The rising concern in the Hubble constant tension ($H_0$ tension) of the cosmological models motivates the scientific community to search for alternative cosmological scenarios that could resolve the $H_0$ tension. In this regard, we aim to work on a torsion-based modified theory of gravity which is an alternative description to the coherence model. We solve numerically for the Hubble...
Observations of the Cosmic Microwave Background (CMB) radiation have made significant contributions to our understanding of cosmology. While temperature observations of the CMB have greatly advanced our knowledge, the next frontier lies in detecting the elusive B-modes and obtaining precise reconstructions of the CMB's polarized signal in general. In anticipation of proposed and upcoming CMB...
We use cosmological N-body simulations to study a local Hubble constant measurement and study the uncertainty introduced by our lack of peculiar velocities. We consider observers to be located in dark matter halos and target galaxies to be distributed amongst dark matter halos. We average over all observers. Our findings show a trend where local measurements have a significant dispersion...
The light-cone (LC) effect arises from the cosmological evolution of the redshifted 21-cm signal along an observer's line of sight (LoS), which is the frequency axis. It is particularly pronounced during the Epoch of Reionization (EoR) when the mean neutral hydrogen fraction (x_HI) and statistical properties change rapidly. The 3D power spectrum only quantifies the ergodic part of the signal...
The count-in-cells (CIC) is a one point spatial statistic that is used to describe the spatial distribution of galaxies in the Universe. Besides the computational simplicity, it can be modelled theoretically to allow estimation of the parameters describing the large-scale structure of the Universe, such as the $\sigma_8$ and bias. In this work, we measure the galaxy CIC distribution at high...
Massive neutrinos are well-known to cause a characteristic suppression in the growth of structures at scales below the neutrino free-streaming length. A detailed understanding of this suppression is essential in the era of precision cosmology we are entering into, enabling us to better constrain the total neutrino mass and possibly probe LCDM cosmological model(s) and beyond. In this talk, I...
We investigate the cosmological applications of new gravitational scalar-tensor theories and we
analyze them in the light of H0 tension. In these theories the Lagrangian contains the Ricci scalar
and its first and second derivatives in a specific combination that makes them free of ghosts, thus
corresponding to healthy bi-scalar extensions of general relativity. We examine two specific...
The mismatch in the present value of Hubble parameter estimated by Supernova based local measurements and CMB based observations is known as Hubble tension. We attempt to resolve the Hubble tension by considering the curvaton scenario. We show that curvaton influences the Hubble parameter if it gains mass after the inflation and can therefore alleviate the Hubble tension.
At all Universe scales, there is a detectable amount of magnetic field. This observed magnetic field has several probable origins, including the possibility that it was produced during the early Universe. There are several models for primordial magnetogenesis, and if the inflationary background is taken into account, breaking conformal symmetry is required to generate a sufficient amount of...
Primordial non-Gaussianity has set strong constraints on models of the early universe. Studies have shown that Loop Quantum Cosmology (LQC), which is an attempt to extend inflationary scenario to planck scales, leads to a strongly scale dependent and oscillatory non-Gaussianity. In particular, the non-Gaussianity function $f_{_{\rm NL}}(k_1,\, k_2,\, k_3)$ generated in LQC, though similar to...
If a significant fraction of dark matter is in the form of compact objects, they will cause microlensing effects in the gravitational wave signals observable by LIGO and Virgo. From the non-observation of microlensing signatures in the binary black hole events from the first two observing runs and the first half of the third observing run, we constrain the fraction of compact dark matter in...
The era of Reheating is an interesting phase of inflationary Universe and it can be parameterized by various parameters like reheating temperature $T_{\text{re}}$, reheating duration $N_{\text{re}}$ and average equation of state parameter $\overline{\omega }_{\text{re}}$, which can be constrained by observationally viable values of scalar power spectral amplitude $A_{\text{s}}$ and spectral...
In this work, we try to compare the cosmological perturbation in the Einstein frame and the Jordan frame for the two-field model. Here we match the metric potentials in both frames to find the equivalence. Further, we evolve the perturbations numerically for selected models.
The study of cosmological perturbations and quantization during inflation has predominantly focused on the Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime. Still, there are very few non-FLRW spacetime cosmological perturbation studies. Among these, the Bianchi I model is one of the simplest anisotropic spacetime models, featuring varying scale factors (a(t)) in orthogonal directions. This...
Cross-correlation between weak lensing of the Cosmic Microwave Background (CMB) and weak lensing of galaxies offers a way to place robust constraints on cosmological and astrophysical parameters with reduced sensitivity to certain systematic effects affecting individual surveys. We measure the angular cross-power spectrum between the Atacama Cosmology Telescope (ACT) DR4 CMB lensing and the...
Motivated by the effectiveness of $f(Q)$ gravity models in fitting observational data at both background and perturbation levels, our study employs a comprehensive dynamical system analysis to independently validate these findings. We focus on two well-studied $f(Q)$ models, specifically the power-law and exponential variants. Our analysis reveals a matter-dominated saddle point in both cases,...
An exact solution for the bulk five-dimensional geometry is derived for F(R) gravity with nonflat de
Sitter 3-branes located at the M4 × Z2 orbifold boundaries. The corresponding form of F(R) that leads to
such an exact solution of the bulk metric is derived, which turns out to have all positive integer powers of R.
In such a scenario, the stability issue of the modulus (radion field) is...
Early data from the James Webb Space Telescope (JWST) has uncovered the
existence of a surprisingly abundant population of very massive galaxies at extremely high
redshift, which are hard to accommodate within the standard ΛCDM cosmology. We explore
whether the JWST observations may be pointing towards more complex dynamics in the dark
energy (DE) sector. Motivated by the ubiquity of...
We investigate the non-Gaussian three-point cross-correlation function between the primordial curvature perturbation and the primordial magnetic field generated via direct gauge-inflaton coupling, for generic non-standard initial vacua. Among the possible triangular configurations of the resulting cross-bispectrum, we find that the squeezed limit leads to a product form decomposition in terms...
In this talk, I discuss the evolution of various measures of quantumness of the curvature perturbation by integrating out the inaccessible entropic fluctuations in the multi-field models of inflation. In particular, I discuss the following measures of quantumness, namely purity, entanglement entropy and quantum discord. The models being considered in this talk are ones that produce large scale...
In this paper, we perform the dynamical system analysis of the cosmological models framed in the extended teleparallel gravity, the $f (T, B)$ gravity. We use the mapping, $f(T, B)=-T+f(T, B)$, and define the dynamical variables to form the autonomous dynamical system. The critical points are obtained in two well-motivated forms of $f (T, B)$, one that involves the logarithmic form of the...
The present work deals with a dynamical systems study of quintessence potentials leading to the present accelerated expansion of the universe. The principal interest is to check for late time attractors which give an accelerated expansion for the universe. Two examples are worked out, namely the exponential and the power-law potential. Furthur we can encountered with the other type of...
Abstract : We study evolution of the universe in modified theories of gravity. The dynamics of the universe is explored in the following theories (i) $f(R)= R + \gamma R^2 + \beta R^{\delta}$ where $\beta$, $\gamma$, $\delta$ are arbitrary constants, (ii) $f(R, GB) = R+ f(GB) $, GB is the Gauss-Bonnet term : $GB=R^{\alpha \beta \gamma \delta} R_{\alpha \beta \gamma \delta} -4...
Although the sources of ultra-high energy cosmic rays (UHECRs) are unknown, the high-quality data acquired by the most modern CR observatories indicate that these CRs are of extragalactic origin. As the intergalactic media are predicted to be filled with turbulent magnetic fields (TMFs), these intergalactic magnetic fields may profoundly impact how UHECRs travel throughout the expanding...
$\mathbb{Z}_3$ symmetric dark matter models have demonstrated remarkable potential in addressing various (astro-)particle physics challenges. In this presentation, I will discuss the diverse ways in which this model can successfully explain the different cosmological observations. We have considered two such promising models: semi-annihilating dark matter (SADM) and Co-SIMP $2\rightarrow 3$...
Recently, a novel modification in the conventional area-entropy relation has been introduced by Barrow, as $S=(A/A_{0})^{1+\Delta/2}$, by taking account of the quantum gravitational deformation effects on the black hole's surface. Recent literature has adopted this horizon entropy to the cosmological domain, leading to significant insights. In this line of thought, we formulated the law of...
The study investigates the evolution of the global 21 cm temperature, a pivotal cosmological probe for understanding the early Universe, employing a novel approach rooted in scalar field dynamics.In this research, we use scalar field models to understand its impact on 21 cm cosmology, aiming to uncover the unexplored nuances in the temperature fluctuations. Furthermore, we try to understand...
The Jordan and Einstein frame representations of scalar-tensor theories of gravity are mathematically equivalent; however, the cosmological evolutions therein can be drastically different. An interesting example is an expansion-collapse duality -- a continually expanding Einstein frame universe can have a dual Jordan frame description that is always contracting. The scenario eventually runs...
We delve into the intricacies of the Bianchi-I cosmological model, driven by the intriguing backdrop of anisotropic cosmic microwave background (CMB) observations. In our pursuit to understand the underlying anisotropy of this model, we introduce anisotropic sources into the framework, augmenting the isotropic matter with dust-like dark matter and dark energy in the form of a cosmological...
The first serendipitous detection of a highly magnified star in a spiral galaxy (z=1.49) lensed by a galaxy cluster, MACS1149 (z=0.54), has opened a new window to observe stars at cosmological distances. Since then, several other lensed stars have been detected in HST imaging of various galaxy clusters, and nearly all galaxy clusters observed by JWST revealed lensed stars candidates. Observing...
This abstract is primarily based on our recent work arXiv:2308.16604. Fast Radio Bursts (FRBs) can be used as a tool to understand different cosmological phenomena because of their distinct features, such as short pulse width, relatively high dispersion measure, etc. On the other hand, over the past decades, researchers have proposed different modified gravity models. In my talk, considering a...
In the paradigm of hierarchical structure formation, galaxies are thought to form and evolve inside a potential well environment of 'collisionless' and 'only gravitationally interacting' form of matter; the dark matter halos. These dark halos have formed at the peaks of initial density fluctuations due to gravitational instability and as observations have revealed, are the sites of most of the...
In this talk ,I will discuss about the process of induced gravity waves due to large scalar fluctuations in the paradigm of quintessential inflation. Numerically solved the Mukhanov-Sasaki equation for different sets of parameters are used to obtain the power spectra. It is been demonstrated that the induced gravity wave signal generated in this framework can falls within the region of the...
We present our Monte-Carlo simulation of galaxy properties: optical and HI. We use this simulation to study the expected number of direct detections in upcoming surveys (MIGHTEE with MeerKAT and WALLABY with ASKAP). We also study the expected detections in redshifted 21cm line emission with HI stacking. We propose that with these surveys HI stacking can be done in bins with a given range of...
We investigate the higher-order quantum gravity effect on inflationary dynamics within the framework of effective field theory. Our analysis encompasses a broad range of inflationary potentials without specific constraints on their form. We examine the tensor-to-scalar ratio and the running of the spectral indices by considering the generalized inflationary parameters with higher-order quantum...
Cosmology today, although precise, is perhaps not accurate. The so-called tensions in the standard $\Lambda$CDM model have been cited as a crisis in the field. With no clear evidence of systematical errors, nor a foolproof alternative theory as of now, the crisis is often attributed to the insufficiency of data at hand, that calls for future missions. In this presentation, I would investigate...
The fluctuations in the 21-cm radiation emitted by the neutral hydrogen(HI) in the Intergalactic medium(IGM) during different stages of the Epoch of reionization (EoR) is expected to be highly non-Gaussian. The degree of non-Gaussianity varies with the nature of the ionizing sources, state of the IGM and the underlying physical processes within the IGM. One of the crucial observable statistic...
Minimally Modified Gravity (MMG) theories are gravity theories that differ from Einstein's General Relativity (GR) but do not propagate any additional degree of freedom in the gravity sector. Such theories have given rise to a new direction to the study of modified gravity theories and their cosmological implications are being investigated enthusiastically. In my talk, I will briefly outline...
We use the PLANCK 2018 and the WMAP data to constraint inflation models driven by a scalar field $\phi$ in the presence of the non-minimal scalar-curvature mixing term $\frac{1}{2}\xi R \phi^2$. We consider four distinct scalar field potentials $\phi^p e^{-\lambda\phi},~(1 - \phi^{p})e^{-\lambda\phi},~(1-\lambda\phi)^p$ and $\frac{\alpha\phi^2}{1+\alpha\phi^2}$ to study inflation in the...
This presentation introduces a software tool for cosmologists interested in cosmic inflation. Through a user-friendly interface, users input potential functions and visualize how theoretical models of inflation align with observational datasets. Real-time symbolic differentiation calculates key parameters like the scalar spectral index ns and the tensor-to-scalar ratio r, which are...
Recently, there have been efforts to examine the contributions to the scalar power spectrum due to the loops arising from the cubic order terms in the action describing the perturbations, specifically in inflationary scenarios that permit a brief epoch of ultra slow roll (USR). A phase of USR inflation leads to significant observational consequences, such as the copious production of...
Magnetic fields are observed throughout the universe on different length scales having different strengths. Galaxies and galaxy clusters have a magnetic field strength of $\sim 10^{-9}~ G$ coherent over a 1KPc scale. We find magnetic fields at $\sim 1 MPc$ scale having a strength of $\sim10^{-16}~ G$ in the intergalactic medium (IGM). Inflationary magnetogenesis is the most profound theory of...
Dark matter haloes in a given mass range are expected to cluster differently based on secondary halo properties such as concentration or spin, a behaviour known as secondary halo bias. While secondary halo bias has been quantified in simulations, observational uncertainties in halo properties make it difficult to measure the signal in data using only two-point clustering. The $k$-Nearest...
This research paper examines the Ricci scalar R and the Gauss-Bonnet invariant G to characterize a cosmological model in flat space-time via $f(R,G)$ gravity. Our model assumes that $f(R,G)$ is an exponential function of $G$ combined with a linear combination of $R$. We scrutinize the observational limitations under a power law cosmology that relies on two parameters - $H_0$, the Hubble...
Accurate component separation of full-sky maps in the radio and microwave frequencies, such as the cosmic microwave background (CMB), relies on a thorough understanding of the statistical properties of the Galactic foreground emissions. These Galactic emissions include Galactic synchrotron, free-free, thermal dust emissions, Anomalous Microwave Emission (AME), etc. Extracting the morphological...
In this work we have discussed the origin of cosmic viscosity with the in of deformed cosmic phase space geometry. We have introduced the Non-Commutative(NC) deformed geometry and shown that the transformation from non-Riemannian geometry to Riemannian geometry (From Non-Commutative to Commutative(C) geometry) can provide the dissipation in cosmology. A single scalar field in deformed...
Recent observations have indicated that all is not well with the standard Lambda-Cold-Dark-Matter (LCDM) model of the Universe. Clues that help constrain the modifications to LCDM are hidden in the large scale structure of the Universe. The fractional density and peculiar velocity are the two main variables that are used to characterize this structure. When the perturbations are small, linear...
While fitting a non-linear model to data, it is common to consider errors only in the dependent variable and treat other variables as perfectly measured. A more flexible model fitting considering errors in independent variables is expected to better estimate the parameters of the model from the same data. We employ a Bayesian method to consider redshift errors in the Pantheon sample of Type-Ia...
Abstract: Production of gravitationally coupled light moduli fields must be suppressed in the early universe, so that its decay products do not alter Big Bang Nucleosynthesis (BBN) predictions for light elements. On the other hand, the moduli quanta can be copiously produced non-thermally during preheating after the end of inflation. In this work, we study the production of moduli in the...
In Loop Quantum Cosmology (LQC), a quantum bounce precedes inflationary epoch. The presence of a quantum bounce leads to a departure from scale invariance of the spectra of primordial perturbations. Studies conducted mostly at the level of the primordial power spectrum show that this departure from scale invariance is a remnant of the bounce and is largely independent of the form of the...
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...
In this study, The power-law solution for an isotropic and homogeneous universe under $f(R, T)$ gravity is examined by taking into account its functional form, $f (R, T) = R + \xi RT$, where $\xi$ is a positive constant. We have constructed the field equation in f(R, T) gravity for homogeneous and isotropic space-time. The solution of the constructed model is given by the $a = \alpha...
The Cosmic Microwave Background continues to be a cornerstone of precision cosmology. It has provided the most accurate parameter constraints for the widely used $\Lambda$ cosmological constant and Cold Dark Matter ($\Lambda$CDM) model, via missions like COBE, WMAP, and Planck. In precision regimes, accounting for the weak lensing of the CMB photons by the large structure gravitational...
Primordial black holes, which could have formed during the early Universe through overdensities in primordial density fluctuations during inflation, are potential candidates for dark matter. We explore the use of lensing parallax of Gamma ray bursts, which results in different fluxes being observed from two different vantage points, in order to probe the abundance of primordial black holes in...
We compare the dark matter(DM) production processes and its parameters space in the background of reheating obtained from two chief systems in the early Universe: the inflaton $\phi$ and the primordial black holes (PBHs). We concentrated on the mechanism where DMs are universally produced only from the PBH decay and the generation of the standard model plasma from both inflton and PBHs....
Analysis of Planck data has revealed to us the presence of several anomalies in the Cosmic Microwave Background (CMB). Many investigations have revealed to us the interconnection between several such anomalies. In this talk, we highlight the primordial connection of some of these anomalies. In particular, we analyse certain templates of the primordial power spectrum and explain how features in...
Observations of the neutral hydrogen (HI) 21-cm signal have the potential to map out the large-scale structures (LSS) of our Universe during the post-reionization era (z ≲ 6). Several present and future experiments are planned to give their efforts to probe the signatures of the LSS inherent in the expected signal over a large redshift range. A correct prediction of the expected signal demands...
The high-redshift observations of galaxies with instruments like the JWST can be complemented with the upcoming SKA, which will map the early IGM via intensity mapping of the redshifted 21cm signal with improved sensitivity over the current generation of radio interferometers. These star-forming galaxies are expected to emit most of the bulk of ionizing photons during the Epoch of Reionization...
I shall discuss the prospects of machine learning algorithms, namely Gaussian processes and neural networks, to reconstruct the evolutionary history of the Universe with present available observational data independent of any cosmological model. Through this reconstruction, one can constrain different cosmological parameters, which can serve as a promising tool in addressing the rising...
Kofman, Linde and Starobinsky had showed that preheating can occur due to a huge amount of particle creation by parametric resonance after the inflationary era of the Universe. In the $\phi^2$ model, they confirmed the existence of narrow and broad resonances as well as stochastic resonance in the presence of an expanding background, by means of exact numerical computation of the corresponding...
We have proposed a new phase space coordinate system for scalar field theory that can provide a detailed analysis of the cosmological evolutionary phases in a more generalized manner. We have studied \textcolor{red}{(how many)} intermediate states of cosmic inflations. We have discussed fixed point analysis for these phases. The new phase space dynamics discussed here provide a new family of...
We have examined data from 852 Coma cluster galaxies from three different catalogs and grouped them according to their velocity and magnitude in two fields to survey the core (Coma1) and the periphery (i.e. southwest of the core and centered on NGC4839; Coma3). We have identified a group of these galaxies that appear to be a dense cluster (main cluster) of 545 galaxies (430 in Coma1 and 115 in...
A plethora of knowledge about the universe’s chronology may be found in the spectral properties of the CMB energy spectrum. The spectral aberrations of the CMB complement all other cosmological investigations. According to the astonishing measurement of the CMB spectrum by COBE/FIRAS, the CMB spectrum resembles a blackbody with a temperature of TCMB = 2.72548 ± 0.00057 K. This paper aims to...
If the dark matter is a Dirac fermion($\chi$) and it has an electric and magnetic dipole moment, it can couple with the Standard Model photon through a dimension five effective operators, suppressed by a New Physics(NP) scale $\Lambda$. We probe the parameter space in terms of Dark Matter mass ($m_\chi$) and the New Physics scale $\Lambda$ via a mono-photon signal at the upcoming...
The cold dark matter (CDM) paradigm provides a remarkably good description of the Universe’s large-scale structure. However, some discrepancies exist between its predictions and observations at very small sub-galactic scales. To address these issues, the consideration of a strong interaction between dark matter particles and dark radiation emerges as an intriguing alternative. In this talk, we...
Recently Ultra Light Dark Matter (ULDM), where DM is described by a scalar field with $m\sim 10^{-22}\ \text{eV}$ has emerged as a promising alternative to the standard Cold Dark Matter (CDM) model. However, viability of models with no self-interactions (also called Fuzzy Dark Matter), is under question as relevant masses are increasingly constrained using various astrophysical and...
There are several observed Gamma Ray flares which are of short duration which cannot be explained by the conventional models of black holes, active galactic nuclei and neutron stars. Some of these also correspond to high redshift values. The nature of the bursts indicate an extremely compact emission region typically associated with magnetic reconnections. We conjecture that these magnetic...
Under the assumption of thermal equilibrium between the horizon and the fluid inside, we conducted a thermodynamic stability analysis on a model designed to mimic the characteristics of the $\Lambda$CDM model, which is the prevailing framework for portraying the cosmic acceleration. The scale factor for this model is defined as $a\sim \sinh^{2/3}(t/t_0)$. The Hayward-Kodama temperature is...
In this work, we present singular bounce scenario
in the framework of the generalised Brans-Dicke (GBD)theory where an evolving BD parameter along with a self-interacting potential is considered. The GBD field equations are derived for an anisotropic space time to provide a more general approach to the cosmic expansion. The evolutionary behaviour of the Brans-Dicke scalar field, dynamical...
The phenomena of Squeezing and chaos have recently been studied in the context of inflation. We apply this formalism in the post-inflationary preheating phase. During this phase, inflaton field undergoes quasi-periodic oscillation, which acts as a driving force for the resonant growth of quantum fluctuation or particle production. Furthermore, the quantum state of the fluctuations is known to...
In this paper, we discuss a general method to obtain exact cosmological solutions in modified gravity, to demonstrate the method it is employed to obtain exact cosmological solutions in f(R,phi) gravity. Here, we show that, given a particular evolution of the Universe, we could obtain different models of gravity that give that evolution, using the same construction. Further, we obtain an exact...
Observations of the cosmic microwave background (CMB) anisotropies have played a key role in developing modern cosmology. Detailed and accurate measurements of the CMB anisotropies tell us a lot about the global properties, the constituents, and the history of the universe. Standard cosmological model assumes Statistical Isotropy and Gaussianity of the CMB anisotropy in FRW cosmology. There...
Some observational deviations from the standard cosmological principles of isotropy and homogeneity lead to create more interest among the researchers on studying anisotropic characteristics of the Universe in recent times. In this context the locally rotationally symmetric Bianchi type I (LRS-BI) metric is appeared to be suitable and simplest candidate for studying anisotropic nature of the...
In this project we focus on testing statistical isotropy and Gaussianity of CMB lensing convergence maps using recently released data of the cosmic microwave background (CMB) radiation from the Atacama Cosmology Telescope
(ACT). The CMB photons are lensed by gravitational potential wells of the
large-scale matter distribution. This CMB temperature data is converted to convergence map by...
Masses of supermassive black holes (SMBH) are known to correlate with the spheroidal component of their host galaxies according to the so-called M-sigma (Magorrian) relation. A further proposal of a correlation between the SMBH mass and halo mass is a focus of research. In this talk, we propose a mechanism for the co-evolution of black holes and their host dark matter haloes based on the...
The Cold Dark Matter (CDM) hypothesis accurately predicts structure formation on cosmological scales and fits the temperature fluctuations of the Cosmic microwave background (CMB) and large-scale structure. However, observations that probe the innermost regions of dark matter halos and the properties of dwarf galaxy satellites have persistently challenged CDM. In contrast, the Modified...
The dominance of dark energy in the universe has necessitated ways to introduce a repulsive gravity source to make $q$ negative. The models for the dark energy range from $\Lambda$-CDM, K-essence, Chaplygin gas, etc. We look at the possibility where the interaction parameter $\Gamma$ plays a vital role in various cosmological models, particularly those involving interactions between dark...
The talk will present a summery of the main results within the Scale Invariant Vacuum (SIV) paradigm as related to the Weyl Integrable Geometry (WIG) as an extension to the standard Einstein General Relativity (EGR). After a short sketch of the mathematical framework, the main results until 2023 [1] will be highlighted in relation to: the inflation within the SIV [2], the growth of the density...
We study the possibility of detecting dark radiation (DR) produced by a combination of interactions with the thermal bath and ultra-light primordial black hole (PBH) evaporation in the early universe. We show that the detection prospects via cosmic microwave background (CMB) measurements of the effective relativistic degrees of freedom ${\rm \Delta N_{eff}}$ get enhanced in some part of the...
Bumblebee gravity theory is a class of vector-tensor theory of gravity with growing interest in literature. We explore a Schwarzschild-type metric corrected by Generalized Uncertainty Principle (GUP) and possessing topological defects within the framework of Bumblebee Gravity. We investigate the thermodynamic quantities associated with the black hole metric, like temperature, entropy and heat...
The Hubble tension refers to the discrepancy in the value of the Hubble constant $H_0$ inferred from the cosmic microwave background observations, assuming the $\Lambda$CDM model of the universe, and that from the distance ladder and other direct measurements. In order to alleviate this tension, we construct a plausible dark energy scenario, within the framework of Horndeski gravity which is...
We study ultra-light Primordial Black hole (PBH) formation from first-order phase transition (FOPT) by considering bubble collisions and false vacuum collapse as the leading mechanisms. While FOPT leads to the generation of gravitational wave (GW) spectrum with typical blue and red-tilted spectrum around a peak frequency, the ultra-light PBH, if dominates the universe for a finite epoch, can...
Ultra-low mass primordial black holes (PBHs), which evaporate far before Big Bang Nucleosynthesis (BBN), are unconstrained to dominate the energy density of our universe for a short duration. We analyze the stochastic gravitational wave background (SGWB) signals from the domination of ultra-low mass PBHs to explain this recent discovery of SGWB from Pulsar Timing Array collaborations at...
Big Bang Nucleosynthesis (BBN) is a strong probe for testing new physics of the early universe. Introducing modified gravity in the very early universe gives rise to some interesting effects. In this work, the effects of $f(R)$ gravity scalarons introduced in Kalita (2018, 2020, 2021) on the BBN era is investigated. Observed BBN constraints on the shift of freezeout temperature and elemental...
