Subject Grouping: Praxis

by Pierre Ramond, Perseus, 0738201162.

Judging by this book, Pierre Ramond must be somebody who spends more time packing his suitcases than travelling. He must therefore be a very well prepared and careful traveller. Two-thirds of Journeys Beyond the Standard Model is devoted to the Standard Model of fundamental particle interactions. However, those first seven chapters contain much more than an introduction. The Standard Model is presented using a modern point of view – the one usually taken by researchers working to extend the theory to a more fundamental level.

The lessons of the first part of the book are of paramount importance in the construction of theories beyond the Standard Model. For instance, emphasis is given to an effective-theory approach, in which higher-dimensional operators are understood as the low -energy manifestation of a fundamental theory emerging at very short distances. The discussion of the approximate symmetries of the fermionic sector (baryon, lepton and flavour symmetries) and Higgs sector (custodial symmetry) not only provides a deeper understanding of the Standard Model structure but clarifies the basic problems encountered in its extensions.

The book requires a previous knowledge of field theory. Nevertheless, the first chapter contains a brief recollection of important results of the spinorial representations of the Lorentz group, of gauge fields with and without spontaneous symmetry breaking, and of group theory. The discussion of group theory, although short, is very lucid and instructive for particle physicists interested in theories beyond the Standard Model. It is written in “Dynkinese”, the group-theoretical language based on Dynkin diagrams. In the Standard Model the group structure is rather simple and the group-theoretical language is a matter of taste. However, research in Grand Unified theories uses Dynkinese, because keeping track of tensorial indices in large group representations is often totally impracticable.

After some history of the Standard Model, its Lagrangian is presented in its full glory. We learn about its astonishing simplicity in terms of principles and its impressive experimental confirmation. One emerges with the conviction that the Standard Model is one of the greatest intellectual achievements of mankind. The discussion in Ramond’s book is clear and complete – one of the best ever published. The studyof the electroweak vacuum is presented with a careful treatment of gauge fixing in theories with spontaneously broken and unbroken gauge symmetry. The book also contains many detailed examples of calculations of Standard Model processes (tree-level decays, loop corrections to electroweak observables and strangeness-changing kaon processes).

A full chapter is devoted to the chiral Lagrangian and its applications at a depth that is unusual for introductory books on the Standard Model. The author is thus able to introduce many concepts (construction of effective theories for strong interactions, non trivial vacuum structure of gauge theories and anomalous global symmetries) frequently used in attempts to formulate theories beyond the Standard Model. Many applications of these concepts are found in the chapter on axions towards the end of the book.

While the presentation of the Standard Model in Ramond’s book is systematic and of extremely high quality, the discussion of theories beyond the Standard Model is more episodic. Indeed, as suggested by the title of the book, Ramond is offering some journeys into the vast territory of new physics; he makes no claim to discuss the complete subject thoroughly.

The first journey describes possible theoretical explanations for neutrino masses, and the experimental evidence for neutrino oscillations in solar and atmospheric neutrino experiments. In the second journey theauthor investigates axion properties and  derives their effective interactions with matter and radiation. The third journey presents the minimal supersymmetric extension of the Standard Model.

All three chapters are successful introductions to their respective subjects. More advanced readers may remain dissatisfied with the space allotted to these topics – especially for supersymmetry, a subject by now too vast to be covered in any depth by a single chapter of a book.

Anybody who wants to start a journey beyond the physics of the Standard Model will find this book a wonderful travelling companion. It provides a clear and insightful description of the structure of the Standard Model and gives the necessary tools to approach the frontier research in the domain of new physics.

Ramond’s book is also very timely, because research in particle physics is now moving from the period of consolidation and confirmation of the Standard Model to a period in which both theoretical speculations and experimental activity will focus on understanding deep questions that lie beyond the Standard Model’s predictability, such as the mechanism of electroweak breaking, the origin of masses and the unification of forces.

Imaginative physicists have produced many possible “ultimate” theories to extend the Standard Model. What are now needed are data to test these hypotheses and guide the speculations. There will be much to gain by the unprecedented investigation of nature at distances of less than 10^-19m. Considerable understanding of the fundamental principles of physical laws can be revealed by undertaking the journeys described in Pierre Ramond’s book, provided that the traveller invests in the Standard Model groundwork excellently surveyed in the book’s initial chapters.

by Gordon Kane, Helix/Perseus, 0 7382 0203 7, 224 pages, hbk $26.

Gordon Kane’s opus offers the general reader an introduction to supersymmetry. In a brief foreword, Ed Witten describes the search for supersymmetry as “one of the great dramas in present-day physics”, and Kane invites the reader to join him in a “leisurely walk” towards a grasp of this theory.

The author is certainly a well qualified guide. The book contains no technical passages inaccessible to the ordinary reader and there are few equations. A number of more arcane concepts relegated to short appendices will be of benefit to the physicist. The ascent is gradual, with many pauses for breath to enjoy the view, and in the final chapters the reader can be assured of acclimatization to the rarefied atmosphere of superstring theory, M-theory and what Kane terms “primary” theory.

From the outset the author distinguishes between well established areas of knowledge, such as the Standard Model, and what he refers to as speculative Research in Progress, as in the case of supersymmetry (SUSY). Similarly, he divides the answers provided by theories into “how” things happen and, on a higher level, “why” they happen.

The foundation of the Standard Model is clearly presented – the forces, the particles and the fields, as well as their governing theoretical principles. The reader is initiated into a straightforward use of Feynman diagrams to understand the processes that occur. The role of spin is underlined, as well as the difference between fermions and bosons, which supersymmetry will by definition associate as “mirrors” of each other. The “how” of the Higgs mechanism in the Standard Model is covered, with details consigned to an appendix.

Kane makes full use of the notion of organizing effective theories by distance scales. A theory valid up to a certain scale is improved, at smaller distances, by its successor, answering the “why” where its predecessor merely addressed the “how”.

An effective theory needs a number of parameters (masses, coupling intensities, etc) that it cannot predict. This will be as true for supersymmetry as it is for the Standard Model, despite the progress that it will bring. Beyond these levels would be a theory not requiring such external props, which Kane calls the “primary theory”. Could this already be in our sights withM-theory? If not, how  many more stages are there?

Kane provides a straightforward and pertinent description of supersymmetry, underlining the importance of the new answers that it will bring. Supersymmetry explains the “why” of the Higgs mechanism, predicting that the top quark must be heavy, which has already been verified experimentally.

Supersymmetry explains why the mass scales between that of observed particles and the distant Planck scale are stable, a serious stumbling block for the Standard Model. It offers possible unification of the various forces observed at very high energy. It also proposes an ideal candidate to explain the “hidden mass” of the universe. It isclearly a broken symmetry because the anticipated  partners of known particles have yet to be observed. One of the main goals of existing accelerators (such as LEP and the Tevatron), and subsequently of the LHC, is to flush out these hidden supersymmetric partner particles.

Naturally the author looks at the most predictive aspect of SUSY phenomenology. Although our understanding of the mass of superparticles is still hazy, current theory in its minimal version predicts at least one Higgs boson, and very light, according to Kane lighter than one-and-a-half times the mass of the Z.

The search for the Higgs boson is naturally the main objective of current experiments. If the theory is right, Kane predicts that the first SUSY signals should be found soon, with a bit of luck even at LEP and probably at Fermilab’s Tevatron.

Finally, Kane unflinchingly tackles the most fundamental questions in an overview of current attempts to formulate a primary theory – superstrings and their synthesis in M-theory. Having attained this vantage point, the reader will discover that the evident beauties of the landscape are overshadowed by further mountain ranges whose peaks are still wreathed in clouds.

Kane also speculates on the future of particle physics and cosmology. Convinced that epistemological scepticism regarding the practical limits of knowledge is not founded on solid arguments, and that the funding for such research should be recognized as a good investment, he hopes that we will achieve a true understanding of the physical universe. He shows that the progress of theories, by increasingly correlating parameters previously considered as independent, will enable us to see the world as less and less accidental and improbable, and will gradually eliminate the temptation to have recourse to anthropic principles.

Particle physics and cosmology research could then be wound up, not because we will have failed to attain the primary theory, but because we will have succeeded in constructing it. One may not share the author’s faith, but his optimism is reassuring.

Kane hopes that the book will remain useful even after the discovery of supersymmetry. Whether and whenever that discovery is made, this instructive, cogent and well written text can in any case be highly recommended.

by Frank Close, Oxford University Press, ISBN 0 19 850380 6.

Communicating science is difficult. In contrast with other fields, it needs long experience before being able to contribute. While creativity in science or the arts is often left to younger people with open minds, when it comes to explaining new developments to  a wide audience, the science communicator first has to master the science itself, its teaching and its popular dissemination.

Frank Close, who has already provided several popular science standards, has all it requires. Here he takes us on a tour of modern science, following a theme, the study of which started early in 19th century: the fascination and appeal of the underlying symmetry of nature, and its attendant asymmetry.

The tour begins and ends in Paris, in a French garden where almost perfect symmetry appears slightly broken, that day, by a damaged statue of Lucifer. With this metaphor of our entire world, accidentally asymmetric but governed by apparently symmetric laws, Close embarks on a journey through the history of the quest to understand where the asymmetry of the universe comes from.

This governs even our own existence: matter overcoming antimatter was a necessary step for there to be anything at all. Moreover, life on Earth, seen through the basic structure of organic molecules, is asymmetric. The mystery of life cannot be understood by physics alone, yet asymmetry is a property of life itself, and this thread continues throughout the book.

First the author reviews symmetry at large, with examples taken from everyday life, featuring common notions and clichés. One of the enigmas dealt with is my own favourite, Martin Gardner’s puzzle: why does a mirror invert left and right, but not top and bottom? Here the author adds much of his own insight and wit (“the muscles which close a mouth are stronger than those which open it – as is well known to all who have sat in committees”). The result is a fascinating panorama, down to the molecular level, of the asymmetries around us, which have first to be discovered before being explained.

The remainder of the book covers the history of the tools needed to explore matter and to reveal its hidden asymmetries. Following the pioneer work of Biot (polarization of light) and Pasteur (study of racemic acid), the end of the 19th century brought major discoveries by scientists investigating the true nature of electricity, continuing the route taken by Faraday and Maxwell.

First came the discovery of X-rays by Roentgen, a key tool for decoding DNA structure half a century later. Immediately after X rays came the discovery of the electron by Thomson, and then of radioactivity (Becquerel and the Curies) and the nucleus (Rutherford). The major cornerstones of modern physics were revealed during those few “magic” years, and they are narrated by Close in a way that reveals the hesitations and inspirations of the actors, the banal errors of those who “could have found” (Lenard, Crookes) but were not quite ready, and the genius of those who made sure that they were in the right place at the right time with the right ideas. What better plea could there be for fundamental research?

All of this leads to modern physics, exploiting the concept of symmetry in a profound way, revealing hitherto unsuspected laws through delicate symmetry breaking. We are introduced to unification schemes based on symmetries broken at our energy scale, but revealed in high-energy experiments. Close explains this in detail and with amusing anecdotes, and how it guided physicists during their major discoveries of the secrets of the matter, right up to the next foreseen step – the quest to find the Higgs boson.

The instrumentation and apparatus required for this quest are impressive. The incredible effort of a worldwide community at CERN for the LHC and its giant experiments help the reader to become familiar with this ultimate search for the origin of mass.

On the way, the chapter on antimatter deserves admiration: antimatter is one of the most difficult notions scientists have to explain. I remember a colleague beginning a public talk by unapologetically defining antimatter as “the negative energy solution to Dirac’s equations”. What is exact is not always clear, and Frank Close takes the time to introduce antimatter, to draw its human side through Dirac’s character and by noting the time it took, from Dirac’s work in 1928 to Anderson’s discovery of the positron in 1932.

The violation of “mirror” P symmetry by the weak force, how this was discovered, the violation of CP symmetry and recent evidence for the violation of time symmetry are all clearly explained, illustrated by analogies with Escher prints to help the mind see patterns in abstract spaces.

We then understand that the universe, once fully symmetric, exhibited asymmetries when freezing, which enabled life to be. Life, intrinsically related to asymmetries, is the theme of this book, and Close revisits what has already been written on this theme, offering us an absorbing and scientifically correct account of symmetry and its deep implications.

by Y Kuramoto and Y Kitaoka, Oxford University Press, ISBN 0 19 851767 X (hbk £75)

In this context “heavy electrons” means electrons in rare-earth and actinide metals that acquire very large effective masses owing to strong local correlations.

by Roger Bowley and Mariana Sanchez, Oxford University Press (2nd edn), ISBN 0 19 8505760 (pbk, £21.99).

This text offers an introduction to the theory of condensed matter and first appeared in 1996. This edition includes three additional chapters on phase transitions and more examples.