Institute Seminar Week

IMSc, Chennai, March 28-April 01, 2011

• Kunal Mukherjee

  Spectral Realizations in Ergodic theory and Masas in Finite von Neumann algebras

  Abstract:

  We discuss some recent progress in maximal abelian subalgebras of finite von Neumann algebras and its relation to the classical problem of spectral realizations in Ergodic theory.

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• Shrihari Gopalakrishna

  Beyond the Standard Model at the LHC

  Abstract:

  I will describe why we think that the standard model of particle physics is not complete, and some examples of new physics that the Large Hadron Collider (LHC) is presently looking for. I will highlight some recent results from the LHC.

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• Krishna Kumar Sabapathy

  Robustness of non-gaussian entanglement against noisy environments.

  Abstract:

  We study the robustness of non-gaussian entanglement in noisy attenuator and amplifier environments. We employ the operator-sum representation of these channels to analytically study the robustness and compare it with Gaussian entanglement in the same scenario. We find that there are simple examples of non-Gaussian states with 1 ebit entanglement that are more robust as compared to all Gaussian states.

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• V S Sunder

  Analysis of self-adjoint operators and their spectra

  Abstract:

  After a crash course on self-adjoint operators with a cyclic vector, we analyse the spectrum and spectral type of a near relative of a well-known operator.

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• Rajeev Singh

  Understanding The Uterine Puzzle : Collective Synchronized Oscillations without Pacemakers

  Abstract:

  In many biological systems, one can identify regions which give rise to oscillations, e.g. pacemaker cells in heart, central pattern generators in brain, etc. However there are other systems where no such pacemakers are present. One such system is uterus. During the gestation there is incoherent activity in the system but near the end of term we see completely synchronized electrical activity which gives rise to coherent contraction which ultimately leads to ejection of fetus. We try to understand such systems by treating the tissue as excitable cells with disorder present in form of passive cells. This approach can be used to understand pacemaking phenomena where it has been suggested that the individual cells do not oscillate spontaneously but rather the oscillations emerge as a result of interactions within a group of cells.

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• G Baskaran

  Repelling electrons crowd together and cooperate ?

  Abstract:

  Electrons in general repell. However, in a solid state environment they can gain energy by crowding and coming closer. When the crowd has a size of a few nanometers it is called nanoscopic phase separation. Crowded electrons have unexpected and strong cooperative behavior; for example ferromagnetism and superconductivity. In a recent collaborative work [1] with an experimental group, we have found that when two insulators (LaAlO3 and SrTiO3) are stuck together, nanoscopic electron droplets are spontaneously formed at the interface. They show signals of local high temperature superconductivity and high temperature ferromagnetism. I will review the physics behind this interesting experimental discovery.
  [1] Ariando, X Wang, G Baskaran et al., Nature Communications, Feb 2011

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• Vikram Shrama

  The Zero Problem

  Abstract:

  The Zero Problem asks whether a given numerical expression is equal to zero. For example, is $\sqrt{2}+\sqrt{3} - \sqrt{\sqrt{5}+\sqrt{24}} = 0$. The problem depends upon the class of numerical expressions; so, for instance, the number above belongs to the set of real numbers formed by taking integers, and the operations of addition, subtraction and square-roots. I will briefly describe an approach to solve the Zero Problem in the algebraic setting, remark on some aspects of its computational complexity, and point to some open problems in our understanding of the problem.

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• Rajarshi Pal

  Approximate joint measurement of spin-$\frac{1}{2}$ observables through a Stern-Gerlach like setup

  Abstract:

  Starting with the postulates of quantum mechanics I shall try to motivate a notion of approximate joint measurement of non-commuting observables like spin angular momentum along x and y directions. I shall follow this by trying to show how to do such a measurement in a Stern-Gerlach like setting.

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• R Ramanujam

  Private vs public, in distributed games

  Abstract:

  We discuss games in which players are spatially distributed and hence have only a partial view of the game arena. In our model, players' information partitions are generated explicitly by means of communication. We suggest a notion of locally consistent equilibrium and present an algorithm to determine the existence of such an equilibrium profile when communication is by means of public announcements. (In contrast, existence of Nash equilibrium is undecidable in the presence of private communications.) The work reported here is joint with Sunil Simon (CWI, Amsterdam).

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• G Rajasekaran

  Dark Energy, Neutrino Condensate and Pseudo-Dirac Neutrinos

  Abstract:

  Cosmologists have discovered that 70 percent of the stuff of the Universe is made of a mysterious entity called Dark Energy. We speculate that this entity might be a neutrino condensate. We show that just as electrons in a metal form a condensate that leads to Superconductivity, neutrinos pervading the Universe can form a condensate leading to Dark Energy. This however requires the neutrinos to be pseudo-Dirac type (which will be explained in the seminar).

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• Krishna Maddaly

  About Random Operators

  Abstract:

  I will discuss here several random operators and why they are interesting, the challenges in dealing with them.

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• Ayan Chatterjee

  Is quantum gravity necessary to understand black hole entropy?

  Abstract:

  It is a well known fact that black holes exist in nature. Quite surprisingly, black holes have thermodynamical properties like temperature and entropy. Boltzmann's arguments indicate that to understand entropy of a system, one has determine its microscopic constituents. In this case, the number of \emph{atoms} is of the order of $10^{80}$- quite large compared to the Avagadro number. Do we need quantum gravity to understand this huge entropy of black holes?

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• S Sridhar

  Can drifting spiral waves cause cardiac chaos?

  Abstract:

  In this talk I will outline our recent results on the study of the drift of spiral waves in a simple model of heterogeneous excitable medium, having gradients in the distribution of ion-channel expression or cellular coupling. I will discuss the anomalous drift of spiral waves toward regions having shorter period or stronger coupling, in reaction-diffusion models of excitable media. Such anomalous drift can promote the onset of complex spatiotemporal patterns, e.g., those responsible for life-threatening arrhythmias in the heart.

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• Chandrashekar Madaiah

  Parrond's game using quantum walk

  Abstract:

  I will present a quantum game in the form of Parrondo's game using quantum walk, a quantum analog of classical random walk. I will present a different strategy for two players A and B with different quantum coin operators, individually losing the game to emerge as joint winners or emerge as individual winners by using their coins alternatively. Significance of the game strategy in information theory and physical applications will also be briefly discussed.

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• Soumya Paul

  Parity and mean-payoff games

  Abstract:

  Parity games are used for the qualitative analysis of open reactive systems whereas mean-payoff games are used for their quantitative analysis. When we require to perform both kind of analyses of such systems, boolean combinations of the parity and the mean-payoff conditions are useful. We study games where one of the players has to play for the conjunction of the parity and mean-payoff objectives. We show that such games enjoy "semi-positional" determinacy and that the winning strategies can be effectively computed.

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• Jesrael K Mani

  Energy Anomaly and Polarizability of Carbon Nanotubes

  Abstract:

  In this talk I will review the work of Levitov et. al. in the study of CNTs in an external electric field. The electronic excitations are described by massless Dirac fermions on a cylinder, provided we include an anomalous term due to ulraviolet cutoff. Using this model, I will show how we can calculate the depolarization - the screening of the field inside the NT cylinder.

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• Amritanshu Prasad

  Relative positions in abelian groups

  Abstract:

  Two pairs of objects have the same relative position if a symmetry takes one pair to the other. We will discuss some invariants of relative positions of subspaces in vector spaces and finite abelian groups.

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• D Indumathi

  From quarks to mesons

  Abstract:

  Particles called mesons are seen to exist in Nature in groups having approximate symmetries. A simple model is presented that tries to capture the essential physics that fragments quarks (the building blocks of these particles) into these mesons.

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• Ronojoy Adhikari

  Statistical hydrodynamics of run-and-tumble particles : sedimentation and trapping

  Abstract:

  We simulate by lattice Boltzmann the nonequilibrium steady states of run-and-tumble particles (inspired by a minimal model of bacteria), interacting by far-field hydrodynamics, subject to confinement. Under gravity, hydrodynamic interactions barely perturb the steady state found without them, but for particles in a harmonic trap such a state is quite changed if the run length is larger than the confinement length: a self-assembled pump is formed. Thus kinetics, and not energetics, determines the nature of the non-equilibrium steady-states.

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• MVN Murthy

  Present status of the INO Project:

  Abstract:

  I will review the India-based Neutrino Project- (1) Location, (2) Physics Goals, (3) R\&D Status and (4) Future prospects.

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• Ghanashyam Date

  Why A Quantum Theory of Gravity?

  Abstract:

  For over fifty years, quantum gravity has been described as one of the most challenging problems of fundamental physics. What is the problem that theorists are supposed to be addressing? I will try to make a case for quantum gravity.

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• Moitri Maiti

  Classical dynamics of Dirac Fermions in 2+1 dimensions

  Abstract:

  We develop a semiclassical formalism for the Dirac fermions in 2+1 dimensions. We start with the single massless Dirac hamiltonian which has spin S. We define the path integral involving the coherent states. When S $>> \hbar$ then the system is said to be in classical regime. We take the appropriate limit by doing a systematic 1/S expansion to find out the corresponding classical equations of motion. The allowed orbits are chosen by Bohr-Sommerfeld quantization. We compare the spectrum obtained with the quantum mechanical in presence and absence of external fields. The semiclassical analysis for the free particle has an exact correspondence with the quantum mechanical results while for the external magnetic field it produces the zero and the lowest energy modes of the quantum spectrum.

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• Kunal Dutta

  On Induced Acyclic Subgraphs in Random Digraphs

  Abstract:

  (Joint work with C. R. Subramanian). Given a simple directed graph D = (V, A), let the size of the largest induced directed acyclic graph (dag) be denoted by mas(D). Consider a random instance, obtained by choosing each of the possible undirected edges independently with probability 2p and then orienting each chosen edge independently in one of two possible directions with probabibility 1/2. We shall talk about some recent progress on the range of concentration, upper and lower bounds of mas(D). These results also carry over to a related model which allows directed 2-cycles.

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• K Shiv Chaitanya

  Generation of all possiable quantum optical coherent states

  Abstract:

  A general master equation for the eigenstates of Janus-faced commutation relations is constructed. The short-term and steady-state solutions of this master equation form a Janus-faced pair and it also shown that the master equation works for all the Janus-faced coherent state operators.

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• Mubeena T

  Twisted conjugacy classes

  Abstract:

  Let G be a group, $\phi \in Aut(G)$. Two elements $x,y\in G$ are $\phi$-twisted conjugate if there is an element $g\in G$ such that $y=gx\phi(g^{-1})$. The equivalence class is called $\phi$-twisted conjugacy class. We will go through some examples for which every automorphism will have infinitely many twisted conjugacy classes, and few non-examples.

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• Sujay Ashok

  Gauge Theories without Feynman Diagrams

  Abstract:

  Quantum Field Theory is a theoretical framework for the study of quantum mechanical models involving infinite degrees of freedom. It is the quantitative basis for the Standard Model of particle physics as well as many condensed matter systems. One of the main physical observables in the context of particle physics is the S-matrix, which encodes the scattering data of particles. Recently there has been tremendous progress in developing new techniques to formulate a dual theory of the S-matrix. I will summarize some of these methods and results and show how they hint at a new conceptual reformulation of the theory where familiar concepts such as locality appear as emergent phenomena while certain symmetries, hidden in the traditional formulation, become manifest.

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• J. Meena Devi

  Functionalized gold particles

  Abstract:

  Gold has been a fascinating material from ancient times and noted for its use in ornaments, artwork and traditional medicine. In modern science and technology, gold particles are functionalized. Functionalization is done by attaching various ligands such as thiols, polymers or biomolecules(proteins, DNA) to gold. Properties of functionalized gold particles can be tuned by using combination of functionalising ligands, and by selectively changing the functional group. Strong interaction between sulphur atoms of thiols and gold form Au-S bonds which favour the chemisorption of thiol molecules into gold surface. I will discuss the molecular dynamics simulation study on the properties of alkanethiolate self assembled monolayer (SAM) on gold surface.

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• Partha Mukhopadhyay

  Tubular neighborhood of target manifold in non-linear sigma model

  Abstract:

  Propagation of a closed string in an arbitrary curved background is described by a two-dimensional quantum field theory known as generalized sigma model. I will discuss a Hamiltonian formulation of the theory using certain infinite dimensional language. In particular, I will describe an approach to set up a semi-classical expansion of the theory with the motivation of computing higher derivative corrections to general relativity.

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• Argha B

  The flow velocity profile near the snout of Satopanth glacier

  Abstract:

  We investigate measured longitudinal velocity profile near the snout of Satopanth glacier. The profile can be explained by assuming a parabolic bedrock shape and a sliding dominated flow, where the magnitude of sliding is proportional to the local ice-thickness. By numerically solving ice flow equations, we show that the contribution due to deformation can be neglected. We also find approximate analytic solutions of the flow equations which reproduces numerical results well.

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• Sitabhra Sinha

  Chimera order in spin systems

  Abstract:

  It has recently been shown that a population of oscillators having identical environments can exhibit a robust, partially ordered state characterized by the coexistence of incoherent, desynchronized domains with coherent, phase-locked domains. Such situations with heterogeneous phase topologies have been termed as chimera states. We have extended this phenomenon to the broader perspective of order-disorder transitions in systems where the interacting elements have discrete states, viz., spin systems. Such models are versatile enough to be used for understanding processes operating in a wide range of physical (e.g., magnetic materials), biological (e.g., neural networks) and social (e.g., opinion formation) systems. We can show by exact analytic treatment that chimera states can occur in a system of Ising spins in thermal equilibrium. We have also numerically established the existence of chimera ordering in 3-dimensional models of layered magnetic materials (such as manganites) suggesting possible means of experimentally observing it.

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• Meena Mahajan

  Composing efficient ZERO tests efficiently

  Abstract:

  For an n-variate polynomial p(X), the ZERO predicate on a Boolean input a in {0,1}^n takes the value 1 (True) if p(a)=0, and 0 (False) otherwise. For uniform families of efficiently computable polynomials, the ZERO predicate can be determined using space logarithmic in n. We can compose ZERO predicates as follows: For a set of n-variate polynomials p_1(X), p_2(X), ... p_t(X), and a t-variate polynomial q(Y), let b_j = ZERO(p_j(a)). The composed predicate on input a determines ZERO(q(b)). We show that determining the composed ZERO predicate is not much harder. And for the POSITIVITY predicate that is True exactly when p(a)>0, the composed predicate is not harder at all.

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• Rajesh Karan

  Electronic Charge reconstruction in Heterostructures

  Abstract:

  Multilayered nanostructures and thin films form the building blocks of most of the devices employed in electronics. Recently there has been an interest in examining new class of these devices that employ strongly correlated electron materials. Dynamical Mean-Field Theories are employed to study such nanostructures. Within this framework, it is not possible to study structures which are made of significantly large number of layers. These are limited to say ten layers. We extend this framework and derive a semiclassical approach to study these nanostructures, and our preliminary results are consistent with the DMFT results. We have planned to study the heterostructure which are made-up of dilute magnetic semiconductor. And this framework one of the part of our main plan.

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• Parameswaran Sankaran

  Playing ping-pong to ensure freedom

  Abstract:

  A classical result of Klein and Fricke, known as ping-pong lemma has been applied in a variety of contexts to study structure of groups. Will illustrate the lemma with a few examples.

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• Md Izhar Ashraf

  Which way does it read?: Determining the direction of writing in undeciphered texts

  Abstract:

  We show how statistical-computational methods can be used to infer the direction of reading for sequences written in an unknown language. Our studies, carried out over a large variety of writing systems, show that the beginning of a sequence has less constraint than the ending. This can be related to the large degree of freedom of choice in choosing the starting sound or symbol in an utterance, relative to severely curtailed freedom in choosing the sounds or symbols that follow later in the sequence. Thus, using entropy measures that quantify the number of possible choices which are allowed at different positions in a sequence, we can distinguish the beginning from the end of a given text - thereby obtaining the direction of writing. Our results for undeciphered texts, namely, the sequences obtained from artifacts of the Indus Valley civilization, confirms the widely held belief (based on indirect archaeological evidence) that they should be read from right to left.

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• R Simon

  A new(?) characterization of the regular $n$-simplex

  Abstract:

  I will first describe what I believe is a new characterization of the regular $n$-simplex, and then briefly outline a nontrivial application.

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