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30 May 2000

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 Physics
by 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
Liquids
and 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.

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