Table of contents

We report on the possibility of detecting a submillimetre-sized extra dimension by observing gravitational waves (GWs) emitted by point-like objects orbiting a braneworld black hole. Matter in the 'visible' universe can generate a discrete spectrum of high frequency GWs with amplitudes moderately weaker than the predictions of general relativity, while GW signals generated by matter on a 'shadow' brane hidden in the bulk are potentially strong enough to be detected using current technology. We know of no other astrophysical phenomena that produce GWs with a similar spectrum, which stresses the need to develop detectors capable of measuring this high-frequency signature of large extra dimensions.

We investigate the possibility of using atom interferometers to detect gravitational waves. We discuss the interaction of gravitational waves with an atom interferometer and analyse possible schemes.

We explicitly construct and characterize all possible independent loop states in (3 + 1)-dimensional loop-quantum gravity by regulating it on a 3D regular lattice in the Hamiltonian formalism. These loop states, characterized by the (dual) angular momentum quantum numbers, describe SU(2) rigid rotators on the links of the lattice. The loop states are constructed using the Schwinger bosons which are harmonic oscillators in the fundamental (spin half) representation of SU(2). Using the generalized Wigner–Eckart theorem, we compute the matrix elements of the volume operator in the loop basis. Some simple loop eigenstates of the volume operator are explicitly constructed.

In this second paper devoted to the equatorial symmetry/antisymmetry of stationary axisymmetric electrovac spacetimes, we show how two theorems proved in our previous paper (Ernst et al 2006 Class. Quantum Grav.23 4945) can be utilized to construct exact solutions that are equatorially symmetric or antisymmetric.

In this paper, the problem of finding an axisymmetric stationary spacetime from a specified set of multipole moments is studied. The condition on the multipole moments, for the existence of a solution, is formulated as a convergence condition on a power series formed from the multipole moments. The methods in this paper can also be used to give approximate solutions to any order, as well as estimates on each term of the resulting power series.

We present an approach to experimentally evaluate gravity gradient noise, a potentially limiting noise source in advanced interferometric gravitational-wave detectors. In addition, the method can be used to provide sub-percent calibration in phase and amplitude. Knowledge of calibration to such certainties shall enhance the scientific output of the instruments in the case of an eventual detection of gravitational waves. The method relies on a rotating symmetrical two-body mass, a dynamic gravity field generator (DFG). The placement of the DFG in the proximity of one of the interferometer's suspended test masses generates a change in the local gravitational field detectable with current interferometric gravitational-wave detectors.

We present a numerical analysis to simulate the response of a spherical resonant gravitational wave detector and to compute its sensitivity. Under the assumption of optimal filtering, we work out the sensitivity curve for a sphere first taking into account only a single transducer, and then using a coherent analysis of the whole set of transducers. We use our model for computing the sensitivity and therefore compare different designs of spherical detectors. In particular, we present the case of 1 m radius bulk and hollow spheres equipped with transducers in a TIGA configuration, and we explore the sensitivity of a hollow sphere as a multi-modal detector.

We prove the existence of static solutions to the cylindrically symmetric Einstein–Vlasov system, and we show that the matter cylinder has finite extension in two of the three spatial dimensions. The same results are also proved for a quite general class of equations of state for perfect fluids coupled to the Einstein equations, extending the class of equations of state considered by Bicak et al (2004 Class. Quantum Grav.21 1583). We also obtain this result for the Vlasov–Poisson system.

The LISA mission is a space interferometer aiming at the detection of gravitational waves in the [10⁻⁴, 10⁻¹] Hz frequency band. In order to reach the gravitational wave detection level, a time delay interferometry (TDI) method must be applied to get rid of (most of) the laser frequency noise and optical bench noise. This TDI analysis is carried out in terms of the coordinate time corresponding to the Barycentric Coordinate Reference System (BCRS), TCB, whereas the data at each of the three LISA stations are recorded in terms of each station proper time. We provide here the required proper time versus BCRS time transformation. We show that the difference in rate of station proper time versus TCB is of the order of 5 × 10⁻⁸. The difference between station proper times and TCB exhibits an oscillatory trend with a maximum amplitude of about 10⁻³ s.

Through the consideration of spherically symmetric gravitating systems consisting of perfect fluids with linear equation of state constrained to be in a finite volume, an account is given of the properties of entropy at conditions in which it is no longer an extensive quantity (it does not scale with the system's size). To accomplish this, the methods introduced by Oppenheim (2003 Phys. Rev.E 68 016108) to characterize non-extensivity are used, suitably generalized to the case of gravitating systems subject to an external pressure. In particular when, far from the system's Schwarzschild limit, both area scaling for conventional entropy and inverse radius law for the temperature set in (i.e. the same properties of the corresponding black hole thermodynamical quantities), the entropy profile is found to behave like 1/r, with r the area radius inside the system. In such circumstances entropy heavily resides in internal layers, in opposition to what happens when area scaling is gained while approaching the Schwarzschild mass, in which case conventional entropy lies at the surface of the system. The information content of these systems, even if it globally scales like the area, is then stored in the whole volume, instead of packed on the boundary.

We use a covariant phase space formalism to give a general prescription for defining Hamiltonian generators of bosonic and fermionic symmetries in diffeomorphism invariant theories, such as supergravities. A simple and general criterion is derived for a choice of boundary condition to lead to conserved generators of the symmetries on the phase space. In particular, this provides a criterion for the preservation of supersymmetries. For bosonic symmetries corresponding to diffeomorphisms, our prescription coincides with the method of Wald et al. We then illustrate these methods in the case of certain supergravity theories in d = 4. In minimal AdS supergravity, boundary conditions such that the supercharges exist as Hamiltonian generators of supersymmetry transformations are unique within the usual framework in which the boundary metric is fixed. In extended AdS supergravity, or more generally in the presence of chiral matter superfields, we find that there exist many boundary conditions preserving supersymmetry for which corresponding generators exist. These choices are shown to correspond to a choice of certain arbitrary boundary 'superpotentials', for suitably defined 'boundary superfields'. We also derive corresponding formulae for the conserved bosonic charges, such as energy, in those theories, and we argue that energy is always positive, for any supersymmetry-preserving boundary conditions. We finally comment on the relevance and interpretation of our results within the AdS/CFT correspondence.

We derive the hydrostatic equilibrium equation of a spherical star for any gravitational Lagrangian density of the form . The Palatini variational principle for the Helmholtz Lagrangian in the Einstein gauge is used to obtain the field equations in this gauge. The equilibrium hydrostatic equation is obtained and is used to study the Newtonian limit for . The same procedure is carried out for the more generally case giving a good Newtonian limit.

Algebraic curvature tensors which are Osserman–IP in the (− − + +)-signature setting are completely determined. As a consequence, it is shown that a four-dimensional pointwise Osserman–IP manifold is a space of constant sectional curvature or, otherwise, at each point the Jacobi operators either vanish or they are two-step nilpotent.

In this paper, we obtain some rigidity theorems on compact manifolds with nonempty boundary. The results may be related to the positivity of some quasi-local mass of Brown–York type. The main argument is to use monotonicity of quantities similar to the Brown–York quasi-local mass in a foliation of quasi-spherical metrics. Together with a hyperbolic version of positivity of a mass quantity, we obtain our main results.

The radiation gauges used by Chrzanowski (his IRG/ORG) for metric reconstruction in the Kerr spacetime seem to be over-specified. Their specification consists of five conditions: four, which we treat here as valid gauge conditions, plus an additional condition on the trace of the metric perturbation. In this work, we utilize a newly developed form of the perturbed Einstein equations to establish a condition—on a particular tetrad component of the stress–energy tensor—under which the full IRG/ORG can be imposed. Using gauge freedom, we are able to impose the full IRG for Petrov type II and type D backgrounds, using a different tetrad for each case. As a specific example, we work through the process of imposing the IRG in a Schwarzschild background, using a more traditional approach. Implications for metric reconstruction using the Teukolsky curvature perturbations in type D spacetimes are briefly discussed.

In this paper, we calculate the induced electrostatic self-energy and self-force for an electrically charged particle placed at rest in the spacetime of a global monopole admitting a general spherically symmetric inner structure to it. In order to develop this analysis we calculate the three-dimensional Green function associated with this physical system. We explicitly show that for points outside the monopole's core the self-energy presents two distinct contributions. The first is induced by the non-trivial topology of the global monopole considered as a point-like object. The second is a correction induced by the non-vanishing inner structure attributed to it. As an illustration of the general procedure the flower-pot model for the region inside the monopole is considered. In this application, it is also possible to find the electrostatic self-energy for points in the region inside the monopole. In the geometry of the global monopole with the positive solid angle deficit, we show that for the flower-pot model the electrostatic self-force is repulsive with respect to the core surface for both exterior and interior regions.

A possible candidate for the late time accelerated expanding universe is phantom energy, which possesses rather bizarre properties, such as the prediction of a Big Rip singularity and the violation of the null energy condition. The latter is a fundamental ingredient of traversable wormholes, and it has been shown that phantom energy may indeed sustain these exotic geometries. Inspired by the evolving dark energy parameter crossing the phantom divide, we consider in this work a varying equation of state parameter dependent on the radial coordinate, i.e., ω(r) = p(r)/ρ(r). We shall impose that phantom energy is concentrated in the neighbourhood of the throat, to ensure the flaring out condition, and several models are analysed. We shall also consider the possibility that these phantom wormholes be sustained by their own quantum fluctuations. The energy density of the graviton one-loop contribution to a classical energy in a phantom wormhole background and the finite one-loop energy density are considered as a self-consistent source for these wormhole geometries. The latter semi-classical approach prohibits solutions with a constant equation of state parameter, which further motivates the imposition of a radial dependent parameter, ω(r), and only permits solutions with a steep positive slope proportional to the radial derivative of the equation of state parameter, evaluated at the throat. The size of the wormhole throat as a function of the relevant parameters is also explored.

We prove well posedness of the initial value problem for the Einstein equations for spatially homogeneous cosmologies with data at an isotropic cosmological singularity in two cases: for all Bianchi types when the matter content is a cosmological constant with collisionless particles of a single mass (possibly zero), and for FRW, Bianchi-type III, Kantowski–Sachs and Bianchi class A with a cosmological constant and a perfect fluid having the radiation equation of state. In both cases, with a positive cosmological constant, these solutions, except possibly for Bianchi-type IX and Kantowski–Sachs, will expand forever, and be geodesically complete into the future.

Using the nonlinear δN formalism, we consider a simple exactly soluble model of multi-component slow-roll inflation in which the nonlinear curvature perturbation can be evaluated analytically.

Spontaneous emission of graviton rates for the quantum bouncer states is evaluated.

Here are two textbooks, both published by Springer and each roughly half devoted to cosmology—the large scale structure and evolution of the Universe. I can imagine a context (not the same context) in which each would be useful. And there the similarities largely end. Bergstrom and Goobar's (hereafter B&G) other topic is particle astrophysics, and they are addressing students who already have some knowledge of advanced quantum mechanics and classical field theory (or who can master some relativistic dynamics and the Dirac equation on the basis of a couple of very information-dense appendices). The book is meant for use at the graduate level, probably the second year by US standards (the authors are from Stockholm).

Schneider (hereafter PS), on the other hand, begins with galaxies, and then alternates between cosmological topics of gradually increasing sophistication (expanding universe to CMB fluctuations) and additional galactic topics—clusters, quasars and all. The book is meant as the second half of an introductory astronomy/astrophysics course for physics majors, and in the US would fit into an upper division `capstone' course.

Each is meant for a single semester class at the target level, and might be squeezed into a 10-week term with elimination of some topics. B&G is a paperback of a second edition, with colour confined to a central block of plates, relatively few graphs and drawings, but lots of complex equations. PS is a hard cover translation from a German original, with colour used freely in astronomical images and graphs throughout, with fewer and less complex equations. Though the nominal difference in copyright date is only two years (2006 for PS, 2004 for B&G), the former is considerably more up to date, mentioning, for instance, that the third year WMAP results are not different enough from the first year to justify redoing drawings and such (I agree).

What can you expect to get if you buy one or both of these? B&G have a homepage of error corrections. There are worked problems in the text and 2–15 problems at the ends of each of the 15 chapters (5 on average). I can do at least some of them. The list of references or suggestions for further reading is partly out of date and gives no indication of the levels of the books mentioned. The preface promises a list of outstanding texts in particle physics and cosmology to appear at the end of the first chapter. Either this is the (rather unsatisfactory) list at the end of the book, or it has disappeared completely. The reader is also referred to the arXiv astro-ph and hep-ph sections and to proceedings of the Texas and TAUP conference series for current information. Some, but not all, of the equations and problems choose c = G = 1 or c = ℏ = 1 units. The discussion of inflation includes flatness, horizon and monopole problems, but not the production and amplitude of primordial fluctuations.

The PS appendices are very basic astronomy, and the units are generally cgs and astronomical (but with a sudden outbreak of light years in one place). The text and author do not have their own website, but readers are referred to both arXiv and ADS. The description of histories of current issues is sometimes superficial (but so is that of B&G). The basic equations relating H, ρ, Λ and others are in the optimal form for actually estimating numerical values (which is less true of B&G). There are particularly good quantitative treatments of gravitational lensing (the author's speciality) and basic cosmological models. Other topics, like active galaxies, are presented attractively but qualitatively, and one might be hard pressed to come up with suitable homework and exam problems covering them. There are some classic `back of the envelope' calculations embedded in the text, but no problems at the ends of the chapters. The treatment of inflation mentions only the flatness and horizon problems, and it may take you a while to find the bits you want. The index lists neither lambda nor the cosmological constant, and inflation is said to appear on pp 307–412. The chapters are of equal length, in traditional textbook fashion.

Neither volume has much to say about issues that are currently `hot'—the importance of extra dimensions, fine tuning of cosmological parameters, possible evidence for cosmic geometry different from the simplest. Discussions of such things will, of course, date a textbook quickly. On the other hand, they are often the items that physics (etc) students will have heard about in colloquia and would like to have clarified. Names appear only as eponyms, from Altarelli Parisi evolution (which is not on the page to which B&G's index refers you) to the Zeeman effect, which is where PS's index says it is.

Can I imagine using either of these as texts? Definitely yes for PS, since it is a possible fit to an astrophysics course that UCI offers as a `vocabulary builder' for students coming out of mainstream physics (and for which we have yet to find an entirely suitable text). We are contemplating a faculty hire or two in astro-particle physics, in which case B&G might well be a good fit to a seminar for students beginning work in that area. If I were asked to teach the course, however, I would probably want an instructor's solution manual for the text problems. One may well exist, though the book does not mention it. Using PS, you will have to make up your own problems (which you can then reasonably be expected to be able to work without help).