Ghanashyam Date

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• Ph. D.
• Professor (visiting) at Chennai Mathematical Institute

This is a brief note on a recently flagged issue \cite{CHK} regarding the precise characterization of quadrupolar truncation of the linearized gravitational waves in de Sitter space-time. An apparent inconsistency was noted while transforming the linearized solution truncated to quadrupolar contribution to the Bondi-Sachs form. A consistent truncat...

These are lecture notes of the QFT-I course I gave in an online mode at Chennai Mathematical Institute. The course focussed on the free relativistic quantum fields, their interactions in the perturbative scattering framework, standard computations of QED processes, radiative corrections at 1-loop with renormalization and an introduction to the tool...

An important class of observables for gravitational waves consists of the fluxes of energy, momentum and angular momentum carried away by them and are well understood for weak gravitational waves in Minkowski background. In de Sitter background, the future null infinity, $\mathcal{J}^+$, is space-like which makes the meaning of these observables su...

An important class of observables for gravitational waves consists of the fluxes of energy, momentum and angular momentum carried away by them and are well understood for weak gravitational waves in Minkowski background. In de Sitter background, the future null infinity, $\mathcal{J}^+$, is space-like which makes the meaning of these observables su...

The concordance model of cosmology favours a universe with a tiny positive cosmological constant. Innocuous as it may seem, a de Sitter background with its space-like null infinity, presents many qualitatively distinct features for a theory of gravitational radiation. Even for compact astrophysical sources, the intuition from Minkowski background i...

The concordance model of cosmology favours a universe with a tiny positive cosmological constant. A tiniest positive constant curvature, profoundly alters the asymptotic structure, forcing a re-look at a theory of gravitational radiation. Even for compact astrophysical sources, the intuition from Minkowski background is challenged at every step. Ne...

Polymer quantization was discovered during the construction of Loop Quantum Cosmology. For the simplest quantum theory of one degree of freedom, the implications for dynamics were studied for the harmonic oscillator as well as some other potentials. For more degrees of freedom, the possibility of continuous, kinematic symmetries arises. While these...

This is a review talk describing the recent work of Martin Bojowald on Loop Quantum Cosmology.

Loop quantum gravity, a non-perturbative and manifestly background free, quantum theory of gravity implies that at the kinematical level the spatial geometry is discrete in a specific sense. The spirit of background independence also requires a non-standard quantum representation of matter. While loop quantization of standard model fields has been...

Fermions constitute an important component of matter and their quantization in presence of dynamical gravity is essential for any theory of quantum gravity. We revisit the classical formulation adapted for a background free quantization. The analysis is carried out with the Hilbert-Palatini form for gravity together with the Nieh-Yan topological te...

These lecture notes were prepared as a basic introduction to the theory of constrained systems which is how the fundamental forces of nature appear in their Hamiltonian formulation. Only a working knowledge of Lagrangian and Hamiltonian formulation of mechanics is assumed. These notes are based on the set of eight lectures given at the {\em Refresh...

A School on Loop Quantum Gravity was held at the IMSc during Sept 8 -- 18, 2009. In the first week a basic introduction to LQG was provided while in the second week the focus was on the two main application, to cosmology (LQC) and to the black hole entropy. These notes are an expanded written account of the lectures that I gave. These are primarily...

Quantum corrections of certain types and relevant in certain regimes can be summarised in terms of an effective action calculable, in principle, from the underlying theory. The demands of symmetries, local form of terms and dimensional considerations limit the form of the effective action to a great extent leaving only the numerical coefficients to...

We set up a canonical Hamiltonian formulation for a theory of gravity based on a Lagrangian density made up of the Hilbert-Palatini term and, instead of the Holst term, the Nieh-Yan topological density. The resulting set of constraints in the time gauge are shown to lead to a theory in terms of a real SU(2) connection which is exactly the same as t...

The sixth International Conference on Gravitation & Cosmology (ICGC-2007) was organized at IUCAA, Pune, 17-21 December 2007. This series of international meetings, held every four years under the auspices of the Indian Association for General Relativity and Gravitation (IAGRG), has now spanned two decades. Previous ICGC meetings were held at Cochin...

The vacuum Gowdy models provide much studied, non-trivial midi-superspace examples. Various technical issues within loop quantum gravity can be studied in these models and one can hope to understand singularities and their resolution in the loop quantization. The first step in this program is to reformulate the model in real connection variables in...

In this second paper on loop quantization of Gowdy model, we introduce the kinematical Hilbert space on which appropriate holonomies and fluxes are well represented. The quantization of the volume operator and the Gauss constraint is straightforward. Imposition of the Gauss constraint can be done on the kinematical Hilbert space to select subspace...

Since the past Iagrg meeting in December 2004, new developments in loop quantum cosmology have taken place, especially with regards to the resolution of the Big Bang singularity in the isotropic models. The singularity resolution issue has been discussed in terms of physical quantities (expectation values of Dirac observables) and there is also an...

Constructing a classical mechanical system associated with a given quantum mechanical one, entails construction of a classical phase space and a corresponding Hamiltonian function from the available quantum structures and a notion of coarser observations. The Hilbert space of any quantum mechanical system naturally has the structure of an infinite...

Loop quantization of diagonalized Bianchi class A models, leads to a partial difference equation as the Hamiltonian constraint at the quantum level. A criterion for testing a viable semiclassical limit has been formulated in terms of existence of the so-called preclassical solutions. We demonstrate the existence of preclassical solutions of the qua...

In classical general relativity, the generic approach to the initial singularity is usually understood in terms of the BKL scenario. In this scenario, along with the Bianchi IX model, the exact, singular, Kasner solution of vacuum Bianchi I model also plays a pivotal role. Using an effective classical Hamiltonian obtained from loop quantization of...

Nonperturbative corrections from loop quantum cosmology (LQC) to the scalar matter sector are already known to imply inflation. We prove that the LQC modified scalar field generates exponential inflation in the small scale factor regime, for all positive definite potentials, independent of initial conditions and independent of ambiguity parameters....

The absence of isotropic singularity in loop quantum cosmology can be understood in an effective classical description as the Universe exhibiting a big bounce. We show that with a scalar matter field, the big bounce is generic in the sense that it is independent of quantization ambiguities and the details of scalar field dynamics. The volume of the...

One of the qualitatively distinct and robust implication of Loop Quantum Gravity (LQG) is the underlying discrete structure. In the cosmological context elucidated by Loop Quantum Cosmology (LQC), this is manifested by the Hamiltonian constraint equation being a (partial) difference equation. One obtains an effective Hamiltonian framework by making...

Various topics were discussed at the parallel session on 'Quantum Aspects of Gravitation' (QAG) of the ICGC-2004. The Hartle-Hawking wave function of the universe in the presence of a negative cosmological constant was discussed. A new mechanism for the generation of matter-antimatter asymmetry based on loop quantum gravity (LQG) was introduced. A...

This is an expanded version of the summary talk given at the conclusion of the ICGC-2004 held at Kochi. Brief introductory remarks are included to provide a slightly wider context to the theme talks.

For a class of solutions of the fundamental difference equation of isotropic loop quantum cosmology, the difference equation can be replaced by a differential equation valid for {\em all} values of the triad variable. The differential equation admits a `unique' non-singular continuation through vanishing triad. A WKB approximation for the solutions...

The absence of isotropic singularity in loop quantum cosmology can be understood in an effective classical description as the universe exhibiting a Big Bounce. We show that with scalar matter field, the big bounce is generic in the sense that it is independent of quantization ambiguities and details of scalar field dynamics. The volume of the unive...

Non-perturbative corrections from loop quantum cosmology (LQC) to the scalar matter sector is already known to imply inflation. We prove that the LQC modified scalar field generates exponential inflation in the small scale factor regime, for all positive definite potentials, independent of initial conditions and independent of ambiguity parameters....

This is a written, expanded version of the summary talk given at the conclusion of the ICGC-2004 held at Cochin. Brief introductory remarks are included to provide a slightly wider context to the theme talks.

The Bianchi IX model has been used often to investigate the structure close to singularities of general relativity. Its classical chaos is expected to have, via the BKL scenario, implications even for the approach to general inhomogeneous singularities. Thus, it is a popular model to test consequences of modifications to general relativity suggeste...

In classical general relativity, the generic approach to the initial singularity is very complicated as exemplified by the chaos of the Bianchi IX model which displays the generic local evolution close to a singularity. Quantum gravity effects can potentially change the behavior and lead to a simpler initial state. This is verified here in the cont...

Homogeneous cosmological models with non-vanishing intrinsic curvature require a special treatment when they are quantized with loop quantum cosmological methods. Guidance from the full theory which is lost in this context can be replaced by two criteria for an acceptable quantization, admissibility of a continuum approximation and local stability....

In classical general relativity, the generic approach to the initial singularity is very complicated as exemplified by the chaos of the Bianchi IX model which displays the generic local evolution close to a singularity. Quantum gravity effects can potentially change the behavior and lead to a simpler initial state. This is verified here in the cont...

The dynamics of physical theories is usually described by differential equations. Difference equations then appear mainly as an approximation which can be used for a numerical analysis. As such, they have to fulfill certain conditions to ensure that the numerical solutions can reliably be used as approximations to solutions of the differential equa...

We consider the quantum mechanics of an electron confined to move on an infinite cylinder in the presence of a uniform radial magnetic field. This problem is in certain ways very similar to the corresponding problem on the infinite plane. Unlike the plane however, the group of symmetries of the magnetic field, namely, rotations about the axis and t...

We review aspects of classical and quantum mechanics of many anyons confined in an oscillator potential. The quantum mechanics of many anyons is complicated due to the occurrence of multivalued wavefunctions. Nevertheless there exists, for arbitrary number of anyons, a subset of exact solutions which may be interpreted as the breathing modes or equ...

Inspired by the discrete evolution implied by the recent work on loop quantum cosmology, we obtain a discrete time description of usual quantum mechanics viewing it as a constrained system. This description, obtained without any approximation or explicit discretization, mimics features of the discrete time evolution of loop quantum cosmology. We di...

Algebraic quantization scheme has been proposed as an extension of the Dirac quantization scheme for constrained systems. Semi-classical states for constrained systems is also an independent and important issue, particularly in the context of quantum geometry. In this work we explore this issue within the framework of algebraic quantization scheme...

We consider space-times which in addition to admitting an isolated horizon also admit Killing horizons with or without an event horizon. We show that an isolated horizon is a Killing horizon provided either (1) it admits a stationary neighbourhood or (2) it admits a neighbourhood with two independent, commuting Killing vectors. A Killing horizon is...

The Zipoy-Voorhees family of static, axisymmetric vacuum solutions forms an interesting family in that it contains the Schwarzschild black hole excepting which all other members have naked singularity. We analyze some properties of the region near singularity by studying a natural family of 2-surfaces. We establish that these have the topology of t...

A general analysis for characterizing and classifying `isolated horizons' is presented in terms of null tetrads and spin coefficients. The freely specifiable spin coefficients corresponding to isolated horizons are identified and specific symmetry classes are enumerated. For isolated horizons admitting at least one spatial isometry, a standard set...

At the classical level anyons with harmonic confinement are known to exhibit two important properties namely partial separability and pseudo-integrability. These stem from the fact that this system is locally identical to isotropic oscillator system but differs in the global topology of the phase space. We clarify the meaning of pseudo-integrabilit...

In the many-anyon problem in two space dimensions, irregular but square integrable solutions of the Schrodinger equation may exist. A class of such solutions is constructed for anyons confined in a harmonic oscillator. It is shown that these may have lower energies than the usual regular solutions, but they do not exist throughout the range between...

The classical ground state of a D- dimensional many body system with two and three body interactions is studied as a function of the strength of the three body interaction. We prove exactly that beyond a critical strength of the three body interaction, the classical ground state of the system is one in which all the particles are on a line. The pos...

We report on a study of a classical, finite system of confined particles in two dimensions with a two-body repulsive interaction. We first develop a simple analytical method to obtain equilibrium configurations and energies for few particles. When the confinement is harmonic, we prove that the first transition from a single shell occurs when the nu...

We report on a study of a finite system of classical confined particles in two-dimensions in the presence of a uniform magnetic field and interacting via a two-body repulsive potential. We develop a simple analytical method of analysis to obtain ground state energies and configurations. We prove analytically the minimum energy configurations are in...

The Einstein equation with T μυ = k μkυ + ℓ μℓυ where k, l are null is considered with spherical symmetry and staticity. The solution has a naked singularity and is not asymptotically flat. However, it may be interpreted as an envelope for any static spherical body making it more massive. Such an interpretation and some of its implications are deta...

These are the proceedings of the XVIII Conference of the Indian Association for General Relativity and Gravitation (IAGRG) held at the Institute of Mathematical Sciences, Madras, INDIA during Feb. 15-17, 1996. The Conference was dedicated the late Prof. S. Chandrasekhar. The proceedings consists of 17 articles on: - Chandrasekhar's work (N. Panchap...

Some of the recent developments in the Ashtekar program of quantization of gravity are discussed in this talk. 1 e-mail: shyam@imsc.ernet.in However, it is well to remember that a theory that is derived from simple and elegant basic ideas need not be a "correct" one. In the case of general relativity, the `simple and the elegant' ideas gave rise to...

The geometry of fracture patterns in a dilute elastic network is explored using molecular dynamics simulation. The network in two dimensions is subjected to a uniform strain which drives the fracture to develop by the growth and coalescence of the vacancy clusters in the network. For strong dilution, it has been shown earlier that there exists a ch...

We analyze the quantum spectrum of a rectangular billiard coupled to flux line. The nearest neighbor spacing distribution shows a transition from Poisson to almost Wigner distribution as the flux parameter is varied even though classically the system remains pseudointegrable and nonchaotic. In fact, the level statistics do not display any generic b...

In this paper we show that (a) all the known exact solutions of the problem of N-anyons in oscillator potential precisely arise from the collective degrees of freedom, (b) the system is pseudo-integrable ala Richens and Berry. We conclude that the exact solutions are trivial thermodynamically as well as dynamically. Comment: 19 pages, ReVTeX, IMSc/...

The spectrum of anyons confined in a harmonic oscillator potential shows both linear and nonlinear dependence on the statistical parameter. While the existence of exact linear solutions has been shown analytically, the nonlinear dependence has been arrived at by numerical and/or perturbative methods. We develop a method which shows the possibility...

We construct a class of exact eigenstates in energy for N anyons in an oscillator potential. These states interpolate linearly in energy between the Bose and Fermi limits of the spectrum.

We compute the homotopy groups \mathbbX\mathbb{X} \mathbbX\mathbb{X} is a compact two dimensional manifold for arbitrary genusg and- denotes the time coordinate. We also present the finite dimensional, unitary, irreducible, inequivalent representations of the appropriate fundamental groups and comment on some of their implications.

A generalization of Witten's non-abelian bosonization to gauge theories can be used to derive an effective action for the strong coupling limit of massive multiflavor QCD in 1 + 1 dimensions. Here we analyze this action and obtain the semi-classical spectrum of soliton solutions corresponding to the two-dimensional baryons. The possible flavor repr...

The BRST transformations of the string fields of the free open spinning string is analyzed. After expanding the string fields into ghost zero modes the BRST transformations are diagonalized and it is found that in the Ramond sector the physical fields are contained in only two string fields. A minimal covariant classical action for both sectors is...

An alternate and more general form of factorization for the Drell-Yan process is derived in perturbation theory. Corresponding generalized anomalous dimensions are defined. Simple calculations verify Mueller's conjecture for the recovery of improved parton-model results at very high energies. The approach offers a general framework to analyze the r...

A general framework is developed to analyse the influence of soft partons on the high energy behaviour of the Drell-Yan cross section.

Thesis (Ph. D.)--State University of New York, 1982. Includes bibliographical references (leaves 144-146).

Preface These lecture notes have been prepared as a rapid introduction to Einstein's General Theory of Relativity. Consequently, I have restricted to the standard four dimensional, metric theory of gravity with no torsion. A basic exposure to geometrical notions of tensors, their algebra and calculus, Riemann-Christoffel connection, curvature tenso...

Preface These lecture notes have been prepared as a rapid introduction to Cosmology within the framework of Einstein's General Theory of Relativity. Consequently, I have restricted to the standard four dimensional, metric theory of gravity with no torsion. A basic exposure to General Relativity is presupposed since this has been covered in other le...

Classically, the approach to a singularity in general relativity is very complicated, as illustrated by the chaotic Bianchi IX model. Quantum gravity effects can potentially change the behavior and lead to a simpler initial state. This is verified here for quantum geometry, using methods of loop quantum cosmology. The chaotic behavior then stops on...