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Blum K.,Institute for Advanced Study | Efrati A.,Weizmann Institute of Science | Grossman Y.,Cornell University | Nir Y.,Weizmann Institute of Science | Riotto A.,Center for Astroparticle Physics
Physical Review Letters | Year: 2012

In the supersymmetric framework, prior to the electroweak phase transition, the existence of a baryon asymmetry implies the existence of a Higgsino asymmetry. We investigate whether the Higgsino could be a viable asymmetric dark matter candidate. We find that this is indeed possible. Thus, supersymmetry can provide the observed dark matter abundance and, furthermore, relate it with the baryon asymmetry, in which case the puzzle of why the baryonic and dark matter mass densities are similar would be explained. To accomplish this task, two conditions are required. First, the gauginos, squarks, and sleptons must all be very heavy, such that the only electroweak-scale superpartners are the Higgsinos. With this spectrum, supersymmetry does not solve the fine-tuning problem. Second, the temperature of the electroweak phase transition must be low, in the (1-10)GeV range. This condition requires an extension of the minimal supersymmetric standard model. © 2012 American Physical Society.

Zhang J.,Shanghai JiaoTong University | Ma C.-P.,University of California at Berkeley | Riotto A.,Center for Astroparticle Physics
Astrophysical Journal | Year: 2014

In the standard excursion-set model for the growth of structure, the statistical properties of halos are governed by the halo mass and are independent of the larger-scale environment in which the halos reside. Numerical simulations, however, have found the spatial distributions of halos to depend not only on their mass but also on the details of their assembly history and environment. Here we present a theoretical framework for incorporating this "assembly bias" into the excursion-set model. Our derivations are based on modifications of the path-integral approach of Maggiore & Riotto that models halo formation as a non-Markovian random-walk process. The perturbed density field is assumed to evolve stochastically with the smoothing scale and exhibits correlated walks in the presence of a density barrier. We write down conditional probabilities for multiple barrier crossings and derive from them analytic expressions for descendant and progenitor halo mass functions and halo merger rates as a function of both halo mass and the linear overdensity δ e of the larger-scale environment of the halo. Our results predict a higher halo merger rate and higher progenitor halo mass function in regions of higher overdensity, consistent with the behavior seen in N-body simulations. © 2014. The American Astronomical Society. All rights reserved..

Caballero I.,University Paris Diderot | Wilms J.,Center for Astroparticle Physics
Memorie della Societa Astronomica Italiana, Supplementi - Journal of the Italian Astronomical Society, Supplement | Year: 2012

Accreting X-ray pulsars are among the most luminous objects in the X-ray sky. In highly magnetized neutron stars (B ∼ 1012 G), the flow of matter is dominated by the strong magnetic field. The general properties of accreting X-ray binaries are presented, focusing on the spectral characteristics of the systems. The use of cyclotron lines as a tool to directly measure a neutron star's magnetic field and to test the theory of accretion are discussed.We conclude with the current and future prospects for accreting X-ray binary studies. © SAIt 2012.

Kehagias A.,National Technical University of Athens | Riotto A.,Center for Astroparticle Physics
Nuclear Physics B | Year: 2013

We study the multifield inflationary models where the cosmological perturbation is sourced by light scalar fields other than the inflaton. We exploit the operator product expansion and partly the symmetries present during the de Sitter epoch to characterize the non-Gaussian four-point correlator in the squeezed limit. We point out that the contribution to it from the intrinsic non-Gaussianity of the light fields at horizon crossing can be larger than the usually studied contribution arising on superhorizon scales and it comes with a different shape. Our findings indicate that particular attention needs to be taken when studying the effects of the primordial NG on real observables, such as the clustering of dark matter halos. © 2012 Elsevier B.V.

De Simone A.,CERN | De Simone A.,International School for Advanced Studies | De Simone A.,National Institute of Nuclear Physics, Italy | Riotto A.,Center for Astroparticle Physics | And 2 more authors.
Journal of Cosmology and Astroparticle Physics | Year: 2013

The AMS-02 collaboration has recently released data on the positron fraction e+/(e-+e+) up to energies of about 350 GeV. If one insists on interpreting the observed excess as a dark matter signal, then we find it is best described by a TeV-scale dark matter annihilating into τ+τ-, although this situation is already severely constrained by gamma-ray measurements.The annihilation into μ+μ- is allowed by gamma-rays more than τ+τ-, but it gives a poorer fit to AMS-02 data. Moreover, since electroweak corrections induce correlations among the fluxes of stable particles from dark matter annihilations, the recent AMS-02 data imply a well-defined prediction for the correlated flux of antiprotons. Under the assumption that their future measurements will not show any antiproton excess above the background, the dark matter interpretation of the positron rise will possibly be ruled out by only making use of data from a single experiment. This work is the first of a program where we emphasize the role of correlations among dark matter signals.© 2013 IOP Publishing Ltd and Sissa Medialab srl.

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