Saha Theory Workshop: Cosmology at the Interface

28 Jan 2015, 09:00 → 30 Jan 2015, 18:30 Asia/Calcutta

Amit Ghosh, Arnab Kundu, Asit De, Gautam Bhattacharyya, Koushik Dutta, Palash Baran Pal

Theory Division of Saha Institute of Nuclear Physics will host its first "Saha Theory Workshop: Cosmology at the Interface" from 28th January to 30th January, 2015. We expect this workshop to become a part of the Theory Division's yearly activities, in which the focus will change depending on the Division's research interests. 

For this time, the focus would be on cosmology and related areas. The program would include both plenary sessions and sessions by contributed talks.

Limited travel funds (train fare within India) are available for young researchers. The institute will arrange for local hospitalities. Even though efforts would be made in accommodating all contributed talks, if necessary, a screeing would be done due to time constraint. Because of a limit on the maximum number of participants, your registration does not automatically confirm your participation. Your confirmation of participation would be sent by email in due time.  Registration of a person would be considered for participation if the person is registered in any Ph.D programme at the least.

For Registration, you do not need any indico account. But for submission of an Abstract, you need to login either by using your gmail/facebook account or create a light-weight Indico/CERN account from the bottom of the "CERN Single Sign On" page. Use 'create/check your account'. Subsequently, you need to activate your account via the link sent to your email address. 

Registration and Abstract Submission: CLOSED

Query: saha.theory.workshop@gmail.com

Website: www.saha.ac.in/theory/theory-workshop

Workshop Photo: http://www.saha.ac.in/web/thd-gallery/thd-photograph

Accommodation Details Accommodation_details.pdf

Basic Information basic_info2.pdf

List of Participants RegistrantsList.pdf

Openning Slides Oppenning_Slides.pdf

Poster Poster

Timetable timetable.pdf

Wireless Details Wireless_Details.docx Wireless_Details.pdf

Workshop Banner BANNER-Saha_theory_workshop.jpg

Workshop Photos http://www.saha.ac.in/web/thd-gallery/thd-photograph

Wednesday 28 January

09:00 → 09:20 Registration

09:20 → 09:30 Openning

09:30 → 11:00 Morning Session I

Convener: Prof. Palash Baran Pal

09:30 Probing Cosmology with Gev-TeV Gamma rays

Speaker: Prof. Pratik Majumdar (SINP, Kolkata)

talk pratik.pdf

10:15 Confronting Galactic and Extragalactic gamma-ray observed by Fermi-LAT with Annihilating Dark Matter in Inert Higgs Doublet Model

Speaker: Prof. Debasish Majumdar (SINP)

talk debashis.pdf

11:00 → 11:30 Tea/Coffee

11:30 → 13:00 Morning Session II

Convener: Prof. Pijushpani BHATTACHARJEE

11:30 Neutrinos and Cosmology

Speaker: Prof. Sandip PAKVASA (University of Hawaiii)

talk pakvasa.pdf

12:15 Black hole superradiance, alternative theories of gravity and floating orbits

Speaker: Prof. Sayan Chakrabarti (IIT, Gauhati)

talk sayan_sinp.pdf

13:00 → 14:00 Lunch

14:00 → 15:30 Afternoon Session I

Convener: Prof. Subhendra Mohanty

14:00 The current status of dark energy

Speaker: Prof. Anjan Ananda SEN (Center For Theoretical Physics, JMI)

14:45 Large scale anisotropy in the Universe

Speaker: Dr Pankaj Jain (IIT,Kanpur)

talk Jain_SINP.pdf Jain_SINP.pptx

15:30 → 16:00 Tea/Coffee

16:00 → 16:45 Afternoon Session II

Convener: Prof. Pratik Majumdar

16:00 Discussion/Q&A: Moderator - Sen, Anjan Ananda

Thursday 29 January

09:30 → 11:00 Morning Session-I

Convener: Prof. Pankaj Jain

09:30 21-cm Cosmology

Speaker: Prof. Somnath BHARADWAJ (IIT Kharagpur)

10:15 Reionization

Speaker: Dr Tirthankar Roy CHOUDHURY (National Centre for Radio Astrophysics, TIFR)

talk Tirthankar_RC.pdf

11:00 → 11:30 Tea/Coffee

11:30 → 13:00 Morning Session-II

Convener: Prof. Amit Ghosh

11:30 Generation of magnetic field before recombination

Speaker: Prof. S. Shankaranarayanan (IISER, Thiruvananthapuram)

talk Shanki-SINP-29Jan.pdf

12:15 Gravitational-wave astronomy

Speaker: Dr AJITH Parameswaran (International Centre for Theoretical Sciences, TIFR, Bangalore)

Slides PAjith_GWA_Saha.pdf

13:00 → 14:00 Lunch

14:00 → 15:15 Astro Physics-I

Convener: Prof. Tirthankar Roy CHOUDHURY

14:00 A Direct Measurement of the Mean Occupation Function of Quasars: Breaking Degeneracies between Halo Occupation Distribution Models

Recent work on quasar clustering suggests a degeneracy in the halo occupation distribution constrained from two-point correlation functions. To break this degeneracy, we make the first empirical measurement of the mean occupation function (MOF) of quasars at z ~ 0.2 by matching quasar positions with groups and clusters identified in the MaxBCG sample. We fit two models to the MOF, a power law and a four-parameter model. The number distribution of quasars in host halos is close to Poisson, and the slopes of the MOF obtained from our best-fit models (for the power-law case) favor an MOF that monotonically increases with halo mass. The best-fit slopes are 0.53 ± 0.04 and 1.03 ± 1.12 for the power-law model and the four-parameter model, respectively. We measure the radial distribution of quasars within dark matter halos and find it to be adequately described by a power law with a slope -2.3 ± 0.4. We measure the conditional luminosity function (CLF) of quasars and show that there is no evidence that quasar luminosity depends on host halo mass, similar to the inferences drawn from clustering measurements. The lack of halo mass dependence in the CLF shows that quasars residing in galaxy clusters have a characteristic luminosity scale.

Speaker: Dr Suchetana Chatterjee (Assistant Professor)

Slides cosm_sinp_SC.pdf cosm_sinp_SC.ppt

14:15 The effect of non-Gaussianity on error predictions for the Epoch of Reionization (EoR) 21-cm power spectrum

Observations of the redshifted 21-cm signal from neutral hydrogen (HI) are a very promising probe of the Epoch of Reionization (EoR), and there is a considerable observational effort underway to detect the EoR 21-cm power spectrum e.g. [GMRT][1], LOFAR, MWA, and PAPER. Observing the EoR 21-cm signal is one of the key scientific goals of the future telescope SKA. It is important to have quantitative predictions of both, the expected EoR 21-cm power spectrum and the sensitivity of the different instruments to measure the expected signal. On the theoretical and computational front, a considerable amount of effort has been devoted to simulate the expected EoR 21-cm signal. There also have been several works to quantify the sensitivity to the EoR signal for different instruments. Many people have recently made quantitative predictions for detecting the EoR 21-cm power spectrum with the MWA, LOFAR, SKA and PAPER respectively. The sensitivity of any instrument to the EoR 21-cm power spectrum is constrained by the errors, a part of which arises from the system noise of the instrument and another component which is inherent to the signal that is being detected (cosmic variance). It is commonly assumed, as in all the sensitivity estimates mentioned earlier, that the system noise and the EoR 21-cm signal are both independent Gaussian random variables. This is a reasonably good assumption at large scales in the early stages of reionization when the HI is expected to trace the dark matter. Ionized bubbles, however, introduce non-Gaussianity and the 21-cm signal is expected to become highly non-Gaussian as the reionization proceeds. We use semi-numerical simulations of the EoR 21-cm signal to study the effect of non-Gaussianities on the error estimates for the 21-cm power spectrum. Not only is this important for correctly predicting the sensitivity of the different instruments, it is also important for correctly interpreting the observation once an actual detection has been made. The entire analysis here focuses on the errors which are intrinsic to the 21-cm signal, and we do not consider the system noise corresponding to any particular instrument. [1]: http://www.gmrt.ncra.tifr.res.in [2]: http://www.lofar.org/ [3]: http://www.haystack.mit.edu/ast/arrays/mwa/ [4]: http://eor.berkeley.edu/ [5]: http://www.skatelescope.org

Speaker: Mr Rajesh Mondal (Indian Institute of Technology Kharagpur)

Slides Rajesh_SINP_29-01-15.pdf

14:30 21 cm signal from cosmic dawn

Observations of redshifted 21 cm radiation from the epoch of reionization promises to provide information on the physical processes during that epoch. Many low frequency interferometers are trying to provide statistical measurements of this signal, such as its power spectrum. Beside observations numerical simulations are essential to derive tight constraints on different aspects of reionization like the nature of first sources, relative level of emission from UV and X-ray sources etc. We present a formalism for generating the $\delta T_b$ distribution using dark matter simulations and an one-dimensional radiative transfer code. Our analysis is able to account for the spin temperature $T_{\rm S}$ fluctuations arising from inhomogeneous X-ray heating and $Ly{\alpha}$ coupling during cosmic dawn. The $\delta T_b$ power spectrum amplitude at large scales ($k \sim 0.1$ Mpc$^{-1}$) is maximum when $\sim 10\%$ of the gas (by volume) is heated above the CMB temperature. The power spectrum shows a “bump”-like feature during cosmic dawn and its location measures the typical sizes of heated regions. Also, one need to consider the effect of peculiar velocities of gas (redshift space distortion) while generating $\delta T_b$ distribution. We find that the effect of peculiar velocities on the power spectrum is negligible at large scales for most part of the reionization history. During early stages (when the volume averaged ionization fraction $\le 0.2$) this is because the signal is dominated by fluctuations in $T_{\rm S}$. For reionization models that are solely driven by stars within high mass ($\gt 10^9 M_{\odot}$) haloes, the peculiar velocity effects are prominent only at smaller scales ($k \gt 0.4$ Mpc$^{-1}$) where patchiness in the neutral hydrogen density dominates the signal. The conclusions are unaffected by changes in the amplitude or steepness in the X-ray spectra of the sources. We also study the effect of the evolution of the signal along the line-of-sight.

Speaker: Mr Raghunath Raghunath Ghara (NCRA-TIFR)

Slides sinp_raghu.pdf

14:45 Generation of large scale magnetic fields in the early universe driven by cosmological neutrinos

I study the generation of cosmic magnetic fields in the primordial plasma of the early universe. A strong large scale magnetic field can be created owing to the instability caused by the parity violating interaction between charged leptons and neutrino-antineutrino gas. For this purpose I calculate the most general expression for the Chern-Simons parameter in this background matter using the imaginary time QFT at finite temperature. Basing on this result I derive the modified Faraday equation which describes the magnetic field evolution. If a nonzero neutrino asymmetry is present, a seed magnetic field can be dynamo amplified. Assuming the causal scenario, i.e. the length scale of the magnetic field being less than the horizon, I obtain the new lower bound on the neutrino asymmetries $\xi = \mu_\nu / T$, where $\mu_\nu$ is the chemical potential of the $\nu\bar{\nu}$ gas and $T$ is its temperature, which is consistent with the well-known Big Bang nucleosynthesis upper bound on $\xi$ in a hot universe plasma. I also discuss the application of the developed formalism for the magnetic fields generation in other astrophysical media. References: 1. M. Dvornikov and V. B. Semikoz, JCAP 05 (2014) 002; arXiv:1311.5267. 2. M. Dvornikov, Phys. Rev. D 90, 041702 (2014); arXiv:1405.3059. 3. M. Dvornikov and V. B. Semikoz, to be submitted to the arXiv soon.

Speaker: Maxim Dvornikov (USP)

Slides Dvornikov_Saha_2015.pdf

15:00 Free slot

14:00 → 15:15 Dark Energy-I

Convener: Prof. Anjan Ananda Sen

14:00 Evolution of Cosmological parameters exhibited by the Starobinsky f(r) gravity model in Einstein frame

f(r) gravity model is a part of modified gravity models proposed to explain the present accelerated expansion of the universe. A scalar degree of freedom can be defined from any f(r) gravity model by redefining the model's variable. We have studied the evolution of cosmological parameters using the scalar degree of freedom of the Starobinsky f(r) gravity model in the Einstein frame. It is found that this model could produce the accelerated expansion of the universe in this frame with the negative equation of state of the scalar field. There are other interesting observations that we have found from this study which we will report here.

Speaker: Mrs Kabita deka (Ph.D. student)

Slides SINP_KABITA.pdf

14:15 A non-canonical scalar model of Dark Energy

In this work we have studied the dynamics of accelerating scenario within the framework of scalar field models possessing a non-canonical kinetic term. In this toy model, the scalar field is allowed to interact with the dark matter component through a source term. We have assumed a specific form for the coupling term and then have studied the dynamics of the scalar field having a constant equation of state parameter. We have also carried out the dynamical system study of such interacting non-canonical scalar field models for power law potentials for some physically relevant specific values of the model parameters. It has been found that the only for two particular stable fixed points of the system, an accelerating solution is possible and the universe will settle down to a $\Lambda$CDM universe in future and thus there is no future singularity in this model.

Speaker: Dr Sudipta Das (Visva-Bharati)

Slides SINPtalk.pdf

14:30 Curvature Singularities in Modified Theories of Gravity

In this Poster/talk, I will be discussing the problem of Curvature Singularity which arises in f(R) theories. The f(R) Theory is a modification of gravitational theory compared to Einstein’s General Relativity. In these theories, we try to modify gravitational lagrangian by adding higher order curvature corrections without spoiling successes of GR. Even though f (R) modifications of late time cosmology is successful in explaining the cosmic acceleration, it is very difficult to simultaneously satisfy the fifth-force constraint. Even in this case, the effective scalar degree of freedom may move to a point (close to its minima) in the field space where the Ricci scalar diverges. We elucidate this point further with a specific example of f (R) gravity that incorporates all viable f (R) gravity models in the literature. In particular, we show that the nonlinear evolution of the field in pressureless contracting dust can easily lead to the curvature singularity, making these theories nonviable.

Speaker: Ms Avani Patel (IISER Bhopal)

Slides csing_f(R)1.pdf

14:45 “ Quintessence and D3-brane/anti-brane universe”

We out-line a plausible scenario leading to a vacuum created pair of D3-brane/anti-brane by a two form in a U(1) gauge theory on a D4-brane world-volume. In particular, we consider the gauge theory on a D4-brane in presence of a background (open string) black hole metric and obtained an effective torsion curvature description in a second order formalism. The scenario is explored to address certain aspects of a quintessence which is believed to be a candidate for the source of dark energy in our universe. It is argued that a quintessence dynamics may be viewed through an axionic scalar on an anti D3-brane world- volume which in turn is paired with our D3-brane universe at a distance. The presence of an extra fifth transverse dimension between the four dimensional brane and anti-brane universes may provide a clue behind an accelerating universe observed in cosmology.

Speaker: Mr Kumar Priyabrat Pandey (University of Delhi, Delhi-110007)

Slides SINPJan2015.pdf

15:00 Free slot

14:00 → 15:15 Inflation-I

Convener: Prof. Pravabati CHIANGANGBAM

14:00 Inflation and Electroweak vacuum stability after LHC, PLANCK and BICEP2

Abstract: Recent observational developments in the fields of high energy physics and cosmology have set some new challenges in their respective fields. Observation of 125 GeV mass Higgs boson has raised the concern about the instability of electroweak vacuum around $10^{10}$ GeV whereas observations by BICEP2, if turns out to be correct, would set the inflationary scale surprisingly close to the GUT scale. In this talk we would extend the Standard model by a $U(1)_{B-L}$ symmetry group where the real part of the $U(1)_{B-L}$ scalar would play the role of inflaton. We would show how a radiatively corrected inflaton quartic potential would produce viable observational signatures for cosmology and how the low inflaton mass would yield a threshold correction to SM Higgs quartic coupling which would naturally cure the instability problem of the electroweak vacuum.

Speaker: Dr Suratna Das (INSPIRE Faculty)

Slides SINP.pdf

14:15 Constraining N=1 supergravity inflationary framework with non-minimal Kähler operators

In this paper we will illustrate how to constrain unavoidable K\"ahler corrections for ${\cal N}=1$ supergravity (SUGRA) inflation from the recent Planck data. We will show that the non-renormalizable K\"ahler operators will induce in general {\it non-minimal kinetic} term for the inflaton field, and two types of SUGRA corrections in the potential - the {\it Hubble-induced mass} ($c_{H}$), and the {\it Hubble-induced A-term} ($a_{H}$) correction. The entire SUGRA inflationary framework can now be constrained from (i) the {\it speed of sound}, $c_s$, and (ii) from the upper bound on the {\it tensor to scalar ratio}, $r_{\star}$. We will illustrate this by considering a heavy scalar degree of freedom at a scale, $M_s$, and a light inflationary field which is responsible for a slow-roll inflation. We will compute the corrections to the kinetic term and the potential for the light field explicitly. As an example, we will consider a visible sector inflationary model of inflation where inflation occurs at the point of {\it inflection}, which can match the density perturbations for the cosmic microwave background radiation, and also explain why the universe is filled with the Standard Model degrees of freedom. We will scan the parameter space of the non-renormalizable K\"ahler operators, which we find them to be order ${\cal O}(1)$, consistent with physical arguments. While the scale of heavy physics is found to be bounded by the tensor-to scalar ratio, and the speed of sound, $ {\cal O}(10^{11}\leq M_s\leq 10^{16})$~GeV, for $0.02\leq c_s\leq 1$ and $10^{-22}\leq r_\star \leq 0.12$. Additionaaly we study the nonlinear evolution of cosmological perturbations on large scales which enables us to compute the curvature perturbation, $\zeta$, without solving the exact perturbed field equations. Further we compute the non-Gaussian parameters $f_{NL}$ , $\tau_{NL}$ and $g_{NL}$ for local type of non-Gaussianities and CMB dipolar asymmetry parameter, $ A_{CMB}$, using the $\delta N$ formalism for a generic class of sub-Planckian models induced by the Hubble-induced corrections for a minimal supersymmetric D-flat direction where inflation occurs at the point of inflection within the visible sector. Hence by using multi parameter scan we constrain the non-minimal couplings appearing in non-renormalizable K\"ahler operators within, ${\cal O}(1)$, for the speed of sound, $0.02\leq c_s\leq 1$, and tensor to scalar, $10^{-22} \leq r_{\star} \leq 0.12$. Finally applying all of these constraints we will fix the lower as well as the upper bound of the non-Gaussian parameters within, ${\cal O}(1-5)\leq f_{NL}\leq 8.5$, ${\cal O}(75-150)\leq\tau_{NL}\leq 2800$ and ${\cal O}(17.4-34.7)\leq g_{NL}\leq 648.2$, and CMB dipolar asymmetry parameter within the range, $0.05\leq A_{CMB}\leq 0.09$.

Speaker: Sayantan Choudhury (urn:Facebook)

Slides sinptalk.pdf

14:30 N-flation in Supergravity

We have constructed a large field N-flation model in the Supergravity framework. In this simple set-up, N fields collectively drive inflation where each field traverses sub-Planckian field values. This has been realised with a generalisation of the single field chaotic inflation in Supergravity. Interestingly,despite of the presence of the field interactions, the dynamics can be described in terms of an effective single field. With the help of a simple example we have explicitly showed how a two field dynamics is effectively reduced to a single field. Then we extended our argument for N fields.The observable predictions of our model i.e. tensor to scalar ratio r and scalar spectral index ns are close to the chaotic inflationary model with quadratic potential

Speaker: Mr Das Kumar (SINP)

Talk N-FLATION___IN__SUPERGRAVITY.pdf

14:45 A note on Chromo Natural Inflation

In this note, we re-examine the Chromo-Natural Inflation model and its generalization in view of recent observational data. We find that the parameter space of the model admits a Non-negligible value of r as well as other cosmological observables consistent with data

Speaker: Dr Atri Deshamukhya (Assam University, Silchar, india)

Slides SAHApresentation_(1).pdf

15:00 Cosmological bounces in spatially flat FRW spacetimes in metric f (R) gravity

1)Brief introduction to cosmological bounce scenario, an alternative to the singular big-bang cosmology. 2)Brief introduction to f(R) gravity: Motivations, Action and field equation, stability issue, conformal equivalence to GR with a scalar field, Einstein frame description. 3)Analysing cosmological bounce in the framework of f(R) gravity: General bouncing condition for FRW metric with k=+1,-1 and 0(we specifically show that a bounce is possible even for k=0, unlike in GR); a general condition for for any f(R) to support a matterless bounce(this is also notably different from GR, where a matterless bounce is impossible); short discussion on stability analysis in our case; analysis of the bounce in Einstein frame(a bounce in the original frame does not necessarily mean a bounce in the conformal Einstein frame) 4)Formulating a system of coupled differential equation in the Einstein frame for the quantitative treatment of the bounce; numerically solving the system to see the behavior of the dynamical quantities in the Einstein frame, and then going back to the original(Jordan) frame to find the actual picture. 4)Evolution of scalar cosmological perturbation through the bounce: Formulating the scalar perturbation evolution equation in presence of a hydrodynamic equation and a scalar field under the framework of GR; solving this to find out the behavior of the scalar perturbations in the Einstein frame, and then going back to the Jordan frame to see the actual picture.

Speaker: Mr Saikat CHAKRABORTY (IIT Kanpur)

Slides presentation.pdf

15:15 → 15:45 Tea/Coffee

15:45 → 17:15 Dark Energy-II

Convener: Prof. Debashis Majumdar

15:45 Current Cosmic Acceleration with Slotheon

I will discuss the cosmological viability of a slow-moving Galileon field in a potential. The Slotheon Lagrangian respects the Galileon symmetry in curved spacetime. I will carry out the detailed investigations of the underlying dynamics of this Lagrangian with an Einstein-Hilbert term and a potential. I will demonstrate that the model can give rise to a viable ghost-free late-time acceleration of the universe. Furthermore, I will also carry out the observational analysis of the model and use observational data from growth, type Ia supernovae data, baryon acoustic oscillations, and the cosmic microwave background to constrain the parameters of the theory.

Speaker: Dr Amna Ali (SINP,Kolkata)

Talk Current_Cosmic_Acceleration_with_Slotheon_amna.pdf

16:00 Gravitational Lensing Bound on The Transition Redshift

In this paper, we use the approach which is independent on matter, to study the accelerated expansion of the Universe. We reconsttruct the deceleration parameter, q(z), to put constrain on the transition redshift $(z_t )$. Transition redshift is the value of redshift at which the expansion of the Universe switches from decelerated to accelerated phase. We reconstruct three different form of deceleration parameter: $q_I (z) = \frac{1}{2} +\frac{q_0}{(1+z)^2}$, $q_{II} (z) =q_1+q_2 z$, and q_{III} (z) = q_3 + q_4 log(1 + z) by using the recent data of age of galaxies and strong lensing. A joint analysis of these two datasets indicate the higher value of the transition redshift $z_t > 1$.

Speaker: Ms Nisha Rani (Delhi University)

Slides sinp_tak.pdf

16:15 Geometry of the universe described by wet dark fluid in f(R, T) theory of gravity

The Bianchi type-III cosmological model in gravity is investigated with the equation of state for wet dark fluid i.e. $P_{WDF}=\omega (\rho_{WDF}-\rho^*)$. Using Volumetric and power law expansion we obtained the exact solution of the field equations. The various astrophysical phenomena namely the look back time, proper distance, luminosity distance, Angular diameter, jerk parameter and cosmic snap with red shift and state-finder parameters are also discussed.

Speaker: Dr Gauranga Charan Samanta (Birla Institute of Technology and Science, Pilani, K k Birla, Goa Campus)

talk Sahaworkshop_G_C_Samanta.pdf

16:30 Pressure anisotropy and dark energy models in scale invariant theory of gravitation

The problem of an anisotropic universe in the form of a diagonal Bianchi type V space-time is investigated in scale invariant theory with dark energy. The matter field is considered in the form of perfect fluid. Pressure anisotropy is considered along different spatial directions. From the constructed cosmological models, we found a dynamic pressure anisotropy which continues along with the cosmic expansion. At a late phase of cosmic evolution, the model enters into a phantom region.

Speaker: Dr Bivudutta Mishra (BITS-Pilani, Hyderabad Campus)

16:45 High-z Supernova Type Ia Data: non-Gaussianity and Direction Dependence

We use the ∆χ2 statistic introduced in Gupta, Saini & Laskar (2008); Gupta, Saini (2010) to study directional dependence, in the high-z supernovae data. This depen- dence could arise due to departures from the cosmological principle or from direc- tion dependent statistical systematics in the data. We apply our statistic to the gold data set from Riess et al. (2004) and Riess et al. (2007), and Union2 catalogue from Amanullah et al. (2010). Our results show that all the three data sets show a weak but consistent direction dependence. In 2007 data errors are Gaussian, however other two data sets show non-Gaussian features.

Speaker: Mr Meghendra Singh Mr. (UPTU Lucknow)

17:00 Effect of phantom dark energy on Gravitational Lensing

Abstract: Recent cosmological observations suggest that the accelerated expansion of the universe is governed by dark energy with the equation of state parameter (w) restricted to the range -1.38 < w < -0.82. This indicates the possibility of dark energy with w < -1. A phantom scalar is regarded as an effective field description of such dark energy component. In the present work we have estimated the influence of phantom dark energy on the Gravitational Lensing phenomenon and explore the possibility, at least in principle, of discriminating phantom dark energy from cosmological constant from local observations.

Speaker: Dr Kabita Sarkar (Salesian College, Siliguri)

Slides Kabita_Sarkar.pdf

15:45 → 17:15 Formal/Dark Energy

Convener: Prof. Golam Hossain

15:45 Horizon dynamics induced by charged and rotating object

We study the perturbation induced by a slowly rotating massive object as it passes through a Rindler horizon. It is shown that the passage of this object effectively induces a process which can be approximately modeled as Delta function type tidal distortions hitting the horizon. Further, following the analysis presented by Amsel, Marolf and Virmani related to the issue of the validity of physical process first law, we establish a condition on the size of the object so that this law holds for the Rindler horizon. We also study the case when a charged object falls across the horizon.

Speaker: Dr Srijit Bhattacharjee (IIT Gandhinagar)

16:00 A simple solution to the fine tuning problem of the cosmological constant

We show that the fine tuning problem of the cosmological constant can be solved in a conformal model, with explicit conformal symmetry breaking. We argue that the model has two different terms which essentially contribute to the cosmological constant. A local conformal transformation leads to a cancellation of these two terms among one another. Hence these produce no physical consequence for cosmic evolution. The model generates a small cosmological constant without requiring any fine tuning.

Speaker: Mr GOPAL Kashyap (IIT KANPUR)

talk SINP_talk.pdf

16:15 A Singularity Free Cosmological Model in General Relativity

A singularity free cosmological model is obtained in a homogeneous and isotropic background with a specific form of the Hubble parameter in the presence of an interacting dark energy represented by a time-varying cosmological constant in general relativity. Different cases so arose have extensively been studied for different values of curvature parameter. Some interesting results have been found with this form of Hubble parameter to meet the possible negative value of the deceleration parameter $\left( -% \frac{1}{3}\leqslant q<0\right) $ as the current observations reveal. For some particular values of these parameters, the model reduces to Berman's model.

Speaker: Dr Shibesh Kumar Jas Pacif Pacif (Manipal University Jaipur)

talk A_Singularity_Free_Cosmological_Model_in_General_Relativity_-_SHIBESH_KUMAR_JAS_PACIF.pdf A_Singularity_Free_Cosmological_Model_in_General_Relativity_-_SHIBESH_KUMAR_JAS_PACIF.pptx

16:30 STRNGE STARS IN KRORI BARUA SPACE-TIME

The singularity free spacetime metric described by Krori-Barua (J. Phys. A, Math. Gen. 8:508, 1975) satisfies all the requirements of a realistic star. Consequently, we explore the possibility of applying the Krori and Barua model to describe ultra-compact objevts like strange stars.

Speaker: Ms INDRANI KARAR (SAROJ MOHAN INSTITUTE OF TECHNOLOGY, GUPTIPARA, HOOGHLY)

16:45 Influence of cosmological expansion on the local accretion phenomena in galaxies

Importance of the late time accelerated expansion of the Universe in the study of astrophysical phenomena in local galactic-scales is highlighted. From the principle of conserved Hamiltonian of the test particle motion a three dimensional Newtonian analogous potential has been obtained in spherical geometry corresponding to Schwarzschild de Sitter space time, that reproduces almost all of the GR features in its entirety with remarkable accuracy. Applying the derived analogous potential the influence of cosmological constant on Bondi accretion rate has been demonstrated.

Speaker: Dr Arunava Bhadra (University of North Bengal)

Slides bhadra_sinp_Cosmo_2015.pdf

17:00 Free Slot

15:45 → 17:15 Inflation-II

Convener: Prof. Supratik Pal

15:45 Modified Natural Inflation in Light of BICEP2

In this paper we explored in detail a phenomenological model of modified single field natural inflation in the light of recent cosmological experiments BICEP2. Our main goal is to construct an inflationary model which not only predicts the important cosmological quantities such as ($ n_s , r $) compatible with the experimental observation but also is consistent with the low energy effective theory framework. Therefore, all the fundamental scale apart from $ M_P $ and quantities of our interest should be within the sub-Planckian region. In order to achieve our goal we modify the usual single field natural inflationary model by a specific form of higher derivative kinetic term called kinetic gravity braiding ( KGB ). One of our guiding principles to construct such a model is the constant shift symmetry of the axion. We choose a particular class of KGB term such that it correctly predicts the required value of ($ n_s , r $) within the expected range based on the recent cosmological observations. Furthermore for a wide range of parameters space we found our model to be valid with the sub-Planckian axion decay constant $f$ and the scale of inflation $\Lambda$. Within the sub-Planckian value of $f$ our model is also consistent with the reheating after the end of inflation. To our surprise, we also find sub-Planckian field excursion for the axion field $\Delta\phi \simeq f$ for the sufficient number of e-folding $N \simeq 50$. We also discussed in detail about the natural preheating mechanism in our model based on the recently proposed Chern-Simons coupling. We found this gravity mediated preheating is very difficult to achieve in our model. With our general analytic argument, we also would like to emphasize that Chern-Simons mediated preheating is very unlikely to happen in any slow-roll inflationary model.

Speaker: Mr Pankaj Saha (Department of Physics, Indian Institute of Technology, Guwahati)

Slides pankaj_saha_theory.pdf

16:00 Signature of Gibbons-Hawking temperature in the BICEP2 measurement of gravitational waves

BICEP2 has detected gravitational waves with large tensor to scalar ratio r=0.2, that is in tension with PLANCK's upper bound r<0.11 from temperature anisotropy. The tension can be resolved if the spectrum of gravitational waves is blue tilted. The spectrum of gravitational waves generated in standard inflationary scenarios is almost scale invariant. But, if we take into account the Hawking radiation during inflation, we can have blue tilted as well as red tilted spectrum of tensor perturbations depending on the choice of observer. In this talk I will discuss the implications of modified tensor spectrum due to Hawking radiation for PLANCK, BICEP2 and other CMB experiments.

Speaker: Dr Akhilesh Nautiyal (Indian Institute of Science Education and Research Bhopal)

16:15 Variable gravity: A suitable framework for quintessential inflation

A unified description of inflation and late-time cosmic acceleration (quintessential inflation) will be discussed in variable gravity frame work. Nonminimal coupling between massive neutrinos and the scalar field is considered in the Einstein frame. Tensor-to-scalar ratio is large ($r>0.1$) such that the scale of inflation is around the GUT scale. Relic gravitational wave spectrum has a blue spectrum due to the presence of kinetic energy dominated regime after inflation. Instant preheating is implemented since ordinary reheating mechanism does not work here. Lyth bound can be evaded in this model. After neutrinos become non-relativistic the nonminimal coupling becomes effective and plays an important roll for the scalar field to exit from the scaling behavior and dominate over the matter giving rise to late time cosmic acceleration.

Speaker: Mr Md. Wali Hossain (Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi-110025)

Slides SINP_Wali.pdf

16:30 Imprint of Isotropy Violated Gravitational Wave Background in CMB

The Standard Cosmological Model is based upon the Cosmological Principle that the Universe on large scales is isotropic and homogeneous. But the recent measurements from Planck temperature field have made a significant detection of dipolar modulated temperature field of Cosmic Microwave Background (CMB) which implies a departure from the isotropic cosmological model. This observed dipolar anisotropy is present only in large angular scale and leads to a scale dependent modulation amplitude. In the talk, speaker will describe a new phenomenological model arising from a non isotropic inflationary model which can explain the observed large scale dipole anisotropy without considering scale dependent modulation amplitude. This model arises due to initial directional dependent inflationary parameters and keep its imprints on both the temperature and polarization field. The key signature of this model is the direction dependent tensor to scalar ratio and also an statistically anisotropy B mode polarization of CMB. This feature is measurable from several missions like Planck, BICEP-2 and PRISM and hence the validity of the model can be investigated. This analysis leads to a detailed understanding of the observed isotopy violation and also shed light on the cosmological model beyond standard $\Lambda$CDM. To investigate the observed statistically anisotropic feature in details from future missions, it is essential to make temperature and polarization realizations of CMB which are manifestly statistically anisotropic. In the talk, the speaker will discuss an efficient and fast numerical code CoNIGS to make statistically anisotropic Gaussian simulations of temperature and polarization field which can incorporate any kind of isotropy violation and can be used for the analysis in any future high resolution CMB missions.

Speaker: Mr Suvodip Mukherjee (IUCAA)

Slides SINP_29_01_Suvodip.pdf

16:45 Free Slot

18:45 → 20:00 Conference Dinner

Friday 30 January

09:30 → 11:00 Morning Session-I

Convener: Prof. Asit De

09:30 Recent Cosmological results from Planck satellite mission

Speaker: Dr Soumen Basak (Astrophysics Department, SISSA)

Slides planck_sinp_talk_basak_soumen.pdf

10:15 Supergravity Inflation

Speaker: Prof. Subhendra Mohanty (PRL, Ahmedabad)

talk Sugra-Inflation.pdf

11:00 → 11:30 Tea/Coffee

11:30 → 13:00 Morning Session-II

Convener: Prof. Somnath Bharadwaj

11:30 Inflation after Planck

Speaker: Dr Supratik PAL (ISI Kolkata)

talk talksinp-suratik.pdf

12:15 Planck Scale Physics and Unruh Effect

Speaker: Dr Golam HOSSAIN (IISER Kolkata)

talk Hossain_Saha_2015.pdf

13:00 → 14:00 Lunch

14:00 → 15:15 Afternoon Session-I

Convener: Prof. Gautam BHATTACHARYYA

14:00 CMB polarization

Speaker: Dr Pravabati Chiangangbam (IIA, Bangalore)

14:45 Discussion/Q&A: Moderator - Sen, Anjan Ananda

15:15 → 15:30 Closing

15:30 → 16:00 Good Bye Tea/Coffee