Cosmic Rays from Dark Matter Annihilation and Big-Bang Nucleosynthesis

Recent measurements of cosmic-ray electron and positron fluxes by PAMELA and ATIC experiments may indicate the existence of annihilating dark matter with large annihilation cross section. We show that the dark matter annihilation in the big-bang nucleosynthesis epoch affects the light element abundances, and it gives stringent constraints on such annihilating dark matter scenarios for the case of hadronic annihilation. Constraints on leptonically annihilating dark matter models are less severer.Comment: 21 pages, 5 figures; added references; corrected the electromagnetic-emission part and got milder constraint from the photodissociation processes by a factor of 50 (v3

Estimations of rail irregularities

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (leaves 74-76).Inspection cars that have been used to measure rail irregularities are costly and need operators. This thesis proposes a method to estimate rail irregularities by measuring accelerations of a passenger car instead of direct measurement by using a conventional inspection car. Using a System Identification technique and data obtained by simulations based on a three-dimensional rail vehicle model with actual rail irregularities, the proposed method identifies an inverse system where inputs are accelerations of a vehicle and outputs are rail irregularities. The resulting model is assessed through comparing the estimated irregularity with the actual irregularity. Validation results show that the estimate agree well with the actual irregularity for the Vertical Irregularity. Though the estimation error for the Lateral Irregularity is larger than that for the Vertical Irregularity, the error is acceptable form a practical point of view. The quality of the estimation is evaluated quantitatively by using the Mean Square Error. In addition, resolution of the estimation is presented in order to demonstrate the accuracy of the estimation. Model uncertainties are assessed for a practical implementation. The effects due to two major uncertainties, mass variations and speed variations, are evaluated by using the Singular Value Decomposition in order to present the limitations of the estimation using a nominal model. In addition, this thesis proposes a compensation method for mass variations and speed variations.by Junji Kawasaki.S.M

Neutrino Signals from Annihilating/Decaying Dark Matter in the Light of Recent Measurements of Cosmic Ray Electron/Positron Fluxes

The excess of cosmic-ray electron and positron fluxes measured by the PAMELA satellite and ATIC balloon experiments may be interpreted as the signals of the dark matter annihilation or decay into leptons. In this letter we show that the dark matter annihilation/decay which reproduces the electron/positron excess may yield a significant amount of high-energy neutrinos from the Galactic center. In the case, future kilometer-square size experiments may confirm such a scenario, or even the Super-Kamiokande results already put constraints on some dark matter models.Comment: 6 pages, 4 figures; References added; extended discussion; to appear in PR

Cosmological constraints on dark matter models with velocity-dependent annihilation cross section

We derive cosmological constraints on the annihilation cross section of dark matter with velocity-dependent structure, motivated by annihilating dark matter models through Sommerfeld or Breit-Wigner enhancement mechanisms. In models with annihilation cross section increasing with decreasing dark matter velocity, big-bang nucleosynthesis and cosmic microwave background give stringent constraints.Comment: 23 pages, 9 figures; Added reference

Neutralino Warm Dark Matter

In the supersymmetric (SUSY) standard model, the lightest neutralino may be the lightest SUSY particle (LSP), and it is is a candidate of the dark matter in the universe. The LSP dark matter might be produced by the non-thermal process such as heavy particle decay after decoupling of the thermal relic LSP. If the produced LSP is relativistic, and does not scatter enough in the thermal bath, the neutralino LSP may contribute as the warm dark matter (WDM) to wash out the small scale structure of O(0.1) Mpc. In this letter we calculate the energy reduction of the neutralino LSP in the thermal bath and study whether the LSP can be the WDM. If temperature of the production time T_I is smaller than 5MeV, the bino-like LSP can be the WDM and may contribute to the small-scale structure of O(0.1) Mpc. The Higgsino-like LSP might also work as the WDM if T_I< 2MeV. The wino-like LSP cannot be the WDM in the favoured parameter region.Comment: 13 pages. Some references are added in revised versio

Constraining SuperWIMPy and Warm Subhalos with Future Submillilensing

We propose to observe QSO-galaxy strong lens systems to give a new constraint on the damping scale of the initial fluctuations. We find that the future observation of submilliarc scale astrometric shifts of the multiple lensed images of QSOs would find \sim 10^{(3-9)} M_{\odot} subhalos inside the macrolens halo. The superweakly interacting massive particles (superWIMPs) produced from a WIMP decay and the warm dark matter (WDM) particles that predict a comoving damping scale larger than \sim 2 kpc can be constrained if \sim 10^3 M_{\odot} subhalos are detected.Comment: 14 pages, 2 figures, revised version accepted for publication in PL

Association between Mammographic Breast Density and Lifestyle in Japanese Women

A high mammographic breast density is considered to be a risk factor for breast cancer. However, only a small number of studies on the association between breast density and lifestyle have been performed. A cross-sectional study was performed using a survey with 29 questions on life history and lifestyle. The breast density on mammography was classified into 4 categories following the BI-RADS criteria. The subjects were 522 women with no medical history of breast cancer. The mean age was 53.3 years old. On multivariate analysis, only BMI was a significant factor determining breast density in premenopausal women (parameter estimate, －0.403;p value, 0.0005), and the density decreased as BMI rose. In postmenopausal women, BMI (parameter estimate, －0.196;p value, 0.0143) and number of deliveries (parameter estimate, －0.388;p value, 0.0186) were significant factors determining breast density;breast density decreased as BMI and number of deliveries increased. Only BMI and number of deliveries were identified as factors significantly influencing breast density. BMI was inversely correlated with breast density before and after menopause, whereas the influence of number of deliveries on breast density was significant only in postmenopausal women in their 50 and 60s