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Axions. Theory, cosmology, and experimental searches. Most papers based on lectures given at the 1st joint ILIAS-CERN-CAST axion training, Geneva, Switzerland, November 2005. (English) Zbl 1157.81002

Lecture Notes in Physics 741. Berlin: Springer (ISBN 978-3-540-73517-5/hbk; 978-3-540-73518-2/ebook). xi, 245 p. (2008).
Axion physics started in 1977 when Robert Peccel and Helen Quinn proposed their solution to the strong CP problem by postulating a new U(1) symmetry. The strong CP problem is a “blemish” of the standard model of particle physics which is one of the most profound and successful theories in modern physics that has been varyfied by numerous experiments to very high accuracy. Associated with the Peccei-Quinn symmetry is a light and weakly-interacting particle that was named by Frank Wilczek “axion”. So far the axion has remained elusive for over 30 years of intensive research, and none of the axion searches, based on either astrophysical observations or pure laboratory based experiments, was able to yield a positive signature for the axion or an axion-like particle.
The motivation of this book was to provide a starting point for graduate students and senior researchers in the field of axions and axion-like particles. The book gives a broad overview on the theoretical reason of axions and axion-like particles, their implication for cosmology and astrophysics, their role as a well-known dark-matter candidate, and experimental axion searches. Most of this book is based on the 1st Joint ILIAS-CERN-CAST axion training in Geneve at CERN in November 2005.
The book consists of two parts, in the first part the axion theory is presented, and the second part deals with observations and experiments. The theoretical part starts with the contribution by R. D. Peccei who describes how the quantum chromodynamics’ (QCD) vacuum structure, necessary to resolve the U(1)\(_A\) problem, predicts the presence of a P, T, and CP violating term proportional to the vacuum angle. To agree with experimental bounds, however, this parameter must be very small. After briefly discussing some other possible solutions to this, so-called, strong CP problem, the chiral solution which has associated with it the axion is presented. The properties and dynamics of axions are treated in detail, focusing particularly on invisible axion models where axions are very light, very weakly coupled, and very long-lived.
The cosmological properties of axions are reviewed by P.Sikivie. He discusses, in chapter 2, the axions produced by thermal processes in the early universe, the evolution of the average axion field between the Pecci-Quinn and QCD phase-transitions, the domain-wall problem and its possible resolution, the population of cold axions produced by vacuum realignment, string decay and domain wall decay, and, finally, axion miniclusters and axion isocurvature perturbations.
Axion emission by hot and dense plasmas is a newly discussed energy-loss channel for stars. Observable consequences include a modification of the solar sound-speed profile, an increase of the solar neutrino flux, a reduction of the helium-burning lifetime of globular-cluster stars, accelerated white-dwarf cooling, and a reduction of the supernova SN 1987 A neutrino burst duration. G. G. Raffelt reviews and updates these arguments and summarizes the resulting axion constraints.
Theories including extra space dimensions offer a possible solution to the hierarchy problem of particle physics. An additional effect of these theories is the possibility for axions to propagate in the higher-dimensional space. B. Lakić, R. Horvat, and M.Krémar explore the potential of the CERN Axion Solar Telescope (CAST) for testing the presence of large extra dimensions.
In chapter 5, a review of the status of axions and axion-like particles is given by E. Massó. Special attention is devoted to the recent results of the PVLAS collaboration, which are in conflict with the CAST data and with the astrophysical constraints. Solutions to the puzzle and the implications for new physics are discussed. The question of axion-like particles being dark matter is also addressed.
The second part of the work, on observations and experiments, starts with electric and magnetic dipole moments of fundamental particles, which had a large influence in shaping the standard model in the past and continue to play a significant role at present by restricting the many possible expansions of the standard model. Y. K. Semertzidis describes in datail the present status and prospects of the dipole moments in storage rings experiments, in the context of other significant electric and magnetic dipole moment efforts.
Photon-axion conversion induced by intergalactic magnetic fields causes an apparent dimming of distant sources, notably of cosmic distance indicators such as supernovae of type Ia (SNe Ia). A. Mirizzi, G. G. Raffelt, and P. D. Serpico review the impact of this mechanism on the luminosity-redshift relation of SNe Ia, on the dispersion of quasar spectra, and on the spectrum of the cosmic microwave background. The original idea of explaining the apparent dimming of distant SNe Ia without cosmic acceleration is strongly constrained by these arguments. However the cosmic equation of state extracted from the SN Ia luminosity-redshift relation remains sensitive to this mechanism.
The chapter by G. Carosi and K. v. Bibber covers the search for dark matter axions based on microwave cavity experiments proposed by P.Sikivie. A major focus of this chapter are two complementary strategies for ultra-low noise detection of microwave photons - the “photon-as-wave” approach (i.e., conventional heterojunction amplifiers and soon to be quantum-limited SQUID devices), and the “photon-as-particle” approach (i.e., Rydberg-atom single-quantum detection). Experimental results are presented. These experiments have already reached well into the range of sensitivity to exclude plausible axion models for limited ranges of mass. The chapter ends with a discussion of future plans and challenges for the microwave cavity experiment.
An vacuum element can be used as a target in a photon-photon collider in order to study its properties. Some of these properties are predicted by quantum electrodynamics, while additional and unexpected properties might be linked to the existence of yet undiscovered axion-like particles interacting with two photons. In this low-energy case (1-2 eV), real photons from a polarized laser beam are scattered off virtual photons provided by a magnetic field. Information on the scattering processes can be obtained by measuring changes in the polarization state of the probe photons. An experiment of such a type, the PVLAS experiment running at the Legnaro Laboratory of the INFN, near Padua, Italy, allows the detection of ellipticity angles of about \(10^{-9}\) rad, in an hour of data taking. Recent results of PVLAS on polarization effects are presented and interpreted in terms of the production of axion-like particles. Finally, the realization of a photon-generation type experiment is briefly illustrated.
There exists a wide variety of experimental approaches that were developed during the last 30 years to detect axions experimentally. R. Battesti et al. try in the last chapter to review the challenging and innovative experimental techniques used to search for axions, and they give an outlook on experiments planned for the near future, e.g. on a new set of laser-based ones.
(Review prepared by C.-V. Meister using “Preface” and parts of chapter “abstracts” of the book.)

MSC:

81-06 Proceedings, conferences, collections, etc. pertaining to quantum theory
83-06 Proceedings, conferences, collections, etc. pertaining to relativity and gravitational theory
00B25 Proceedings of conferences of miscellaneous specific interest
83F05 Relativistic cosmology
81V22 Unified quantum theories
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