The moduli problem at the perturbative level

Moduli fields generically produce strong dark matter -- radiation and baryon -- radiation isocurvature perturbations through their decay if they remain light during inflation. We show that existing upper bounds on the magnitude of such fluctuations can thus be translated into stringent constraints on the moduli parameter space m_\sigma (modulus mass) -- \sigma_{inf} (modulus vacuum expectation value at the end of inflation). These constraints are complementary to previously existing bounds so that the moduli problem becomes worse at the perturbative level. In particular, if the inflationary scale H_{inf}~10^{13} GeV, particle physics scenarios which predict high moduli masses m_\sigma > 10-100 TeV are plagued by the perturbative moduli problem, even though they evade big-bang nucleosynthesis constraints.Comment: 4 pages, 3 figures (revtex) -- v2: an important correction on the amplitude/transfer of isocurvature modes at the end of inflation, typos corrected, references added, basic result unchange

Fermi Detection of the Pulsar Wind Nebula HESS J1640-465

We present observations of HESS J1640-465 with the Fermi-LAT. The source is detected with high confidence as an emitter of high-energy gamma-rays. The spectrum lacks any evidence for the characteristic cutoff associated with emission from pulsars, indicating that the emission arises primarily from the pulsar wind nebula. Broadband modeling implies an evolved nebula with a low magnetic field resulting in a high gamma-ray to X-ray flux ratio. The Fermi emission exceeds predictions of the broadband model, and has a steeper spectrum, possibly resulting from a distinct excess of low energy electrons similar to what is inferred for both the Vela X and Crab pulsar wind nebulae.Comment: 6 pages, 5 figures, accepted for publication in Ap

Detecting stable massive neutral particles through particle lensing

Stable massive neutral particles emitted by astrophysical sources undergo deflection under the gravitational potential of our own galaxy. The deflection angle depends on the particle velocity and therefore non-relativistic particles will be deflected more than relativistic ones. If these particles can be detected through neutrino telescopes, cosmic ray detectors or directional dark matter detectors, their arrival directions would appear aligned on the sky along the source-lens direction. On top of this deflection, the arrival direction of non-relativistic particles is displaced with respect to the relativistic counterpart also due to the relative motion of the source with respect to the observer; this induces an alignment of detections along the sky projection of the source trajectory. The final alignment will be given by a combination of the directions induced by lensing and source proper motion. We derive the deflection-velocity relation for the Milky Way halo and suggest that searching for alignments on detection maps of particle telescopes could be a way to find new particles or new astrophysical phenomena.Comment: 17 pages, 7 figures. Accepted by PR

Properties of Faint Distant Galaxies as seen through Gravitational Telescopes

This paper reviews the most recent developments related to the use of lensing clusters of galaxies as Gravitational Telescopes in deep Universe studies. We summarize the state of the art and the most recent results aiming at studying the physical properties of distant galaxies beyond the limits of conventional spectroscopy. The application of photometric redshift techniques in the context of gravitational lensing is emphasized for the study of both lensing structures and the background population of lensed galaxies. A presently ongoing search for the first building blocks of galaxies behind lensing clusters is presented and discussed.Comment: Review lecture given at "Gravitational Lensing: a unique tool for cosmology",Aussois, France, January 2003. To appear in ASP Conf. S., eds. D. Valls-Gabaud & J.-P. Kneib, 26 pages, 8 figure

Trans-Planckian Dark Energy?

It has recently been proposed by Mersini et al. 01, Bastero-Gil and Mersini 02 that the dark energy could be attributed to the cosmological properties of a scalar field with a non-standard dispersion relation that decreases exponentially at wave-numbers larger than Planck scale (k_phys > M_Planck). In this scenario, the energy density stored in the modes of trans-Planckian wave-numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account naturally for the dark energy. The present article examines this model in detail and shows step by step that it does not work. In particular, we show that this model cannot make definite predictions since there is no well-defined vacuum state in the region of wave-numbers considered, hence the initial data cannot be specified unambiguously. We also show that for most choices of initial data this scenario implies the production of a large amount of energy density (of order M_Planck^4) for modes with momenta of order M_Planck, far in excess of the background energy density. We evaluate the amount of fine-tuning in the initial data necessary to avoid this back-reaction problem and find it is of order H/M_Planck. We also argue that the equation of state of the trans-Planckian modes is not vacuum-like. Therefore this model does not provide a suitable explanation for the dark energy.Comment: RevTeX - 15 pages, 7 figures: final version to appear in PRD, minor changes, 1 figure adde

Integral field spectroscopy with SINFONI of VVDS galaxies. II. The mass-metallicity relation at 1.2 < z < 1.6

This work aims to provide a first insight into the mass-metallicity (MZ) relation of star-forming galaxies at redshift z~1.4. To reach this goal, we present a first set of nine VVDS galaxies observed with the NIR integral-field spectrograph SINFONI on the VLT. Oxygen abundances are derived from empirical indicators based on the ratio between strong nebular emission-lines (Halpha, [NII]6584 and [SII]6717,6731). Stellar masses are deduced from SED fitting with Charlot & Bruzual (2007) population synthesis models, and star formation rates are derived from [OII]3727 and Halpha emission-line luminosities. We find a typical shift of 0.2-0.4 dex towards lower metallicities for the z~1.4 galaxies, compared to the MZ-relation in the local universe as derived from SDSS data. However, this small sample of eight galaxies does not show any clear correlation between stellar mass and metallicity, unlike other larger samples at different redshift (z~0, z~0.7, and z~2). Indeed, our galaxies lie just under the relation at z~2 and show a small trend for more massive galaxies to be more metallic (~0.1 logarithmic slope). There are two possible explanations to account for these observations. First, the most massive galaxies present higher specific star formation rates when compared to the global VVDS sample which could explain the particularly low metallicity of these galaxies as already shown in the SDSS sample. Second, inflow of metal-poor gas due to tidal interactions could also explain the low metallicity of these galaxies as two of these three galaxies show clear signatures of merging in their velocity fields. Finally, we find that the metallicity of 4 galaxies is lower by ~0.2 to 0.4 dex if we take into account the N/O abundance ratio in their metallicity estimate.Comment: 7 pages, 4 figures, accepted in A&A Comments: Comments: more accurate results with better stellar mass estimate

Blue Grama Grass Genotype Affects Palatability and Preference by Semi-arid Steppe Grasshoppers

The semi-arid shortgrass steppe ecosystem of North America is dominated by blue grama grass (Bouteloua gracilis), a species with substantial intraspecific variability, ecological significance, and economic value. Yet no studies have addressed within species differences in blue grama palatability or insect herbivore preference with respect to plant traits. We performed an experimental study to test the palatability and preference of two blue grama genotypes, wild type versus cultivar, by grasshopper herbivores in the Gomphocerinae subfamily. We found strong evidence that cultivar blue grama was more palatable than wild type and that grasshoppers preferred cultivar plants. Although we could not detect differences in silica content between the two types, we found that cultivar plants were larger, had lower water content, and surprisingly, had reduced nutrient value (greater C:N). These results suggest that intraspecific variation in blue grama size and water content could influence feeding choices by this group of grasshoppers. Conservation managers will have to consider such variation when considering how remnant and restored prairies might be affected by these arthropod herbivores