1,688 research outputs found
Radio constraints on dark matter annihilation in the galactic halo and its substructures
Annihilation of Dark Matter usually produces together with gamma rays
comparable amounts of electrons and positrons. The e+e- gyrating in the
galactic magnetic field then produce secondary synchrotron radiation which thus
provides an indirect mean to constrain the DM signal itself. To this purpose,
we calculate the radio emission from the galactic halo as well as from its
expected substructures and we then compare it with the measured diffuse radio
background. We employ a multi-frequency approach using data in the relevant
frequency range 100 MHz-100 GHz, as well as the WMAP Haze data at 23 GHz. The
derived constraints are of the order =10^{-24} cm3 s^{-1} for a DM
mass m_chi=100 GeV sensibly depending however on the astrophysical
uncertainties, in particular on the assumption on the galactic magnetic field
model. The signal from single bright clumps is instead largely attenuated by
diffusion effects and offers only poor detection perspectives.Comment: 12 pages, 7 figures; v2: some references added, some discussions
enlarged; matches journal versio
Angular Signatures of Annihilating Dark Matter in the Cosmic Gamma-Ray Background
The extragalactic cosmic gamma-ray background (CGB) is an interesting channel
to look for signatures of dark matter annihilation. In particular, besides the
imprint in the energy spectrum, peculiar anisotropy patterns are expected
compared to the case of a pure astrophysical origin of the CGB. We take into
account the uncertainties in the dark matter clustering properties on
sub-galactic scales, deriving two possible anisotropy scenarios. A clear dark
matter angular signature is achieved when the annihilation signal receives only
a moderate contribution from sub-galactic clumps and/or cuspy haloes.
Experimentally, if galactic foregrounds systematics are efficiently kept under
control, the angular differences are detectable with the forthcoming GLAST
observatory, provided that the annihilation signal contributes to the CGB for a
fraction >10-20%. If, instead, sub-galactic structures have a more prominent
role, the astrophysical and dark matter anisotropies become degenerate,
correspondingly diluting the DM signature. As complementary observables we also
introduce the cross-correlation between surveys of galaxies and the CGB and the
cross-correlation between different energy bands of the CGB and we find that
they provide a further sensitive tool to detect the dark matter angular
signatures.Comment: 13 pages, 8 figures; improved discussion; matches published versio
From an insulating to a superfluid pair-bond liquid
We study an exchange coupled system of itinerant electrons and localized
fermion pairs resulting in a resonant pairing formation. This system inherently
contains resonating fermion pairs on bonds which lead to a superconducting
phase provided that long range phase coherence between their constituents can
be established. The prerequisite is that the resonating fermion pairs can
become itinerant. This is rendered possible through the emergence of two kinds
of bond-fermions: individual and composite fermions made of one individual
electron attached to a bound pair on a bond. If the strength of the exchange
coupling exceeds a certain value, the superconducting ground state undergoes a
quantum phase transition into an insulating pair-bond liquid state. The gap of
the superfluid phase thereby goes over continuously into a charge gap of the
insulator. The change-over from the superconducting to the insulating phase is
accompanied by a corresponding qualitative modification of the dispersion of
the two kinds of fermionic excitations. Using a bond operator formalism, we
derive the phase diagram of such a scenario together with the elementary
excitations characterizing the various phases as a function of the exchange
coupling and the temperature.Comment: 10 pages, 5 figure
Field-induced Orbital Patterns in Ferromagnetic Layered Ruthenates
We study the evolution of orbital patterns in ferromagnetic layered
ruthenates due to the competition of Coulomb interactions, compressive c axis
and orthorhombic distortions in the presence of a polarizing orbital field
coupled to the angular momentum. By means of the exact diagonalization on a 2x2
cluster and a cluster embedded analysis where inter-plaquette interaction is
treated on mean field level, we determine the ground-state phase diagram.
Specifically, we demonstrate that, via the activation of two or three of t_2g
local orbital configurations, an external field applied along different
symmetry directions can lead to inequivalent orbital correlated states.
Starting from an antiferro-orbital pattern, for the easy axis case an orbital
ordered phase is induced, having strong next nearest neighbors ferro-orbital
correlations. Otherwise, a field applied along the hard axis leads a reduction
of local orbital moment in a way to suppress the orbital order.Comment: 11 page
High Energy Neutrinos with a Mediterranean Neutrino Telescope
The high energy neutrino detection by a km^3 Neutrino Telescope placed in the
Mediterranean sea provides a unique tool to both determine the diffuse
astrophysical neutrino flux and the neutrino-nucleon cross section in the
extreme kinematical region, which could unveil the presence of new physics.
Here is performed a brief analysis of possible NEMO site performances.Comment: 4 pages, 3 figures, Proceedings of the 30th ICRC 200
Disentangling neutrino-nucleon cross section and high energy neutrino flux with a km^3 neutrino telescope
The energy--zenith angular event distribution in a neutrino telescope
provides a unique tool to determine at the same time the neutrino-nucleon cross
section at extreme kinematical regions, and the high energy neutrino flux. By
using a simple parametrization for fluxes and cross sections, we present a
sensitivity analysis for the case of a km^3 neutrino telescope. In particular,
we consider the specific case of an under-water Mediterranean telescope placed
at the NEMO site, although most of our results also apply to an under-ice
detector such as IceCube. We determine the sensitivity to departures from
standard values of the cross sections above 1 PeV which can be probed
independently from an a-priori knowledge of the normalization and energy
dependence of the flux. We also stress that the capability to tag downgoing
neutrino showers in the PeV range against the cosmic ray induced background of
penetrating muons appears to be a crucial requirement to derive meaningful
constraints on the cross section.Comment: 10 pages, 28 figure
Effect of magnetic fluctuations on the normal state properties of Sr_2RuO_4
We investigate the normal state transport properties of SrRuO and we
show that a consistent explanation of the experimental results can be obtained
assuming that the system is near a quantum phase transition. Within the
framework of a self-consistent spin fluctuation theory, we calculate the
temperature variation of some relevant physical quantities and we discuss a
possible microscopic origin of the quantum phase transition.Comment: 5 pages, 4 figures, to appear on Europhysics Letter
On line power spectra identification and whitening for the noise in interferometric gravitational wave detectors
In this paper we address both to the problem of identifying the noise Power
Spectral Density of interferometric detectors by parametric techniques and to
the problem of the whitening procedure of the sequence of data. We will
concentrate the study on a Power Spectral Density like the one of the
Italian-French detector VIRGO and we show that with a reasonable finite number
of parameters we succeed in modeling a spectrum like the theoretical one of
VIRGO, reproducing all its features. We propose also the use of adaptive
techniques to identify and to whiten on line the data of interferometric
detectors. We analyze the behavior of the adaptive techniques in the field of
stochastic gradient and in the
Least Squares ones.Comment: 28 pages, 21 figures, uses iopart.cls accepted for pubblication on
Classical and Quantum Gravit
Clustering properties of ultrahigh energy cosmic rays and the search for their astrophysical sources
The arrival directions of ultrahigh energy cosmic rays (UHECRs) may show
anisotropies on all scales, from just above the experimental angular resolution
up to medium scales and dipole anisotropies. We find that a global comparison
of the two-point auto-correlation function of the data with the one of
catalogues of potential sources is a powerful diagnostic tool. In particular,
this method is far less sensitive to unknown deflections in magnetic fields
than cross-correlation studies while keeping a strong discrimination power
among source candidates. We illustrate these advantages by considering ordinary
galaxies, gamma ray bursts and active galactic nuclei as possible sources.
Already the sparse publicly available data suggest that the sources of UHECRs
may be a strongly clustered sub-sample of galaxies or of active galactic
nuclei. We present forecasts for various cases of source distributions which
can be checked soon by the Pierre Auger Observatory.Comment: 11 pages, 8 figures, 4 tables; minor changes, matches published
versio
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