Light spin-1/2 or spin-0 Dark Matter particles

We recall and precise how light spin-0 particles could be acceptable Dark Matter candidates, and extend this analysis to spin-1/2 particles. We evaluate the (rather large) annihilation cross sections required, and show how they may be induced by a new light neutral spin-1 boson U. If this one is vectorially coupled to matter particles, the (spin-1/2 or spin-0) Dark Matter annihilation cross section into e+e- automatically includes a v_dm^2 suppression factor at threshold, as desirable to avoid an excessive production of gamma rays from residual Dark Matter annihilations. We also relate Dark Matter annihilations with production cross sections in e+e- scatterings. Annihilation cross sections of spin-1/2 and spin-0 Dark Matter particles are given by exactly the same expressions. Just as for spin-0, light spin-1/2 Dark Matter particles annihilating into e+e- could be responsible for the bright 511 keV gamma ray line observed by INTEGRAL from the galactic bulge.Comment: 10 page

Constraints on the parity-violating couplings of a new gauge boson

High-energy particle physics experiments allow for the possible existence of a new light, very weakly coupled, neutral gauge boson (the U boson). This one permits for light (spin-1/2 or spin-0) particles to be acceptable Dark Matter candidates, by inducing sufficient (stronger than weak) annihilation cross sections into e+e-. They could be responsible for the bright 511 keV gamma ray line observed by INTEGRAL from the galactic bulge. Such a new interaction may have important consequences, especially at lower energies. Parity-violation atomic-physics experiments provide strong constraints on such a U boson, if its couplings to quarks and electrons violate parity. With the constraints coming from an unobserved axionlike behaviour of this particle, they privilegiate a pure vector coupling of the U boson to quarks and leptons, unless the corresponding symmetry is broken sufficiently above the electroweak scale.Comment: 6 page

Probing the SUSY breaking scale at an e−e−e^-e^- collider

If supersymmetry is spontaneously at a low energy scale then the resulting gravitino would be very light. The interaction strength of the longitudinal components of such a light gravitino to electron-selectron pair then becomes comparable to that of electroweak interactions. Such a light gravitino could modify the cross-section for e^_L e^_R-->\tilde {e}_L\tilde {e}_R from its MSSM value. Precision measurement of this cross-section could therefore be used to probe the low energy SUSY breaking scale.Comment: Plain Tex, 7 pages, No figure

Supersymmetry and Gauge Invariance Constraints in a U(1)×\times U(1)′^{\prime }-Higgs Superconducting Cosmic String Model

A supersymmetric extension of the $U(1)\times U(1)^{\prime }$-Higgs bosonic superconducting cosmic string model is considered,and the constraints imposed upon such a model due to renormalizability, supersymmetry, and gauge invariance are examined. For a simple model with a single $U(1)$ chiral superfield and a single $$ chiral superfield, the Witten mechanism for bosonic superconductivity (giving rise to long range gauge fields outside of the string) does not exist. The simplest model that can accommodate the requisite interactions requires five chiral supermultiplets. This superconducting cosmic string solution is investigated.Comment: 17 pages, revtex, no figures; to appear in Phys. Rev.

Effective Two Higgs Doublets in Nonminimal Supersymmetric Models

The Higgs sectors of supersymmetric extensions of the Standard Model have two doublets in the minimal version (MSSM), and two doublets plus a singlet in two others: with (UMSSM) and without (NMSSM) an extra U(1)'. A very concise comparison of these three models is possible if we assume that the singlet has a somewhat larger breaking scale compared to the electroweak scale. In that case, the UMSSM and the NMSSM become effectively two-Higgs-doublet models (THDM), like the MSSM. As expected, the mass of the lightest CP-even neutral Higgs boson has an upper bound in each case. We find that in the NMSSM, this bound exceeds not very much that of the MSSM, unless tan(beta) is near one. However, the upper bound in the UMSSM may be substantially enhanced.Comment: 8 pages, 1 table, 3 figure

Marked differences in foraging area use and susceptibility to predation between two closely-related tropical seabirds

Ecological theory predicts that closely-related species must occupy different niches to coexist. How marine top predators achieve this during breeding, when they often gather in large multi-species colonies and are constrained to central-place foraging, has been mostly studied in productive temperate and polar oceans with abundant resources, but less so in poorer, tropical waters. Here, we track the foraging movements of two closely-related sympatric seabirds—the white-tailed and red-tailed tropicbirds Phaethon lepturus and P. rubricauda—breeding on Aldabra Atoll, Seychelles, to investigate potential mechanisms of niche segregation and shed light on their contrasting population trends. Combining data from GPS, immersion, depth and accelerometry loggers, we show that the two species have similar behaviour at sea, but are completely segregated spatially, with red-tailed tropicbirds flying further to feed and using different feeding areas than white-tailed tropicbirds. Using nest-based camera traps, we show that low breeding success of both species—which likely drives observed population declines—is caused by high nest predation. However, the two species are targeted by different predators, with native avian predators mainly targeting red-tailed tropicbird nests, and invasive rats raiding white-tailed tropicbird nests when they leave their eggs unattended. Our findings provide new insight into the foraging ecology of tropicbirds and have important conservation implications. The extensive range and spatial segregation highlight the importance of considering large-scale protection of waters around tropical seabird colonies, while the high level of nest predation provides evidence in support of rat eradication and investigating potential nest protection from native avian predators

Testing the equivalence principle: why and how?

Part of the theoretical motivation for improving the present level of testing of the equivalence principle is reviewed. The general rationale for optimizing the choice of pairs of materials to be tested is presented. One introduces a simplified rationale based on a trichotomy of competing classes of theoretical models.Comment: 11 pages, Latex, uses ioplppt.sty, submitted to Class. Quantum Gra

Implications of Low Energy Supersymmetry Breaking at the Tevatron

The signatures for low energy supersymmetry breaking at the Tevatron are investigated. It is natural that the lightest standard model superpartner is an electroweak neutralino, which decays to an essentially massless Goldstino and photon, possibly within the detector. In the simplest models of gauge-mediated supersymmetry breaking, the production of right-handed sleptons, neutralinos, and charginos leads to a pair of hard photons accompanied by leptons and/or jets with missing transverse energy. The relatively hard leptons and softer photons of the single e^+e^- \gamma \gamma + \EmissT event observed by CDF implies this event is best interpreted as arising from left-handed slepton pair production. In this case the rates for l^{\pm} \gamma \gamma + \EmissT and \gamma \gamma + \EmissT are comparable to that for l^+l^- \gamma \gamma + \EmissT.Comment: 18 pages, Latex, tables correcte