Previous Talks 

CHEP Seminar

Title: Universal features of 2 → N scattering in QCD and gravity from shockwave collisions

Speaker: Raju Venugopalan (Brookhaven National Lab)

Abstract: A remarkable double copy relation of Einstein gravity to QCD in Regge asymptotics is Γμν=(1/2)CμCν−(1/2)NμNν, where Γμν is the gravitational Lipatov vertex in the 2→3 graviton scattering amplitude, Cμ its Yang-Mills counterpart, and Nμ the QED bremssstrahlung vertex. In QCD, the Lipatov vertex is a fundamental building block of the BFKL equation describing 2→N scattering of gluons at high energies. Likewise, the gravitational Lipatov vertex is a key ingredient in a 2-D effective field theory framework describing trans-Planckian 2→N graviton scattering. We construct a quantitative correspondence between a semi-classical Yang-Mills framework for radiation in gluon shockwave collisions and its counterpart in general relativity. In particular, we demonstrate the Lipatov double copy in a dilute-dilute approximation corresponding to RS,L, RS,H ≪b, with RS,L, RS,H the respective emergent Schwarzchild radii generated in shockwave collisions and b is the impact parameter. We outline extensions of the correspondence developed here to the dilute-dense computation of gravitational wave radiation in close vicinity of one of the black holes, the construction of graviton propagators in the shockwave background, and a renormalization group approach to compute 2→N amplitudes that incorporates graviton reggeization and coherent graviton multiple scattering.

Date & time: 8th February 2024, 4 pm

Venue: LH3

CHEP Seminar

Speaker: Siddharth Prabhu, TIFR Mumbai

Title: Conformality of non-conformal correlators

Abstract: Recasting the flat space S-matrix as a boundary observable naturally leads us to a study of position space correlators. We describe the analytic structure of correlators of massless fields, and provide a description of the scattering submanifold i.e the space of all insertions that scatter in the bulk. Even though these correlators are not conformal, they can be recast as conformally invariant correlators, in other words, as functions of conformal cross ratios. This provides a new way to compute flat space massless correlators exactly. We apply this method to find exact answers for some Feynman diagrams involving massless fields, including several loop examples. We also show that flat space correlators of massive fields can be expressed as infinite sums of conformal correlators.

Time:  2:30 pm, 8th  February (Thursday) 2024

Venue: Lecture Hall 3, Physical Sciences Building

CHEP Seminar

Speaker: Vinayak Raj, IIT Kanpur

Title: Islands and dynamics at the interface

Abstract: We investigate a family of models described by two holographic CFT$_2$s coupled along a shared interface. The bulk dual geometry consists of two AdS$_3$ spacetimes truncated by a shared end-of-the-world (EOW) brane. A lower-dimensional effective model comprising of JT gravity coupled to two fat CFT$_2$ baths is subsequently realized by considering small fluctuations on the EOW brane and implementing a partial dimensional reduction where the transverse fluctuations of the EOW brane are identified as the dilaton field. We compute the generalized entanglement entropy for bipartite states through the island prescription in the effective lower-dimensional picture and obtain precise agreement in the limit of large brane tension with the corresponding doubly holographic computations in the bulk geometry. Furthermore, we obtain the corresponding Page curves for the Hawking radiation in this JT braneworld.

Time:  2 pm, 7th  February (Wednesday) 2024

Venue: Lecture Hall 3, Physical Sciences Building

CHEP Seminar

Speaker: Sridip Pal, Caltech

Title: Tauberian Theorems and High Energy Modular Bootstrap

based on arXiv:2307.02587 [hep-th] with Jiaxin Qiao and arXiv:2212.04893 [hep-th] with Jiaxin Qiao and Slava Rychkov

Time:  2:30 pm, 18th  January (Thursday)

Venue: Lecture Hall 3, Physical Sciences Building

CHEP Seminar

Speaker: Akshay Yelleshpur Srikant (Oxford)

Title: Two approaches to flat space holography 

Abstract: In this talk, I will outline the basic features of two approaches to flat space holography - Celestial and Carrollian - and how they are both related to the S-Matrix. I will then discuss correlation functions, their singularities and symmetries. 

Date: 5th January, 2024

Time: 2 pm

Venue: LH3

CHEP Seminar

Speaker: Jeevan Chandra Namburi, Cornell University

Title: On ETH and microstate averaging in quantum gravity

Abstract: In the talk, I shall describe the construction of black hole solutions in AdS$_{d+1}$ sourced by spherically symmetric thin shells of pressureless dust from which one can extract a universal function governing the statistics of microstate dynamics. This function determines the partition functions of the multi-boundary Euclidean wormhole geometries constructed by branching around the time-symmetric apparent horizon of these black holes, and in turn these wormholes help describe a replica formalism to coarse grain the black hole microstates. I shall then construct static star solutions in AdS$_{d+1}$ using thin shells with positive surface pressure and use these solutions to construct new single-boundary wormhole solutions which can estimate global charge violating amplitudes in quantum gravity. Finally, I shall show that the partition functions of multi-boundary wormholes constructed from stars are also consistent with the prediction from averaging black hole microstates. These results illustrate the universality of ETH-like statistics in quantum gravity.

Time:  11 am, 4th  January (Thursday) 2024.

Venue: Lecture Hall 3, Physical Sciences Building

CHEP SEMINAR

Speaker: Aditya Hebbar (Ecole Polytechnique, CPHT)  

Title: Constraining Glueball Couplings

Date and Time: at 3 pm on 3rd January, 2024

Abstract: We set up a numerical S-matrix bootstrap problem to rigorously constrain bound state couplings given by the residues of poles in elastic amplitudes. We extract upper bounds on these couplings that follow purely from unitarity, crossing symmetry, and the Roy equations within their proven domain of validity. First we consider amplitudes with a single spin 0 or spin 2 bound state, both with or without a self-coupling. Subsequently we investigate amplitudes with the spectrum of bound states corresponding to the estimated glueball masses of pure SU(3) Yang-Mills. In the latter case the 'glue-hedron', the space of allowed couplings, provides a first-principles constraint for future lattice estimates.

CHEP SEMINAR

Speaker: Shailesh Lal, Beijing Institute of Mathematical Sciences and Applications

Title: Neural Networks as Ansätze: Applications to Quantum Integrability

Abstract: We develop a novel neural network architecture, that learns solutions to the Yang Baxter equation for R matrices of difference form. This method already enables us to learn all solution classes of the 2d Yang Baxter equation. We propose and test paradigms for exploring the landscape of Yang Baxter equation solution space aided by these methods. Further, we shall also comment on the application of these methods to generating new solutions of the Yang Baxter equation. The talk is based on joint work with Suvajit Majumder and Evgeny Sobko available in part in arXiv:2304.07247.

Time: 3:30 pm, 19th  December (Tuesday) 2023

Venue: Lecture Hall 3, Physical Sciences Building

CHEP SEMINAR

Speaker: Manish Ram Chander, IMSc Chennai

Title: Theory dependence of black hole interior reconstruction

Abstract: An AdS eternal black hole in equilibrium with a finite temperature bath presents a Hawking-like information paradox due to a continuous exchange of radiation with the bath. The non-perturbative gravitational effect, the replica wormhole, cures this paradox by introducing a non-trivial entanglement wedge for the bath after Page time. In this talk, I will discuss the theory dependence of this non-perturbative effect by randomising the boundary conditions of some of the bulk matter fields in a model of JT gravity. Using the island formula and the extended strong subadditivity due to Carlen and Lieb, I will show that at late times the black hole interior is contained inside the entanglement wedge of a reference Hilbert space that encodes the information about the random boundary conditions. Consequently, the reconstruction of the black hole interior from the radiation, in particular the region near the singularity, requires a detailed knowledge of the theory.

Time: 4 pm, 14th  November (Tuesday) 2023

Venue: Lecture Hall 3, Physical Sciences Building

CHEP SEMINAR

Speaker: Nishant Gupta, IMSc, Chennai

Title: All chiral W-algebra extensions of so(2,3).

Date, time & venue:11th October (tomorrow) 2023 at 4pm in LH3.

Abstract: We show that there are four chiral W-algebra extensions of so(2,3) algebra and construct them explicitly. We do this by a simple identification of each of the inequivalent embeddings of a copy of sl(2,R) in the so(2,3) algebra. Then, using the standard 2D chiral CFT techniques we find the corresponding W-algebra extensions. Two of the four W-algebra are new, one of which may be thought of as the conformal bms3 algebra valid for finite values of its central charge, and the İnönü Wigner contraction of the other chiral W-algebra is a sector in celestial CFT that provides the holographic description of tree-level MHV graviton amplitudes. We then show how one obtains the latter chiral W-algebra as the asymptotic symmetry algebra of 3D conformal gravity and possibly of AdS4 gravity.

CHEP SEMINAR

Speaker: Narasimha Reddy, University of Lethbridge

Title: Non-Abelian Gauge Fields and Gravitational Waves 

Abstract: Gravitational waves (GWs) provide a new window to observe the universe. Detecting GWs requires an understanding of the interaction of GWs with the matter. In particular, we want to understand the role of primordial gravitational waves in the early universe cosmological processes like QCD Phase Transition. As a first step, we discuss the interaction of gravitational waves with SU(2) Yang-Mills waves in different backgrounds. We also discuss the interaction of GWs with the symmetry-broken phase of gauge fields. We also discuss the GW effect on condensates and quark-gluon plasma fluctuations. 

Date & time: 11th October, 2023 at 7pm

Venue: Online.

CHEP SEMINAR

Speaker: Pratik Nandy, Yukawa Institute for Theoretical Physics, Kyoto

Title: Recent progress on Krylov complexity

Abstract: The Hamiltonian evolution of a quantum system can cause a simple operator to become a complicated operator. This process reflects the scrambling of quantum information in the system. We probe such operator growth by Krylov complexity, quantifying the difficulty of simulating the operator evolution using a Krylov space method. We review the current progress and challenges of applying this approach to closed and open systems and illustrate some examples from the SYK model to quantum field theories.

Date and time: 10th October (tomorrow) 2023 at 3pm in LH3.

CHEP SEMINAR

Speaker: Pavan Dharanipragada, IMSc Chennai.

Title: Constructing a local AdS holographic dual from the ERG of a CFT

Date, Time & Venue: 3rd October 2023, at 4 pm in LH-3.

Abstract: The extra dimension in AdS/CFT, which is the radial direction in the bulk has the interpretation of the scale of the boundary theory. The programme of interpreting the bulk radial equations of motion as the boundary RG equations is called Holographic RG. I will present our work which does not assume the AdS/CFT correspondence, and begins with the boundary Wilsonian action, to obtain the bulk action from the exact RG of the boundary. I begin with the boundary theory, which is the free O(N) model in 3 dimensions, the AdS dual of which is the Vasilier higher spin theory in 4 dimensions. Deforming this theory with the scalar, vector current, and the energy momentum tensor, triggers an RG evolution. From the Polchinski ERG equation of this action, an evolution operator can be written and reintrepreted as a 4 dimensional functional integral. It becomes necessary to work a ``flipped" version of this ERG equation in order to make contact with AdS-CFT. I will describe the field redefinition that maps the action in the functional integral obtained to the AdS theory that is local at quadratic level. Then I will show how a local graviton scalar scalar interaction in the bulk can be obtained by suitable approximation.

CHEP Seminar

Speaker: Hemant Rathi, IIT-Roorkee

Title: $AdS_2/CFT_1$ holography at finite charge density

Date and Venue: 30th August 2023 at 3pm,  LH3.

Abstract:

I will briefly discuss $AdS_2/CFT_1$ holography, also known as JT/SYK duality, and explore various generalizations of JT gravity involving $U(1)$ gauge fields and $SU(2)$ Yang-Mills interactions. In particular, we will investigate the effects of non-trivial gauge couplings on the thermal properties of black holes/wormholes and examine the possibilities of the Hawking-Page transition and wormhole to black hole phase transition in two dimensions. Additionally, we will examine the transformation properties of the boundary stress-energy tensor under diffeomorphism and U(1) gauge transformation, thereby computing the central charge associated with the 1D boundary theory.

CHEP Seminar

Title : Marginal deformations of N = 2 SCFTs and Graviton spectrum

Speaker : Sourav Roychowdhury, Indian Association for the Cultivation of Science (IACS), Kolkata, India.

Date and Time: 24th August 2023 at 4pm 

Venue: LH3

Abstract : In this talk I will discuss the holographic dual of N = 2 SCFTs along with its marginal deformation. In particular I will show that due to the presence of the deformation factor, we yield a continuous graviton spectrum in deformed background. I will make comments on possible dual gauge theory operators corresponds to these modes.

The talk is based on the following paper:

S. Roychowdhury and D. Roychowdhury, “Spin 2 spectrum for marginal deformations of 4d N = 2 SCFTs,”

JHEP 03, 083 (2023), arXiv: 2301.12757 .

CHEP Seminar

Speaker: Jnanadeva Maharana, IOP Bhubaneshwar

Title: IS THE SCATTERING AMPLITUDE ANALYTIC IN A FIELD THEORY WITH A COMPACT SPATIAL COORDINATE?

Abstract: 

We consider a massive scalar field in five dimensional spacetime and then compactify one spatial dimension on a circle. In the context of potential scattering, Khuri considered a case when one spatial coordinate is compactified. He showed that, using Green function technique, the forward amplitude violates dispersion relation. If that will be true for QFT the consequences are serious. We show for above mentioned QFT that forward dispersion relation is safe. We also prove nonforward dispersion 

relation in compactified QFT.

Time: 3:30 pm, 10th  August (Thursday) 2023

Venue: Lecture Hall 3, New Physical Sciences Building

CHEP Seminar

Speaker: Ruchira Mishra, University of Chicago

Title: Applied nonrelativistic conformal field theory: scattering-length and effective-range corrections to nuclear physics

Abstract: In a range of energy, neutrons are described by the nonrelativistic conformal field theory of unitarity fermions, perturbed by one relevant and an infinite number of irrelevant operators.  We develop a formalism which provides a definition of local operators in that nonrelativistic conformal field theory.  We compute the scattering-length and effective-range corrections to the two-point functions of primary charge-3 operators.  These calculations allow us to find the first corrections to the scale-invariant behaviours of the rate of nuclear reactions with three neutrons in the final state in the regime when the neutrons have small relative momenta.

Time: 4 pm, 25th  July 2023 (Tuesday)

Venue: E1-14, New Meeting Room

CHEP Seminar

Speaker: Sayantani Bhattacharya, NISER Bhubaneswar.

Title: The zeroth law of black hole thermodynamics in arbitrary higher derivative theories of gravity

Date and Time: 16th June 2023 at 2:30 pm.

Venue: LH3

Abstract:  

We consider diffeomorphism invariant theories of gravity with arbitrary higher derivative terms in the Lagrangian as corrections to the leading two derivative theory of Einstein’s general relativity. We construct a proof of the zeroth law of black hole thermodynamics in such theories. We assume that a stationary black hole solution in an arbitrary higher derivative theory can be obtained by starting with the corresponding stationary solution in general relativity and correcting it order by order in a perturbative expansion in the coupling constants of the higher derivative Lagrangian. We prove that surface gravity remains constant on its horizon when computed for such stationary black holes, which is the zeroth law. We argue that the constancy of surface gravity on the horizon is related to specific components of the equations of motion in such theories. We further use a specific boost symmetry of the near horizon space-time of the stationary black hole to constrain the off-shell structure of the equations of motion. Our proof for the zeroth law is valid up to arbitrary order in the expansion in the higher derivative couplings.

CHEP Seminar

Speaker: Sachin Jain, IISER Pune

Title: Bulk Locality of Higher Spin theories, a CFT perspective

Abstract: It has been recently pointed out that HS theories are not local from bulk perspective. Our aim would be to explore possibility to make bulk theory local or find a subsector local by breaking HS symmetry weakly. In this discussion Momentum space CFT will play key role. I'll  briefy review recent progress made on 3d CFT in momentum space.

Time: 3 pm, 9th  May (Tuesday) 2023.

Venue: Lecture Hall 3, New Physical Sciences Building

CHEP Seminar 

Speaker: Abhiram Kidambi, Kavli IPMU, Tokyo University

Title: Gravitational Path Integrals in N = 4 string theory

Abstract: Using the microscopics (CFT) calculation of BPS BH entropy in N = 4 string theory, we improve on the localization techniques of the quantum entropy function. 

We find that the result involves a sum over Euclidean backgrounds including orbifolds of the Euclidean attractor geometry. We further show how a rewriting of the degeneracy formula is amenable, at a semi-classical level, to a gravitational interpretation involving 2D Euclidean wormholes.

Time: 2:30pm, 2nd May 2023. 

Venue: LH3.

CHEP Seminar

Speaker: Surbhi Khetrapal, University of Hyderabad.

Title: Quantum chaos in low dimensional quantum systems

Date and Time: 19th April 2023 at 2:30 pm.

Venue: LH-3.

Abstract: In this talk we will look at quantum chaos in two types of quantum systems: 1) A system of bosons in a Harmonic trap with weak contact interaction: in this case, the existence of quantum chaos is characterised by Wigner-Dyson distribution in the level-spacing statistics. 2) Conformal field theory (CFT) in two dimensions at large central charge, where quantum chaos is characterised by the out-of-time-ordered correlator (OTOC). (a) First, we will look at a computation of the OTOC in a CFT with unequal temperatures for left- and right- moving modes dual to a rotating black-hole. We find that the OTOC exhibits periodic oscillations about an average Lyapunov growth. We also study the OTOC in the extremal limit of the dual black-hole, and find that there are short periods of exponential growth in this largely integrable system. (b) Secondly, we compute the OTOC in a zero temperature 2d CFT under evolution by a certain combination of Virasoro generators (L_{+1}+L_{-1}), usually encountered in the study of inhomogeneous quenches. A bound was proposed on the growth of the OTOC set by the operator growth (i.e. rate at which an operator becomes more complex under evolution). In this theory, we find that the OTOC saturates this bound. We explain the bound saturation by expressing the Hamiltonian as the modular Hamiltonian of CFT with half-space traced out.

CHEP Seminar

Speaker: Onkar Parrikar, TIFR Mumbai. 

Title: Canonical Purification, Bulk reconstruction and the Quantum extremal shock

Date and Time​: 24th March,2023 at 2:30 pm.

Venue:​ LH3.

Abstract: We will discuss the canonical purification (with respect to one of the parties) of pure, bi-partite states obtained by turning on sources in the Euclidean path integral. In holographic conformal field theories, the Lorentzian bulk dual of the canonical purification consists of the corresponding entanglement wedge glued to its CPT image at the quantum extremal surface. However, the mismatch in the classical expansions at the QES due to quantum corrections needs to be supported by a shock in the bulk matter stress tensor in order for the bulk to satisfy Einstein's equations. Working perturbatively to first order in double-trace sources around the thermofield double state, we will demonstrate that the state of the bulk matter in the dual to the canonically purified boundary CFT state precisely has this quantum extremal shock in the bulk stress tensor. Along the way, we will discuss applications of these results to entanglement wedge reconstruction beyond HKLL. 

CHEP Seminar (Online)

Title: Quantum complexity and bulk timelike singularities

Speaker: Gaurav Katoch, IIT Hyderabad.

Date and Time: 13th March, Monday at 2.30 pm.

Abstract: In this talk, I will discuss the possibility of using holographic complexity as an alternative tool to the Gubser criterion in diagnosing bulk timelike singularities. Gubser criterion allows those naked timelike singularities which arise in the extremal limits of geometries containing cloaked singularities. I will present three examples we studied that hinted at the viability of action complexity as a reliable probe in the investigation of timelike singularities.  We propose that if the holographic (action) complexity of the quantum states dual to the bulk geometry containing naked timelike singularities is less than that of empty AdS, then that singularity cannot arise in the semiclassical limit of a UV-complete theory of quantum gravity.

YouTube Link: https://youtu.be/M6BaffgorUc

CHEP Seminar

Speaker: Pratik Rath, University of California, Santa Barbara.

Title: Multipartite entanglement in Holography and Tensor Networks

Date and Time: 9th March 2023, at 2.30 pm.

Venue: Lecture Hall 3, New Physical Sciences Building.

Abstract: In this talk, I will discuss various measures of multipartite entanglement such as the entanglement negativity and reflected entropy. I will use random tensor networks as a toy model for the replica trick, and apply lessons learnt from it to holographic systems. This will teach us about replica symmetry breaking and the failure of bit threads in capturing tripartite entanglement.

CHEP Seminar

Speaker: Tanay Milind Kibe, IIT Madras

Title: Encoding quantum information into black holes.

Date and Time:  17th February 2023, 4:00 pm

Venue: Online on Teams.

Abstract: Black holes past their Page time are extremely intriguing objects that display interesting information processing properties. Information thrown into such black holes after Page time is rapidly (after scrambling time) revealed into the Hawking radiation, whereas the information about the interior takes a long time to be revealed. Hayden and Harlow have argued that the time scale to decode the information about the interior from the radiation is extremely large compared to the evaporation time scale of the black hole, thus avoiding many paradoxes. Motivated to understand such features we study simple quantum systems coupled to an asymptotically AdS2 black hole and show how the initial state of the quantum system is encoded into the semi-classical black hole. These results can be applied to a class of black hole microstate models to understand some of the information processing properties of black holes such as information mirroring.

YouTube link: https://youtu.be/XyHkSCQnF9s

CHEP Seminar

Speaker:  Aradhita Chattopadhyaya ( Dublin Institute for Advanced Studies )

Title:  Numerical experiments on coefficients of instanton partition functions

Date and Time:  15th February 2023,  4:00 pm

Venue:  Lecture Hall 3, New Physical Sciences Building.

Abstract:   We analyze the coefficients of partition functions of Vafa-Witten theory for the complex projective plane ℂℙ2. We experimentally study the growth of the coefficients for gauge group SU(2) and SU(3), which are examples of mock modular forms of depth 1 and 2 respectively. We also introduce the notion of ``mock cusp form'' and study an example of weight 3 related to the SU(3) partition function.  Numerical experiments on the first 200 coefficients suggest that the coefficients of a mock modular form of weight k grow as the coefficients of a modular form of weight k, that is to say as 

nk−1. On the other hand, the coefficients of the mock cusp form appear to grow as n3/2, which exceeds the growth of classical cusp forms of weight 3. We provide bounds using saddle point analysis, which however largely exceed the experimental observation.

Faculty Seminar

Speaker: Prof. Chethan Krishnan,  CHEP,  IISc  Bangalore.

Title: Fuzzballs and Random Matrices 

Date and Time:  15th Feb 2023,  Wednesday 2:30 PM

Venue : LH-3

Abstract:

The fuzzball proposal is a controversial idea in string theory that claims that the true nature of black holes is that spacetime "stops" at the horizon. It has some encouraging features, but also some discouraging ones. One of the discouraging features is that (it is generally believed that) the fuzzball paradigm cannot realize the expectation that black holes are quantum chaotic systems, highly efficient at scrambling information. In order to satisfy this expectation, fuzzballs will have to have the spectral features of a random matrix, which is supposed to be challenging. In this talk, I will discuss an extremely simple calculation that suggests that this expectation is likely wrong, and that the fuzzball paradigm almost certainly can incorporate the key features of random matrix spectra. The calculation also suggests interesting new ideas about random matrices and the nature of their spectra.

CHEP Seminar

Speaker: Arnab Rudra, IISER Bhopal.

Title: On-shell Supersymmetry and higher-spin amplitudes

Date and Time: 13th February 2023 at 4 p.m.

Venue: Lecture Hall 3, New Physical Science Building. 

Abstract: We investigate the constraint from supersymmetry on the interaction of higher spin particles. We use on-shell Supersymmetry to constrain the three-point function of two massless particles and one massive particle in 3+1 dimensions. We use this framework to write down the tree-level four-point function of massless particles for theories with 4, 8 and 16 supercharges. In particular, we derive the expressions for four-photon/gluon amplitudes with a massive higher spin exchange in theories with N=4 Supersymmetry in 3+1 dimensions. If time permits, we will mention the extension of this story to higher dimensions.  

Reference: The talk is primarily based on 2209.06446 and the references mentioned in that preprint. 

CHEP Seminar

Speaker: Gautam Mandal, DTP, TIFR Mumbai.

1st Talk:

Title: Black hole evaporation, nonlinear noise and Thermalization in SYK

Date and Time: 9th February 2023 at 3.30 pm (Time changed)

Venue: Lecture Hall 3, New Physical Science Building.

Abstract: We describe a model of evolving pure states in an SYK model coupled to a bath, where the coupling is nonlinear. Once the bath is integrated out, the effective SYK model has non-Markovian evolution. The system shows some unconventional thermalization. The AdS dual provides an exact microscopic model of Black hole evaporation.  

2nd Talk:

Title: Target Space Entanglement

Date and Time: 10th February 2023 at 11.00 am (Please note the unusual timing).

Venue:  Lecture Hall 3, New Physical Science Building.

Abstract: Motivated by the Bekenstein Hawking formula and the area law behaviour of entanglement entropy, we propose that in any UV finite theory of quantum gravity with a smooth spacetime, the total entropy for a pure state in a co-dimension one spatial region, to leading order, is given by S = A/4G_N, where A is the area of the co-dimension two boundary.

CHEP Seminar

Title: Dispersion Relations:  From Classical Optics to String Theory

Speaker:  N.D. Hari Dass, Retd. Senior Professor, IMSc

Date and Time:  8th February 2023, 4:00 pm

Venue:  Lecture Hall 3, New Physical Sciences Building.

Abstract: I shall give a pedalogical narration of how a simple, but intriguing relation about colors impacted the most modern developments in physics, even to the point of anticipating String Theory. The strong thread that held these pearls of scientific creativity was the powerful mathematical idea of analyticity, which in this physical context turned out, rather surprisingly,  to be a consequence of the deeply cherished physical principle of Causality.

The talk will be at a level accessible to a wide audience.

Math-Physics Journal Club(CHEP) Talk

Title: Supersymmetric black holes and T\bar{T} deformation

Speaker: Swapnamay Mondal, Trinity College, Dublin

Date and Time: 3rd  February, 4:00 pm

Venue: Lecture Hall 3, New Physical Sciences Building.

Abstract:

The entropy of supersymmetric black holes in string theory compactifications can be related to that of a D- or M-brane system, which in many cases can be further reduced to a two-dimensional conformal field theory (2d CFT). For black holes in M-theory, this relation involves a decoupling limit where the black hole mass diverges. We suggest that moving away from this limit corresponds to a specific irrelevant perturbation of the 2d CFT, namely the supersymmetric completion of the T\bar{T} deformation. We demonstrate that the black hole mass matches precisely with the T \bar{T} deformed energy levels, upon identifying the T \bar{T} deformation parameter with the inverse of the leading term of the black hole mass. We discuss implications of this novel realization of the T \bar{T} deformation, including a Hagedorn temperature for wrapped M5-branes.

Title: Searches for supersymmetry, leptoquarks and muon high-level trigger at CMS

Speaker: Dr. Bibhuprasad Mahakud (CMS experiment, Purdue University, USA)

Time and Date: 2:30 p.m. on 29th Jan 2020 (Wednesday)

Venue: Multimedia Room, New Physical Sciences Building

Abstract:

Large Hadron Collider (LHC) at CERN is one of the finest human endeavour to understand the physics of the standard model (SM) and beyond. Despite being phenomenally successful, SM has several drawbacks: it does not explain dark matter, the stability of Higgs boson mass etc. In this context, the talk will summarize my work on  searches for supersymmetry in multijet final states,  leptoquarks in electron final states, some pileup mitigation techniques and muon high-level trigger (HLT). The muon HLT at Compact Muon Solenoid (CMS) experiment filters uninteresting  data from proton-proton collision using advanced algorithms implemented in software. Besides showing the results,  I will also discuss some general statistical techniques with reference to the above analyses. All the searches use the data collected by CMS experiment at a proton-proton centre of mass energy of 13 TeV.

Title: Feynman Integral: From Integration-By-Parts reduction to Intersection Theory

Speaker: Dr. Manoj Kumar Mandal (University of Padova) 

Date and Time:  2.00 p.m. (Thursday) January 23, 2020

Venue: D1-06, New Physical Sciences Building

Abstract: 

Scattering amplitudes encode crucial information about collision phenomena in our universe, from the smallest to the largest scales. Evaluation of multi-loop Feynman integrals are an integral part of the determination of these scattering amplitudes and related quantities. The Feynman integrals obey linear relations, which are exploited by employing the standard Integration-By-parts identities to simplify the evaluation of scattering amplitudes: they can be used both for decomposing the scattering amplitudes in terms of a basis of functions, referred to as master integrals (MIs), and for the evaluation of the latter using the differential equation. I will show that they are better understood using the Intersection Numbers, which act as scalar products between the vector spaces of the Feynman Integral. Application to few Feynman integrals at one- and two-loops will be shown, thereby sketching the first step towards potential applications to generic multi-loop integrals.

Title: Upgrade of the CMS Drift Tube muon detector system and associated activities

Speaker: Dr. Saranya Ghosh (CMS experiment, RWTH Aachen University, Germany)

Time and Date: 3.00 p.m. on 20th Jan 2020 (Monday)

Venue: Multimedia Room, New Physical Sciences Building

Abstract: 

Drift Tubes (DT) chambers make up the muon detector system in the central region of the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC). The LHC is planned to be upgraded to the High Luminosity LHC (HL-LHC) after 2025, and the electronics for the DT system is to be upgraded to deal with the higher rates expected in the new environment of the HL-LHC. Prototypes of the upgraded electronics system are already being tested during the second long shutdown period of the LHC, between 2019 and 2020. The details of the CMS DT system and its upgrade will be discussed in this presentation, with a special focus on the calibration of the DT system.

​Title: Deriving the AdS_3/CFT_2 correspondence

     Speaker: Rajesh Gopakumar (ICTS)

Venue: LH 3 New physics building, 2.30pm, 19th December

    Abstract:

It was recently argued that string theory on AdS3 × S3 × T4 with one unit (k = 1) of NS-NS flux is exactly dual to the symmetric orbifold CFT Sym^N(T4). In this paper we show how to directly relate the n-point correlators of the two sides to one another. In particular, we argue that the correlators of the world-sheet theory are delta-function-localised in string moduli space to those configurations that allow for a holomorphic covering map of the S2 -boundary of AdS3 by the world-sheet. This striking feature can be seen both from a careful Ward identity analysis, as well as from semi-classically exact AdS3 solutions that are pinned to the boundary. The world-sheet correlators therefore have exactly the same structure as in the Lunin-Mathur construction of symmetric orbifold CFT correlators in terms of a covering surface — which now gets identified with the world-sheet. Together with earlier results this essentially demonstrates how the k = 1 AdS3 string theory becomes equivalent to the spacetime orbifold CFT in the genus expansion.

Speaker : Tathagata Ghosh

Date and time : 17/12/2019(Tuesday), 3:00pm

Venue: LH3, New Physical Sciences building

Title: Lepton Number Charged Scalar at the LHC

Abstract:

In this talk, I'll discuss the neutrino non-standard interaction induced by leptonic scalars, $\phi$, which are SM gauge-singlets, and carry two units of lepton-number-charge. These leptonic scalars are forbidden from interacting with the Standard Model (SM) fermions at the renormalizable level and if one allows for higher-dimensional operators, couple predominantly to SM neutrinos. For masses at or below the electroweak scale, $\phi$ decays exclusively into neutrinos. Its unique production signature at hadron collider experiments like the LHC would be via the vector boson fusion process and lead to same-sign dileptons, two forward jets in opposite hemispheres, and missing transverse energy. I'll show that the sensitivity of high-energy colliders is largely complementary to that of low-energy and precision measurements of the decays of charged leptons, charged mesons, W and Z bosons, neutrino beam experiments like MINOS, searches for light dark matter in NA64 and searches for neutrino self-interactions at IceCube and in cosmological observations. For $\phi$ mass larger than a few GeV, our projected LHC sensitivity would surpass all existing bounds.

Talk slides can be downloaded from here

Speaker: Shubham Maheshwari (Groningen)

Date and time: 17th December, 11 AM

Location: LH3, New Physical Sciences Building

Title -  Perturbations in higher derivative gravity beyond maximally symmetric spacetimes

Abstract -

I will introduce non-local gravity which avoid ghosts despite the presence of higher derivatives. Such theories may avoid the usual pathologies of gravity because they contain an infinite number of derivatives. But the question of well-behavedness of perturbations around specific backgrounds, needs to still be addressed. For maximally symmetric spacetimes, this was done before. We look into perturbations of such theories around certain non-maximally symmetric backgrounds, and show that indeed there exists theories of this type with no ghosts. 

Reference: arXiv:1905.03227

Speaker: Abhishek Mohapatra

Date and time: 16th December, 2019, Friday, 3 p.m.

Venue: LH3, New Physical Sciences building

Title:  Double Heavy baryons and Corrections to Heavy Quark- Diquark Symmetry

Abstract:

Doubly heavy baryons (QQq) and singly heavy antimesons $( \bar{Q} q)$ are related by the heavy quark-diquark (HQDQ) symmetry because in the heavy quark limit, the light degrees of freedom in both the hadrons are expected to be in identical configurations. Hyperfine splittings of the ground states in both systems are nonvanishing at ${\cal O}(1 / m_Q)$ in the heavy quark mass expansion and HQDQ symmetry relates the hyperfine splittings in the two sectors. In this talk, I will point out the existence of both perturbative and nonperturbative corrections to leading hyperfine splitting from HQDQ symmetry. The perturbative correction scales in powers of $\alpha_S$ and nonperturbative correction scales in powers of $\Lambda_QCD/m_Q$.   In the extreme heavy quark limit in which the potential between the quarks in the diquark is Coulombic, the perturbative correction to the hyperfine splittings is only a few percents or smaller for values of $\alpha_S$  relevant to doubly charm and doubly bottom systems.  We also argue that nonperturbative corrections to the prediction for the hyperfine splittings are suppressed by $(Λ_QCD/m_Q)^2$ which leads to hyperfine splitting corrections of order 10% in the charm sector and smaller in heavier systems. Eventually, I will compare my results to the lattice  calculations for hyperfine splittings.

Speaker: Shankha Banerjee.

Date and time: 13th December 2019, Friday, 2:30 p.m.

Venue: LH3, New Physical Sciences building.

Title: Constraining the Higgs-gauge couplings at the HL-LHC

Abstract:

In this talk, I will focus on the measurements of the Higgs couplings to the electroweak bosons, in the context of an effective field theory. I will also discuss the possibility of strongly constraining the couplings affecting the charged triple gauge boson vertices upon studying the Zh and Wh channels in the boosted Higgs regime. I will show the potential of the High-luminosity run of the LHC, to constrain such couplings to stronger degrees than LEP had constrained earlier. Finally, I will discuss the prospects of disentangling the various tensor structures in the hZZ/hWW vertices upon considering the full analytical structure of the Zh/Wh production and using the full angular information to resurrect the interference terms.

Talk slides can be downloaded from here

Pedagogical Lecture Series on Conformal Bootstrap

Kausik Ghosh, CHEP

Venue: LH-3, New Physical Sciences Building

3rd Dec    Tuesday (2:30-4.00 pm)

Basics of CFT and the bootstrap formulation in position space.

4th Dec    Wednesday (11:00 am-12.30 pm)

Mellin space approach to CFT bootstrap

5th Dec    Thursday (2:30-4.00 pm)

Mellin Bootstrap in 1d, comments on other modern developments and open problems.

Special CHEP Colloquium

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Title:  NMR simulation of topological phases

Date: 20/11/2019, Wednesday 

Time: 4.00 pm

Venue: Auditorium, New Physical Science building

Speaker: Prof Ling-Yan Hung (Fudan University)

Abstract:

We will talk about recent progress in NMR technologies simulating topological phases. NMR simulators are the prototypes of quantum computers. Its high fidelity and long coherent times have allowed the class of simulators to be the first to demonstrate the implementation of quantum algorithms such as the Shor algorithm for factorization.  

 We will describe how states are prepared, how they are evolved in time and various tricks that we can play with it, including measurements of topological properties such as modular matrices, and thus potentially applied to identifying phases of matter in future simulations.

References: Z Luo, J Li, Z Li, LY Hung, Y Wan, X Peng, J Du

Nature Physics 14 (2), 160

K Li, Y Wan, LY Hung, T Lan, G Long, D Lu, B Zeng, R Laflamme

Physical review letters 118 (8), 080502

Title: psi(2S) enhancement at high pT: An indication of QGP formation in p-Pb collision at LHC.

Speaker:  S. Ganesh

Date and time: 11/11/2019, 3:00pm (Monday)

Venue: Lecture Hall 3

Abstract:

Quark-Gluon Plasma (QGP) is a state of matter speculated to exist after the Big Bang, and reproduced at the LHC and RHIC. While, Pb-Pb collisions at LHC does produce QGP, uncertainty exists over the production of QGP in p-Pb collisions. Psi(2S) enhancement at high pT is proposed as a novel signature, which if found can indicate that QGP is indeed formed in p-Pb collisions at the LHC.

Talk slides can be downloaded from here

Title : Discovery prospects with jets at LHC

Speaker: Dr. Debarati Roy (ATLAS experiment, University of the Witwatersrand, Johannesburg)

Time and Date:  3.00 p.m. on 6th November 2019 (Wednesday)

Venue: Lecture Hall 3, New Physical Sciences Building

Abstract: 

Jets are collimated bunches of hadrons, originating from quarks and gluons. They are produced in high energy proton-proton collisions at the Large Hadron Collider (LHC). It has direct manifestations to study different aspects of QCD and thus provide useful inputs to improve Monte Carlo model predictions in order to achieve precise measurements for Standard Model processes. LHC is a jet factory and thus either jets are the most dominating background in almost all new particle searches or it itself can act as a proxy of a new particle decaying hadronically. The higher is the energy of the LHC the more collimated is the hadronic decay products, resulting in the formation of a large radius jet. The internal structure of this jet is pretty much different from the structure of a QCD jet. Therefore this property is extensively utilized for signal background discrimination for a new particle search. Jet study is a wide ranging, a very rapidly developing field in LHC, widening the scope of its discovery potential at every new energy regime LHC runs. In this presentation, I will talk about some distinct features of jets, some recent jet measurements and jet related search where I have a significant contribution.

Talk slides can be downloaded from here

PHYSICS COLLOQUIUM

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          Speaker: Prof. Jayant Murthy (Indian Institute of Astrophysics)

          Title:  New advances in the diffuse ultraviolet background

          Date: 18th  October 2019 (Friday)

         Time: 4:00 P.M.

          Venue: Physical Sciences Auditorium

Abstract:

Although an important part of our Galaxy, interstellar dust is difficult to characterize. Historically, most of our information about dust has come from observations of extinction curves against background stars but these are limited to those directions where there are suitable stars. Infrared observations of the thermal emission from dust heated by the interstellar radiation field fills the sky and has yielded considerable information about the properties and the distribution of the dust. Ultraviolet observations of the scattered light from the dust have been difficult and sparse until the launch of the GALEX mission. I will discuss my extraction of this diffuse light from the GALEX data and what it tells us about the properties of interstellar dust. My primary focus will be on the modeling I am now doing and on its successes and deficiencies. I will also present our latest results on the background at the Galactic poles where we have discovered a new component of the extragalactic radiation field, one for which we do not yet know the source.

Speaker: Prof Aswin Balasubramanian

Affiliation: Rutgers University

Title: Geometric tools for mass deformed 4d N=2 theories 

Date: 17th September, 2:30pm. 

Venue: LH3, New Physical Sciences Building

Abstract: 

4d N=2 SUSY theories have proved to be an attractive laboratory for gaining insight into non-perturbative behaviour of QFTs. They have also acted as a rich source of connections between physics and modern mathematics which includes topics like four manifold invariants, wall crossing formulae and more recently, the geometry Langlands program. I will survey some of these ideas and then proceed to talk about how the geometry of the Hitchin integrable system can be used to understand the infrared behaviour of a large class of mass deformed 4d "Class S" N=2 SCFTs and their 3d N=4 cousins. The last part is based on recent work with J. Distler ( arXiv:1810.10652 ).

Title: Recent Probes of the Physics Beyond the Standard Model

Speaker: Dr. Amit Chakraborty (IISc) 

Date and Time:  2.00 p.m. (Friday) September 6, 2019

Venue: Lecture Hall 3, New Physical Sciences Building 

Abstract:

The discovery of the Higgs boson at the Large Hadron Collider experiment was believed to be a precursor towards the realization of the physics beyond the Standard Model (BSM). However, no direct sign of new physics is observed to date. This situation poses unique challenges (and opportunities) from both theoretical and experimental perspectives. In this talk, I'll review a few recent developments in the area of particle physics phenomenology. In particular, the aim would be to highlight the application of traditional techniques as well as state-of-the-art Machine Learning methods to improve current understanding of the Standard Model physics and enhance the discovery potential of the BSM physics at the ongoing and future collider experiments.

Title: Parton Distribution Functions for Discovery Physics

Speaker: Prof. Amanda Cooper Sarkar (University of Oxford) 

Date and Time:  3.00 p.m. (Monday) August 26, 2019

Venue: Lecture Hall 3, New Physical Sciences Building 

Abstract:

The uncertainty on parton distribution functions has become the largest uncertainty on searches for physics Beyond the Standard Model, both for direct searches for exotic phenomena and for precision measurements of SM parameters which may deviate from SM values. The current state of the art and prospects for improvement will be reviewed.

Talk slides can be downloaded from here

PHYSICS COLLOQUIUM

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          Speaker: Prof. Subir Sarkar (University of Oxford) 

 Title:  Is the universe isotropic?

Date: 23rd  August 2019 (Friday)

Time: 4:00 P.M.

Venue: Physical Sciences Auditorium

Abstract: 

It is a foundational `principle’ of the standard cosmological model that the universe is (statistically) isotropic when averaged over large scales. Recent surveys of the distribution of galaxies and studies of the relic cosmic microwave background radiation now make it possible to test this - with some intriguing results. I will discuss the implications of these findings, in particular for the usual inference that the expansion rate is accelerating, as if driven by a dominant component of ‘dark energy’. 

Talk slides can be downloaded from here

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Title: LZ experiment for dark matter search

Speaker: Prof. Henning Flaecher

Affiliation: University of Bristol, UK

Venue: Multimedia Room, Physical Sciences Building

Time: 4:30 pm, Thursday, 8th August 2019

Host: Dr. Somnath Choudhury

Abstract:

LUX-ZEPLIN (LZ) is a xenon-based direct detection dark matter experiment, currently under construction one mile below ground at the Sandford Undeground Research Facility in the USA. The experiment's 5.6 tonnes of fiducial volume will be a 22-fold increase over its predecessor, LUX. This will allow the experiment to be sensitive to 40 GeV WIMPs with spin-independent cross-sections as low as 1.6x10^{-48} cm^2 at 90% C.L. following an exposure of 1000 live days, which will begin in 2020. LZ is designed around a two-phase xenon time projection chamber, contained in an ultra-low background titanium cryostat, and surrounded by several auxiliary veto systems including an outer liquid xenon layer and a gadolinium-doped liquid scintillator detector. This presentation gives an overview of the experiment, its current status and timeline, and the predicted sensitivity and backgrounds.

Title: Constraining Dark Matter Models with Experiment

Speaker: Prof. Henning Flaecher

Affiliation: University of Bristol, UK

Venue: Lecture Hall 3, Physical Sciences Building

Time: 3 pm, Wednesday, 7th August 2019

Host: Dr. Somnath Choudhury

Abstract:

The nature of Dark Matter is one of the great unresolved questions in particle physics and cosmology. The prevalent hypothesis is that it is a new, only weakly interacting fundamental particle. As such, we hope to be able to produce it in colliders or to detect its interactions with nuclei in direct detection experiments. In this seminar I will discuss in how far experimental measurements constrain the parameter space of two specific dark matter models.

The first concerns simplified dark matter models with leptophobic mediator of spin 1. By performing a global analysis combining results from the LHC, direct detection searches and the relic dark matter density limits are set on the parameter space of the model, i.e., the masses and couplings.

The second analysis focusses on a specific NMSSM model, where gluinos and squarks decay to the NLSP, which in turn decays to the LSP - the dark matter candidate - plus a higgs boson. This is of particular interest as for light LSPs, the experimental signature results in only small amounts of missing energy, which is difficult to detect at the LHC.

At the end of the seminar I will briefly touch on what’s next for the LHC.