Galactic cosmic-ray anisotropy and its heliospheric modulation, inferred from the sidereal semidiurnal variations observed in the rigidity range 300–600 GV with multidirectional muon telescope at Sakashita underground station

The existence of sidereal semidiurnal variation of cosmic-ray intensity in a rigidity region 10²-10³ GV has been reported by many researchers, but there is no consensus of opinion on its origin. In this paper, using the observed semidiurnal variations in a rigidity range (300–600 GV) with 10 directional muon telescopes at Sakashita underground station (geog. lat. = 36°, long. = 138°E, DEPTH = 80 m.w.e.), the authors determine the magnitudes (η₁, η₂) and directions (a₁, a₂) of the first- and second-order anisotropies in the following galactic cosmic-ray intensity distribution (j)

jdp = j₀{1 + η₁P₁(cos χ₁) + η₂P₂(cos χ₂)}dp

, where P_nis the nth order spherical function and χ_n is the pitch angle of cosmic rays with respect to a_n. For the determination, the influence of cosmic-ray's heliomagnetospheric modulation, geomagnetic deflection and nuclear interaction with the terrestrial material and also of the geometric configuration of the telescopes are taken into account. Usually, the semidiurnal variation is produced by the second-order anisotropy. The present observation, however, requires also the first-order anisotropy which usually produces only the diurnal variation, but can produce also the semidiurnal variation as a result of the heliospheric modulation. The first- and second-order anisotropies are characterized with η₁) > 0 and η₂ < 0 have almost the same direction (a₁ a₂) specified by the right ascension ( 0.75 h) and declination (δ 50°S) and, therefore, they can be expressed, as a whole, by an axis-symmetric anisotropy of loss-cone type (i.e. deficit intensities in a cone). It is noteworthy that this anisotropy approximately coincides with that inferred from the air shower observation at Mt Norikura in the rigidity region 10⁴ GV.     

Density profiles of dark matter halos with anisotropic velocity tensors

We present density profiles, that are solutions of the spherical Jeans equation, derived under the following two assumptions: (i) the coarse grained phase-density follows a power-law of radius, ρ/σ³ ∝ r⁻, and (ii) the velocity anisotropy parameter is given by the relation β_a(r)=β₁+2β₂ (r/r_*)/[1+(r/r_*)²] where β₁, β₂ are parameters and r_* equals twice the virial radius, r_vir, of the system. These assumptions are well motivated by the results of N-body simulations. Density profiles have increasing logarithmic slopes γ, defined by γ=−d ln ρ/d ln r. The values of γ at r=10^−2.5r_vir, a distance where the systems could be resolved by large N-body simulations, lie in the range 1.0–1.6. These inner values of γ increase for increasing β₁ and for increasing concentration of the system. On the other hand, slopes at r=r_vir lie in the range 2.42–3.82. A model density profile that fits well the results at radial distances between 10⁻³r_vir and r_vir and connects kinematic and structural characteristics of spherical systems is described.     

Gamma-ray and synchrotron emission from neutralino annihilation in the Large Magellanic Cloud

We calculate the expected flux of γ-ray and radio emission from the LMC due to neutralino annihilation. Using rotation curve data to probe the density profile and assuming a minimum disk, we describe the dark matter halo of the LMC using models predicted by N-body simulations. We consider a range of density profiles including the NFW profile, a modified NFW profile proposed by Hayashi et al. (2003) to account for the effects of tidal stripping, and an isothermal sphere with a core. We find that the γ-ray flux expected from these models may be detectable by GLAST for a significant part of the neutralino parameter space. The prospects for existing and upcoming Atmospheric Cherenkov Telescopes (ACTs) are less optimistic, as unrealistically long exposures are required for detection. However, the effects of adiabatic compression due to the baryonic component may improve the chances for detection by ACTs. The maximum flux we predict is well below EGRET's measurements and thus EGRET does not constrain the parameter space. The expected synchrotron emission generally lies below the observed radio emission from the LMC in the frequency range of 19.7–8550 MHz. As long as σv<2×10⁻²⁶ cm³ s⁻¹ for a neutralino mass of 50 GeV, the observed radio emission is not primarily due to neutralinos and is consistent with the assumption that the main source is cosmic rays. We find that the predicted fluxes, obtained by integrating over the entire LMC, are not very strongly dependent on the inner slope of the halo profile, varying by less than an order of magnitude for the range of profiles we considered.     

Constraining cosmological models with cluster power spectra

Using extensive N-body simulations we estimate redshift space power spectra of clusters of galaxies for different cosmological models (SCDM, TCDM, CHDM, ΛCDM, OCDM, BSI, τCDM) and compare the results with observational data for Abell–ACO clusters. Our mock samples of galaxy clusters have the same geometry and selection functions as the observational sample which contains 417 clusters of galaxies in a double cone of galactic latitude |b|>30° up to a depth of 240 h⁻¹ Mpc. The power spectrum has been estimated for wave numbers k in the range 0.03k0.2 h Mpc⁻¹. For k>k_max0.05 h Mpc⁻¹ the power spectrum of the Abell–ACO clusters has a power-law shape, P(k)∝kⁿ, with n≈−1.9, while it changes sharply to a positive slope at k<k_max. By comparison with the mock catalogues SCDM, TCDM (n=0.9), and also OCDM with Ω₀=0.35 are rejected. Better agreement with observation can be found for the ΛCDM model with Ω₀=0.35 and h=0.7 and the CHDM model with two degenerate neutrinos and Ω_HDM=0.2 as well as for a CDM model with broken scale invariance (BSI) and the τCDM model. As for the peak in the Abell–ACO cluster power spectrum, we find that it does not represent a very unusual finding within the set of mock samples extracted from our simulations.     

Spectrum of the relic neutrino background from past supernovae and cosmological models

It is greatly expected that the relic neutrino background from past supernovae will be detected by Superkamiokande (SK) which is now under construction. We calculate the spectrum and the event rate at SK systematically by using the results of simulations of a supernova explosion and reasonable supernova rates. We also investigate the effect of a cosmological constant, Λ, on the spectrum, since some recent cosmological observations strongly suggest the existence of Λ. We find following results. (1) The spectrum has a peak at about 3 MeV, which is much lower than that of previous estimates (6–10 MeV). (2) The event rate at SK in the range from 10 MeV to 50 MeV, where the relic neutrinos from past supernovae are dominant, is about 25h₅₀²(R_SN/0.1 yr⁻¹)(n_Gh₅₀⁻³/0.02 Mpc⁻³) events per year, where R_SN is the supernova rate in a galaxy, n_G is the number density of galaxies, and h₅₀ = H₀/(50 km/s Mpc), where H₀ is the Hubble constant. (3) The event rate is almost insensitive to Λ. The flux increases in the low energy side (< 10 MeV) with increasing Λ, but decreases in the high energy side (> 10 MeV) in models in which the integrated number of supernovae in one galaxy is fixed.     

A method of analysing the emission lines of solar prominences

A new method of analysing the emission spectrum of solar prominences is presented, in which the source function is allowed to vary with optical depth. Least-squares fitting of the observed profile determines simultaneously the optical depth τ₀, the Doppler width Δλ_D and the factor characterising the variation of the source function. This method is applied to the early Balmer lines in ten prominences of Ref. [1]. The results show that the source function of the self-reversed H line increases towards the centre of the prominence, the value at the centre is 1.2–2.5 times the value at the edge. Neglect of this variation will give too large values of τ₀. The degree of attenuation by selfabsorption also depends on this variation. Discussion of the variation gives support to the view that the main exciting mechanism in solar prominences is the scattering of the incident radiation.     

Galactic gamma halo by heavy neutrino annihilations?

The diffused gamma halo around our Galaxy recently discovered by EGRET could be produced by annihilations of heavy relic neutrinos N (of fourth generation), whose mass is within a narrow range (M_Z/2<m_N<M_Z). Neutrino annihilation in the halo may lead to either ultrarelativistic electron pairs whose Inverse Compton Scattering on infrared and optical galactic photons could be the source of observed GeV gamma rays, or prompt 100 MeV–1 GeV photons (due to neutral pion secondaries) born by reactions. The consequent gamma flux (10⁻⁷–10⁻⁶ cm⁻² s⁻¹ sr⁻¹) is well comparable to the EGRET observed one, and it is also compatible with the narrow window of neutrino mass 45 GeV <m_N<50 GeV, recently required to explain the underground DAMA signals.The presence of heavy neutrinos of fourth generation do not contribute much to solve the dark matter problem of the Universe, but may be easily detectable by outcoming LEP II data.     

Auroral N2(c′4Σu → aΠg emission

Inspection of recent spectra presented by Sivjee (1983) show evidence of the 0–4 and 0–5 bands of the N₂(c′₄¹Σ_u⁺ → a¹Π_g) Gaydon-Herman system. In conjunction with earlier spectra, it is now possible that this band system is a significant auroral component, with an intensity approx. 7% that of the N2 2P system. The absence in aurorae of the potentially far stronger N₂(c′₄¹Σ_u⁺ → X¹Π_g) system is discussed. It is that the O₂(A³Σ_u⁺ → X³Σ_g⁻) band system is indiscernible in Sivjee's auroral spectra, under conditio the foreground nightglow is expected to be clearly visible. On the other hand, at least one relatively strong O₂(A′³Δ_u → a¹Δ_g) band appears to be present in these spectra.     

Comparison of high-energy galactic and atmospheric tau neutrino flux

We compare the tau neutrino flux arising from the galaxy and the earth atmosphere for 10³E/GeV10¹¹. The intrinsic and oscillated tau neutrino fluxes from both sources are calculated. The intrinsic galactic ν_τ flux (E10³ GeV) is calculated by considering the interactions of high-energy cosmic-rays with the matter present in our galaxy, whereas the oscillated galactic ν_τ flux is coming from the oscillation of the galactic ν_μ flux. For the intrinsic atmospheric ν_τ flux, we extend the validity of a previous calculation from E10⁶ GeV up to E10¹¹ GeV. The oscillated atmospheric ν_τ flux is, on the other hand, rather suppressed. We find that, for 10³E/GeV5×10⁷, the oscillated ν_τ flux along the galactic plane dominates over the maximal intrinsic atmospheric ν_τ flux, i.e., the flux along the horizontal direction. We also briefly mention the presently envisaged prospects for observing these high-energy tau neutrinos.     

On the Schumann resonances on Mars

A conductive ionosphere and a totally non-conductive layer of the atmosphere close to the surface of the planet form a quasispherical concentric resonator. This provides in principle for the possibility of the existence of global resonances of an electromagnetic field generated by thunderstorm activity or by hydromagnetic waves excited in an upper ionosphere and transformed into ordinary electromagnetic waves while penetrating the resonator. We have obtained an estimate of resonance frequencies of a Martian resonator: ƒ₁ 13–14 Hz,ƒ₂ 24–26 Hz, ƒ₃ 35–38 Hz, etc. for two essentially different models of electron density distribution in the low ionosphere of Mars. The corresponding estimated quality values are low: Q_n 2–4. A relatively wide range of the quality variation depending on a model of averaged altitudinal electron density distribution in the low ionosphere of Mars yields the criterion for an adequate model.     

Cyclotron amplification of geomagnetic micropulsations Pc1 in the magnetosphere

A numerical analysis of cyclotron instabilities is carried out by computing the dispersion relation for a three component cold plasma-beam system. Rates of growth and damping for various values of the stream density are calculated from the dispersion relation. The rates of growth and damping increase monotonically as the number density of the proton stream increases. It is found that the frequencies at the rates of maximum growth and the damping decrease slightly to lower frequencies and a sharp peak at these frequencies becomes blunt. The minimum e-folding times of an ion cyclotron wave for (a) σ_s = 10⁻⁴, σ_i = 10⁻² and (b) σ_s = 10⁻¹, σ_i = 10⁻² are about 3·84 and 0·16 sec respectively in the vicinity of the equatorial plane at 6 Re, where σ_s and σ_i are the ratios of the beam density N_s and the helium ion (H₆⁺) density N_i to the total positive ions in the plasma-beam system.     

Limits on the TeV flux of diffuse gamma rays as measured with the HEGRA air shower array

Using data from the HEGRA air shower array, taken in the period from April 1998 to March 2000, upper limits on the ratio I_γ/I_CR of the diffuse photon flux I_γ to the hadronic cosmic ray flux I_CR are determined for the energy region 20–100 TeV. The analysis uses a gamma–hadron discrimination which is based on differences in the development of photon- and hadron-induced air showers after the shower maximum. A method which is sensitive only to the non-isotropic component of the diffuse photon flux yields an upper limit of I_γ/I_CR (at 54 TeV) <2.0×10⁻³ (at the 90% confidence level) for a sky region near the inner galaxy (20°< galactic longitude <60° and |galactic latitude |<5°). A method which is sensitive to both the isotropic and the non-isotropic component yields global upper limits of I_γ/I_CR (at 31 TeV) <1.2×10⁻² and I_γ/I_CR (at 53 TeV) <1.4×10⁻² (at the 90% confidence level).     

Generalized limits to the number of light particle degrees of freedom from big bang nucleosynthesis

We compute the big bang nucleosynthesis limit on the number of light neutrino degrees of freedom in a model-independent likelihood analysis based on the abundances of ⁴He and ⁷Li. We use the two-dimensional likelihood functions to simultaneously constrain the baryon-to-photon ratio and the number of light neutrinos for a range of ⁴He abundances Y_p = 0.225–0.250, as well as a range in primordial ⁷Li abundances from (1.6 to 4.1) ×10⁻¹⁰. For (⁷Li/H)_p = 1.6 × 10⁻¹⁰, as can be inferred from the ⁷Li data from Population II halo stars, the upper limit to N_ν based on the current best estimate of the primordial ⁴He abundance of Y_p = 0.238 is N_ν < 4.3 and varies from N_ν < 3.3 (at 95% C.L.) when Y_p = 0.225 to N_ν < 5.3 when Y_p = 0.250. If ⁷Li is depleted in these stars the upper limit to N_ν is relaxed. Taking (⁷Li/H)_p = 4.1 × 10⁻¹⁰, the limit varies from N_ν < 3.9 when Y_p = 0.225 to N_ν 6 when Y_p = 0.250. We also consider the consequences on the upper limit to N_ν if recent observations of deuterium in high-redshift quasar absorption-line systems are confirmed.     

The Cr and Sr sources in BOREXINO as tools for neutrino magnetic moment searches

We calculate the event rates induced by a ⁵¹Cr ν_e source and by a ⁹⁰Sr---⁹⁰Y source in BOREXINO through elastic scattering on electrons, assuming a nonzero neutrino magnetic moment μ_ν. We consider a source activity of about 2 MCi and estimate the solar ν (“source-off”) background for various oscillation scenarios. It is shown that values of μ_ν as low as 0.5 × 10⁻¹⁰μ_B ( 0.2 × 10⁻¹⁰μ_B) can be proved with the ⁵¹Cr source (⁹⁰Sr source) in about 100 days of data taking.     

A new investigation on neutralino dark matter: relic density and detection rates

The main properties of the neutralino dark matter are revisited in the light of the new theoretical developments in Susy theories and of the recent constraints from accelerators and underground experiments. The neutralino relic abundance and the detection rates relevant for direct and indirect searches are evaluated in the minimal supersymmetric standard model (MSSM) with the full inclusion of the (one-loop) radiative corrections, both to the Higgs masses and to the trilinear Higgs self-coupling. The relevance of these corrections for the neutralino-neutralino annihilation cross-section, and thus for the relic density, is discussed in detail. Large regions of the parameter space are considered, including those where the neutralino only provides a fraction of the local dark matter density; in these domains the standard value for the local density is appropriately scaled down. Some general properties of the detection rates as functions of the MSSM parameters are also elucidated; in particular it is shown that in the regions of the parameter space where scaling of the local density occurs, the rates are largely independent of two of the model free parameters. The relevance of the Kamiokande upper bounds to the upgoing muon fluxes is discussed in connection with the possible neutrino outputs from the Earth and from the Sun due to neutralino accumulation and annihilation in these macroscopic bodies. Finally, the complementarity between the search for neutralino dark matter and the discovery potential of future accelerators is discussed.     

Constraining the power spectrum using clusters

We analyze an extended redshift sample of Abell/ACO clusters and compare the results with those coming from numerical simulations of the cluster distribution, based on the truncated Zel'dovich approximation (TZA), for a list of eleven dark matter (DM) models. For each model we run several realizations, so that we generate a set of 48 independent mock Abell/ACO cluster samples per model, on which we estimate cosmic variance effects. Other than the standard CDM model, we consider (a) Ω₀ = 1 CDM models based on lowering the Hubble parameter and/or on tilting the primordial spectrum; (b) Ω₀ = 1 Cold + Hot DM models with 0.1 ≤Ω_ν ≤0.5; (c) low-density flat ΛCDM models with 0.3 ≤Ω₀ ≤0.5. We compare real and simulated cluster distributions by analysing correlation statistics, the probability density function, and supercluster properties from percolation analysis. We introduce a generalized definition of the spectrum shape parameter Γ in terms of σ₂₅/σ₈, where σ_ris the rms fluctuation amplitude within a sphere of radius r. As a general result, we find that the distribution of galaxy clusters provides a constraint only on the shape of the power spectrum, but not on its amplitude: a shape parameter 0.18 Γ 0.25 and an effective spectral index at the 20 h⁻¹ Mpc scale −1.1 n_eff −0.9 are required by the Abell/ACO data. In order to obtain complementary constraints on the spectrum amplitude, we consider the cluster abundance as estimated using the Press-Schechter approach, whose reliability is explicitly tested against N-body simulations. By combining results from the analysis of the distribution and the abundance of clusters we conclude that, of the cosmological models considered here, the only viable models are either Cold + Hot DM ones with 0.2 Ω_ν 0.3, better if shared between two massive ν species, and ΛCDM ones with 0.3 Ω₀0.5.     

Application of the complete linearization method to the analysis of solar prominence emission spectrum

We analysed the emission spectra of solar prominences using the complete linearization method [5] and found simultaneously the optical depth at the line centre τ₀, the doppler width of the line Δλ_D and the damping width a. The results show 1) that the complete linearization method has a larger radius of convergence, 2) that we must consider the variation of the source function with depth, when determining τ₀, and 3) that the calculated values of the damping constant for the H, Hβ of hydrogen and H and K lines of Calcium are all much greater than the theoretical values from doppler broadening and radiation damping, showing that other mechanisms besides these two also contribute to the broadening of prominence lines.     

On the joint robust estimation of parameters and variance

A method of joint estimation of the parameters and the variance σ² in the linear model is presented in this paper. The M-estimators with finite rejection points are adopted for estimating the parameters. In order to estimate the variance σ², the Grubbs statistics and the Kurtosis test statistics are adopted to test the residual sequence {;r_i};. And the sample variance of {;r_i}; after discarding the outliers is taken as the estimation of σ². This method of estimating σ² is less computational demanding and more accurate, compared with the well-known method which takes 1.483 med_i |r_i| as the estimation of σ. The breakdown point of the above estimation of σ² is more than 20%, while the brekdown point is less than 10%, if only the Grubbs statistics is used.     

Le guidage des whistlers par le champ magnetique

In this paper the question is examined of how the v.l.f. radio-waves are guided along the magnetic field. Energy passes through the magnetic field under two sets of conditions. Corresponding to the “nose-whistlers” explained by Helliwell, the first one occurs when the wave-normal itself is in the direction of the magnetic field. This does not happen in the second case when the remarkable property is also shown that all frequencies are propagated at the same velocity V₀ = cƒ_H/2ƒ₀ (ƒ_H gyrofrequency, ƒ₀ frequency of the plasma). Considerations of energy point out that, if such a propagation is not easily observable in the case of an isotropic emission, it is not the same thing for an emission produced by erenkov effect, which is able to produce all energy by this mode of propagation, provided the particle's velocity has a low fixed value (˜ 10,000 km/sec in the exosphere). All frequencies being emitted at the same time and following the same path wtih the same velocity, we can explain the broadband noise observed during the reception of whistlers. The required velocity of particles is exactly the velocity V₀. This coincidence is explained in an appendix, and extended to other anisotropic media.