Equivalence Principle Violation in Weakly Vainshtein-Screened Systems

Massive gravity, galileon and braneworld models that modify gravity to explain cosmic acceleration utilize the nonlinear field interactions of the Vainshtein mechanism to screen fifth forces in high density regimes. These source-dependent interactions cause apparent equivalence principle violations. In the weakly-screened regime violations can be especially prominent since the fifth forces are at near full strength. Since they can also be calculated perturbatively, we derive analytic solutions for illustrative cases: the motion of massive objects in compensated shells and voids and infall toward halos that are spherically symmetric. Using numerical techniques we show that these solutions are valid until the characteristic scale becomes comparable to the Vainshtein radius. We find a relative acceleration of more massive objects toward the center of a void and a reduction of the infall acceleration that increases with the mass ratio of the halos which can in principle be used to test the Vainshtein screening mechanism.Comment: 7 pages, 4 figure

Searching For Dark Matter Subhalos In the Fermi-LAT Second Source Catalog

The dark matter halo of the Milky Way is expected to contain an abundance of smaller subhalos. These subhalos can be dense and produce potentially observable fluxes of gamma rays. In this paper, we search for dark matter subhalo candidates among the sources in the Fermi-LAT Second Source Catalog which are not currently identified or associated with counterparts at other wavelengths. Of the nine high-significance, high-latitude (|b|>60 degrees), non-variable, unidentified sources contained in this catalog, only one or two are compatible with the spectrum of a dark matter particle heavier than approximately 50-100 GeV. The majority of these nine sources, however, feature a spectrum that is compatible with that predicted from a lighter (~5-40 GeV) dark matter particle. This population is consistent with the number of observable subhalos predicted for a dark matter candidate in this mass range and with an annihilation cross section of a simple thermal relic (sigma v~3x10^{-26} cm^3/s). Observations in the direction of these sources at other wavelengths will be necessary to either reveal their astrophysical nature (as blazars or other active galactic nuclei, for example), or to further support the possibility that they are dark matter subhalos by failing to detect any non-gamma ray counterpart.Comment: 8 pages, 4 figure

Report of a joint Norwegian-Soviet acoustic survey on blue whiting, spring 1991

During spring 1991 the second Norwegian-Soviet joint survey on the blue whiting spawning stock was carried out. The result of a ship-to-ship calibration of the acoustic instruments allowed a 1:1 relationship between the two vessels acoustic data to be used. According to this, the data were then combined and presented as common results. Blue whiting was recorded from south of the Porcupine bank to north of Shetland, but this year the densest concentrations over the Porcupine bank were distributed more to the east than previous years. While the abundance in the southern part of the surveyed area was approximately the same as estimated the last years, it was found to be significantly reduced in the north. The over all spawning stock size was then estimated to 4.4 mill. tonnes which is 1 mill. tonnes less than observed in 1990. The 1989-yearclass as expected was found to be the richest one, with a contribution of 23% of the stock. Although the temperature below 200 m depth in the southern part was in general higher than in 1990, the maturation process of the blue whiting gonads was observed to be somewhat retarded with the peak of spawning 1-2 weeks later than in 1990

CoGeNT, DAMA, and Light Neutralino Dark Matter

Recent observations by the CoGeNT collaboration (as well as long standing observations by DAMA/LIBRA) suggest the presence of a $\sim 5$-10 GeV dark matter particle with a somewhat large elastic scattering cross section with nucleons ($\sigma\sim 10^{-40}$ cm$^2$).Within the context of the minimal supersymmetric standard model (MSSM), neutralinos in this mass range are not able to possess such large cross sections, and would be overproduced in the early universe. Simple extensions of the MSSM, however, can easily accommodate these observations. In particular, the extension of the MSSM by a chiral singlet superfield allows for the possibility that the dark matter is made up of a light singlino that interacts with nucleons largely through the exchange of a fairly light ($\sim$30-70 GeV) singlet-like scalar higgs, \hi. Such a scenario is consistent with all current collider constraints and can generate the signals reported by CoGeNT and DAMA/LIBRA. Furthermore, there is a generic limit of the extended model in which there is a singlet-like pseudoscalar higgs, \ai, with \mai\sim \mhi and in which the $\chi^0\chi^0$ and b\anti b, s\anti s coupling magnitudes of the \hi and \ai are very similar. In this case, the thermal relic abundance is automatically consistent with the measured density of dark matter if \mchi is sufficiently small that \chi^0\chi^0\to b\anti b is forbidden.Comment: 6 pages, published versio

No Indications of Axion-Like Particles From Fermi

As very high energy (~100 GeV) gamma rays travel over cosmological distances, their flux is attenuated through interactions with the extragalactic background light. Observations of distant gamma ray sources at energies between ~200 GeV and a few TeV by ground-based gamma ray telescopes such as HESS, however, suggest that the universe is more transparent to very high energy photons than had been anticipated. One possible explanation for this is the existence of axion-like-particles (ALPs) which gamma rays can efficiently oscillate into, enabling them to travel cosmological distances without attenuation. In this article, we use data from the Fermi Gamma Ray Space Telescope to calculate the spectra at 1-100 GeV of two gamma ray sources, 1ES1101-232 at redshift z=0.186 and H2356-309 at z=0.165, and use this in conjunction with the measurements of ground-based telescopes to test the ALP hypothesis. We find that the observations can be well-fit by an intrinsic power-law source spectrum with indices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and that no ALPs or other exotic physics is necessary to explain the observed degree of attenuation.Comment: 7 pages, 4 figures. v3: Matches published version, the analysis of H2356-309 is revised, no change in conclusion