## The Meeting

Shivalik HEPCATS meetings are intended to foster discussions and collaborations among researchers in and around the Shivalik range of the Himalayas. The meetings will take place, ideally once every six months, at various institutes located in the region.

This is the 5th edition of this meeting series.

The webpages of the previous editions of the meetings are available here:
Shivalik HEPCATS Meeting - Summer 2021
Shivalik HEPCATS Meeting - Winter 2020
Shivalik HEPCATS Meeting - Summer 2020
Shivalik HEPCATS Meeting - Winter 2019

What is HEPCATS?

HEPCATS stands for High Energy Physics, Cosmology, Astrophysics, Theory and Simulations.

Venue/Time

The Winter 2021 Meeting will be hosted by IISER Mohali. It will run in a hybrid mode (at Lecture Hall 5 of IISER Mohali and over Zoom). The meeting begins at 9:50AM on December 18, 2021 (Saturday) ends at 5:30PM the same day.

Registration

You may register for the meeting by contacting one of the organizers.

You may join the meeting via this Zoom link:
Shivalik HEPCATS Meeting - Winter 2021 - Zoom Link

Organizers

The organizers of the meeting are:
Dr. Jasjeet Bagla,
Dr. Harvinder Jassal,
Dr. Anosh Joseph,
Dr. Kinjalk Lochan,
Dr. Ambresh Shivaji, and
Dr. K P Yogendran.

Local Coordinators

The local coordinators of the meeting are:

Dr. Jasjeet Bagla, Dr. Minati Biswal, Mr. Navdeep Dhindsa, Dr. Harvinder Kaur Jassal, Dr. Anosh Joseph, Ms. Mandeep Kaur, Mr. Arpith Kumar, Dr. Kinjalk Lochan, Ms. Vamika Longia, Mr. Harkirat Sahota, Mr. Pramod Sharma, Mr. Akash Singh, Dr. Ambresh Shivaji, Mr. I. K. Wasimakram, and Dr. K P Yogendran.

Funding

We acknowledge funding from IISER Mohali.

Accommodation

You may book your accommodation at the IISER guesthouse on payment basis. The link to the institute guesthouse is here.

Tea/Coffee/Lunch

For those of you who are attending the meeting physically at IISER Mohali campus, tea/coffee/lunch will be provided in the foyer of the Lecture Hall Complex. Kindly maintain the protocols of social distancing while you are in the Lecture Hall Complex.

## Schedule

Time Speaker Affiliation Title Resources
09:50AM - 10:00AM Anosh Joseph Welcome Remarks -- --
Session 1 Chair: Jasjeet Bagla
10:00AM - 10:20AM Hemant Rathi IIT Roorkee Holographic JT gravity with quartic couplings ---
10:25AM - 10:45AM Swati Gavas IISER Mohali Probing universality of halo mass function using scale-invariant models ---
10:50AM - 11:10AM Vamika Longia IISER Mohali 2D SU(2) Yang-Mills Theory using Tensor Networks ---
11:15AM - 11:45AM Coffe/Tea Break Location: LHC Foyer
Session 2 Chair: Kinjalk Lochan
11:45AM - 12:05PM Ayan Chatterjee Central University of Himachal Pradesh Exact solutions in higher curvature theories ---
12:10PM - 12:30PM Pinaki Roy IISER Mohali Short Waiting Time Thermonuclear X-rays Bursts in 4U 1636-536: Challenge to existing ignition models? ---
12:35PM - 12:55PM Gopal Yadav IIT Roorkee Deconfinement Phase Transition from Entanglement Entropy and ${\mathscr {M}} \chi$PT Compatibility ---
01:00PM - 02:30PM Lunch Break Location: LHC Foyer
Session 3 Chair: Ambresh Shivaji
02:30PM - 02:50PM Suraj Chopra IISER Mohali Quantum Rigid Body Dynamics ---
02:55PM - 03:15PM Misba Afrin Jamia Millia Islamia Can the EHT probe rotating black holes in Horndeski theory? ---
03:20PM - 03:40PM Sanjay Pant IIT Ropar Effect of backreaction on holographic thermal correlators: From entanglement to chaos ---
03:40PM - 04:00PM Coffe/Tea Break Location: LHC Foyer
Session 4 Chair: Harvinder Jassal
04:00PM - 04:20PM Shafqat Ul Islam Jamia Millia Islamia [CANCELLED!] Investigating strong gravitational lensing effects by rotating Simpson–Visser black holes ---
04:25PM - 04:45PM Nisha Chahal NIT Jalandhar Quark matter in (2+1)-flavor Polyakov quark meson model at non-zero isospin ---
04:50PM - 05:10PM Jasjeet Bagla IISER Mohali Gravitational Lensing of incoherent wave packets of Gravitational Waves ---
05:15PM - 05:35PM K. P. Yogendran IISER Mohali The BTZ black hole spectrum ---
05:40PM - 05:45PM Anosh Joseph Closing Remarks --
05:45PM - 06:00PM Coffe/Tea Break Location: LHC Foyer

## Abstracts of Talks

Time/Speaker Title/Abstract
10:00AM - 10:20AM

Hemant Rathi (IIT Roorkee)
Title: Holographic JT gravity with quartic couplings

Abstract: We construct the most general theory of 2D Einstein-dilaton gravity coupled with U(1) gauge fields that contains all the 2-derivative and the 4-derivative interactions allowed by the diffeomorphism invariance. We renormalise the 2D action and obtain the vacuum solution as well as the black hole solution. The vacuum solution in the UV is dominated by Lifshitz_2 with dynamical exponent (z = 7/3) while on the other hand, the spacetime curvature diverges as we move towards the deep IR limit. We calculate the holographic stress tensor and the central charge for the boundary theory. We also compute the Wald entropy for 2D black holes and interpret its near horizon divergence in terms of the density of states. We compare the Wald entropy with the Cardy formula and obtain the eigenvalue of the Virasoro operator for our model. Finally, we explore the near horizon structure of 2D black holes and calculate the central charge corresponding to the CFT near horizon. We further show that the near horizon CFT may be recast as a 2D Liouville theory with higher derivative corrections. We study the Weyl invariance of this generalised Liouville theory and identify the Weyl anomaly associated with it.
10:25AM - 10:45AM

Swati Gavas (IISER Mohali)
Title: Probing universality of halo mass function using scale-invariant models

Abstract: Sheth Tormen mass function is widely used to quantify the abundance of dark matter halos. It is an improvement over the Press Schechter mass function as it uses ellipsoidal collapse in place of spherical collapse. Both of these mass functions can be written in a form that is universal, i.e., independent of cosmology and power spectrum, when scaled in suitable variables. However, cosmological simulations have shown this universality is approximate. In this work, we have probed the power spectrum dependence of halo mass function through a suite of N-body simulations of eight power-law models in an Einstein-de Sitter cosmology. This choice of cosmology and power-law power spectrum ensures self-similar evolution of dark matter distribution. This allows for isolating the power spectrum dependence of mass function. In this talk, we present fits for the parameters in the Sheth-Tormen mass function and show that there is a clear non-universality in that the values of these parameters depend on the index of the power law power spectrum. A theoretical explanation requires further development of the theoretical basis of the theory of mass function. In particular, we believe that the contribution of tidal interactions across perturbations at different scales may be responsible for this departure from universality.
10:50AM - 11:10AM

Vamika Longia (IISER Mohali)
Title: 2D SU(2) Yang-Mills theory using Tensor Networks

Abstract: Two-dimensional lattice Yang-Mills theory is analytically solvable. We can exactly compute the partition function of this theory using Tensor Network methods where one can expand the partition function in terms of characters of the gauge group for a particular irreducible representation. We derive a fundamental tensor corresponding to the partition function and compute the plaquette expectation value. In practice we compare the plaquette variable with the available exact result in the complex gauge coupling plane.
11:45AM - 12:05PM

Ayan Chatterjee (Central University of Himachal Pradesh)
Title: Exact solutions in higher curvature theories

Abstract: Exact solutions are not rare in General Relativity, but are so for higher curvature theories. However, even in 4 dimensions, it is important to search for these solutions. I shall present an effort to derive such solutions with symmetry.
12:10PM - 12:30PM

Pinaki Roy (IISER Mohali)
Title: Short Waiting Time Thermonuclear X-rays Bursts in 4U 1636-536: Challenge to existing ignition models?

Abstract: Thermonuclear (Type I) X-ray bursts are sudden surges in X-ray emission from an accreting neutron star in a Low-Mass X-ray Binary (LMXB). They result from the unstable burning of hydrogen and helium on the surface of the neutron star. X-ray bursts have been found to recur on timescales of hours or days. Burst occurring within 45 minutes of the preceding burst is conventionally labelled as short waiting time (SWT) burst. In this talk, I will present results from the spectro-timing analysis of 4U 1636-536 observed with NuSTAR and AstroSat. In three observations of 207 ks total exposure, we identify 31 thermonuclear X-ray bursts including five doublets and a triplet. Recurrence time as short as 3.8 minutes is seen in one of the doublets. To the best of our knowledge, this is the shortest recurrence time known for this source. We will discuss the plausible origin of short-recurrence time X-ray bursts and compare our observational results with proposed models of the neutron star envelope.
12:35PM - 12:55PM

Title: Deconfinement Phase Transition from Entanglement Entropy and ${\mathscr {M}} \chi$PT Compatibility

Abstract: Construction of ${\mathscr {M}}$-theory dual of thermal QCD-like theories at intermediate coupling was missing in the literature. This was taken care of by authors from our group in arXiv:2004.07259[hep-th] by incorporating ${\cal O}(R^4)$ terms in the gravity dual that was earlier constructed in arXiv:1306.4339[hep-th] by our group. This talk is based on some portion of our two papers, (i) arXiv:2011.04660[hep-th] and (ii) arXiv:2108.05372[hep-th]. In this talk, I will describe deconfinement phase transition in thermal QCD-like theories from the perspective of entanglement entropy. By dividing one of the spatial coordinates into segment of length $l$ and its compliment. There are two Ryu-Takayanagi surfaces - connected and disconnected. Below a critical value of $l$(which is denoted by $l_{crit}$), it is the connected surface that dominates the entanglement entropy and above the critical value of $l$, it is the disconnected surface that dominates the entanglement entropy. This is interpreted as confinement-deconfinement phase transition in thermal QCD-like theories. In arXiv:2011.04660[hep-th], by matching one of the LECs of NLO $SU(3)$ $\chi$PT Lagrangian computed holographically with its phenomenological data, we found that a specific combination of integration constants appearing in ${\mathscr {M}}$-theory metric perturbation has a definite sign. I will explain how we derived aforementioned constraint in arXiv:2108.05372[hep-th].
02:30PM - 02:50PM

Suraj Chopra (IISER Mohali)
Title: Quantum Rigid Body Dynamics

Abstract: TBA
02:55PM - 03:15PM

Misba Afrin (Jamia Millia Islamia)
Title: Can the EHT probe rotating black holes in Horndeski theory?

Abstract: The general belief that the Kerr metric describes the astrophysical black holes as encapsulated in the no-hair theorem remains an untested assumption. To probe the astrophysical nature of the M87* black hole, we take up rotating hairy black holes in the framework of Horndeski gravity with an additional hair parameter $h$ besides mass $M$ and spin $a$. The Event Horizon Telescope (EHT) constraints --- circularity deviation $\Delta C \leq 0.1$ and angular diameter $\theta_{d}=42 \pm 3 \mu as$ -- place upper bounds on both $a$ and negative values of $h$. Within this constrained parameter region ($a$-$h$) where the Horndeski black holes are viable candidates for the M87*, a systematic bias analysis quantifies the distinguishability of the Horndeski theory from GR over a substantial parameter region and motivates the test of the GR against the Horndeski gravity with electromagnetic observations viz., using the EHT resolution.
03:20PM - 03:40PM

Sanjay Pant (IIT Ropar)
Title: Effect of backreaction on holographic thermal correlators: From entanglement to chaos

Abstract: We study the effect of backreaction on the entanglement structure and on the chaotic dynamics for a large N strongly coupled thermal plasma. We use the holographic conjectures proposed by Ruy, Takayanagi and Umemoto to compute the holographic entanglement entropy and holographic entanglement of purification and observe the effect of backreaction on these respective measures. We apply the shockwave analysis as a holographic tool to diagnose the effect of backreaction on chaos. Finally we confirm the realization of chaos as the spread of entanglement.
04:00PM - 04:20PM

Shafqat Ul Islam (Jamia Millia Islamia)
Title: [CANCELLED!] Investigating strong gravitational lensing effects by rotating Simpson–Visser black holes

Abstract: We investigate strong-field gravitational lensing by rotating Simpson-Visser black hole, which has an additional parameter ($0\leq l/2M \leq1$), apart from mass ($M$) and rotation parameter ($a$). A rotating Simpson-Visser metric correspond to (i) a Schwarzschild metric for $l/2M=a/2M=0$ and $M \neq 0$, (ii) a Kerr metric for $l/2M=0$, $|a/2M|< 0.5$ and $M \neq 0$ (iii) a rotating regular black hole metric for $|a/2M|< 0.5$, $M \neq 0$ and $l/2M$ in the range $00.5$ and $l/2M\neq 0$. We find a decrease in the deflection angle $\alpha_D$ and also in the ratio of the flux of the first image and all other images $r_{mag}$. On the other hand, angular position $\theta_{1}$ increases more slowly and photon sphere radius $x_{m}$ decreases more quickly, but angular separation $s$ increases more rapidly, and their behaviour is similar to that of the Kerr black hole. The formalism is applied to discuss the astrophysical consequences in the supermassive black holes NGC 4649, NGC 1332, Sgr A* and M87* and find that the rotating Simpson-Visser black holes can be quantitatively distinguished from the Kerr black hole via gravitational lensing effects. We find that the deviation of the lensing observables $\Delta\theta_1$ and $\Delta s$ of rotating Simpson Visser black holes from Kerr black hole for \$0
04:25PM - 04:45PM

Nisha Chahal (NIT Jalandhar)
Title: Quark matter in (2+1)-favor Polyakov quark meson model at non-zero isospin

Abstract: We investigate the phase structure and thermodynamics of the Polyakov loop-extended three flavored quark-meson model at different values of quark chemical potential and temperature. We explore the effect of isospin chemical potential and baryon chemical potential on phase transition from confined hadronic state to deconfined quarks. The model is extended by the inclusion of vector-interactions and isospin asymmetric matter along with Polyakov loop. Due to the induction of isospin chemical potential, the phase structure of QCD is modified and hence play a significant role in identifying the transition temperature more precisely.
04:50PM - 05:10PM

Jasjeet Bagla (IISER Mohali)
Title: Gravitational Lensing of incoherent wave packets of Gravitational Waves

Abstract: Gravitational Waves have been detected from mergers of compact objects like neutron stars and black holes. A number of such events have been observed in the last six years. The signal from such events is coherent in that the amplitude and phase vary in a very precise manner and can be predicted given the parameters of the merging objects. Gravitational lensing of such signals has been studied and it has been shown that micro-lensing needs to be analyzed in the wave limit as the geometric optics limit is not valid. Another class of sources of gravitational waves are cataclysmic events like supernovae. Here the signal is incoherent and can be described as a noisy wavepacket. We present diagnostic tests to check for microlensing of such signals.
05:15PM - 05:35PM

K. P. Yogendran (IISER Mohali)
Title: The BTZ black hole spectrum

Abstract: I will present a proposal for the spectrum of this Conformal field theory by displaying a modular invariant partition function. I will also try to convey its relevance for black hole physics in the context of string theory.

## Participants

No Name Affiliation
1. Navdeep Singh Dhindsa IISER Mohali
3. Jasjeet Singh Bagla IISER Mohali
4. Harkirat Singh Sahota IISER Mohali
5. Anosh Joseph IISER Mohali
6. Ankit Dhanuka IISER Mohali
7. Kartik Joshi IISER Mohali
8. Nishat Fiza IISER Mohali
9. Swati Gavas IISER Mohali
10. Hemant Rathi IIT Roorkee
11. Minati Biswal IISER Mohali
12. Shagun Kaushal IIT Ropar
13. Kanwaljeet Singh Channey Chandigarh University
14. Sanatan Jaminy IISER Mohali
15. Harvinder Kaur Jassal IISER Mohali
16. Mandeep Kaur IISER Mohali
17. NItin Joshi IIT Ropar
18. Ayan Chatterjee Central University of Himachal Pradesh
19. Anirban Saha Shoolini University
20. Arpith Kumar IISER Mohali
21. Ambresh Shivaji IISER Mohali
22. Meenu IIT Ropar
23. Pinaki Roy IISER Mohali
24. Suresh C. Jaryal Central University of Himachal Pradesh
25. James Watt IISER Mohali
26. K P Yogendran IISER Mohali
27. Akash Singh IISER Mohali
28. Sanjay Pant IIT Ropar
29. Bharat Kumar Sirasva IISER Mohali
30. Nikhil Bansal IISER Mohali
31. Dipayan Mukherjee IISER Mohali
33. Navdeep Arya IISER Mohali
34. Vaishali Guleria Chandigarh University
36. Kinjalk Lochan IISER Mohali
37. Vishal Bhardwaj IISER Mohali
38. Nirmalya Kajuri IIT Mandi
39. Vamika IISER Mohali
40. Pramod Sharma IISER Mohali
41. Arpit Maurya IIT Ropar
42. Ajay Sharma IISER Mohali
43. Abhishek Samlodia IISER Mohali
44. Himanshu Jain IISER Mohali
45. Bana Singh IISER Mohali
46. Nisha Chahal NIT Jalandhar
47. Misba Afrin Jamia Millia Islamia
48. Shafqat Ul Islam Jamia Millia Islamia
49. Sauraj Bharti IISER Mohali
50. Sushant Ghosh Jamia Millia Islamia
51. Roshan Kaundinya IISER Mohali
52. I. K. Wasimakram IISER Mohali
53. Abhinna Sundar IISER Mohali
54. Kala G. Pradeep IISER Mohali