Possibilities with dark matter, Some minimum bias conclusions

• Biswarup Mukhopadhyaya

Non-thermal dark matter at reheating: production and evolution

• Avirup Ghosh

Constraints on ultralight axions and gauge bosons from geodetic and frame-dragging measurements (Postponed)

• TANMAY PODDAR (Tata Institute of Fundamental Research)

The geodetic and frame-dragging effects are the direct consequences of the spacetime curvature near Earth which can be probed from the Gravity probe B (GP-B) satellite. The satellite result matches quite well with Einstein’s general relativistic result. The gyroscope of the satellite which measures the spacetime curvature near Earth contains lots of electrons and nucleons. Ultralight axions, and vector gauge bosons, can interact with these electrons and nucleons through different spin dependent and spin-independent operators and change the drift rate of the gyroscope. Some of these ultralight particles can either behave as a long range force between some dark sector or Earth and the gyroscope or they can behave as a background oscillating dark matter fields or both. These ultralight particles can contribute an additional precession of the gyroscopes, limited to be no larger than the uncertainty in the GP-B measurements.Compared with the experimental results, we obtain bounds on different operator couplings.

Probing low scale leptogenesis with inflationary blue-tilted GWs

• Satyabrata Datta (Saha Institute of Nuclear Physics)

In Low scale leptogenesis(LSL) models there is a possibility of dynamically generating a small RH neutrino mass when a long-lived scalar field is coupled weakly to the RH neutrinos despite having a large VEV, $v_\Phi$. Considering such a scenario, the correlation shared by the non-standard scalar era driven by $\Phi$ and $M_i$s offers a unique opportunity to study the fingerprints of LSL on primordial gravitational waves. We study the gravitational waves originating due to the inflationary blue-tiled tensor power spectrum and propagating through the scalar epoch, which depending upon $M_i$s provides two important insights. Firstly, if LSLs are taken seriously even for very high scale reheating GWs with a significant blue tilt don’t violate the BBN bound. Secondly, It provides an opportunity to test LSLs with a low frequency and a complementary high frequency doubly peaked GW background. If recent results on GWs from PTAs are taken at face value and used at low frequencies as a measure, allows one to get possible signatures of LSL mechanisms at higher frequencies.

Chasing dark matter substructures in electron recoil direct detection experiments

• Tarak Nath Maity (Indian Institute of Science)

Recent sky surveys have discovered a large number of stellar substructures. It is highly likely that there are dark matter (DM) counterparts to these stellar substructures. We examine the implications of DM substructures for electron recoil (ER) direct detection (DD) rates in dual-phase xenon experiments. We have utilized the results of the LAMOST survey and considered a few benchmark substructures in our analysis. Assuming that these substructures constitute $\sim 10\%$ of the local DM density, we study the discovery limits of DM-electron scattering cross sections considering one kg-year exposure and 1 electron threshold. With this exposure and threshold, it is possible to observe the effect of the considered DM substructure for the currently allowed parameter space. We also explore the sensitivity of these experiments in resolving the DM substructure fraction. For all the considered cases, we observe that DM having mass $\mathcal{O}(10)\,$MeV has a better prospect in resolving substructure fraction as compared to $\mathcal{O}(100)\,$MeV scale DM.

Dark Matter Approach of a Left-Right Symmetric Model

• Sanchari Bhattacharyya (University of Calcutta)

We investigate a left-right symmetric model respecting $SU(3)_C \otimes SU(2)_L \otimes U(1)_L \otimes SU(2)_R \otimes U(1)_R$ local gauge symmetry. This model contains a large number of heavy exotic particles including the full \textbf{27}-plet fermions of $E_6$. In this fermion sector there are two fermions, one is Dirac-like and another is Majorana-like, who are eligible to be dark matter (DM) candidates giving rise to a two-component DM scenario. In order to deal with a large DM-nucleon scattering cross-section we introduce a dimension-6 effective four-fermi operator explaing the interaction among Standard Model (SM) quarks and DM candidates. We constrain the value of the coefficient of such an operator from the data of the experiments like XENON or LUX. We also constrain our parameter spaces using the recent PLANCK data.

CMB imprints of high scale non-thermal leptogenesis

• Abhijit Kumar Saha (Indian Association for the Cultivation of Science)

Room: Meghnad Saha Auditorium We study the imprints of high scale non-thermal leptogenesis on cosmic microwave background (CMB) from the measurements of inflationary spectral index (ns) and tensor-to-scalar ratio (r), which otherwise is inaccessible to the conventional laboratory experiments. We argue that non-thermal production of baryon (lepton) asymmetry from subsequent decays of inflaton to heavy right handed neutrinos (RHN) is sensitive to the reheating dynamics in early Universe after the end of inflation. Such dependence provides detectable imprints on the ns−r plane which is well constrained by the Planck experiment. We investigate two separate cases, (i) inflaton decays to radiation dominantly and (ii) inflaton decays to RHN dominantly which subsequently decays to the SM particles to reheat the Universe adequately. We obtain the corresponding estimates for ns and r and find the latter case to be more predictive in view of recent Planck/BICEP data. We furnish the results considering α− attractor inflationary models, however the prescription proposed here is quite generic and can be implemented to various kinds of single field inflationary models given the conditions for non-thermal leptogeneis is satisfied

Ruling out light axions : The writing is on the wall

• Subir Sarkar (University of Oxford)

We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry. Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic catastrophe if it comes to dominate the Universe. The network may be made unstable by invoking a ‘tilt’ in the axion potential due to Planck scale suppressed non-renormalisable operators. Alternatively the random walk of the axion field during inflation can generate a ‘bias’ favouring one of the degenerate vacuua, but we find that this mechanism is in practice irrelevant. Consideration of the axion abundance generated by the decay of the wall network then requires the Peccei-Quinn scale to be rather low — thus ruling out e.g. the DFSZ axion with mass below ∼ 60 meV, where most experimental searches are in fact focussed.

Direct Detection of Dark Matter at SNOLab

• Jeter Hall (SNOLab)

Room: Meghnad Saha Auditorium The SNOLAB laboratory is two kilometers underground in Sudbury, Ontario, Canada. I will describe the overall scientific program with emphasis on the various experiments focused on the direct detection of dark matter, a focus of the experimental program at SNOLAB. There are currently eight active dark matter experiments running, in design, or in construction: SuperCDMS, PICO-40, PICO-500, DEAP-3600, DAMIC, SENSEI, OSCURA, and NEWS-G.

A Highly Sensitive Radon Emanation Measurement System at SNOLAB

• Dimpal Chauhan (SNOLAB)

Room: Meghnad Saha Auditorium Rare event search experiments, such as those searching for neutrino interactions, neutrinoless double-beta decay, and dark matter, often have significant backgrounds from radon (Rn-222) and its progeny. These experiments must be constructed from low-background materials to minimize these backgrounds as much as possible. Radon may be emitted from the material surface and can propagate throughout the detector. Therefore, measuring radon emanation is an objective of many low background experiments. A highly sensitive radon emanation counting system, which includes a low-radioactivity acrylic emanation chamber, a radon transferring apparatus, and a low-background ZnS(Ag) scintillation cell, has been developed at SNOLAB and is used to study radon emanation of different materials. This presentation will describe the mechanism required for the effective transfer of radon from the emanation chamber into the scintillation cell, its sensitivity, and efficiency obtained for this system.

Alpha Quenching Factor in Liquid Argon

• Susnata Seth (Department of Physics, Carleton University, Ottawa, Ontario, K1S 5B6, Canada and Arthur B. McDonald Canadian Astroparticle Physics Research Institute, Queen’s University, Kingston Ontario K7L 3N6, Canada)

Room: Meghnad Saha Auditorium The DEAP-3600 (Dark matter Experiment using Argon Pulseshape discrimination) experiment located at SNOLAB utilizes liquid argon as a target material. It searches for the scintillation light signal induced by Weakly Interacting Massive Particle (WIMP) candidates of dark matter via spin-independent interactions. For the DEAP-3600 detector, alpha particles are one of the intrinsic backgrounds which originate primarily from short- and long-lived radon ($^{222}$Rn) progeny. In order to identify and mitigate alpha-induced backgrounds, the quenching of alpha particles in liquid argon must be understood. In this work we performed a relative measurement of alpha quenching using scintillation light signals in the high energy region (order of MeV). We have probed the uncertainty of extrapolating the quenching factor to the low-energy region. Details of the analysis procedure and fits to Birks’ law for alpha quenching will be presented here.

Exploring the direct detection of WIMP dark matter at Jaduguda Underground Science Laboratory (JUSL)

• Suraj Ali (Jadavpur University)

Room: Meghnad Saha Auditorium The observational evidences like the rotational velocity of stars, gravitational lensing etc point to the existence of huge non-luminous matter which is known as Dark Matter (DM). One of the favoured candidates of DM is Weakly Interacting Massive Particles (WIMPs). The WIMPs can be directly detected by measuring the recoil nuclei from the WIMPs-nuclear elastic scattering in the detector material. Superheated liquid detector (SLD) with C2H2F4 (b.p. = -26.3 oC) liquid has the potential to detect the low mass WIMPs. It is already theoretically established that the C2H2F4 SLD has the potential to probe WIMPs-nucleon spin-independent cross section with a projected sensitivity levels (at 90% C.L.) better than 4.6 × 10^-41 cm^2 at WIMP masses down to ∼4 GeV with a total exposure of ∼1000 kg.day for a zero background consideration. The major advantage of SLD is that few backgrounds can be rejected by adjusting the operating temperature and pressure of the detector. Underground laboratories also help us to shield the experiment from backgrounds like cosmic interference. The initial run of the experiment has been started at the Jaduguda Underground Science Laboratory (JUSL), UCIL, Jharkhand, India, at 555m deep underground from the surface. The measurement was stated at JUSL with an exposure of 1.3 kg.days at the ambient temperature having the threshold of about 7 keV. The R & D has begun to increase in several steps the sensitivity of the detector to reach the theoretically predicted region by increasing the mass and exposure of the detector. The background measurements at JUSL have almost been completed and the further measurements specially on the neutron spectrum and radon level are going on.

Strong cosmic censorship conjecture for a charged BTZ black hole

• Chiranjeeb Singha

Room: Meghnad Saha Auditorium The strong cosmic censorship conjecture, whose validation asserts the deterministic nature of general relativity, has been studied for charged BTZ black holes in three-dimensional general relativity, as well as for Nth-order pure Lovelock gravity in d=2N+1 spacetime dimensions. Through both analytical and numerical routes, we have computed the ratio of the imaginary part of the quasi-normal mode frequencies with the surface gravity at the Cauchy horizon. The lowest of which corresponds to the key parameter associated with the violation of strong cosmic censorship conjecture. Our results demonstrate that this parameter is always less than the critical value (1/2), thereby respecting the strong cosmic censorship conjecture. This is in complete contrast to the four or, higher-dimensional black holes, as well as for rotating BTZ black holes, where the violation of strong cosmic censorship conjecture exists.

The MAGIC of Gamma-Ray Astronomy

• David Paneque (Max-Planck-Institut f¨ur Physik)

Room: Meghnad Saha Auditorium

Prospects of Multi-messenger astronomy in the era of third generation of gravitational wave detectors

• Biswajit Banerjee (Gran Sasso Science Institute (GSSI))

Room: Meghnad Saha Auditorium The physics governing the production of the early emission of gamma‑ray bursts (GRBs) is still poorly understood. The early emission is usually caught by a wide field of view gamma‑ray instruments in the range of 10 keV-10 MeV, but to date, at higher energies (above 100 GeV) it has not been detected yet. I will discuss the multi-messenger observational strategies to detect the early emission of short GRBs at very-high-energies (VHE; E > 10 GeV) in the era of the third generation gravitational wave detectors Einstein Telescope (ET) and Cosmic Explorer (CE). We evaluate the joint detection efficiency by the Cherenkov Telescope Array (CTA) . We take into account the expected capabilities to detect and localise gravitational wave events in the inspiral phase of the neutron star binaries and to provide an early-warning alert for upcoming short GRBs, thanks to the proposed low frequency response of ET. We discuss possible VHE components from the synchrotron self Compton components in the leptonic GRB model, high energy tail of the hadronic GRB model as well as external inverse Compton emission as viable candidates in the energy band of 10 GeV - 10 TeV. I will also discuss our discovery of the GeV emission from a compact binary merging event which opened a window for probing the MWL emission with an extended emission. This further increases the possibility of detection of the compact mergers in high energy and very high energy gamma-rays.

Physics of Jets from Multi-Wavelength Monitoring of Blazars

• Ritban Chatterjee (Presidency University)

Room: Meghnad Saha Auditorium

Do plasma composition affect the accretion and jets associated with the compact objects?

• Indranil Chattopadhyay (ARIES)

Room: Meghnad Saha Auditorium Ordinarily gas composition do not affect the solutions of hydrodynamic (or MHD) equations of motion until explicit radiative cooling is considered, since radiative cooling depends on the electron number density! Matter around compact objects are very hot and are fully ionized and naturally consists of ions and electrons. We show that for different fraction of ions, the enthaply of the flow vary significantly even when the temperature is same. Direct consequence of which is that the flow solutions vary significantly with the composition. We show that jet solutions launched with the same injection parameters evolve differently for different composition. The effect is enhanced for flow in presence of gravity. In this talk we discuss the implications in details.

Supernova remnants as Galactic PeVatron candidates

• Agnibha De Sarkar (Raman Research Institute)

Room: Meghnad Saha Auditorium Observations by the Large High Altitude Air Shower Observatory (LHAASO) have opened a new era of gamma-ray astrophysics. Since becoming operational in 2020, LHAASO has detected more than a dozen ultra-high energy (UHE) gamma-ray sources, most of which are unidentified. The detection of these UHE gamma-ray sources indicates the presence of cosmic ray (CR) accelerators in the Milky Way Galaxy, which can accelerate particles up to PeV energies, commonly known as PeVatrons. Several classes of Galactic sources, such as supernova remnants (SNRs), pulsar wind nebulae (PWNe), and young stellar clusters, have been posited to be potential PeVatron candidates. After it was confirmed that Crab PWN is indeed a PeVatron, the idea gained steam that PWNe must be the leading source class to be PeVatrons in the Galaxy. However, further theoretical explorations of other LHAASO-detected UHE gamma-ray sources seem to tell a different story. In this talk, I will discuss the other side of the story, i.e., whether the spectral and morphological features of the LHAASO-detected UHE gamma-ray sources can be consistently modeled by the interaction between SNRs associated with dense molecular clouds (MCs). By considering multiple LHAASO-detected UHE gamma-ray sources, I will show that the SNR+MC systems can reproduce several observational features of these UHE gamma-ray sources, which indicates that SNRs have the potential to be considered as viable Galactic PeVatron candidates, along with PWNe.

Cosmic ray interactions with molecular clouds using GEANT4 simulation

• Abhijit Roy (Aryabhatta Research Institute of Observational Sciences)

Room: Meghnad Saha Auditorium Galactic cosmic rays (protons and atomic nuclei etc) are produced in plausible sources like supernova explosions, pulsar wind nebula, etc. The kinetic energy of these particles can extend over many orders of electron volts. It is expected that PeV cosmic rays are produced in these Galactic sources. After leaving their point of origin, they travel through the interstellar medium. Dense gas regions like molecular clouds in the interstellar medium provide target hydrogen gas density for the interaction of cosmic rays. This further creates a variety of secondary particles, i.e., gamma-rays, neutrinos, etc. Even though many experimental and theoretical studies have been conducted in the past, we still have a lot to learn about the origin, production, and acceleration processes of the highest-energy GCR particles. In this context, we have used the GEANT4 Monte Carlo simulation toolkit to simulate the production of secondary cosmic ray particles as a result of the primary GCR particle interaction and propagation through these dense molecular clouds. These investigations are useful to identify PeV cosmic ray sources near a molecular cloud in our Galaxy.

Gravitational waves - a Quantum Field Theory perspective

• Subhendra Mohanty (PRL, Ahemdabad)

Understanding nature's densest objects and the cosmos with gravity's messenger

• Sukanta Bose (Inter University Centre for Astronomy and Astrophysics)

I will summarize the LIGO-Virgo observations to date and aspects of the progress made in characterizing neutron stars and probing the demography of stellar-mass black holes in binary systems. How these detections are being employed, sometimes in association with electromagnetic observations, to understand gravity and the cosmos will also be discussed.

Intermediate-mass black holes-mergers in the IGWN

• Archna Pai

Cosmology potential with a decihertz gravitational wave observatory

• Sanjit Mitra (IUCAA, Pune)

The direct detection of gravitational waves (GW) by groundbased laser interferometric detectors, operating in the ~10Hz to a few kHz frequency band, and electromagnetic (EM) follow-up of GW events have added a new dimension to observational cosmology. A GW observatory in the decihertz frequency band can open yet another significant window to the universe, like observatories in various EM bands have done in the past. A decihertz GW observatory promises various interesting science cases which may not be meaningfully pursuable otherwise. It can bring a major boost to the number of EM follow up of binary mergers, thereby significantly accelerating the process of precise estimation of the Hubble constant and resolving tensions in current cosmology. Perhaps most exotic of all, it may also provide a relatively foreground-free window to observe the primordial stochastic GW background generated in the very early universe.

Particle Swarm Optimisation in GW signal Detection

• Rajesh Kumble Nayak (IISER Kolkata)

Particle Swarm Optimisation(PSO) is a Stochastic maximisation scheme which quickly converges to global maxima. We apply PSO to maximise the match between the GW signal and the modelled template waveform. One of the advantages of PSO-based detection is that we do not need pre-determined template placement, which allows the search to be extended to an arbitrary parameter space. In contrast to standard search methods, the parameter estimated at the search is accurate. We present our analysis of GW detection using the PSO algorithm.

Continuous gravitational waves from spinning neutron stars: status and outlook

• Reinhard Prix (AEI, MPI-Hannover)

Since the first detection of a black-hole merger in 2015, we have found nearly 100 merger signals from compact objects (mostly black holes but also four involving neutron stars). However, continuous gravitational waves (CWs) emitted directly from deformed spinning neutron stars have still not been detected and could be the next big breakthrough in gravitational-wave astronomy. In this talk, I will give an overview of the challenges and opportunities of searching for continuous waves and the current status and outlook of the global search effort. Two relevant questions to consider are: Can we reasonably expect a CW detection in the near future, and what (astro-)physical insights can we potentially gain from such a detection (or from its absence)?

On the quark content of neutron star core

• Rana Nandi (Shiv Nadar University: Dadri, Uttar Pradesh, IN)

Modelling the dense nuclear matter equation of state consistent with the astrophysical observations

• Prasanta Char (Université de Liege,Liege, BE)

Neutron stars are excellent laboratories to study the physics of matter at extreme conditions which are beyond the scope of any terrestrial experiments. Recent multimessenger observations of neutron stars such as the measurements of the tidal deformability from the gravitational wave observation, and the simultaneous mass and radius measurements of several pulsars in X-rays by the Neutron Star Interior Composition Explorer (NICER) instrument aboard the International Space Station along with the discoveries of massive radio pulsars in the last decades have significant implications for the understanding of the equation of state of dense nuclear matter. In this talk, I will discuss how these pieces of information are combined with nuclear experimental data to constrain the properties and the composition of the interior of neutron stars. I will also review the correlation between certain nuclear empirical parameters such as the symmetry energy, and incompressibility with the macroscopic structure parameters such as the radius, and tidal deformability of the star.

Spanning the full range of neutron star properties within a microscopic description

• Tuhin Malik

The high density behavior of nuclear matter is analyzed within a relativistic mean field description with non-linear meson interactions. To assess the model parameters and their output, a Bayesian inference technique is used. The Bayesian setup is limited only by a few nuclear saturation properties, the neutron star maximum mass larger than 2 M$_\odot$, and the low-density pure neutron matter equation of state (EOS) produced by an accurate N$^3$LO calculation in chiral effective field theory. Depending on the strength of the non-linear scalar vector field contribution, we have found three distinct classes of EOSs, each one correlated to different star properties distributions. If the non-linear vector field contribution is absent, the gravitational maximum mass and the sound velocity at high densities are the greatest. However, it also gives the smallest speed of sound at densities below three times saturation density. On the other hand, models with the strongest non-linear vector field contribution, predict the largest radii and tidal deformabilities for 1.4 M$_\odot$ stars, together with the smallest mass for the onset of the nucleonic direct Urca processes and the smallest central baryonic densities for the maximum mass configuration. {These models have the largest speed of sound below three times saturation density, but the smallest at high densities, in particular, above four times saturation density the speed of sound decreases approaching approximately $\sqrt{0.4}c$ at the center of the maximum mass star. On the contrary, a weak non-linear vector contribution gives a monotonically increasing speed of sound.} {A 2.75 M$_\odot$ NS maximum mass was obtained in the tail of the posterior with a weak non-linear vector field interaction. This indicates that the secondary object in GW190814 could also be an NS.}

Imprints of Non-standard cosmology on Leptogenesis

• Amit Dutta Banik (Indian Statistical Institute, Kolkata)

We discuss how a nonstandard multiple scalar field cosmology can change the thermal history of the universe, affecting minimal high scale leptogenesis. The produced lepton asymmetry, due to the decays of heavy Majorana right-handed neutrinos responsible for generating Standard Model neutrino masses via the type-I seesaw, is affected as well.

Rapid parameter estimation of compact binary sources using a meshfree approach

• Lalit Pathak

The LIGO community uses Bayesian inference extensively to estimate the parameters of gravitational wave (GW) signals recorded in the network of interferometric detectors. The enhanced sensitivities of the upcoming and future detectors would have two-fold consequences, the increased computational cost of parameter estimation (PE) and the large detection rate. Therefore, it becomes imperative to develop techniques to accelerate the PE to prioritize the limited observational resources for EM follow-ups. In this work, we demonstrate a computationally efficient method to rapidly estimate the posterior distribution of source parameters using mesh-free interpolation aided by dimensional reduction techniques. In our approach, we bypass the waveform generation at any sampling point and directly estimate the likelihood values via our interpolation scheme over the likelihood surface. We report a maximum speedup of ~ 4000 at a negligible loss of accuracy ~ $O(10^{-5})$ for a single detector and project a maximum speedup of ~ 650 at a similar accuracy for a network of three detectors across the different compact binary systems in comparison to traditional techniques of PE. Moreover, our scheme is generic and can be applied across various fields wherever Bayesian inference is employed to reconstruct model parameters.

Conference Dinner Charnock's KB 26, Broadway Rd, SEC-III, Bidhannagar, Kolkata Location on Google Map: https://goo.gl/maps/shMGw1fTEFDk3hdM9

Neutrino physics : Current Status and future trends

• Srubabati Goswami (Physical Research Laboraotory)

The first decade of neutrino astronomy with IceCube, and the way forward

• Md. Rameez (TIFR)

Looking for baryogenesis parameter space for Inverse seesaw model

• Ananya Mukherjee (SINP, Kolkata)

About generating small Yukawa couplings naturally from trans-Planckian asymptotic safety

• Soumita Pramanick (Theoretical Physics Division, Physical Research Laboratory (PRL), Ahmedabad, India)

[Based on JHEP 08 (2022) 262 (arXiv:2204.00866 [hep-ph]) by Kamila Kowalska, Soumita Pramanick, and Enrico Maria Sessolo] It was shown that arbitrarily small Yukawa couplings could be generated naturally for gauge-Yukawa systems in trans-Planckian asymptotic safety framework due to the presence of a non-interactive infrared-attractive fixed point. Apart from the non-interactive infrared-attractive fixed point, more ultraviolet-attractive fixed points are also present ensuring well-defined nature of the theory at infinitely high scale. This technology was used for a system of Yukawa couplings of the Standard Model extended by three right-handed neutrinos and asymptotically safe solutions for Dirac neutrinos satisfying the experimental constraints on neutrino masses and mixing could be achieved for Normal Ordering. This general mechanism can also yield the feeble Yukawa interactions needed for correct relic density via freeze-in for sterile-neutrino dark matter models.

Searching for gravitational waves from new physics with pulsar timing arrays

• Kai Schmitz (Westfaelische Wilhelms-Universitaet Muenster (DE))

Reconstruction of nuclear matter parameters in a Bayesian approach

• SK MD Adil Imam (SINP, Kolkata)

The posterior distributions of nuclear matter properties are reconstructed using a Bayesian technique from the EoS of neutron star matter. Appropriate prior distributions are chosen to put constraints on lower-order parameters as imposed by the finite nuclei observables. The calculations are performed on two sets of pseudo data on the EoS whose real models are known. The accompanying uncertainties are also greater and the median values of second or higher order NMPs exhibit considerable deviation from their true values. The sources of these inherent uncertainties are discussed.

Probing high energy scales and weakly coupled BSM via Gravitational Waves

• Anish Ghoshal (University of Warsaw, Poland)

Insights into high-energy emission from kpc-scale jets launched from black holes

• Agniva Roychowdhury (University of Maryland, Baltimore County)

The origin of X-ray emission from >kpc-scale jets and very high energy (>GeV) emission in radio-loud AGN are highly underconstrained. This work brings together the relevant open questions and ways to answer them by considering two particular cases: a unusual TeV LSP BL Lac AP Librae and an FR-I radio galaxy 3C 78, both having a >kpc-jet and a very broad spectral energy distribution (SED). For the former, we find that the very-high energy emission needs to be explained by a combination of inverse Compton scattering of CMB and ALMA-detected dust photons. For the latter, we develop a *new* physically motivated two-zone model to partially explain its broad SED. For each of these cases, we compute the corresponding jet power and provide prescriptions to link real observations of jet Lorentz factor with spectral modelling. Our work throws new light on inspecting spectral energy distributions of radio-loud AGN to investigate the origin of high-energy emission.

Implication of nonstandard interaction in the generation of microscopic black hole events from ultra high energy neutrinos

• Trisha Sarkar (Indian Institute of Technology Jodhpur)

Ultra high energy (UHE) neutrinos are capable of producing microscopic black holes (MBH) by colliding with the nucleons present in the Earth's atmosphere in presence of large extra dimensions (LED) [**DOI: 10.1103/PhysRevD.65.124015**]. The signature of these events can be identified with highly efficient terrestrial neutrino telescopes, like IceCube detector. The nature of these exotic events can be differentiated from the events generated by the ordinary neutrino nucleon scattering process allowed in standard model (SM) [DOI: **10.1007/JHEP04(2020)187**]. We explore the effect of non standard interaction (NSI) on the events generated by these MBHs and analyse whether the scenario of NSI can influence the number of such events significantly [DOI:**10.1140/epjc/s10052-022-10674-6**].

A template-based search for exotic gravitational wave signals from astrophysical compact binaries

• Abhishek Sharma (Indian Institute of Technology Gandhinagar)

Matched filtering technique is used to search for gravitational waves in the data obtained from terrestrial detectors like Advanced LIGO and Virgo. The data is filtered through a template bank constructed over a deemed parameter space to detect the signal. The current search framework uses template waveforms assuming General Relativity (GR) as the correct description of gravity in a highly dynamical regime. If an astrophysical gravitational wave signal carries a significant departure from GR, current template based search would fail to detect such a signal. On the other hand, modeling compact binaries in an alternative theory of gravity is a challenging task and currently no accurate waveform models are known for any alternative theories (except a few numerical simulations), therefore, possible departure from GR waveforms are accommodated by introducing fractional deviations in various coefficients of the Post-Newtonian (PN) expansion of gravitational wave phasing. We accommodate the deviation terms in geometric template placement to search for exotic signals that may carry departures from GR predicted waveforms. In this work, we consider 1$\sigma$ uncertainty of the deviation parameters measured from GW170817 and target the exotic signals from BNS (binary neutron star) like events.

Hubble from Bubble - A new cosmic distance measure

• Subhabrata Majumdar

Beyond-Gaussian statistics for cosmological clustering - k-Nearest Neighbor Distributions

• Arka Banerjee (Indian Institute of Science Education and Research)

Statistical measurements of the clustering of galaxies is one of the main observables from cosmological surveys, containing information both about the initial conditions of the Universe - such as the physics of inflation - as well as about those components that drive the expansion of the Universe today - Dark Energy, the nature of Dark Matter, and massive neutrinos. While most cosmology analyses in the past have focused on two-point functions of the galaxy distribution to probe these questions, there has been growing recognition that there is significant information in higher order N-point functions of the highly nonlinear galaxy distributions. In this talk, I will introduce the formalism for a new measure of cosmological clustering - the k-Nearest Neighbor distributions. These distributions are formally sensitive to all N-point functions, while being computationally inexpensive to measure. I will discuss how these statistics can also be easily extended to describing cross-correlations of different cosmological datasets. Finally I will discuss the potential improvements in constraints on various cosmological parameters when using these statistics over two-point functions, as well as current efforts in measuring these on actual data.

Viscous cosmological model and the validity of near equilibrium condition in the context of $f(R,T)$ gravity.

• Vishnu A Pai (Ph.D. Student)

Recent studies on viscous cosmology show that, while explaining the recent accelerated expansion of the universe in the context of Einstein's gravity, the near-equilibrium condition for the viscous fluid could not be maintained unless a cosmological constant is included in the theory. This, however, denies the ability to explain the recent acceleration of the universe as caused by the viscous matter alone. In this article, we show that, in the context of $f(R,T)$ gravity, it is possible to achieve the late accelerated expansion of the universe, which is caused by the bulk viscous matter, by satisfying the near equilibrium condition for viscous fluid, even without including a cosmological constant. We also describe the various cosmological features of this model.

High-energy neutrinos from the Sun as a discovery tool for dark matter - electron scattering

• Ranjan Laha (Indian Institute of science (IN))

Phenomenology of cosmological moduli fields

• Kaushik Dutta (IISER Kolkata)

Investigating field-fluid non-minimal coupling in the context of Dynamical Stability Approach

• Anirban Chatterjee (Indian Institute of Technology Kanpur, India)

Standard model of cosmology (Λ-CDM model) mainly suffers from two drawbacks, first one is the fine tunning problem and second one is a cosmic-coincidence problem. In this standard model of cosmology, Λ represents the cosmological constant and CDM denotes the cold-dark matter. Another important downside of the Λ-CDM model from the observational perspective is the discrepancy between the present observed value of Hubble’s constant and with predicted value of Hubble’s constant from theory. These fundamental discrepancies motivate us to study different kinds of cosmological models based on the coupled field-fluid sectors. Based on these above considerations, we can build a theoretical framework for coupled field-fluid sector. Where field sector is made of a non-cannonical scalar field (k-essence sector) and the fluid sector is composed of pressureless dust. The nonminimal coupling term is introduced at the Lagrangian level. We employ the variational approach with respect to independent variables that produce modified k-essence field equations and the Friedmann equations. We have analyzed the coupled field-fluid framework explicitly using the dynamical system technique. After examining these models it is seen that both models are capable of producing accelerating attractor solutions satisfying adiabatic sound speed conditions.

Modified cosmology through Barrow entropy and its thermodynamic implications

• Nandhida Krishnan P (Department of Physics, Cochin University of Science and Technology)

Barrow modified the entropy relation for the black hole horizon, as $S \sim A^{1+\frac{\Delta}{2}} $, by taking account of the quantum corrections at the black hole surface, where the exponent $\Delta$ ranges from $0\leq \Delta \leq 1.$ In the cosmological context, we adopted this entropy and defined dark energy termed as Barrow holographic dark energy (BHDE) using the holographic principle with Granda-Oliveros scale as the IR cut-off. We treat BHDE as a dynamical vacuum having a constant equation of state $\omega_{\Lambda}=-1$, we also investigated the late acceleration of the universe, with BHDE and dark matter as components, and the interaction between them has been incorporated phenomenologically. In the absence of interaction between the dark sectors, we found that the model predicts a $\Lambda$CDM-like evolution of the universe with an effective cosmological constant. Further, we constrained the model parameters using the combined data set of Supernovae type Ia Pantheon data (SN Ia) and observational Hubble data (OHD). Additionally, we analyzed the thermodynamics of the universe by concentrating on the generalized second law of thermodynamics and entropy maximization and found that the generalized second law is valid and the model predicts an end de Sitter phase of maximum entropy.

Effects of Reheating on Moduli Stabilization

• KHURSID ALAM (IISER-KOLKATA)

Moduli potential loses its minima due to external energy sources of inflaton energy density or radiation produced at the end of inflation. But, the non-existence of minima does not necessarily mean destabilization of moduli. In fact, the destabilization of moduli is always dependent on the initial field values of the fields. In this work, we study carefully how the effects of reheating ease the problem of moduli destabilization. The associated time scale to produce the thermal bath allows a larger initial field range to stabilize the field. Contrary to the usual notion, the allowed initial field range is larger for higher temperatures when the effective potential is of a run-away nature. This eases the moduli destabilization problem for heavy mass moduli. For low mass moduli (≲ 30 TeV), the allowed field range still causes the cosmological moduli problem by violating the BBN constraints unless its initial abundance is suppressed.