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.