Relic neutralinos in a best-fitted MSSM

We examine the properties of relic neutralinos in the regions of the parameter space selected by recent fits to all the electroweak observables within the Minimal Supersymmetric Standard Model. We discuss the relic neutralino cosmic abundance and the direct detection rates for these most likely supersymmetric configurations. We employ the relevant experimental bounds to constrain the set of the best-fit configurations and discuss the discovery potential of the direct search for relic neutralinos.     

Impacts of solar ultraviolet-B radiation on terrestrial ecosystems of Tierra del Fuego (southern Argentina). An overview of recent progress.

The southern part of Tierra del Fuego, in the southernmost tip of South America, is covered by dense Nothofagus spp. forests and Sphagnum-dominated peat bogs, which are subjected to the influence of ozone depletion and to increased levels of solar ultraviolet-B radiation (UV-B). Over the last 5 years we have studied some of the biological impacts of solar UV-B on natural ecosystems of this region. We have addressed two general problems: (i) do the fluctuations in UV-B levels under the influence of the Antarctic ozone 'hole' have any measurable biological impact, and (ii) what are the long-term effects of solar (ambient) UV-B on the Tierra del Fuego ecosystems? In this paper, we provide an overview of the progress made during the first 4 years of the project. We highlight and discuss the following results: (1) ambient UV-B has subtle but significant inhibitory effects on the growth of herbaceous and graminoid species of this region (growth reduction < or = 12%), whereas no consistent inhibitory effects could be detected in woody perennials; (2) in the species investigated in greatest detail, Gunnera magellanica, the inhibitory effect of solar UV-B is accompanied by increased levels of DNA damage in leaf tissue, and the DNA damage density in the early spring is clearly correlated with the dose of weighted UV-B measured at ground level; (3) the herbaceous species investigated thus far show little or no acclimation responses to ambient UV-B such as increased sunscreen levels and DNA repair capacity; and (4) ambient UV-B has significant effects on heterotrophic organisms, included marked inhibitory effects on insect herbivory. The results from the experiments summarized in this review clearly indicate that UV-B influences several potentially important processes and ecological interactions in the terrestrial ecosystems of Tierra del Fuego.     

Excitation of 6 Li above the breakup threshold in the 6 Li + 208 Pb system around the Coulomb barrier

The excitation energy above the breakup threshold of the Li system, after the interaction of ⁶Li nuclei with a ²⁰⁸Pb target, was deduced from the invariant mass of the system. Data were collected with a large-solid-angle detector set-up at four beam energies around the Coulomb barrier. The excitation of the ⁶Li nucleus above the breakup threshold (1.47 MeV) has a quite similar behavior at each measured beam energy and angle; it is peaked at MeV above the threshold and shows an exponential decay on the high energy side, which is a clear signature of a direct breakup process. The experimental excitation energies are reproduced both in shape and absolute value by 1) fully quantum-mechanical Coupled-Channel calculations with coupling to discretized-continuum ⁶Li excitations, 2) semi-classical Coupled-Channel approach, where the relative motion is treated along a classical trajectory.Received: 2 June 2003, Published online: 18 November 2003PACS: 25.70.Ji Fusion and fusion-fission reactions - 25.70.Mn Projectile and target fragmentation - 24.10.Eq Coupled-channel and distorted-wave modelsThis revised version was published online in December 2003 with corrections to the communicators name.     

PHOTOMORPHOGENIC PROCESSES IN THE AGRICULTURAL ENVIRONMENT

We review recent advances in our understanding of how photomorphogenic mechanisms influence processes of significance for agriculture, including weed seed germination, acclimation to solar UV-B radiation, and plant interactions in canopies. It has been demonstrated recently that seeds of some weed species acquire the ability to germinate in response to very low photon fluences during burial. Short sunlight pulses perceived by seeds during tillage appear to be important signals of soil disturbance. Regarding UV-B acclimation there is increasing evidence for the involvement of a specific UV-B photoreceptor in pigmentation and morphological responses to UV-B. The protective role played by UV-B-induced flavonoids has been experimentally demonstrated. Concerning plant interactions in canopies it has been shown that, by perceiving light signals through phytochrome and blue-UV-A photoreceptors, plants obtain information about the characteristics of the surrounding vegetation well before their resources are reduced as a consequence of neighbors' activities. There appears to be a large potential for improving cropping systems by manipulating the light environment or by changing the photomorphogenic behavior of crop plants. However, relatively little is known about how the expression and agronomic significance of photomorphogenic responses are influenced by other factors of the plant's environment.     

Recent results of the IGEX 76Ge double-beta decay experiment

The International Germanium Experiment (IGEX) has now analyzed 117 mol yr of data from its isotopically enriched (86% ⁷⁶Ge) germanium detectors. Applying pulse shape discrimination (PSD) to the more recent data, the lower bound on the half-life for neutrinoless double-beta decay of ⁷⁶Ge is deduced: T _1/2(0ν)>1.57×10²⁵ yr (90% C.L.). This corresponds to an upper bound on the Majorana neutrino mass parameter, 〈m _ν〉, between 0.33 eV and 1.35 eV depending on the choice of theoretical nuclear matrix elements used in the analysis.     

Soft leptogenesis in Higgs triplet model

We consider the minimal supersymmetric triplet seesaw model as the origin of neutrino masses and mixing as well as of the baryon asymmetry of the Universe, which is generated through soft leptogenesis employing a CP-violating phase and a resonant behavior in the supersymmetry breaking sector. We calculate the full gauge-annihilation cross section for the Higgs triplets, including all relevant supersymmetric intermediate and final states, as well as coannihilations with the fermionic superpartners of the triplets. We find that these gauge annihilation processes strongly suppress the resulting lepton asymmetry. As a consequence of this, successful leptogenesis can occur only for a triplet mass at the TeV scale, where the contribution of soft supersymmetry breaking terms enhances the CP and lepton asymmetry. This opens up an interesting opportunity for testing the model in future colliders.     

New results of the WIMP search with the first IGEX Ge detectors

To search for cold dark matter (CDM) particles, the data from two (Ge-76 and Ge-natural) detectors, fabricated in the first phase of the IGEX collaboration, were accumulated and analyzed for a period from May 1995 to May 1999. The use of effective passive and active shielding together with pulse shape discrimination allowed us to perform long-term measurements with an energy threshold of 2 keV at a level of the residual background 0.1 counts/(kg keV d). New restrictions on masses of weakly interacting massive particles and the cross section of their elastic scattering on nuclei have been obtained from the data corresponding to 810 d of live time. The derived exclusion plots compete with the best bounds obtained so far. Annual modulations of the CDM signal have been also investigated. It is shown that the planned operation of all IGEX detectors (at Canfranc and Baksan) with the recently achieved low-energy thresholds gives a chance to achieve the DAMA annual modulation sensitivity region in a nearest future.     

Towards measurement of recoils below 4 keV with the ROSEBUD experiment

An experiment to look for light WIMPs with sapphire bolometers is to be installed in the Canfranc Underground Laboratory (at 2450 m.w.e) in the Spanish Pyrenees. In the first stage two small 25g bolometers with NTD-Ge sensors, operating at 25mK, with an energy threshold of 300eV and FWHM energy resolution of 120eV at 1.5keV will perform a background test experiment. The features of the bolometers, the radioactivity measurements of the components and the set-up and status of the experiment are reported.