26814250
Anisotropies in the gamma‐ray sky from millisecond pulsars
Pulsars emerge in the Fermi era as a sizable population of gamma-ray sources. Millisecond 
pulsars (MSPs) constitute an older subpopulation whose sky distribution extends to high 
Galactic latitudes, and it has been suggested that unresolved members of this class may 
contribute a significant fraction of the measured large-scale isotropic gamma-ray background 
(IGRB). We investigate the possible energy-dependent contribution of unresolved MSPs to 
the anisotropy of the Fermi-measured IGRB. For observationally motivated MSP population 
models, we show that the preliminary Fermi anisotropy measurement places an interesting 
constraint on the abundance of MSPs in the Galaxy and the typical MSP flux, about an order of 
magnitude stronger than constraints on this population derived from the intensity of the IGRB 
alone. We also examine the possibility of an MSP component in the IGRB mimicking a dark 
matter signal in anisotropy-based searches, and conclude that the energy dependence of an 
anisotropy signature would distinguish MSPs from all but very light dark matter candidates.
119404050
Constraining the cosmic abundance of stellar remnants with multi - TeV gamma-rays
If stellar remnants are cosmologically significant, the infrared flux from the remnant progenitors would contribute to the opacity of multi-TeV γ-rays. The multi-TeV γ-ray horizon is established to be at a redshift z > 0.034 by the observation of the blazar Mrk 501. By requiring that the optical depth due to γγ → e+e- be less than 1 for a source at z = 0.034, we limit the cosmological density of stellar remnants, Ωrm ≤ (2-4) × 10-3 h (h70 is the Hubble constant in units of 70 km s-1 Mpc-1), and thus strongly constrain stellar remnants as a cosmologically significant source of dark matter.
36572119
Radiative decays of massive relic particles and the submillimeter background.
We consider the interaction of the decay photons of an unstable relic particle species with the microwave background radiation. The radiative decays of these particles delay recombination and serve as an energy source for the resultant plasma. Nonrelativistic Compton scattering by these electrons couples the decay photons to the microwave background, producing submillimeter distortions. If the decay products close the Universe, they must decay with a radiative branching ratio larger than 2.5/times/10/sup /minus/5/ in order to produce recently observed excess submillimeter background radiation. To be consistent with measurements of the uv background, their mass /ital m//much gt/114 keV and their decay redshift /ital Z//sub /ital d///much gt/5200.
8649559
Interactions of ultrahigh-energy neutrinos.
Cross sections for the charged-current interactions of ultrahigh-energy neutrinos with nucleons are evaluated in light of recent improvements in our knowledge of nucleon structure functions. For 10/sup 19/-eV neutrinos, the cross section is an order of magnitude larger than the values traditionally used in astrophysical calculations. Some consequences for event rates from generic astrophysical neutrino sources are noted.
43916778
Constraints on 17-keV neutrinos.
Recent experiments indicate that a 17-keV neutrino mixes with {nu}{sub {ital e}} with 1% probability. We discuss the constraints from neutrinoless double {beta} decay, cosmology, and astrophysics that any model possessing a 17-keV neutrino must obey. Several recently proposed models are shown to be incompatible with these constraints.
45996526
Bounds on halo-particle interactions from interstellar calorimetry.
The light from distant stars makes cartography of the luminous material within galaxies possible, the simplest observation being the distinctive shape of the galaxy. In spiral galaxies, for example, most of the light emanates from a small central nucleus and an extended diskshaped region. In addition to the obvious density information this light provides, by examining the optical and 21-cm spectral lines we obtain "rotation curves," maps of the orbital velocities of the components of a galaxy as a function of their distance from the center. From this we deduce that the total mass distribution in spiral galaxies is approximately that of an isothermal sphere: The mass density falls as r~ 2 , where r is the distance from the center of the galaxy. l The gravitational potential and the mass inferred from these rotation curves is in conflict with the distribution of luminous matter observed—gravitating matter outweighs luminous matter by a factor of 3 to 10. This discrepancy is observed in elliptical galaxies as well. The resolution of this paradox lies in "dark matter," nonluminous, gravitating, material in spherical halos surrounding galaxies. Many suggestions have been made as to the form this matter might take, from "condensed matter" such as substellar size macroscopic objects made of baryons, to a diffuse collection of some species of "elementary" particles such as axions or massive neutrinos. It has generally been assumed that if the galactic halo is composed of elementary particles, then these halo particles must be weakly interacting; otherwise, it is argued, they would be dragged into the disk of the galaxy as ordinary matter collapses. Recently, De Riijula, Glashow, and Sarid have pointed out that this reasoning could be false: If halo particles are very massive, they may not lose energy fast enough to collapse into the disk with baryons during the formation of the galaxy. Moreover, if halo particles interact relatively strongly with ordinary matter, they will not show up in traditional searches for dark matter which rely on the particles interacting weakly enough to penetrate the Earth. In particular, the authors of Ref. 2 propose that the halo of our Galaxy could be composed of CHAMPs, charged particles with a mass of between a few tens to 10 TeV. 4 In this Letter we show that the existence of neutral interstellar clouds constrains the interaction of any particulate dark-matter candidate with atomic hydrogen to be quite small. We show that, even for a halo particle of mass 1 PeV (10 GeV), the cross section with hydrogen must be smaller than the typical atomic cross section that we expect for a positively charged particle bound to an electron. This argument eliminates such positively charged particles as a dark-matter possibility, as well as any other object that has a similar cross section. In outline, the argument is simple: If the clouds are in equilibrium, the rate at which energy is deposited by collisions with dark-matter particles must be smaller than the rate at which the cloud can cool. In the remainder of this paper we use this argument to constrain the interaction cross section of dark matter with hydrogen, and conclude with some remarks on the general viability of charged dark matter. If the dark-matter particles which form the galactic halo interact with hydrogen, neutral or ionized, their interactions will be largely elastic as the relative velocity is of order of the average velocity of a halo particle (here we assume a spherical halo with a Maxwellian velocity distribution having an rms velocity Vh of approximately 9x 10~c) and is less than aemc, the typical "velocity" of an electron bound to a proton. The recoiling hydrogen atom or proton will gain a momentum less than or of order rripVh and will quickly share most of its energy through elastic collisions with other hydrogen atoms and protons. Therefore, most of the energy deposited by the interactions of a halo particle will go into heating the interstellar medium and will not be quickly lost in radiation. The heating rate per nucleon due to halo-particle interactions may be computed in terms of the transport cross section crtr for hydrogen-halo-particle or protonhalo-particle scattering,
350710
Magnetocardiography with a modular spin-exchange relaxation-free atomic magnetometer array.
We present a portable four-channel atomic magnetometer array operating in the spin-exchange relaxation-free regime. The magnetometer array has several design features intended to maximize its suitability for biomagnetic measurement, specifically foetal magnetocardiography, such as a compact modular design and fibre-coupled lasers. The modular design allows the independent positioning and orientation of each magnetometer. Using this array in a magnetically shielded room, we acquire adult magnetocadiograms. These measurements were taken with a 6-11 fT Hz(-1/2) single-channel baseline sensitivity that is consistent with the independently measured noise level of the magnetically shielded room.
32501332
Hybrid spin-exchange optical pumping of 3He.
We demonstrate spin-exchange optical pumping of 3He using a "hybrid" K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and 3He atoms then transfer the angular momentum to the 3He with much greater efficiency than Rb-3He. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches 1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.