Krishan L. Duggal – författare

This work has been written with a two-fold approach in mind: firstly, it adds to the theory of submanifolds the missing part of lightlike (degenerate) submanifolds of semi-Riemannian manifolds, and, secondly, it applies relevant mathematical results to branches of physics. It presents important results on null curves, lightlike hypersurfaces and their applications to relativistic electromagnetism, radiation fields, killing horizons and asymptotically flat spacetimes in a consistent way. Many differences between non-degenerate and degenerate geometry are highlighted, and open problems for both mathematicians and physicists are given.

This text provides information on metric (i.e. Killing, homothetic and conformal), connection (i.e. affine, conformal and projective), curvature collineations and curvature inheritance symmetries. It attempts to present not only a comprehensive account of a very large number of papers on symmetries of spacetimes and Riemannian manifolds, but also the Lie group/algebra structures of symmetry vectors, their kinematics/dynamics, compact hypersurfaces (dealing with the initial value problem in general relativity) and lightlike hypersurfaces. This book also contains information on symmetries of Kaehler, contact and globally framed manifolds.

This book provides an upto date information on metric, connection and curva­ ture symmetries used in geometry and physics. More specifically, we present the characterizations and classifications of Riemannian and Lorentzian manifolds (in particular, the spacetimes of general relativity) admitting metric (i.e., Killing, ho­ mothetic and conformal), connection (i.e., affine conformal and projective) and curvature symmetries. Our approach, in this book, has the following outstanding features: (a) It is the first-ever attempt of a comprehensive collection of the works of a very large number of researchers on all the above mentioned symmetries. (b) We have aimed at bringing together the researchers interested in differential geometry and the mathematical physics of general relativity by giving an invariant as well as the index form of the main formulas and results. (c) Attempt has been made to support several main mathematical results by citing physical example(s) as applied to general relativity. (d) Overall the presentation is self contained, fairly accessible and in some special cases supported by an extensive list of cited references. (e) The material covered should stimulate future research on symmetries. Chapters 1 and 2 contain most of the prerequisites for reading the rest of the book. We present the language of semi-Euclidean spaces, manifolds, their tensor calculus; geometry of null curves, non-degenerate and degenerate (light like) hypersurfaces. All this is described in invariant as well as the index form.

This book provides an upto date information on metric, connection and curva­ ture symmetries used in geometry and physics. More specifically, we present the characterizations and classifications of Riemannian and Lorentzian manifolds (in particular, the spacetimes of general relativity) admitting metric (i.e., Killing, ho­ mothetic and conformal), connection (i.e., affine conformal and projective) and curvature symmetries. Our approach, in this book, has the following outstanding features: (a) It is the first-ever attempt of a comprehensive collection of the works of a very large number of researchers on all the above mentioned symmetries. (b) We have aimed at bringing together the researchers interested in differential geometry and the mathematical physics of general relativity by giving an invariant as well as the index form of the main formulas and results. (c) Attempt has been made to support several main mathematical results by citing physical example(s) as applied to general relativity. (d) Overall the presentation is self contained, fairly accessible and in some special cases supported by an extensive list of cited references. (e) The material covered should stimulate future research on symmetries. Chapters 1 and 2 contain most of the prerequisites for reading the rest of the book. We present the language of semi-Euclidean spaces, manifolds, their tensor calculus; geometry of null curves, non-degenerate and degenerate (light like) hypersurfaces. All this is described in invariant as well as the index form.

Since the second half of the 20th century, the Riemannian and semi-Riemannian geometries have been active areas of research in di?erential geometry and its - plications to a variety of subjects in mathematics and physics. A recent survey in Marcel Berger's book [60] includes the major developments of Riemannian ge- etry since 1950, citing the works of di?erential geometers of that time. During the mid 1970s, the interest shifted towards Lorentzian geometry, the mathematical theory used in general relativity. Since then there has been an amazing leap in the depth of the connection between modern di?erential geometry and mathematical relativity, both from the local and the global point of view. Most of the work on global Lorentzian geometry has been described in a standard book by Beem and Ehrlich [34] and in their second edition in 1996, with Easley. As for any semi-Riemannian manifold there is a natural existence of null (lightlike)subspaces, in 1996,Duggal-Bejancupublished a book[149] on the lig- like (degenerate) geometry of submanifolds needed to ?ll an important missing part in the general theory of submanifolds.Since then the large number of papers published on lightlike hypersurfaces and general theory of submanifolds of semi- Riemannian manifolds has created a demand for publication of this volume as an update on the study of lightlike geometry. The objective is to focus on all new geometric results (in particular, those availableonlyafterpublicationoftheDuggal-Bejancubook)onlightlikegeometry with proofs and their physical applications in mathematical physics.

This book has been written with a two-fold approach in mind: firstly, it adds to the theory of submanifolds the missing part of lightlike (degenerate) submanifolds of semi-Riemannian manifolds, and, secondly, it applies relevant mathematical results to branches of physics. It is the first-ever attempt in mathematical literature to present the most important results on null curves, lightlike hypersurfaces and their applications to relativistic electromagnetism, radiation fields, Killing horizons and asymptotically flat spacetimes in a consistent way. Many striking differences between non-degenerate and degenerate geometry are highlighted, and open problems for both mathematicians and physicists are given. Audience: This book will be of interest to graduate students, research assistants and faculty working in differential geometry and mathematical physics.

This book is about the light like (degenerate) geometry of submanifolds needed to fill a gap in the general theory of submanifolds. The growing importance of light like hypersurfaces in mathematical physics, in particular their extensive use in relativity, and very limited information available on the general theory of lightlike submanifolds, motivated the present authors, in 1990, to do collaborative research on the subject matter of this book. Based on a series of author''s papers (Bejancu [3], Bejancu-Duggal [1,3], Dug­ gal [13], Duggal-Bejancu [1,2,3]) and several other researchers, this volume was conceived and developed during the Fall ''91 and Fall ''94 visits of Bejancu to the University of Windsor, Canada. The primary difference between the lightlike submanifold and that of its non­ degenerate counterpart arises due to the fact that in the first case, the normal vector bundle intersects with the tangent bundle of the submanifold. Thus, one fails to use, in the usual way, the theory of non-degenerate submanifolds (cf. Chen [1]) to define the induced geometric objects (such as linear connection, second fundamental form, Gauss and Weingarten equations) on the light like submanifold. Some work is known on null hypersurfaces and degenerate submanifolds (see an up-to-date list of references on pages 138 and 140 respectively). Our approach, in this book, has the following outstanding features: (a) It is the first-ever attempt of an up-to-date information on null curves, lightlike hypersur­ faces and submanifolds, consistent with the theory of non-degenerate submanifolds.