Stars as Laboratories for Fundamental Physics

The Astrophysics of Neutrinos, Axions, and Other Weakly Interacting Particles

University of Chicago Press, Chicago, 1996, xxii, 664 p, 188 line drawings, 34 tables. 1996, ISBN 0-226-70272-3

Raffelt presents the many uses of stellar astrophysics for research in basic particle physics. He focuses primarily on the properties and nongravitational interactions of elementary particles. Numerous graphs and figures complement the text.

Stars as Laboratories for Fundamental Physics is a valuable reference for cosmologists, astrophysicists, and particle physicists.

Preface Acknowledgments 1: The Energy-Loss Argument 2: Anomalous Stellar Energy Losses Bounded by Observations 3: Particles Interacting with Electrons and Baryons 4: Processes in a Nuclear Medium 5: Two-Photon Coupling of Low-Mass Bosons 6: Particle Dispersion and Decays in Media 7: Nonstandard Neutrinos 8: Neutrino Oscillations 9: Oscillations of Trapped Neutrinos 10: Solar Neutrinos 11: Supernova Neutrinos 12: Radiative Particle Decays from Distant Sources 13: What Have We Learned from SN 1987A? 14: Axions 15: Miscellaneous Exotica 16: Neutrinos: The Bottom Line App. A. Units and Dimensions App. B. Neutrino Coupling Constants App. C. Numerical Neutrino Energy-Loss Rates App. D. Characteristics of Stellar Plasmas References Acronyms Symbols Subject Index

Reviews

L'Astronomie, Vol. 110 (Dec. 1996)

Le sous-titre "The astrophysics of neutrinos, axions and other weakly interacting particles" montre le domaine concerné. Après avoir discuté les "sources" de ces éléments et les differénts effets de la propagation dans le milieu interstellaire, láuteur étudie en détail les objets pour lesquels on dispose de données, cést-á-dire le Soleil et la supernova 1987 A observée dans le nuage de Magellan. Il termine en se tournant vers l'avenir: quels son les effets ou les objets observables, compte tenu des nouveaux moyens d'observation mis en oeuvre. Cet ouvrage forme un ensemble consistant réservé aux spécialistes.

Choice, Vol. 34, No. 4 (Dec. 1996)

J.J. Beatty, Pennsylvania State University, University Park Campus

In recent years, one of the most exciting fields of astrophysics has been the use of astrophysical objects to constrain the laws of subatomic physics. In this monograph, Raffelt reviews the implicants of stellar evolution and structure. He discusses the effect of new particle types on the energetics of stellar evolution, neutrino interactions and oscillations, the solar neutrino problem, and bounds on axions. Of special importance is the review of the implications derived from supernova SN1987A. The arguments are essentially self-contained, but previous familiarity with stellar structure and with elementary particle physics is necessary to follow the details of the more advanced portions of the book. A book of great value to those working in stellar astrophysics or particle physics, with its accessible overview of the field for astronomers and physicists working in related areas. Graduate; faculty.

Endeavour, Vol. 20, No. 4 (1996)

S. Ramadurai

A firm foundation for the scientific revolution was laid by detailed planetary studies and the enunciation of Kepler's laws - at least in the domain of `macroscopic physics', where gravitation plays a dominant role. However, in the case of `microscopic physics', in which non-gravitational forces dominate, astronomy played only a minor role. Here, fundamental laws, discovered by controlled experiments conducted in terrestrial laboratories, are applied to explain diverse astronomical observations. But the situation has changed dramatically over the past few years, as the laboratory experiments have reached the limits of human ingenuity and affordable financial outlay. Once again one is forced to turn to astronomical objects - a ready-made laboratory waiting for observations. With the giant strides in detection techniques, ushered in by laboratory experiments, it is possible to make sophisticated observations with unprecedented precision, which should lead to new discoveries in fundamental physics. Thus, there is a need for understanding in detail multifarious fundamental processes taking place in the stars. The present book attempts to fulfil this need.

The author has been successfully applying weak-interaction physics to stars for over a decade. Hence he is able to quickly shift the focus from the conventional energy loss processes to the anomalous ones seen in white dwarfs and neutron stars (Chapter 1 and 2). But the main emphasis of the book is on the interaction of the weakly interacting particles (known and unknown), which is covered in detail over several chapters (3-6). The next three chapters cover the non-standard physics to be discovered by careful studies of the weakly interacting particles of standard and non-standard neutrinos. Here the arguments are congently presented and a case for non-standard neutrinos is clearly made. The chapter on solar neutrinos summarize the aspects of neutrino physics which are going to be in the forefront for years to come. The next two chapters set out the scenario for the full discussion of what we have learnt from SN1987 A, which is covered ably in Chapter 13. The role of axions and other exotica is discussed in the next two chapters, which offer quite a lot of hypothetical, but detailed discussions. Appropriately, the last chapter, is entitled `Neutrinos: The Bottom Line'.

One distinguishing feature of this book is the detailed computations as well as the more or less complete derivation of the several quantities arising out of the complex field of weak-interaction physics. In a fast-changing field like the current one, it is very hard to keep pace with new results. Hence it is gratifying to note that the fundamental processes discussed in the book will stand the test of time.

One final warning and recommendation: this book is not meant for casual readers. It is aimed at research workers willing to put in considerable effort to study and make use of the knowledge in applying the results to the laboratory with exotic conditions like neutron stars, black holes, etc. They will be rewarded considerably.

Nature (Nov. 1996)

Michel L. Cherry, Department of Physics and Astronomy, Louisiana State University, USA

The Standard Model of particle physics has been spectacularly successful. Yet there are hints of new physics (particularly involving neutrinos), and questions remain unanswered. Particle physicists are increasingly turning to astrophysics as they search for clues to lead them beyond the Standard Model - clues, for example, about neutrinos with finite mass or non-standard interactions, or the existence of axions or other new particles. The burst of neutrinos seen from supernova 1987A was well explained by models of the supernova collapse process. A flux of undetected axions would have produced an extra channel for energy loss from the collapsing core, so that the observed neutrino emission in fact set stringent limits on the presence of axions.

Georg Raffelt gives an extensive and expert review of this new speculative research area on the boundary between particle physics and astrophysics. He emphasizes the fundamental physics, and provides a detailed compendium of results for the serious student.

The Observatory, Vol. 116, No. 1135 (Dec. 1996), pg. 416.

R.J. Tayler

It is more than fifty years since George Gamow suggested that weakly interacting particles with long mean free paths might carry away energy from the hot interiors of stars and speed up the late stages of stellar evolution. The only weakly interacting particle then known was the electron neutrino. Gramow's URCA process is not now believed to be of very great importance, but it is known that there are more effective neutrino-emitting reactions, which are important in supergiants and in massive stars which are going to be supernovae and in the early cooling of neutron stars and white dwarfs. In addition, neutrinos emitted at the time of the explosion of SN1987A in the Large Magellanic Cloud were detected on Earth.

It is known that there are two additional types of neutrino, the muon neutrino and the tau neutrino. Particle physicists also speculate that there may be further weakly interacting particles, which have not yet detected, including the very-low-mass axion and more massive cold dark matter particles, which many cosmologists believe to be the main form of matter in the Universe. The properties of these hypothetical particles are uncertain, even if they do exist, and although the neutrinos are better understood, they probably possess small masses and may also have magnetic moments, both of which would influence their interaction with matter.

All types of weakly interacting particle can be produced inside stars and enhance their energy losses. This leads to a two-way interaction between particle physics and stellar evolution. Particles with hypothetical properties can be included in theoretical models of stars and the resulting predictions of their evolution can be compared with the observed properties of stars. This can then be used to constrain the properties of the particles; if, for example, stars are predicted to cool ten times as fast as they are observed to do, this is a strong argument against the existence of particles with the assumed properties. Of course, the stellar-evolution arguments do not really constrain the particle properties; if particles are ulitmately discovered with specific properties, stellar evolution will have to accommodate them. It does, however, make their existence implausible.

Twenty-five years ago the topic of stellar evolution and weakly interacting particles would probably have been covered in a review article of twenty to thirty pages. It says much for the theoretical developments that Georg Raffelt has now written a book of more than 650 pages and at the same time has said that he has excluded some topics which might have been included. This is a very well-written book by an author whose own contributions to the field, both the fundamental particle physics and the applications to astrophysics, have been substantial. The largest part of the book is concerned with the known particles, neutrinos. There are chapters on solar neutrinos and on supernova neutrinos as well as a very detailed discussion of possible non-standard properties of neutrinos. There is in addition a general account of the properties of all possible types of weakly interacting particle.

The general message of the book will be clear to anyone who is interested in the field, but a very good understanding of theoretical particle physics will be necessary to obtain full value from it. It will be particularly useful to anyone who is thinking of starting work in the subject.

Science (Nov. 1, 1996)

Lincoln Wolfenstein, Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA

The foundation of astrophysics is the belief that the same laws of physics that hold on Earth govern what goes on in the stars. Thus we can use nuclear cross-sections, atomic energy levels, and fundamental laws discovered in our terrestrial laboratories to calculate stellar processes. However, there may be relevant fundamental physics that has not yet been discovered on Earth. This leads to the possibility that new laws of physics may be discovered by studying the stars. It is this possibility that is the subject of Raffelt's book.

The physics of interest to Raffelt concerns the properties of elementary particles, primarily neutrinos and hypothetical particles called axions. In fact, more than half the book is devoted to neutrinos. The importance of neutrinos for astrophysics derives from the fact that they are the only known particles that interact only weakly. This means that if they are produced at high temperatures inside stars they can escape more easily than other particles and so can be a major agent of energy loss. In the case of a collapsing star leading to a type II supernova, nearly all of the energy of collapse (of order 10^{53} ergs) is emitted in the form of neutrinos over a period of about 10 seconds. The fact that neutrinos can escape easily from deep inside a star means that neutrino astronomy could make possible the study of stellar regions that cannot be directly explored in any other way. In particular, the detection of neutrinos from the sun has confirmed our general picture of the nuclear reactions occurring there.

The one indication of new physics from astrophysical observations is the quantitative disagreement between the measured neutrino fluxes from the sun and the results of detailed calculations. This could be explained by oscillations of electron-neutrinos from the sun into another type of neutrino if neutrinos have mass. Indeed, this is the strongest evidence available in favor of a nun-zero neutrino mass. The subject of neutrino oscillations and solar neutrinos is covered very clearly in the book. Though the treatment is not as detailed as that in Neutrino Astrophysics by John Bahcall (Cambridge Univ. Press, 1989), it is very adequate and up to date.

The detection of neutrinos from a supernova in the Large Magellanic Cloud in 1987 (SN1987A), even though they were only 19 or 20 in number, was one of the most important astrophysical events of recent times. These were the first neutrinos observed from a source outside the solar system, and they actually came from outside our own galaxy. Raffelt develops in detail theoretical analysis, much of it his own original work, on the propagation of neutrinos in dense media such as supernova cores. A variety of conclusions have been drawn from the observation of SN1987A neutrinos, ruling out exotic sources of energy loss, limiting the Dirac mass and magnetic moments of neutrinos, and constraining neutrino opacity. There is also a summary of recent analyses of the effect of possible neutrino oscillations on the supernova mechanism as well as on R-process nucleosynthesis.

Theoreticians like to invent theories with new types of particles. One class involves almost massless spin-zero particles, called Nambu-Goldstone bosons, which arise from the spontaneous breaking of a global symmetry. There is no compelling reason to believe in any such particles, but much analysis has centered on the particle called the axion, which could be a candidate for dark matter. Raffelt discusses various possible processes involving axions that make it possible to constrain the axion couplings from astrophysical observations. A more popular candidate for dark matter is one of the class known as supersymmetric particles, but these are only briefly mentioned.

It should be emphasized that the ``fundamental physics''\ of the title has a very limited meaning. Stars can tell us about general relativity, nucleosynthesis, atomic physics, and much else, but these are not the subjects of this book. Also the book does not discuss the goals of proposed future neutrino astronomy projects like an expanded AMANDA at the South Pole, where the best hope is to find neutrinos from active galactic nuclei. Within the restricted range of topics covered the book is authoritative and thorough.

CERN Courier (Nov. / Dec. 1996), pg. 18

Alvaro De Rùjula

Ever since Roemer, in 1675, analysed the timing of the occultations of the satellites of Jupiter to conclude that the speed of light is not infinite, fundamental physics has found in astronomy, astrophysics and cosmology not only inspiration, but also concrete answers to fundamental questions. As the title of this book reflects, the trend continues to this day.

This thick volume of some 650 pages is authored by a leading expert on the field. It thoroughly covers what stars have to tell us about some particles that do exist (neutrinos) and others whose existence is quite defensible (axions). It contains a mercifully brief chapter on "Miscellaneous Exotica", but no more than one paragraph on the emission of gravitational waves by the binary pulsar PS 1913+16.

Some subjects, such as the clash between observed and expected solar neutrino fluxes, do not have clear-cut resolutions at the moment; their presentation requires a pinch of opinion. In this, the author shows very good taste, in the usual sense (that is, more often than not, his judgements agree with those of the reviewer).

The list of references is quite exhaustive, often reflecting more of a collector's spirit than a potentially more useful thorough sifting. The style is clear, making the book an easy consulting tool, and a must for any scientific library or serious practitioner of the field.

Physikalische Blätter, Vol. 53, No. 10 (1997) pg. 1032

Wolfgang Hillebrandt, Garching

Es ist meistens eine schwierige und häufig auch undankbare Aufgabe, ein Buch über ein ausgesprochen interdisziplinäres Arbeitsgebiet zu schreiben, das sich zusätzlich noch um Umbruch befindet und ständig mit neuen Erkenntnissen überrascht. Es besteht dann die Gefahr, dass man sich als Autor um der Aktualität willen in Spekulationen verliert und dabei keinem der beteiligten Felder gerecht wird. Daneben ist der Anspruch gewaltig; denn in den seltensten Fällen gibt es schon Lehrbücher, auf die man sich beziehen kann, wenn es um die grundlegenden Fragen geht. Georg Raffelt ist in dem vorliegenden Buch dieser Spagat erstaunlich gut gelungen, und ich zolle ihm dafür meine Hochachtung. Er ist nicht der Versuchung erlegen, im klassischen Sinne ein Lehrbuch über Astro-Teilchenphysik schreiben und dabei auch noch die gesamte aktuelle Literatur einbeziehen zu wollen. Vielmehr hat er den Stil eines Reviews gewählt, ohne dabei darauf zu verzichten, wenn immer es ihm notwendig erschien, auch einmal die Grundlagen anzusprechen und eventuell sogar herzuleiten.

Hauptthema des Buchs ist der in den letzten Jahren überaus erfolgreiche Versuch, aus der Astrophysik solche Informationen über die Teilchenphysik zu gewinnen, die mit Beschleunigern und anderen Laborexperimenten nur sehr schwer oder gar nicht zu erhalten sind. Die inzwischen schon fast "klassischen" Beispiele sind der zu geringe Neutrinofluss von der Sonne, der auf "neue Physik" jenseits des Standardmodells der Teilchenphysik hindeutet, und die Neutrinodetektionen im Zusammenhang mit der Supernova in der Grossen Magellanschen Wolke 1987, die zu neuen Grenzen für Neutrinoeigenschaften geführt haben, die um Grössenordnungen restriktiver sind als die von Laborexperimenten. Diesen und anderen "astrophysikalischen Laboratorien", Roten Riesen, Weissen Zwergen, Neutronensternen, etc., widmet Raffelt den meisten Raum in seinem Buch. Die Kosmologie wird immer nur am Rande als "Labor" erwähnt, wenn sie für die Argumentation notwendig ist. Im Mittelpunkt stehen schwach wechselwirkende Teilchen (denn nur für sie lassen sich die Methoden anwenden) und insbesondere Neutrinos und Axionen, obwohl Raffelts Argumentationsketten in gleicher Weise für andere (hypothetische) neue Teilchen gelten.

Wie bereits gesagt, das Buch ist kein Lehrbuch im klassischen Sinn, und es wird sicher Leser enttäuschen, die ein solches suchen. Aber es gibt einen umfassenden Überblick über die Astro-Teilchenphysik mit einer Literaturliste, die bis 1995 alle relevanten Arbeiten enthält, und mit Illustrationen und einer Formelsammlung, die es für viele Jahre zu einem Standard-Nachschlagewerk für Astrophysiker und Teilchenphysiker machen werden, und es ist nützlich für Studenten, die schon über ein solides Fundament in beiden Feldern verfügen, aber gerne auch die Zusammenhänge verstehen würden.