Inflation predicts a primordial gravitational wave spectrum that is slightly “red.” In this Brief Report, we compute both the amplitude and spectral form of the primordial tensor spectrum predicted by cyclic or ekpyrotic models under the assumption that perturbations pass smoothly through the bounce. The spectrum is exponentially suppressed compared to inflation on long wavelengths. The strongest constraint is that the energy density in gravitational waves is less than 10% of the critical density at nucleosynthesis.

We study numerically the continuum limit corresponding to the nontrivial fixed point of Dyson’s hierarchical model. We discuss the possibility of using the critical amplitudes as input parameters. We determine numerically the leading and subleading critical amplitudes of the zero-momentum connected $2l$-point functions in the symmetric phase up to the 20-point function for randomly chosen local measures. Using these amplitudes, we construct quantities which are expected to be universal in the limit where very small log-periodic corrections are neglected: the $U^{\mathrm{}\left(2l\right)\mathrm{}\star }$ (proportional to the connected $2l$-point functions) and the $r_{2l}$ (proportional to one-particle irreducible functions). We show that these quantities are independent of the local measure with at least five significant digits. We provide clear evidence for the asymptotic behavior $U^{\mathrm{}\left(2l\right)\mathrm{}\star }\propto \mathrm{}\left(2l\right)$ and reasonable evidence for $r_{2l}\propto \mathrm{}\left(2l\right).\mathrm{}$ These results signal a finite radius of convergence for the generating functions. We provide numerical evidence for a linear growth for universal ratios of subleading amplitudes. We compare our $r_{2l}$ with existing estimates for other models.

We calculate the one-loop effective action of a scalar field with general mass and coupling to the curvature in the detuned Randall-Sundrum brane world scenario, where the four-dimensional branes are anti–de Sitter. We make use of conformal transformations to map the problem to one on the direct product of the hyperbolic space ${\mathrm{H}}^4$ and the interval. We also include the cocycle function for this transformation. This Casimir potential is shown to give a sizable correction to the classical radion potential for small values of brane separation.

We present the first results from our new general relativistic, Lagrangian hydrodynamics code, which treats gravity in the conformally flat (CF) limit. The evolution of fluid configurations is described using smoothed particle hydrodynamics (SPH), and the elliptic field equations of the CF formalism are solved using spectral methods in spherical coordinates. The code was tested on models for which the CF limit is exact, finding good agreement with the classical Oppenheimer-Volkov solution for a relativistic static spherical star as well as the exact semianalytic solution for a collapsing spherical dust cloud. By computing the evolution of quasiequilibrium neutron star binary configurations in the absence of gravitational radiation back reaction, we have confirmed that these configurations can remain dynamically stable all the way to the development of a cusp. With an approximate treatment of radiation reaction, we have calculated the complete merger of an irrotational binary configuration from the innermost point on an equilibrium sequence through merger and remnant formation and ringdown, finding good agreement with previous relativistic calculations. In particular, we find that mass loss is highly suppressed by relativistic effects, but that, for a reasonably stiff neutron star equation of state, the remnant is initially stable against gravitational collapse because of its strong differential rotation. The gravity wave signal derived from our numerical calculation has an energy spectrum which matches extremely well with estimates based solely on quasiequilibrium results, deviating from the Newtonian power-law form at frequencies below 1 kHz, i.e., within the reach of advanced interferometric detectors.

In this paper the $\mathrm{SU}\left(N\right)\mathrm{}$ Einstein-Skyrme system is considered. We express the chiral field [which is not a simple embedding of the $\mathrm{SU}\left(2\right)\mathrm{}$ field] in terms of harmonic maps. In this way, $\mathrm{SU}\left(N\right)\mathrm{}$ spherical symmetric equations can be obtained easily for any N and the gravitating Skyrmion solutions of these equations can be studied. In particular, the $\mathrm{SU}\left(3\right)\mathrm{}$ case is considered in detail and three different types of gravitating Skyrmions with topological charge four, two, and zero, respectively, are constructed numerically. Note that the configuration with zero topological charge corresponds to mixtures of Skyrmions and anti-Skyrmions.

A sum-over-histories generalized quantum theory is developed for homogeneous minisuperspace type A Bianchi cosmological models, focusing on the particular example of the classically recollapsing Bianchi type-IX universe. The decoherence functional for such universes is exhibited. We show how the probabilities of decoherent sets of alternative, coarse-grained histories of these model universes can be calculated. We consider in particular the probabilities for classical evolution defined by a suitable coarse graining. For a restricted class of initial conditions and coarse grainings we exhibit the approximate decoherence of alternative histories in which the universe behaves classically and those in which it does not. For these situations we show that the probability is near unity for the universe to recontract classically if it expands classically. We also determine the relative probabilities of quasiclassical trajectories for initial states of WKB form, recovering for such states a precise form of the familiar heuristic $“J\cdot d\Sigma ”$ rule of quantum cosmology, as well as a generalization of this rule to generic initial states.

Despite the interest in dark matter and dark energy, it has never been shown that they are in fact two separate substances. We provide the first strong evidence that they are separate by ruling out a broad class of so-called unified dark matter models that have attracted much recent interest. We find that they produce oscillations or exponential blowup of the dark matter power spectrum inconsistent with observation. For the particular case of generalized Chaplygin gas models, 99.999% of the previously allowed parameter space is excluded, leaving essentially only the standard $\Lambda \mathrm{CDM}$ limit allowed.

The electric fields associated with thunderclouds change the intensity of secondary cosmic rays observed on the ground. This effect has been investigated using several detectors located at the Mount Norikura Cosmic Ray Observatory where excesses of 1% and more of the average counting rate may be observed when the Observatory is covered by thunderclouds. A frequency analysis of the time series of days with such excesses for the period 26 October 1990 to 15 January 2002 shows the expected summer maximum in the rate of occurrence and, more surprisingly, a 26-day variation. An electric field mill was installed to help determine the relationship between the intensity variations and the strength and direction of the field near the detector system: the excess is usually observed when a negative electric field (accelerating negative charges downward) greater than 10 kV/m is present in the atmosphere above the observatory. Based on Monte Carlo simulations we predict that excess counting rates measured without charge discrimination will be expected as a consequence of the excess of positive muons among the secondary cosmic rays.

We present the analysis of between 50 and 100 h of coincident interferometric strain data used to search for and establish an upper limit on a stochastic background of gravitational radiation. These data come from the first LIGO science run, during which all three LIGO interferometers were operated over a 2-week period spanning August and September of 2002. The method of cross correlating the outputs of two interferometers is used for analysis. We describe in detail practical signal processing issues that arise when working with real data, and we establish an observational upper limit on a $f^{-3}$ power spectrum of gravitational waves. Our 90% confidence limit is ${\Omega }_0{h}_{100}^2<~23\pm 4.6$ in the frequency band 40–314 Hz, where $h_{100}$ is the Hubble constant in units of 100 km/sec/Mpc and ${\Omega }_0$ is the gravitational wave energy density per logarithmic frequency interval in units of the closure density. This limit is approximately ${10}^4$ times better than the previous, broadband direct limit using interferometric detectors, and nearly 3 times better than the best narrow-band bar detector limit. As LIGO and other worldwide detectors improve in sensitivity and attain their design goals, the analysis procedures described here should lead to stochastic background sensitivity levels of astrophysical interest.

The infrared attractive force of the bulk gauge interactions is applied to soften the supersymmetric flavor problem in the orbifold SU(5) grand unified theory of Kawamura. Then this force aligns in the infrared regime the soft supersymmetry breaking terms out of their anarchical disorder at a fundamental scale, in such a way that flavor-changing neutral currents as well as dangerous CP-violating phases are suppressed at low energies. It is found that this dynamical alignment is sufficiently good compared with the current experimental bounds, as long as the diagonalization matrices of the Yukawa couplings are CKM-like.

We report the first evidence for a nonzero beam-spin azimuthal asymmetry in the electroproduction of positive pions in the deep-inelastic kinematic region. Data for the reaction $e\overrightarrow{p}{e}^{\prime }{\pi }^{+}X$ have been obtained using a polarized electron beam of 4.3 GeV with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The amplitude of the $\sin \phi$ modulation increases with the momentum of the pion relative to the virtual photon, z. In the range $z=0.5\mathrm{}–0.8$ the average amplitude is $0.038\pm 0.005\pm 0.003$ for a missing mass $M_X>1.1\mathrm{}\mathrm{GeV}$ and $0.037\pm 0.007\pm 0.004$ for $M_X>1.4\mathrm{}\mathrm{GeV}.$

Noncommuting spatial coordinates are studied in connection with the motion of a charged particle in a strong generic magnetic field. We derive a relation involving the commutators of the coordinates, which generalizes the one realized in a strong constant magnetic field. As an application, we discuss the coordinate noncommutativity in a slowly varying magnetic field.

Exact, nonsingular, time-dependent solutions of Maxwell-Einstein gravity with and without dilatons are constructed by double Wick rotating a variety of static, axisymmetric solutions. This procedure transforms arrays of charged or neutral black holes into s-brane (spacelike brane) solutions, i.e., extended, short-lived spacelike defects. Along the way, new static solutions corresponding to arrays of alternating-charge Reissner-Nordstrøm black holes, as well as their dilatonic generalizations, are found. Their double Wick rotation yields s-brane solutions which are periodic in imaginary time and potential large-N duals for the creation or decay of unstable D-branes in string theory.

We study the properties and phenomenology of particlelike states originating from D branes whose spatial dimensions are all compactified. They are nonperturbative states in string theory and we refer to them as D matter. In contrast to other nonperturbative objects such as ’t Hooft–Polyakov monopoles, D-matter states could have perturbative couplings among themselves and with ordinary matter. The lightest D particle (LDP) could be stable because it is the lightest state carrying certain (integer or discrete) quantum numbers. Depending on the string scale, they could be cold dark matter candidates with properties similar to that of WIMPs or wimpzillas. The spectrum of excited states of D matter exhibits an interesting pattern which could be distinguished from that of Kaluza-Klein modes, winding states, and string resonances. We speculate about possible signatures of D matter from ultrahigh energy cosmic rays and colliders.

We find de Sitter and flat space solutions with all closed string moduli stabilized in four-dimensional supergravity theories derived from heterotic and type II string theories, and explain how all the previously known obstacles to finding such solutions can be removed. Further, we argue that if the compact manifold allows a large enough space of discrete topological choices then it is possible to tune the parameters of four-dimensional supergravity such that a hierarchy is created, and the solutions lie in the outer region of moduli space in which the compact volume is large in string units, the string coupling is weak, and string perturbation theory is valid. We show that at least two light chiral superfields are required for this scenario to work; however, one field is sufficient to obtain a minimum with an acceptably small and negative cosmological constant. We discuss the cosmological issues of the scenario and the possible role of anthropic considerations in choosing the vacuum of the theory. We conclude that the most likely stable vacua are in or near the central region of moduli space where string perturbation theory is not strictly valid, and that anthropic considerations cannot help much in choosing a vacuum.

We study the four dimensional effective action of a system of D6-branes wrapped on the $K3\mathrm{}$ manifold times a torus, allowing the volume of the internal manifolds to remain dynamical. An unwrapped brane is at best a Dirac monopole of the dual RR sector field to which it couples. After wrapping, a brane is expected to behave as a BPS monopole, where the Higgs vacuum expectation value is set by the size of the $K3.\mathrm{}$ We determine the moduli space of an arbitrary number of these wrapped branes by introducing a time dependent perturbation of the static solution and expanding the supergravity equations of motion to determine the dynamics of this perturbation, in the low velocity limit. The result is the hyper-Kähler generalization of the Euclidean Taub-NUT metric presented by Gibbons and Manton. We note that our results also pertain to the behavior of bound states of Kaluza-Klein monopoles and wrapped NS5-branes in the $T^4$ compactified heterotic string.

Dynamical gauge symmetry breaking on the orbifold $T^2{/Z}_2$ is shown to occur through the quantum dynamics of Wilson line phases. Different sets of boundary conditions on $T^2{/Z}_2$ can be related to each other by Wilson line phases, forming equivalence classes. The effective potential for Wilson line phases is evaluated at the one-loop level in $\mathrm{SU}\left(2\right)\mathrm{}$ gauge theory. Depending on the fermion content, the $\mathrm{SU}\left(2\right)\mathrm{}$ symmetry can be broken either completely or partially to $U\left(1\right)\mathrm{}$ without introducing additional Higgs scalar fields. When $\mathrm{SU}\left(2\right)\mathrm{}$ is completely broken, each of three components of the gauge fields may acquire a distinct mass. Masses are generated through the combination of $T^2$ twists and dynamics of Wilson line phases.

Using perturbative techniques, we investigate the existence and properties of a static solution for the Einstein equation with a negative cosmological constant, which we call the deformed black hole. We derive a solution for a static and axisymmetric perturbation of the Schwarzschild–anti-de Sitter black hole that is regular in the range from the horizon to spacelike infinity. The key result is that this perturbation simultaneously deforms the two boundary surfaces—i.e., both the horizon and spacelike two-surface at infinity. Then we discuss the Abbott-Deser mass and the Ashtekar-Magnon one for the deformed black hole, and according to the Ashtekar-Magnon definition, we construct the thermodynamic first law of the deformed black hole. The first law has a correction term which can be interpreted as the work term that is necessary for the deformation of the boundary surfaces. Because the work term is negative, the horizon area of the deformed black hole becomes larger than that of the Schwarzschild–anti-de Sitter black hole, if compared under the same mass, indicating that the quasistatic deformation of the Schwarzschild–anti-de Sitter black hole may be compatible with the thermodynamic second law (i.e., the area theorem).

Using numerical techniques, we study the collapse of a scalar field configuration in the Newtonian limit of the spherically symmetric Einstein-Klein-Gordon system, which results in the so called Schrödinger-Newton (SN) set of equations. We present the numerical code developed to evolve the SN system and related topics, like equilibrium configurations and boundary conditions. Also, we analyze the evolution of different initial configurations and the physical quantities associated with them. In particular, we readdress the issue of the gravitational cooling mechanism for Newtonian systems and find that all systems settle down onto a zero-node equilibrium configuration.

Large-distance modification of gravity may be the best mechanism for solving the cosmological constant problem. A simple model of the large-distance modification—four-dimensional (4D) gravity with a hard mass term—is problematic from the theoretical standpoint. Here we discuss a different model, brane-induced gravity, that effectively introduces a soft graviton mass. We study the issues of unitarity, analyticity, and causality in this model in more than five dimensions. We show that a consistent prescription for the poles of the Green’s function can be specified so that 4D unitarity is preserved. However, in certain instances 4D analyticity cannot be maintained when the theory becomes higher dimensional. As a result, one has to sacrifice 4D causality at distances of the order of the present-day Hubble scale. This is a welcome feature for solving the cosmological constant problem, as was recently argued in the literature. We also show that, unlike 4D massive gravity, the model has no strong-coupling problem at intermediate scales.