Hiroyuki Yoshiguchi

Propagation of Ultra-High-Energy Cosmic Rays above 1019 eV in a Structured Extragalactic Magnetic Field and Galactic Magnetic Field

We present numerical simulations of the propagation of ultra-high-energy cosmic rays (UHECRs) above 1019 eV in a structured extragalactic magnetic field (EGMF) and simulate their arrival distributions at the Earth. We use the IRAS PSCz catalog in order to construct a model of the EGMF and source models of UHECRs, both of which reproduce the local structures observed around the Milky Way. We also consider modifications of UHECR arrival directions by the Galactic magnetic field. We follow an inverse process of their propagation from the Earth and record the trajectories. This enables us to calculate only trajectories of UHECRs arriving at the Earth, which saves CPU time. From these trajectories and our source models, we construct arrival distributions of UHECRs and calculate their harmonic amplitudes and two-point correlation functions. We estimate the number density of sources that best reproduces the Akeno Ground Air Shower Array (AGASA) observation. As a result, we find that the most appropriate number density of the sources is ~5 × 10-6 Mpc-3. This constrains the source candidates of UHECRs. We also demonstrate sky maps of their arrival distribution with the event number expected by future experiments and examine how the EGMF affects their arrival distribution. A main result is the diffusion of clustering events, which are obtained from calculations in the absence of the EGMF. This tendency allows us to reproduce the observed two-point correlation function better.

Dynamical stability of six-dimensional warped flux compactification

We show the dynamical stability of a six-dimensional braneworld solution with warped flux compactification recently found by the authors. We consider linear perturbations around this background spacetime, assuming axisymmetry in the extra dimensions. The perturbations are expanded in scalar-, vector-, and tensor-type harmonics of the four-dimensional Minkoswki spacetime and we analyse each type separately. It is found that there is no unstable mode in any sector and that there are zero modes only in the tensor sector, corresponding to the four-dimensional gravitons. We also obtain the first few Kaluza–Klein modes in each sector.

Warped flux compactification and brane gravity

We find a simple exact solution for a six-dimensional braneworld which captures some essential features of warped flux compactification, including a warped geometry, compactification, a magnetic flux and one or two 3-brane(s). In this set-up we analyse how the Hubble expansion rate on each brane changes when the brane tension changes. It is shown that the effective Newtons constant resulting from this analysis agrees with that inferred by simply integrating extra dimensions out. On the basis of the result, a general formula for the effective Newtons constant is conjectured and its application to cosmology with type IIB warped string compactification is discussed.

A New method for calculating arrival distribution of ultra-high energy cosmic rays above 10**19-eV with modifications by the galactic magnetic field

We present a new method for calculating arrival distribution of ultra-high-energy cosmic rays (UHECRs), including modifications by the Galactic magnetic field. We perform numerical simulations of UHE antiprotons, which are injected isotropically at the Earth, in the Galaxy and record the directions of velocities at the Earth and outside the Galaxy for all of the trajectories. We then select some of them so that the resultant mapping of the velocity directions outside the Galaxy of the selected trajectories corresponds to a given source location scenario, applying Liouvilles theorem. We also consider energy-loss processes of UHE protons in the intergalactic space. Applying this method to the source location scenario that is adopted in our recent study and can explain the Akeno Giant Air Shower Array (AGASA) observation above 4 × 1019 eV, we calculate the arrival distribution of UHECRs, including lower energy (E > 1019 eV) ones. We find that our source model can reproduce the large-scale isotropy and the small-scale anisotropy on UHECR arrival distribution above 1019 eV observed by the AGASA. We also demonstrate the UHECR arrival distribution above 1019 eV, with the event number expected by future experiments in the next few years. The interesting feature of the resultant arrival distribution is the arrangement of the clustered events in the order of their energies, reflecting the directions of the Galactic magnetic field. This is also pointed out by Alvarez-Muniz, Engel, & Stanev. This feature will allow us to obtain some kind of information about the composition of UHECRs and the magnetic field with increasing amount of data.

Arrival Distribution of Ultra-High-Energy Cosmic Rays: Prospects for the Future

We predict the arrival distribution of ultra-high-energy cosmic rays (UHECRs) above 4 × 1019 eV with the event number expected by future experiments in the next few years. We perform event simulations with the source model that is adopted in our recent study and can explain the current Akeno Giant Air Shower Array (AGASA) observation. At first, we calculate the harmonic amplitude and the two-point correlation function for the simulated event sets. We find that significant anisotropy on a large angle scale will be observed when ~103 cosmic rays above 4 × 1019 eV are detected by future experiments. The Auger array will detect cosmic rays with this event number in a few years of operation. The statistics of the two-point correlation function will also increase. The angle scale at which the events have strong correlation with each other corresponds to the deflection angle of UHECRs propagating in the extragalactic magnetic field (EGMF), which in turn can be determined by the future observations. We further investigate the relation between the number of events clustered in a direction and the distance of their sources. Despite the limited amount of data, we find that the C2 triplet events observed by the AGASA may originate from a source within 100 Mpc from us at 2 σ confidence level. Merger galaxy Arp 299 (NGC 3690 + IC 694) is the best candidate for their source. If data accumulate, the UHECR sources within ~100 Mpc can be identified significantly from observed event clusterings. This will provide some kinds of information about poorly known parameters that influence the propagation of UHECRs, such as extragalactic and Galactic magnetic fields and the chemical composition of observed cosmic rays. Also, we will reveal the origin of UHECRs with our method of identifying their sources. Finally, we predict the arrival distribution of UHECRs above 1020 eV that is expected to be observed if the current HiRes spectrum is correct and discuss their statistical features and implications.

Statistical Significance of Small-Scale Anisotropy in Arrival Directions of Ultra-High-Energy Cosmic Rays

Recently, the High Resolution Flys Eye (HiRes) experiment has indicated that there is no small-scale anisotropy in the arrival distribution of ultra-high-energy cosmic rays (UHECRs) above E > 1019 eV, contrary to the Akeno Giant Air Shower Array (AGASA) observation. In this paper we discuss the statistical significance of this discrepancy between the two experiments. We calculate the arrival distribution of UHECRs above the 1019 eV predicted by the source models constructed using the Optical Redshift Survey galaxy sample. We apply a new method developed by us for calculating arrival distribution in the presence of the Galactic magnetic field. The great advantage of this method is that it enables us to calculate the UHECR arrival distribution with lower energy (~1019 eV) than previous studies within a reasonable time by following only the trajectories of UHECRs actually reaching the Earth. It has been realized that the small-scale anisotropy observed by the AGASA can be explained with the source number density ~10-6 to 10-5 Mpc-3, assuming a weak extragalactic magnetic field (B ≤ 1 nG). We find that the predicted small-scale anisotropy for this source number density is also consistent with the current HiRes data. We thus conclude that the statement by the HiRes collaboration that they do not find small-scale anisotropy in the UHECR arrival distribution is not statistically significant at present. We also examine the future prospect of determining the source number density with an increasing amount of observed data.

Numerical study on the propagation of ultra-high-energy cosmic rays in the Galactic magnetic field

We study the propagation of ultra-high-energy cosmic rays (UHECRs) with E > 1018 eV in the Galactic magnetic field (GMF). We present numerical simulations for the propagation of antiprotons from the Earth toward the outside of the Galaxy in the GMF and calculate the sky map of the position of antiprotons that have reached the boundary. This sky map is interpreted as the relative probability distribution for the ability of protons to reach the Earth for the case of isotropic source distribution, considering Liouvilles theorem. Basically, we adopt a GMF model that is composed of the spiral and dipole magnetic fields. We also consider the propagation of UHECRs in both of these two components of the magnetic field. This enables us to see the effect of each component on the arrival distribution of UHECRs. The main effect of the dipole magnetic field is to deflect antiprotons toward high Galactic longitudes, because this field is directed toward the north Galactic pole in the Galactic plane. In particular, antiprotons injected in the direction ~300° are strongly deflected and then rotated by the strong magnetic field in the vicinity of the Galactic center. The ideal form of the dipole magnetic field causes the clear pattern of the sky map of the positions of antiprotons that have reached the boundary when they are plotted by color according to the rotation number of the orbits. On the other hand, the spiral field mainly deflects antiprotons injected at the Earth toward the north Galactic pole, i.e., toward the Virgo cluster. This is because the spiral field in the solar system is in the direction of l ~ 90°. Even if the dipole magnetic filed is also included, we find that almost all UHECRs come from the direction of the Virgo cluster, because the spiral magnetic field in the solar system is stronger than the dipole field. This result suggests the nuclei component of UHECRs from the Virgo cluster as an attractive possibility for the origin of UHECRs.

Propagation of Ultra-High Energy Cosmic Rays from Sources in the Super-Galactic Plane

We have performed the detailed numerical simulations on the propagation of the UHE protons in the energy range

Quantization of scalar perturbations in brane-world inflation

E=(10^{19.5} - 10^{22.0}

Bulk gravitational field and dark radiation on the brane in a dilatonic brane world

) eV in the relatively strong extra-galactic magnetic field with strength