) data from \textit{Planck}: from this dataset combination we infer $H_0=68.02^{+0.49}_{-0.60}\,{\rm km}/{\rm s}/{\rm Mpc}$ and the 2$σ$ lower limit $ξ>-0.12$, among the strongest limits ever reported on the DM-DE coupling strength $ξ$ for the particular model considered. Contrary to what has been observed for the $Λ$CDM model and simple extensions thereof, we find that the CMB+FS combination returns tighter constraints compared to the CMB+BAO one, suggesting that there is valuable additional information contained in the broadband of the power spectrum. We test this finding by running additional CMB-free analyses and removing sound horizon information, and discuss the important role of the equality scale in setting constraints on DM-DE interactions. Our results reinforce the critical role played by redshift-space galaxy clustering measurements in the epoch of precision cosmology, particularly in relation to tests of non-minimal dark sector extensions of the $Λ$CDM model.

astro-ph.CO↗

arXiv2022

Reconstruction of the dark sectors' interaction: A model-independent inference and forecast from GW standard sirens

Interacting dark matter (DM) - dark energy (DE) models have been intensively investigated in the literature for their ability to fit various data sets as well as to explain some observational tensions persisting within the $Λ$CDM cosmology. In this work, we employ the Gaussian processes (GP) algorithm to perform a joint analysis by using the geometrical cosmological probes such as Cosmic chronometers, Supernova Type Ia, Baryon Acoustic Oscillations, and the H0LiCOW lenses sample to infer a reconstruction of the coupling function between the dark components in a general framework, where the DE can assume a dynamical character via its equation of state. In addition to the joint analysis with these data, we simulate a catalogue with standard siren events from binary neutron star mergers, within the sensitivity predicted by the Einstein Telescope, to reconstruct the dark sector coupling with more accuracy in a robust way. We find that the particular case, where $w = -1$ is fixed on the DE nature, has a statistical preference for an interaction in the dark sector at late times. In the general case, where $w(z)$ is analysed, we find no evidence for such dark coupling, and the predictions are compatible with the $Λ$CDM paradigm. When the mock events of the standard sirens are considered to improve the kernel in GP predictions, we find a preference for an interaction in the dark sector at late times.

astro-ph.CO↗

arXiv2021

Relaxing cosmological tensions with a sign switching cosmological constant

Inspired by the recent conjecture originated from graduated dark energy that the Universe has recently transitioned from anti-de Sitter vacua to de Sitter vacua, we extend the $Λ$CDM model by a cosmological constant ($Λ_{\rm s}$) that switches sign at a certain redshift $z_\dagger$, and we call this model $Λ_{\rm s}$CDM. We discuss the construction and theoretical features of this model and find out that, when the consistency of $Λ_{\rm s}$CDM with the CMB data is ensured, (i) $z_\dagger\gtrsim1.1$ is implied by the condition that the Universe monotonically expands, (ii) $H_0$ and $M_B$ (type Ia supernovae absolute magnitude) values are inversely correlated with $z_\dagger$ and reach $H_0\approx74.5~{\rm km\, s^{-1}\, Mpc^{-1}}$ and $M_B\approx-19.2\,{\rm mag}$ for $z_\dagger=1.5$, in agreement with the SH0ES measurements, and (iii) $H(z)$ presents an excellent fit to the Ly-$α$ measurements provided that $z_\dagger\lesssim 2.34$. We further investigate the model constraints by using the full Planck CMB data set, with and without BAO data. We find that the CMB data alone does not constrain $z_\dagger$, but the CMB+BAO data set favors the sign switch of $Λ_{\rm s}$ providing the constraint: $z_\dagger=2.44\pm0.29$ (68% C.L.). Our analysis reveals that the lower and upper limits of $z_\dagger$ are controlled by the Galaxy and Ly-$α$ BAO measurements, respectively, and the larger $z_{\dagger}$ values imposed by the Galaxy BAO data prevent the model from achieving the highest local $H_0$ measurements. In general, $Λ_{\rm s}$CDM (i) relaxes the $H_0$ tension while being fully consistent with the TRGB measurements, (ii) relaxes the $M_B$ tension, (iii) removes the discrepancy with the Ly-$α$ measurements, (iv) relaxes the $S_8$ tension, and (v) finds a better agreement with the BBN constraints on the physical baryon density. [Abridged]

astro-ph.CO↗

arXiv2021

Minimal theory of massive gravity in the light of CMB data and the $S_8$ tension

We investigate the Minimal Theory of Massive Gravity (MTMG) in the light of different observational data sets which are in tension within the $Λ$CDM cosmology. In particular, we analyze MTMG model, for the first time, with the Planck-CMB data, and how these precise measurements affect the free parameters of the theory. The MTMG model can affect the CMB power spectrum at large angular scales and cause a suppression on the amplitude of the matter power spectrum. We find that on adding Planck-CMB data, the graviton has a small, positive, but non-zero mass at 68\% confidence level, and from this perspective, we show that the tension between redshift space distortions measurements and Planck-CMB data in the parametric space $S_8 - Ω_m$ can be resolved within the MTMG scenario. Through a robust and accurate analysis, we find that the $H_0$ tension between the CMB and the local distance ladder measurements still remains but can be reduced to $\sim3.5σ$ within the MTMG theory. The MTMG is very well consistent with the CMB observations, and undoubtedly, it can serve as a viable candidate amongst other modified gravity theories.

astro-ph.CO↗

arXiv2021

Remedy of some cosmological tensions via effective phantom-like behavior of interacting vacuum energy

Since physics of the dark sector components of the Universe is not yet well-understood, the phenomenological studies of non-minimal interaction in the dark sector could possibly pave the way to theoretical and experimental progress in this direction. Therefore, in this work, we intend to explore some features and consequences of a phenomenological interaction in the dark sector. We use the Planck 2018, BAO, JLA, KiDS and HST data to investigate two extensions of the base $Λ$CDM model, viz., (i) we allow the interaction among vacuum energy and dark matter, namely the I$Λ$CDM model, wherein the interaction strength is proportional to the vacuum energy density and expansion rate of the Universe, and (ii) the I$Λ$CDM scenario with free effective neutrino mass and number, namely the $ν$I$Λ$CDM model. We also present comparative analyses of the interaction models with the companion models, namely, $Λ$CDM, $νΛ$CDM, $w$CDM and $νw$CDM. In both the interaction models, we find non-zero coupling in the dark sector up to 99\% CL with energy transfer from dark matter to vacuum energy, and observe a phantom-like behavior of the effective dark energy without actual ``phantom crossing". The well-known tensions on the cosmological parameters $H_0$ and $σ_8$, prevailing within the $Λ$CDM cosmology, are relaxed significantly in these models wherein the $ν$I$Λ$CDM model shows consistency with the standard effective neutrino mass and number. Both the interaction models find a better fit to the combined data compared to the companion models under consideration.

astro-ph.CO↗

arXiv2021

Software Estimations Risk in Pakistan Software Industry

Software and IT industry in Pakistan have seen a dramatic growth and success in past few years and is expected to get doubled by 2020, according to a research. Software development life cycle comprises of multiple phases, activities and techniques that can lead to successful projects, and software evaluation is one of the vital and important parts of that. Software estimation can alone be the reason of product success factor or the products failure factor. To estimate the right cost, effort and resources is an art. But it is also very important to include the risks that may arise in the in a software project which can affect your estimates. In this paper, we highlight how the risks in Pakistan Software Industry can affect the estimates and how to mitigate them.

cs.SE↗

arXiv2021

Measurements of $H_0$ and reconstruction of the dark energy properties from a model-independent joint analysis

Gaussian processes (GP) provide an elegant and model-independent method for extracting cosmological information from the observational data. In this work, we employ GP to perform a joint analysis by using the geometrical cosmological probes such as Supernova Type Ia (SN), Cosmic chronometers (CC), Baryon Acoustic Oscillations (BAO), and the H0LiCOW lenses sample to constrain the Hubble constant $H_0$, and reconstruct some properties of dark energy (DE), viz., the equation of state parameter $w$, the sound speed of DE perturbations $c^2_s$, and the ratio of DE density evolution $X = ρ_{\rm de}/ρ_{\rm de,0}$. From the joint analysis SN+CC+BAO+H0LiCOW, we find that $H_0$ is constrained at 1.1\% precision with $H_0 = 73.78 \pm 0.84$ km s$^{-1}$Mpc$^{-1}$, which is in agreement with SH0ES and H0LiCOW estimates, but in $\sim$6.2$σ$ tension with the current CMB measurements of $H_0$. With regard to the DE parameters, we find $c^2_s < 0$ at $\sim$2$σ$ at high $z$, and the possibility of $X$ to become negative for $z > 1.5$. We compare our results with the ones obtained in the literature, and discuss the consequences of our main results on the DE theoretical framework.

astro-ph.CO↗

arXiv2020

Rastall gravity extension of the standard $Λ$CDM model: theoretical features and observational constraints

We present a detailed investigation of the Rastall gravity extension of the standard $Λ$CDM model. We review the model for two simultaneous modifications of different nature in the Friedmann equation due to the Rastall gravity: the new contributions of the material (actual) sources (considered as effective source) and the altered evolution of the material sources. We discuss the role/behavior of these modifications with regard to some low redshift tensions, including the so-called $H_0$ tension, prevailing within the standard $Λ$CDM. We constrain the model at the level of linear perturbations, and obtain the first constraints through a robust and accurate analysis using the latest full Planck CMB data, with and without including BAO data. We find that the Rastall parameter $ε$ (null for general relativity) is consistent with zero at 68\% CL (with a tendency towards positive values, $-0.0001 < ε< 0.0007$ (CMB+BAO) at 68\% CL), which in turn implies no significant statistical evidence for deviation from general relativity, and also a precision of $\mathcal{O}(10^{-4})$ for the coefficient $-1/2$ of the term $g_{μν}R$ in the Einstein field equations of general relativity (guaranteeing the local energy-momentum conservation). We explore the consequences led by the Rastall gravity on the cosmological parameters in the light of the observational analyses. It turns out that the effective source dynamically screens the usual vacuum energy at high redshifts, but this mechanism barely works due to the opposition by the altered evolution of CDM. Consequently, two simultaneous modifications of different nature in the Friedmann equation act against each other, and do not help to considerably relax the so-called low redshift tensions. Our results may offer a guide for the research community that studies the Rastall gravity in various aspects of gravitation and cosmology.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined III: $f σ_8$ and $S_8$

The standard $Λ$ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few tensions and anomalies became statistically significant with the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension of the Planck data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models for solving this tension, and we discuss the importance of trying to fit with a single model a full array of data and not just one parameter at a time.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined II: The Hubble Constant Tension

The current cosmological probes have provided a fantastic confirmation of the standard $Λ$ Cold Dark Matter cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this Letter of Interest we will focus on the $4.4σ$ tension between the Planck estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we will list a few interesting new physics models that could solve this tension and discuss how the next decade experiments will be crucial.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined I: Perspectives for the Next Decade

The standard $Λ$ Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances present between the different cosmological probes, as the Hubble constant $H_0$ value, the $σ_8 - S_8$ tension, and the anomalies present in the Planck results. Finally, we will give an overview of upgraded experiments and next-generation space-missions and facilities on Earth, that will be of crucial importance to address all these questions.

astro-ph.CO↗

arXiv2020

Cosmology Intertwined IV: The Age of the Universe and its Curvature

A precise measurement of the curvature of the Universe is of primeval importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early Universe scenarios. The recent observations, while broadly consistent with a spatially flat standard $Λ$ Cold Dark Matter ($Λ$CDM) model, are showing tensions that still allow (and, in some cases, even suggest) a few percent deviations from a flat universe. In particular, the Planck Cosmic Microwave Background power spectra, assuming the nominal likelihood, prefer a closed universe at more than 99\% confidence level. While new physics could be in action, this anomaly may be the result of an unresolved systematic error or just a statistical fluctuation. However, since a positive curvature allows a larger age of the Universe, an accurate determination of the age of the oldest objects provides a smoking gun in confirming or falsifying the current flat $Λ$CDM model.

astro-ph.CO↗