Quintessence, the Mystery of the Missing Mass in the Universe by Lawrence Krauss, Basic Books, 04650337402.
Cosmology has a lot going for it at the moment. Unprecedented amounts of data characterizing the universe at almost every possible energy and lengthscale make it one of the richest scientific fields around. Theorists scramble to explain all of the disparate results, while experimentalists and observers push the limits of what, only a few years ago, was not thought possible. In the middle of all this activity, Lawrence Krauss's book Quintessence(a re-edition of his 1989 Fifth Essence) arrives to assess what is going on.
There is a growing trend in astrophysical and particle cosmology to believe (or at least sell the idea) that cosmology is "solved". Again and again researchers in the field say something like: "things are finally falling into place", so that we now have a standard model for structure formation. Often this represents a very theoretical and prejudiced view in selecting which data to believe.
Krauss himself embraces the latest high-redshift supernova results and consequent evidence for a cosmological constant as a confirmation of the "new standard cosmological model'' that he developed with collaborators in the mid-1980s. He is not alone in doing this, but such an attitude seriously compromises the evolution of the field.
It is the glaring inconsistencies and the conceptually inexplicable fixes that we should be trying to tackle. For example, we assume that the universe is homogeneous (and we know that the cosmic microwave background is very smooth), but when we look at the distribution of luminous matter it is strongly clustered as far as we can see; we believe that galaxies follow the underlying distribution of mass, but when we try to compare catalogues of different galaxies we end up having to invoke biasing mechanisms to make them all consistent.
My view is that cosmology is opening up and complexifying, not closing down and focusing on an existing component theory. Having declared my prejudices when starting this book, the truth is that I enjoyed it a lot. Although Krauss does try to oversell the inflationary cosmology and the derived cold dark matter scenario, this theme does not dominate the narrative. He does a great job of explaining the existence of dark matter, critically assessing the different pieces of experimental evidence and ensuring that he can relate these results with understandable physical principles. Particularly impressive is his description of the cosmic virial theorem (relating the kinematics of systems of gravitating bodies with the overall underlying mass) and his careful attempts to explain freezeout and relic abundances.
Many of the fundamental concepts needed in contemporary cosmology are outlined in the book and I see it as a great source of explanations for a wider audience. It was inevitable that this book would be revised. When Krauss wrote The Fifth Essenceat the end of the 1980s, it was at the end of a decade of fruitless searches for cosmological relics (he relates the story of the "Cabrera Monopole", which was never properly explained away).
The search for dark matter in the universe really took off in the 1990s, with bolometric and scintillation direct detection experiments being set up all over the world, the microlensing searches producing arguable evidence for clumped baryonic dark matter in our halo and the new weak lensing experiments mapping out the dark mass in clusters. Krauss systematically goes through these different technological advances, explaining why they happened and what scientific returns to expect. I particularly liked his description of the use of bolometric detectors in direct detection experiments, and his clear explanation of the phonon/ionization method used by the CDMS experiments at Berkeley. It conveys the beauty of experimental physics - how clever ideas and masterful work can really transcend physical limitations. Krauss has also done a reasonable job of avoiding the sociological folklore of characters and egos. He succumbs vary rarely, the most notable occasion being in his description of his work on WIMP detection and axions (and he likes Glashow's quips).
The bottom line is that Lawrence
Krauss has been able to give us a glimpse of an open,
fascinating problem in physics that is far from being solved:
the existence and essence of dark matter. The book can be
read by the layperson but is also useful for scientists and
non-specialists in cosmology.
Pedro G Ferreira,
Oxford.
Supersymmetry - Unveiling the Ultimate Laws of Nature 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 with M-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 is clearly 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.
Daniel Treille,
CERN.
Journeys Beyond the Standard
Model 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 study of 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 the author 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.
Gian Francesco Giudice, Theoretical Physics
Division, CERN.
Introduction to High
Energy Physics by Donald H Perkins (4th edition),
Cambridge University Press 0 521 62196 8,
£30/$49.95.
Does Donald Perkins' classic Introduction to High Energy Physicsneed another review? When the first edition appeared in 1972, it quickly established itself as one of the most authoritative and successful textbooks on particle physics. However, the latest revision appeared in 1987 - before the advent of physics at LEP, the SLC, the Tevatron and HERA - and was beginning to show its age.
Donald Perkins' distinguished career as an experimental particle physicist has been intimately connected with physics at CERN, where he has been a prime mover of many landmark experiments on neutrino scattering with bubble chambers. He has served as chairman of the Scientific Policy Committee and as UK delegate to the CERN Council. After retiring from his chair at Oxford, he has found the time to tackle a new edition.
The result is worth the wait: this is not just a straightforward update, it is a major rewrite, and the most comprehensive revision so far. It goes without saying that the book covers all significant developments of the past 15 years. Equally important, it has been reorganized thoroughly, such that the discussion is now firmly embedded in the classification of particles and forces of the Standard Model. A welcome addition are two new chapters that treat "Physics beyond the Standard Model" and "Particle physics and cosmology" in much more detail than previous editions and present the relevance of particle physics in a wider scientific context.
Notwithstanding the revised and more logical organization, the fourth edition does not sacrifice any of the qualities that have made previous versions so popular with students and lecturers alike. It focuses on phenomenological concepts rather than theoretical rigour, prefers illustrative examples and intuitive approaches to completeness and abstraction, and emphasizes the historical dimension to illustrate that particle physics is, more than ever, a fast-moving field.
To retain the same page count as previous editions, some material had to be omitted: this is less regrettable for the chapter on "Hadron-hadron interactions" than for most of the appendices, which provided much handy reference material. Useful additions to the supplementary material are a glossary, a historical account of "Milestones in particle physics" and a bibliography.
The latter is
somewhat of a mixed success - while being a good guide to
many classic books and papers, it omits many excellent, recent
review articles that could take the novice reader to the
forefront of current research in greater detail than is possible
in a textbook. However, these are minor flaws when
compared with the outstanding qualities of a book that once
again is well poised to introduce generations of future
researchers to the fascination of particle
physics.
Rüdiger Voss,
CERN.
Gauge Theory of Elementary
Particle Physics: Problems and Solutions by Ta-Pei Cheng
and Ling-Fong Li, Oxford University Press 0 19 850621 X,
£23.95.
Designed as a companion volume to Gauge Theory of Elementary Particle Physicsby the same authors, this 300-page collection of problems over the full range of field theory applications has very helpful solutions and further explanations.
The Theory of
Quantum Liquids by Philippe Nozières and David Pines,
Perseus Advanced Book Classics 0738202290, pbk
$49.
Long available as two volumes (Normal Fermi Liquidsand Superfluid Bose Liquids),these reliable classics are now available as a combined volume in paperback.
Unifying themes in Complex
Systems edited by Yaneer Bar-Yam, Perseus,
07738200492, hbk $60.
These are the proceedings of the International Conference on Complex Systems, in the New England Complex Systems Institute Series on Complexity.
Principles of Applied
Mathematics: Transformation and Approximation by
James P Keener (updated and revised), Perseus 0 7382 0129
4, $60.
The new edition of this successful book includes material on wavelet analysis, multigrid methods and homogenization theory, and the introduction of popular software tools. The exercises have been extended, and hints and solutions are now provided.