ICGC 2019

				Talks Selected for Workshop -2



Title	First name		Last name	Affiliation	Abstract
Prof.	CS		Unnikrishnan	Tata Institute of Fundamental Research	Title: Modified General Relativity Anchored on Cosmological Basis and the Centenary Einstein Equations Abstract : A century of experimental tests and observations have reinforced the status of the general theory of relativity as the correct theory of gravity, applicable in all scales where it has been tested already. The recent observations of the gravitational waves from astrophysical sources have extended this confidence into its radiation sector as well. The speculation on anomalies at very large and very small scales are have not gone far. However, the vast sector of cosmological observations and discoveries were not anticipated when the theory was formulated. I will point out and then prove that there is a significant modification to the original Einstein equations that drastically alters the theory, while being fully consistent with all the precision tests and observations hitherto. This surprising result is well motivated by arguments of internal consistency and cosmological observations. I will show that the resulting 'centenary Einstein equations' are fully consistent with both the mathematical requirements and agreement with observational results, but provides an entirely new framework. The modified theory has larger scope in dynamics and hence, complete. One of the key predictions involve the maximal violation of the Einstein Equivalence Principle in the untested context of clocks in an accelerated frame. References: 1. C. S. Unnikrishnan, Modified General Relativity and the Centenary Einstein Equations, GR22 Conference, Valencia (2019).

Dr.	Nikhel		Gupta	School of Physics, University of Melbourne	Title: Fractional Polarisation of Extragalactic Sources in the 500-square-degree SPTpol Survey \n--------\nAbstract: We study the polarisation properties of extragalactic sources at 95 and 150,GHz in the SPTpol 500,deg$^2$ survey. We estimate the polarised power by stacking maps at known source positions, and correct for noise bias by subtracting the mean polarised power at random positions in the maps. We show that the method is unbiased using a set of simulated maps with similar noise properties to the real SPTpol maps. We find a flux-weighted mean-squared polarisation fraction $langle p^2 rangle= [8.9pm1.1] times 10^{-4}$ at 95,GHz and $[6.9pm1.1] times 10^{-4}$ at 150~GHz for the full sample. This is consistent with the values obtained for a sub-sample of active galactic nuclei. For dusty sources, we find 95,per cent upper limits of $langle p^2 rangle_{rm 95}<16.9 times 10^{-3}$ and $langle p^2 rangle_{rm 150}<2.6 times 10^{-3}$. We find no evidence that the polarisation fraction depends on the source flux or observing frequency. The 1-$sigma$ upper limit on measured mean squared polarisation fraction at 150,GHz implies that extragalactic foregrounds will be subdominant to the CMB E and B mode polarisation power spectra out to at least $elllesssim5700$ ($elllesssim4700$) and $elllesssim5300$ ($elllesssim3600$), respectively at 95 (150),GHz.

Mr.	Fazlu		Rahman	Indian Institute of Astrophysics, Bangalore	Gaussianity and Statistical Isotropy of Galactic Foreground Emissions\n\nThe PLANCK satellite has provided very high-resolution full-sky maps of emissions in the range 30 to 857 GHz. These raw maps consist of the CMB, Galactic foreground emissions from our galaxy, extragalactic point sources, etc. In the era of precision cosmology, accurate component separation is very crucial for construing the physics in the cosmic epochs. Any residual contamination in the â€˜cleanedâ€™ CMB data results in misinterpreting the cosmological parameters and hence, the history of the universe. Precise component separation relies on the thorough understanding of the Galactic foregrounds. Using Minkowski tensors, we analyze the statistical properties of the two major components, Galactic synchrotron and thermal dust using the renewed Haslam map and Planck PR 2018. We focus on the properties â€“ non-Gaussianity and statistics related to the alignment of structures â€“ of these two emissions, which are crucial mainly for the detection of primordial non-Gaussianity, polarization B-modes, etc. in the upcoming CMB missions. Further, these studies are interesting in their own right as they can decipher their distributions in the Galaxy and the physical properties of the matter causing these emissions

Mr.	Atrideb		Chatterjee	National Centre for Radio Astrophysics	Weakly interacting cold dark matter (CDM) particles, which are otherwise extremely successful in explaining various cosmological observations, exhibit a number of problems on small scales. One possible way of solving these problems is to invoke (so-called) warm dark matter (WDM) particles with masses m x âˆ¼ keV. Since the\nformation of structure is delayed in such WDM models, it is natural to expect that they can be constrained using observations related to the first stars, e.g., the 21 cm signal from cosmic dawn. In this work, we use a detailed galaxy formation model, Delphi, to calculate the 21 cm signal at high-redshifts and compare this to the recent\nEDGES observations. We find that while CDM and 5 keV WDM models can obtain a 21 cm signal within the observed redshift range, reproducing the amplitude of the\nobservations require the introduction of an excess radio background. On the other hand, WDM models with m x âˆ¼\n3 keV can be ruled out since they are unable to match\neither the redshift range or the amplitude of the EDGES signal, irrespective of the parameters used. If time permits we will also discuss how primordial magnetic field can be constrained using the EDGES observation.

Dr.	ANKAN		MUKHERJEE	Centre for Theoretical Physics, Jamia Millia Islamia.	Constraining the dark energy statefinder hierarchy in a kinematic approach:\n\nIn the present work, we have adopted a kinematic approach for constraining the extended null diagnostic of concordance cosmology, known as the statefinder hierarchy. A Taylor series expansion of the Hubble parameter has been utilised for the reconstruction. The coefficients of the Taylor series expansion are related to the kinematical parameters like the deceleration parameter, cosmological jerk parameter etc. The present values of the kinematical parameters are constrained from the estimated values of those series coefficients. A Markov chain Monte Carlo analysis has been carried out using the observational measurements of Hubble parameter at different redshifts, the distance modulus data of type Ia supernovae and baryon acoustic oscillation data to estimate the coefficient of series expansion of the Hubble parameter. The parameters in the statefinder diagnostic are related to the kinematical parameters. The statefinder diagnostic can form sets of hierarchy according to the order of the kinematical parameters. The present values of statefinder parameters have been constrained. The first set in the statefinder hierarchy allows LCDM to be well within the 1-Ïƒ confidence region, whereas the second set is in disagreement with the corresponding LCDM values at more than 1-Ïƒ level. Another dark energy diagnostic, namely the Om-parameters, is found to be consistent with concordance cosmology.\n\n(Ref. A. Mukherjee, N. Paul and H. K. Jassal, JCAP01(2019)005.)

Dr.	Raghavan		Rangarajan	Ahmedabad University	Models of spontaneous baryogenesis have an interaction term $partial_mutheta j^mu_B$ in the Lagrangian, where $j^mu_B$ is the baryonic current and $theta$ can be a pseudo-Nambu-Goldstone boson. Since the time component of this term, $dottheta j^0_B$, equals $dottheta n_B$ for a spatially homogeneous current, it is usually argued that this term implies a splitting in the energy of baryons and antibaryons thereby providing an effective chemical potential for baryon number. In thermal equilibrium, one then obtains $n_B sim dottheta T^2$. We however argue that a term of this form in the Lagrangian does not contribute to the single particle energies of baryons and antibaryons. We show this for both fermionic and scalar baryons. But, similar to some recent work, we find that despite the above result the baryon number density obtained from a Boltzmann equation analysis can be proportional to $dottheta T^2$. Our arguments are very different from that in the standard literature on spontaneous baryogenesis.

Mr.	Ranbir		Sharma	PhD in Physics, IISER Mohali	In this work we employ the technique of Principal Component Analysis (PCA) for the reconstruction of different late-time cosmological parameter. We emphasize on the reconstruction of dark energy equation of state parameter from the observational data-sets. Two different approaches are adopted in the present work to reconstruct the equation of state parameter. First one is derived-approach where we reconstruct the observable quantities of the data sets, namely the Hubble parameter and the supernova distance modulus from the observation then subsequently reconstruct the allowed equation\nof state parameter. In the direct-approach we reconstruct the dark energy equation of state parameter directly from the data sets without any intermediate reconstruction.\nWe show that a combination of PCA algorithm and calculation\nof correlation coefficients can be used as a reconstruction tool. The derived-approach is found to be statistically preferred over the direct-approach. We carried out the analysis with both simulated and real data sets of Hubble parameter measurements and distance modulus measurements of type Ia supernova. The reconstructed equation of state indicates towards a\ntime evolving nature of dark energy.

Ms.	Akanksha		Kapahtia	Indian Institute of Astrophysics and IISc Bengaluru	Morphology of the 21cm brightness temperature during EoR using Contour Minkowski Tensor We use real space morphological descriptors called Betti numbers and Contour Minkowski Tensor (CMT) on 21cm brightness temperature excursion sets, to study the ionization and heating history of the intergalactic medium (IGM) . The ratio of the eigenvalues of the CMT denoted by ��, gives shape information while it's trace gives the contour length of holes and connected regions. We use the publicly available code 21cmFAST to generate the matter density, neutral hydrogen fraction, spin temperature and brightness temperature field in a redshift range of ��=20.22 to ��=6. We study the redshift evolution of three quantities --- the Betti number counts ��_(��,ℎ��), the characteristic size ��_ch and the shape anisotropy parameter ��_ch. We obtain different regimes of morphological evolution of brightness temperature corresponding to the various stages of the ionization and heating history of the IGM (Kapahtia et al. arXiv:1904.06840). Therefore, we show that the CMT can be used as a complimentary statistic to the power spectrum to obtain constraints on different models of EoR. We also show how the trace of CMT can be used as a tool to obtain a characteristic bubble size during the EoR (Kapahtia et al. JCAP,10,011 (2018)).

Mr.	Abinash	Kumar	Shaw	Indian Institute of Technology Kharagpur	The Epoch of Reionization (EoR) is the unexplored piece of cosmic history of the universe. A plentiful of constant effort is continuing to observe EoR and its underlying physics, with the help of radio-interferometers, using 21-cm hyperfine transition in neutral hydrogen as a probe. Measuring the power spectra (PS) of EoR 21-cm signal is primary goal of the ongoing and future EoR experiments. The 21-cm PS measurements will lead to the direct insight of the processes and sources responsible for reionization. An accurate estimation of the PS and its errors are required for precisely constraining the reionization parameters. Previous works have commonly assumed the EoR 21-cm signal as a Gaussian random field and estimated the errors in the power spectrum and further constrained the parameters. However recent simulation shows the EoR 21-cm signal is inherently highly non-Gaussian in nature and the error estimates of the PS contains additional from the trispectrum. Non-Gaussianity also makes the errors in the different Fourier modes correlated. We have studied the impact of non-Gaussianity on the error estimates of the EoR 21-cm PS considering an observation using upcoming SKA-Low. We have incorporated the effects of antenna baseline distribution, primary beam effects, system temperature to the error estimates. We have also included the effects of foregrounds considering three scenarios.\nWe find that the non-Gaussianity is really important in a range k=0.1-1 Mpc^{-1} during later stages (z~8) of reionization and also for large observing hours. The SKA-Low detection have more sensitivity in this k range and the deviations in the error variance from Gaussian predictions (>50%) at z~8. Trispectra also introduce significant correlations (-0.4< r <0.8) between errors at different k modes. We conclude that the non-Gaussianity is really important in observing the EoR PS from its later stages, however the Gaussianity is still a valid assumption the previous stages at least for highly sensitive observations.

Mr.	Sarvesh	Kumar	Yadav	Indian Institute of Science Education and Research Bhopal	We used a new statistics to test the hypothesis that temperature field of the cosmic microwave background is consistent with a statistically homogeneous and isotropic\nGaussian random field defined on celestial sphere by testing uniformity of phases of Planckâ€™s COMMANDER map. It is non-parametric, based on theory of ordered statistics, and known as Rao Spacing statistics. We have performed the test on individual modes upto l = 128.To find the anamolous sets of phases, we used 10000 simulated random phases and used 0.05 and 0.95 significance as our cut-off for lower and upper levels respectively. We find that phases corresponding to most of the modes are uniform with some exceptions. We suspect that non-uniform modes may be primordial or non-primordial or some type of sysytematic effect.

Ms.	Archita		Bhattacharyya	Indian Statistical Institute, Kolkata	Dark Energy not only has background effects through its equation of state $w$, but also it can cluster through its sound speed $c_s$, subject to certain conditions. As is well-known, for dynamical models, dark energy perturbations get sourced into matter perturbations through metric perturbations which is always accompanied by the term $(1+w_{DE})$. Hence, for dynamical dark energy models with $w_{DE}$ close $-1$, their perturbations get almost decoupled from metric leaving nearly null imprints on matter power spectra. Furthermore, Quintessence models with its sound speed equal to speed of light, washes out almost any inhomogeneities occurred within sub-Hubble scales, hence making detectability of dark energy perturbations far more difficult than already is. We look for these imprints by going beyond Quintessence considering an Early Dark Energy parametrization that not only have a non-negligible energy density at early times, but also it can achieve $w_{DE}$ far from $-1$, making dark energy perturbations detectable in sub-horizon scales. We have shown that with the help of current datasets, it is possible to constrain sound speed of dark energy to a low value ($c^2_{s,DE} sim 0.14$), along with a much higher range allowed for early dark energy density, with strong constraints on it ($Omega_e sim 0.02$). We discuss effects of different datasets on this parametrization along with possible explanation for deviation on certain parameter(s) comparing between $csde=1$ case and the case where it is kept open.

Mr.	Shabbir		Shaikh	IUCAA, Pune	Title: Joint Bayesian analysis of large angular scale CMB temperature anomalies (arXiv:1902.10155, JCAP08(2019)007)\nAbstract: Cosmic microwave background measurements show an agreement with the concordance cosmology model. However, there are a few notable anomalies: Power Suppression, the lack of large scale power in the temperature data compared to what is expected in the concordance model, and Cosmic Hemispherical Asymmetry, a dipolar breakdown of statistical isotropy. An expansion of the CMB covariance matrix in Bipolar Spherical Harmonics naturally parametrizes both these large-scale anomalies. This allows an exhaustive, fully Bayesian joint analysis of the angular power spectrum and violations of statistical isotropy. In this work, we shed light on the scale dependence of the Cosmic Hemispherical Asymmetry. We assume a scale-dependent dipole modulation model with a two-parameter power-law form for the dipole amplitude. We sample the posterior probability distribution of the amplitude and the direction of the dipole and the power-law index jointly with the angular power spectrum using the Hamiltonian Monte Carlo method. We also evaluate the Bayes factor to compare the Cosmic Hemispherical Asymmetry model with the isotropic model. We find that the data prefer but do not substantially favor the anisotropic model. The large-scale power suppression does not soften when jointly inferring both the isotropic power spectrum and the parameters of the anisotropic model, indicating no evidence that these anomalies are coupled.

Ms.	Ruchika		Kaushik	PhD scholar	We do a comprehensive study of the Bayesian evidences for a large number of dark energy models\nusing a combination of latest cosmological data from SNIa, CMB, BAO, Strong lensing time delay,\nGrowth measurements, measurements of Hubble parameter at different redshifts and measurements\nof angular diameter distance by Megamaser Cosmology Project . We consider a variety of scalar field\nmodels with different potentials as well as different parametrisations for the dark energy equation of\nstate. Among 21 models that we consider in our study, we do not find strong evidences in favour of\nany evolving dark energy model compared to Î›CDM. For the evolving dark energy models, we show\nthat purely non-phantom models have much better evidences compared to those models that allow\nboth phantom and non-phantom behaviours. Canonical scalar field with exponential and tachyon\nfield with square potential have highest evidences among all the models considered in this work.\nWe also show that a combination of low redshift measurements decisively favours an accelerating\nÎ›CDM model compared to a non-accelerating power law model.

Mr.	SAUGATA		BARAT	Student	Title: Modeling Gravitational Wave Sources at High Redshifts: The X-ray Counterpart\n\nAuthor: Saugata Barat, Kaustav Mitra, Sagnick Mukherjee, Dr. Suchetana Chatterjee\n\n\nAbstract:\n\nX-Ray source population studies have been carried out for nearby sources where individual point sources can be resolved and X-Ray Luminosity Functions(XLF) have been constructed (eg. Grimm et. al 2003). Such studies are extremely hard to do for high redshift galaxies as the point sources cannot be resolved. We have used a sample of normal galaxies from the All Wavelength Groth Strip Survey (AEGIS) and divided the sample into redshift bins and then perform a stacking analysis of the X-ray images taken from Chandra. We fit the observed counts as a linear combination of two power laws corresponding to LMXBs and HMXBs to obtain the fractional contribution of LMXBs to the total observed counts. From this information we can contruct a luminosity function for XRBs at high redshifts. XRB populations can be particularly interesting for the Gravitational Wave community as these sources evolve into potential gravitational wave sources. Information about the luminosity functions can be useful in obtaining a constraint on the number of such merger events.

Ms.	Srijita		Sinha	Indian Institute of Science Education and Research Kolkata	Title: Density perturbation in an interacting holographic dark energy model\n\nAbstract:\nThis work deals with the evolution of the density contrasts for a cosmological model where along with the standard cold dark matter (CDM), the present Universe also contains holographic dark energy (HDE). The characteristic infra-red (IR) cut-off is taken as the future event horizon. The HDE is allowed to interact with the CDM. The equations for the density contrasts are integrated numerically. It is found that irrespective of the presence of an interaction, the matter perturbation has growing modes. The HDE is also found to have growth of perturbation, so very much like the CDM, thus can also cluster. The interesting point to note is that the density contrast corresponding to HDE has a peak at recent past and is decaying at the present epoch. Another feature is that IR cut-off as the event horizon does not naturally produce accelerated expansion of the Universe in the presence of an interaction.

Mr.	Chetan		Bavdhankar	NCBJ, Warsaw, Poland	The peculiar velocity of galaxies is one of the very important probes of the cosmological model (Strauss and Willick (1995)). Since peculiar velocities are induced only by gravity, they can be used to obtain various cosmological parameters such as mean matter density or the growth of structure (Nusser and Davis (2011)). The large-scale fluctuations of the matter distribution can be determined using bulk flows where a given volume of the sample shows the net peculiar motion of galaxies.\n\nSupernova type Ia (SNeIa) is the best available indicator of peculiar velocity with an average ~5% distance errors. We merge all spectroscopic confirmed SNeIa and gather a rich catalogue of peculiar velocities. We then study host galaxies of SNeIa and use their possible environment to gather ~65,500 mock galaxies from Millenium XXL simulation. We then perform statistical analysis on this mock catalogue to test our dipole estimator and later we plan to apply it on our original peculiar velocity sample and using analysis on mocks we plan to explain the significance of our results. With the peculiar velocities of SNeIa host galaxies, we expect to observe a dipole pattern where direction and magnitude of the dipole point towards the resultant motion of the Local Group of galaxies in the Universe.

Prof.	L		Sriramkumar	Indian Institute of Technology Madras, Chennai	Title: Can bouncing scenarios generate primordial features?\n\nAbstract: Inflation and bouncing scenarios constitute alternative paradigms for the generation of the primordial perturbations. It has been repeatedly noticed that certain features in the primordial scalar power spectrum improve the fit to the cosmological data. In the context of inflation, the fact that the trajectory is an attractor permits the generation of such features. However, the bouncing models often require fine tuned initial conditions and such scenarios will be ruled out if future observations confirm the presence of features in the primordial spectrum. Amongst the bouncing scenarios, it is only the ekpyrotic models that allow attractors. In this work, we demonstrate, for the first time, that ekpyrotic scenarios can generate specific features that have been considered in the context of inflation.

Mr.	Ragavendra		H.V.	Indian Institute of Technology Madras	Title: Imprints of the onset of inflation on the scalar bispectrum. \n\nAbstract: \nWe study methods of achieving the much desired suppression of scalar power over large scales of the observable CMB sky and attempt at differentiating among various such models based on their imprints on the scalar bispectrum. One easy-to-achieve method for power suppression is having a finite duration of inflation that invariably has a maximum scale above which modes are never inside the Hubble radius during inflation. This suppresses the power of those set of modes which have their initial conditions imposed in the super-Hubble regime. Interestingly, in this case, the contributions from boundary terms of the third order action outweigh the bulk contributions to the bispectrum over the scales that correspond to deviation from scale invariance. This makes the shape of the bispectrum unique for this model of inflation with finite duration and essentially the same across different potentials that may drive the background. We also consider other models that achieve power suppression, like punctuated inflation and Starobinsky model, and infer that, despite their similarity at the level of power spectra, they can be easily distinguished by their bispectra in more than one way. In the latter models, the consistency condition governing bispectrum in the squeezed limit is always obeyed while it is violated in the case of finite duration inflation. Also, the bispectra arising in the latter models have contributions only due to the bulk terms of the action and have no model independent shape. This makes the study of non-Gaussianities in CMB all the more interesting in that we may not just rule out models, but also potentially infer about the temporal boundary of the inflationary epoch and determine if the observed large scale suppression is indeed a signature of physics at the beginning of inflation.

Dr.	Sharvari		Nadkarni-Ghosh	IIT Kanpur	Many current and future observational efforts aim to map the matter distribution on the sky on very large scales. To analyse this vast data and constrain models we need not only accurate estimates, which can be provided by numerical simulations, but also theoretical insight into these results. While perturbation theory provides analytic answers, its expressions are cumbersome and its range of validity is limited. On the other hand, local collapse models, such as spherical and ellipsoidal collapse are simpler and have been widely used as a proxy for the non-linear regime. One main reason for this is because these models provide analytic solutions for pure matter cosmologies. However, the models can be generalised to other non-standard cosmologies. In this talk, we will consider some recent applications of this approach particularly in the context of early dark energy and modified gravity. In particular, one can obtain the one-point probability distribution function (PDF) of the non-linear matter density field and we find that it agrees with recent fits provided by numerical simulations. By applying ideas from dynamical systems theory to these local models, it is also possible to find `invariant relationsâ€™ between the perturbation variables. One such example is the non-linear extension of the density-velocity divergence relation (non-linear DVDR). We will demonstrate how it is possible to exploit these invariant relations to remove parameter degeneracies. \n\n\n\nReferences: \n\n1. S. Nadkarni-Ghosh, MNRAS 428 (2013) \n\n2. S. Nadkarni-Ghosh and A. Singhal, MNRAS 457 (2016)\n\n3. A. Mandal and S. Nadkarni-Ghosh, in preparation. \n\n4. S. Choudhury, T. Sarkar and S. Nadkarni-Ghosh, in preparation.

Mr.	Arnab		Chakraborty	Department of Astrophysics, Astronomy and Space Engineering, IIT - Indore	Understanding the low-frequency radio sky in depth is necessary to subtract foregrounds in order to detect the redshifted 21 cm signal of neutral hydrogen from the Cosmic Dawn, Epoch of Reionization (EoR) and post-reionization era. Here, we present the upgraded Giant Meterwave Radio Telescope (uGMRT) observation of the ELAIS N1 field made at 300-500 MHz. We present the angular power spectrum (APS) of foregrounds (Galactic and extragalactic) present in this field. We show the effects of direction-dependent and direction-independent calibration in the estimation of APS of diffuse galactic synchrotron radiation (DGSE). We have found that the effects of direction-dependent calibration can be ignored with higher tapering of the field of view in comparison with direction-independent calibration. For the first time, we estimated the spectral characteristics of the APS or Multi-Frequency Angular Power Spectrum (MFAPS) of diffuse Galactic synchrotron emission (DGSE) over the wide frequency bandwidth of 200 MHz from radio interferometric observations. We found that the spectral index of APS of DGSE is consistent with previous all-sky measurements by a single dipole antenna. We present a radio source catalog containing 2528 sources and normalized source counts derived from that. The normalized source counts are in agreement with previous observations of the same field, as well as model source counts from the Square Kilometre Array Design Study (SKADS) simulation. It shows a flattening below 1 mJy which corresponds to the rise in population of star forming galaxies and radio-quiet AGN. We also present the angular and spatial clustering of sources using this radio catalog of ELAIS N1 field. This work demonstrates the improved capabilities of the uGMRT.

Dr.	Daniele		Sorini	Institute for Astronomy, University of Edinburgh	The 10^120 discrepancy between the predicted and observed values of the cosmological constant (Lambda) is one of the major outstanding questions in cosmology. The small but non-zero value of Lambda poses coincidence problems within the LCDM framework, such as the matter-Lambda equality occurring roughly at present time. Lombriser & Smer-Barreto (2017) pointed out an even more statistically significant coincidence between the reionization epoch and radiation-Lambda equality. We explore this issue further from a multiverse perspective, by developing an analytic model consistently describing reionization and star formation history in different universes within a wide range of values for the cosmological constant. We investigate whether the radiation-Lambda equality coincides with reionization in all universes, or whether this happens only within a narrow range of Lambda around the value observed in our Universe. We also determine whether the combined information of reionization and star formation history in our model can improve anthropic arguments to explain the observed value of Lambda.

Dr.	Sayantani		Bera	Inter-University Centre for Astronomy and Astrophysics	Title : Constraining the Hubble parameter with galaxy-binary black hole cross-correlation measurements\n\nAbstract : The Hubble parameter is significantly important in understanding the evolution history of the universe. Thus, measuring the Hubble parameter with improved precision has been an important goal in physics. However there seems to be significant discrepancy between the locally measured value of Hubble parameter using supernovae observations and high redshift measurements using CMB (Cosmic\nMicrowave Background) observations. In this work, we aim to constrain the Hubble parameter using a third way, namely the binary black hole mergers as revealed by LIGO-VIRGO observations. It has been proposed that the distance-redshift relation can be constrained using gravitational wave observations from binary black hole mergers. The distance to the mergers is constrained from LIGO data, while we work on constraining the true redshifts of the mergers using information from the large scale structure. Since all galaxies and binary black holes are part of the underlying large scale structure, the objects at same redshifts will exhibit a strong correlation, while objects at different redshifts will be uncorrelated. We use this to calibrate the redshift distribution of binary black holes by calculating the cross-correlation between galaxies with known redshifts and black holes with unknown redshifts. This technique can be used to measure the redshifts for all the sources for which the electro-magnetic spectrum study is not possible, giving a constraint on the Hubble parameter.

Dr.	V		Sreenath	Inter-University Centre for Astronomy and Astrophysics	Title : Loop quantum cosmology in a Bianchi I spacetime\n\nAbstract: Loop quantum cosmology provides an extension of inflationary paradigm to the Planck era, wherein, the big bang singularity is replaced by a quantum bounce. As the universe contracts before the bounce, any anisotropy present in the early universe will grow and the universe will become highly anisotropic at the bounce. Nevertheless, as the universe expands and then undergoes inflation after the bounce, it is expected that any anisotropy generated during the contracting phase will be diluted by the end of inflation. Even though the background spacetime will become eventually isotropic, there is a possibility that anisotropy at the bounce could leave its imprints on the primordial perturbations. In this talk I would like to discuss the evolution of perturbations through a quantum bounce in a Bianchi I spacetime and talk about our efforts in constraining anisotropy at the bounce in the light of data from cosmic microwave background.

Mr.	Tony		Pinhero	Indian Statistical Institute, Kolkata	We propose a new broad class of multi-field non-canonical inflationary models as an extension of multi-field conformal cosmological attractors. This also generalizes the recently discovered class of non-canonical conformal attractors for single field inflation. Kinetic terms of this class of models are phenomenologically arising from N=1 supergravity and from N=1 superconformal theory, with two conformal scalar compensator fields in the latter. We show that the inflationary dynamics and predictions of this class of models are stable with respect to the significant modification of both radial and angular part of the potential, but it is very sensitive to its minuscule modification in the geometry of the field space metric. We also show that our framework can pass the latest observational constraints set by Planck 2018.

Dr.	Pankaj		Saha	Post Doctoral Fellow	Understanding the properties of dark matter has been proved to be one of the most challenging problems of particle phenomenology. In this work, we tried to understand the phenomenology of dark matter in light of very well understood properties of Cosmic Microwave Background (CMB) anisotropy. To connect these two, inflation and its subsequent evolution, known as the reheating phase play an important role. Following previous analysis, we first established one to one correspondence between the CMB power spectrum and the reheating temperature assuming the perturbative reheating scenario. Further by incorporating a possible dark matter candidate through radiation annihilation process during reheating and the current value of dark matter abundance, we constrain the dark matter parameter space through the inflationary power spectrum for different inflationary models.

Dr.	CHANDRACHUD	BIJAY VASWAR	DASH	Birla Institute of Technology and Science,Pilani	Understanding the accelerated cosmic acceleration is one of the most important feature in cosmology.We study the possibilities to constrain dark energy by modelling equation of state of Dark energy. We also study f(R) gravity theories using imprint on the BAO power spectrum. Finally we make prediction for sensitivities at which the BAO features on the cross-correlation signal can be detected using future radio observations using SKA and Lyman-alfa forest from SDSS quasar survey. The cross-correlation of post re-ionisation 21 signal and Lyman-alpha forest being used as a useful probe for cosmological evolution and structure formation. We study Fisher matrix analysis for constraining a wide range of dark energy models as well as various f(R) gravity theories.

Ms.	Suvedha	Suresh	Naik	Manipal Centre for Natural Sciences, Manipal Academy of Higher Education, Manipal, Karnataka	Title: A hunt for primordial features due to particle production during inflation\n\nAuthors: Suvedha Suresh Naik , Kazuyuki Furuuchi\nAffiliation: Manipal Centre for Natural Sciences (MCNS), Centre of Excellence, MAHE, Manipal 576104\n\nAbstract:\nThe imprints of Primordial Density Perturbations (PDPs) have\nbeen observed as tiny temperature anisotropies in the Cosmic Microwave Background (CMB) radiations. The observational data of CMB are well explained by the concordance Î›CDM model which assumes an almost scale invariant power spectrum of PDPs. We studied the particle physics model of cosmic inflation based on compactification of higher dimensional gauge theory. The model predicts bump-like features in the power spectrum of PDPs. Such features arise from the cosmological particle production during inflation. We present the possible constraints on bump-like featured model obtained from the latest CMB observations.\nKeywords: cosmology: cosmic background radiation, inflation, large-scale structure of Universe, observations, theory

Dr.	Sampurn		Anand	IIT Madras	In recent past, it has been reported that the measurements of Ïƒ8 from large scale structure observations is in conflict with measurement of the same quantity from Planck CMB within Î›CDM framework. Similar discordance has also been found in the value of H0 and Î©m as well. Under the strong presumption that all the data used are accurate and free from systematics, analysis done suggests that the currently established concordance model needs to be supplemented by some new physics. We will consider an effective theory of large scale structure, which incorporates dissipative effects, and show that the presence of viscosity can remove these conflicts simultaneously.

Ms.	Madhurima		Choudhury	Indian Institute of Technology Indore	One of the key science goals of most of the ongoing or upcoming low-frequency experiments like EDGES, SARAS, and the SKA, is the study of the cosmic Dark Ages, Cosmic Dawn and Epoch of Reionization (EoR) using the all-sky averaged redshifted HI 21cm signal. This signal can be detected by averaging over the entire sky, using a single radio telescope, in the form of a Observations of the 21 cm transition line of neutral hydrogen would be an important and promising probe into the cosmic Dark Ages and Epoch of Reionization. One of the major challenges for the detection of this signal is the accuracy of the foreground source removal and extracting the cosmological signal. Several novel techniques have been explored already to remove bright foregrounds from both interferometric as well as total power experiments. We present the results from our investigations on the application of Artificial Neural Networks to extract the faint 21cm global signal amidst the sea of bright galactic foregrounds, while considering the effects of the instrument as well.

Dr.	Samir		Choudhuri	NCRA-TIFR	Measurements of the diffuse Galactic synchrotron emission (DGSE) is relevant for the 21-cm studies from the Epoch of Reionization. The study of the synchrotron emission is also useful to quantify the fluctuations in the magnetic field and the cosmic ray electron density of the turbulent interstellar medium (ISM) of our Galaxy. Here, we present all-sky brightness temperature distribution of the foreground using the TIFR GMRT Sky Survey at 150 MHz. We believe the measured brightness temperature to be dominated by the DGSE. Also, we present the results for different angular scales probed the GMRT. We compared our results with the single-dish measurements and found consistent with the scaled version of Haslam 408 MHz single-dish map.

Prof.	Anjan	Ananda	Sen	Centre For Theoretical Physics, Jamia Millia Islamia	We analyse various low-redshift cosmological data from Type-Ia Supernova, Baryon Acoustic Oscillations, Time-Delay measurements using Strong-Lensing, $H(z)$ measurements using Cosmic Chronometers and growth measurements from large scale structure observations for $Lambda$CDM and some different dark energy models. By calculating the Bayesian Evidence for different dark energy models, we find out that the $Lambda$CDM still gives the best fit to the data with $H_{0}=70.3^{+1.36}_{-1.35}$ Km/s/Mpc (at $1sigma$). This value is in $2sigma$ or less tension with various low and high redshift measurements for $H_{0}$ including SH0ES, Planck-2018 and the recent results from H0LiCOW-XIII. The derived constraint on $S_{8}=sigma_{8}sqrt{{Omega_{m0}}/{0.3}}$ from our analysis is $S_{8} = 0.76^{+0.03}_{-0.03}$, fully consistent with direct measurement of $S_{8}$ by KiDS+VIKING-450+DES1 survey. We hence conclude that the $Lambda$CDM model with parameter constraints obtained in this work is consistent with different early and late Universe observations within $2sigma$. We therefore, do not find any compelling reason to go beyond concordance $Lambda$CDM model.

Mr.	Suman		Chatterjee	Indian Institute of Technology Kharagpur	Title : Prospects and challenges for detecting the 21-cm power\nspectrum with the Ooty Wide Field Array (OWFA)\n\nAbstract : Observations of the cosmological redshifted neutral hydrogen (HI) 21-cm (1420 MHz) signal, which arises from the ground state hyperfine transition of the HI, holds the potential of probing the large scale structures of the Universe. The Ooty Radio Telescope (ORT) is currently being upgraded to a linear radio-interferometric array, the Ooty Wide Field Array (OWFA). The\nOWFA operates at a nominal frequency of 326.5 MHz which corresponds to the 21-cm signal from z = 3.35. Measuring the redshifted HI 21-cm power spectrum is one of the major science\ngoals of OWFA. We explore the possibility of performing an HI intensity mapping survey with the OWFA. Predictions show that the OWFA is capable of measuring the HI signal from the post-reionization era and produce robust cosmological measurements. \nGalactic and extragalactic foregrounds which are 4âˆ’5 orders of magnitude larger than the signal itself, pose a severe challenge to the HI 21-cm signal detection. This challenging scenario is further complicated by wide-field effects, calibration error, error in the primary beam modelling. We use simulations to predict the impact of these on the detection of the HI 21-cm signal. We also discuss possibilities of using the foreground avoidance and other mitigation techniques to remove the foregrounds for the detection of the HI 21-cm signal with OWFA.