International Journal of Modern Physics D

The Pioneer 10/11 spacecraft yielded the most precise navigation in deep space to date. However, their radiometric tracking data has consistently indicated the presence of a small, anomalous, Doppler frequency drift. The drift is a blue shift, uniformly changing with a rate of ~6 × 10^-9Hz/s and can be interpreted as a constant sunward acceleration of each particular spacecraft of a_P = (8.74±1.33) × 10^-10m/s² (or, alternatively, a time acceleration of a_t = (2.92±0.44) × 10^-18s/s²). This signal has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained. We discuss the current state of the efforts to retrieve the entire data sets of the Pioneer 10 and 11 radiometric Doppler data. We also report on the availability of recently recovered telemetry files that may be used to reconstruct the engineering history of both spacecraft using original project documentation and newly developed software tools. We discuss possible ways to further investigate the discovered effect using these telemetry files in conjunction with the analysis of the much extended Pioneer Doppler data. In preparation for this new upcoming investigation, we summarize the current knowledge of the Pioneer anomaly and review some of the mechanisms proposed for its explanation. We emphasize the main objectives of this new study, namely (i) analysis of the early data that could yield the true direction of the anomaly and thus, its origin, (ii) analysis of planetary encounters, which should say more about the onset of the anomaly (e.g. Pioneer 11's Saturn flyby), (iii) analysis of the entire dataset, which should lead to a better determination of the temporal behavior of the anomaly, (iv) comparative analysis of individual anomalous accelerations for the two Pioneers with the data taken from similar heliocentric distances, (v) the detailed study of on-board systematics, and (vi) development of a thermal-electric-dynamical model using on-board telemetry. The outlined strategy may allow for a higher accuracy solution for the anomalous acceleration of the Pioneer spacecraft and, possibly, will lead to an unambiguous determination of the origin of the Pioneer anomaly.

Meson spectra given as fluctuations of a D7-brane are studied under the background driven by the dilaton. This leads to a dual gauge theory with quark confinement due to the gauge condensate. We find that the effect of the gauge condensate on the meson spectrum is essential in order to make a realistic hadron spectrum in the non-supersymmetric case. In the supersymmetric case, however, only the spectra of the scalars are affected, but they are changed in an opposite way compared to the non-supersymmetric case.

We investigate the possibility that part of the dark matter is not made out of the usual cold dark matter (CDM) dust-like particles, but is in the form of a fluid of strings with barotropic factor w_s = -1/3 of cosmic origin. To this aim, we split the dark matter density parameter into two terms and investigate the dynamics of a spatially flat universe filled with baryons, CDM, a fluid of strings and dark energy, modeling the latter as a cosmological constant or a negative pressure fluid with a constant equation of state w < 0. To test the viability of the models and to constrain their parameters, we use the Type Ia supernovae Hubble diagram and data on the gas mass fraction in galaxy clusters. We also discuss the weak field limit of a model comprising a significant fraction of dark matter in the form of a fluid of strings and show that this mechanism makes it possible to reduce the need for the elusive and up to now undetected CDM. We finally find that a model comprising both a cosmological constant and a fluid of strings fits the data very well and eliminates the need for phantom dark energy, thus representing a viable candidate for alleviating some of the problems plaguing the dark side of the universe.

We have considered the multidimensional cosmological implications of a decay law for the Λ term that is proportional to , where β is a constant and a is the scale factor of RW-space–time. We discuss the cosmological consequences of a model for the vanishing pressure for the case k = 0. It has been observed that such models are compatible with the result of recent observations and the cosmological term Λ gradually reduces as the universe expands. In this model, Λ varies as the inverse square of time, which matches its natural units. The proper distance, the luminosity distance-redshift, the angular diameter distance-redshift, and look back time-redshift for the model are presented in the framework of higher dimensional space–time. The model of the Freese et al. (Nucl. Phys. B287, 797 (1987)) for n = 2 is retrieved for the particular choice of A₀ and also the Einstein–de Sitter model is obtained for . This work has thus generalized to higher dimensions the well-known result in four-dimensional space–time. It is found that there may be a significant difference, in principle at least, to the analogous situation in four-dimensional space–time.

Numerical evolution of the spherically symmetric, massive Klein–Gordon field is presented using a new adaptive mesh refinement (AMR) code with fourth order discretization in space and time, along with compactification in space. The system is non-interacting, thus the initial disturbance is entirely radiated away. The main aim is to simulate its propagation until it vanishes near . By numerical investigations of the violation of the energy balance relations, the space–time boundaries of "well-behaving" regions are determined for different values of the AMR parameters. An important result is that mesh refinement maintains precision in the central region for a longer time even if the mesh is only refined outside of this region. The speed of the algorithm was also tested; in the case of ten refinement levels the algorithm was two orders of magnitude faster than the extrapolated time of the corresponding unigrid run.

We study the motion of a pseudo-classical charged particle with spin in the space–time of a gravitational pp wave in the presence of a uniform magnetic field.