Relic density and PAMELA events in a heavy wino dark matter model with Sommerfeld effect

In a wino LSP scenario the annihilation cross section of winos gravitationally bound in galaxies can be boosted by a Sommerfeld enhancement factor which arises due to the ladder of exchanged W bosons between the initial states. The boost factor obtained can be in the range S ~ 10^4 if the mass is close to the resonance value of M ~ 4 TeV. In this paper we show that if one takes into account the Sommerfeld enhancement in the relic abundance calculation then the correct relic density is obtained for 4 TeV wino mass due to the enhanced annihilation after their kinetic decoupling. At the same time the Sommerfeld enhancement in the \chi \chi --> W^+ W^- annihilation channel is sufficient to explain the positron flux seen in PAMELA data without significantly exceeding the observed antiproton signal. We also show that (e^- + e^+) and gamma ray signals are broadly compatible with the Fermi-LAT observations. In conclusion we show that a 4 TeV wino DM can explain the positron and antiproton fluxes observed by PAMELA and at the same time give a thermal relic abundance of CDM consistent with WMAP observations.Comment: 24 pages, 12 figures, 1 table; title corrected in arxiv metadat

Secure Anonymous Routing for MANETs Using Distributed Dynamic Random Path Selection

Most of the MANET security research has so far focused on providing routing security and confidentiality to the data packets, but less has been done to ensure privacy and anonymity of the communicating entities. In this paper, we propose a routing protocol which ensures anonymity, privacy of the user. This is achieved by randomly selecting next hop at each intermediate. This protocol also provides data security using public key ciphers. The protocol is simulated using in-house simulator written in C with OpenSSL crypto APIs. The robustness of our protocol is evaluated against known security attacks

Coherent network analysis for continuous gravitational wave signals in a pulsar timing array: Pulsar phases as extrinsic parameters

Supermassive black hole binaries are one of the primary targets for gravitational wave searches using pulsar timing arrays. Gravitational wave signals from such systems are well represented by parametrized models, allowing the standard Generalized Likelihood Ratio Test (GLRT) to be used for their detection and estimation. However, there is a dichotomy in how the GLRT can be implemented for pulsar timing arrays: there are two possible ways in which one can split the set of signal parameters for semi-analytical and numerical extremization. The straightforward extension of the method used for continuous signals in ground-based gravitational wave searches, where the so-called pulsar phase parameters are maximized numerically, was addressed in an earlier paper (Wang et al. 2014). In this paper, we report the first study of the performance of the second approach where the pulsar phases are maximized semi-analytically. This approach is scalable since the number of parameters left over for numerical optimization does not depend on the size of the pulsar timing array. Our results show that, for the same array size (9 pulsars), the new method performs somewhat worse in parameter estimation, but not in detection, than the previous method where the pulsar phases were maximized numerically. The origin of the performance discrepancy is likely to be in the ill-posedness that is intrinsic to any network analysis method. However, scalability of the new method allows the ill-posedness to be mitigated by simply adding more pulsars to the array. This is shown explicitly by taking a larger array of pulsars.Comment: 30 pages, 11 figures, revised version, published in Ap

Measuring Fundamental Parameters of Substellar Objects. II: Masses and Radii

We present mass and radius derivations for a sample of very young, mid- to late M, low-mass stellar and substellar objects in Upper Sco and Taurus. In a previous paper, we determined effective temperatures and surface gravities for these targets, from an analysis of their high-resolution optical spectra and comparisons to the latest synthetic spectra. We now derive extinctions, radii, masses and luminosities by combining our previous results with observed photometry, surface fluxes from the synthetic spectra and the known cluster distances. These are the first mass and radius estimates for young, very low mass bodies that are independent of theoretical evolutionary models (though our estimates do depend on spectral modeling). We find that for most of our sample, our derived mass-radius and mass-luminosity relationships are in very good agreement with the theoretical predictions. However, our results diverge from the evolutionary model values for the coolest, lowest-mass targets: our inferred radii and luminosities are significantly larger than predicted for these objects at the likely cluster ages, causing them to appear much younger than expected. We suggest that uncertainties in the evolutionary models - e.g., in the choice of initial conditions and/or treatment of interior convection - may be responsible for this discrepancy. Finally, two of our late-M objects (USco 128 and 130) appear to have masses close to the deuterium-fusion boundary (9--14 Jupiters, within a factor of 2). This conclusion is primarily a consequence of their considerable faintness compared to other targets with similar extinction, spectral type and temperature (difference of 1 mag). Our result suggests that the faintest young late-M or cooler objects may be significantly lower in mass than the current theoretical tracks indicate.Comment: 54 pages, incl. 5 figs, accepted Ap