Gamma-ray lines and One-Loop Continuum from s-channel Dark Matter Annihilations

The era of indirect detection searches for dark matter has begun, with the sensitivities of gamma-ray detectors now approaching the parameter space relevant for weakly interacting massive particles. In particular, gamma ray lines would be smoking gun signatures of dark matter annihilation, although they are typically suppressed compared to the continuum. In this paper, we pay particular attention to the 1-loop continuum generated together with the gamma-ray lines and investigate under which conditions a dark matter model can naturally lead to a line signal that is relatively enhanced. We study generic classes of models in which DM is a fermion that annihilates through an s-channel mediator which is either a vector or scalar and identify the coupling and mass conditions under which large line signals occur. We focus on the "forbidden channel mechanism" advocated a few years ago in the "Higgs in space" scenario for which tree level annihilation is kinematically forbidden today. Detailed calculations of all 1-loop annihilation channels are provided. We single out very simple models with a large line over continuum ratio and present general predictions for a large range of WIMP masses that are relevant not only for Fermi and Hess II but also for the next generation of telescopes such as CTA and Gamma-400. Constraints from the relic abundance, direct detection and collider bounds are also discussed.Comment: 32 pages, 13 figures; v2: minor clarifications, summary paragraph added; v3: matches published version, minor clarifications, results unchange

Warped Unification, Proton Stability and Dark Matter

Many extensions of the Standard Model have to face the problem of new unsuppressed baryon-number violating interactions. In supersymmetry, the simplest way to solve this problem is to assume R-parity conservation. As a result, the lightest supersymmetric particle becomes stable and a well-motivated dark matter candidate. In this paper, we show that solving the problem of baryon number violation in non supersymmetric grand unified theories (GUT's) in warped higher-dimensional spacetime can lead to a stable Kaluza-Klein particle. This exotic particle has gauge quantum numbers of a right-handed neutrino, but carries fractional baryon-number and is related to the top quark within the higher-dimensional GUT. A combination of baryon-number and SU(3) color ensures its stability. Its relic density can easily be of the right value for masses in the 10 GeV--few TeV range. An exciting aspect of these models is that the entire parameter space will be tested at near future dark matter direct detection experiments. Other exotic GUT partners of the top quark are also light and can be produced at high energy colliders with distinctive signatures.Comment: 4 pages, 4 figures; v2: some comments added, figures updated; v3: Final version to appear in Phys. Rev. Let

Gravitational Waves from Warped Spacetime

We argue that the RSI model can provide a strong signature in gravitational waves. This signal is a relic stochastic background generated during the cosmological phase transition from an AdS-Schwarschild phase to the RS1 geometry that should occur at a temperature in the TeV range. We estimate the amplitude of the signal in terms of the parameters of the potential stabilizing the radion and show that over much of the parameter region in which the phase transition completes, a signal should be detectable at the planned space interferometer, LISA.Comment: 18 pages, 15 figures; v2: discussion improved, in particular on the justification of the thick wall approximation. 6 figures added. 4 pi factor corrected in perturbativity bound. N-dependence displayed. Conclusions unchanged. JHEP versio

Observation of vortex coalescence in the anisotropic spin-triplet superconductor Sr2_{2}RuO4_{4}

We present direct imaging of magnetic flux structures in the anisotropic, spin-triplet superconductor Sr$_{2}$RuO$_{4}$ using a scanning $\mu$SQUID microscope. Individual quantized vortices were seen at low magnetic fields. Coalescing vortices forming flux domains were revealed at intermediate fields. Based on our observations we suggest that a mechanism intrinsic to the material stabilizes the flux domains against the repulsive vortex-vortex interaction. Topological defects like domain walls can provide this, implying proof for unconventional chiral superconductivity.Comment: submitted to PR

Dirac Neutrino Dark Matter

We investigate the possibility that dark matter is made of heavy Dirac neutrinos with mass in the range [O(1) GeV- a few TeV] and with suppressed but non-zero coupling to the Standard Model Z as well as a coupling to an additional Z' gauge boson. The first part of this paper provides a model-independent analysis for the relic density and direct detection in terms of four main parameters: the mass, the couplings to the Z, to the Z' and to the Higgs. These WIMP candidates arise naturally as Kaluza-Klein states in extra-dimensional models with extended electroweak gauge group SU(2)_L* SU(2)_R * U(1). They can be stable because of Kaluza-Klein parity or of other discrete symmetries related to baryon number for instance, or even, in the low mass and low coupling limits, just because of a phase-space-suppressed decay width. An interesting aspect of warped models is that the extra Z' typically couples only to the third generation, thus avoiding the usual experimental constraints. In the second part of the paper, we illustrate the situation in details in a warped GUT model.Comment: 35 pages, 25 figures; v2: JCAP version; presentation and plots improved, results unchange

Crystal growth and characterization of the ruthenate superconducting compound: Sr2RuO4

International audienceSr2RuO4 is a copper-free layered perovskite superconductor with the tetragonal K2NiF4-type structure. The precise nature of the pairing in the superconducting state of this material is still under debate. In this paper, we report about crystal growth and characterization of this compound. The crystals were grown by a floating zone technique using a light furnace equipped with double elliptical mirrors starting from off-stoichiometric Sr2RuO4. The crystals have been checked by X-ray diffraction and microanalysis. The superconducting properties were measured by AC-susceptibility, magnetization and specific heat. High crystalline quality centimetre-sized crystals have been grown and best crystals exhibit superconducting transitions at View the MathML source (typical dimensions : 4.5 mm diameter and 70 mm length with the (0 0 1) axis perpendicular to growth direction). The unconventional superconductors are characterized by a drastic impurity effect on the superconducting properties. We try to establish a correlation between the defect concentration and the physical properties of Sr2RuO4

Transferts et stockage de l’eau et des sels dans le profil pédologique des sols halomorphes camarguais

La répartition spatiale des différentes espèces de salicornes en Camarque est conditionnée, 1) par les variations de la compo sition chimique et la dynamique saisonnière des solutions salines dans la zone d’aération des sols halomorphes, 2) par la salinité et la dynamique des eaux souterraines, 3) par la durée de la submersion des sols en période pluvieuse. Ces conditions sont à leur tour régies par les facteurs de la pédogénèse locale : morphologie de basse plaine littorale sub-horizontale (nappe aquifère peu profonde et salée), héritage sédimentaire holocène (texture fine du matériau) et climat (évaporation > précipitations). Les mouvements verticaux des solutions du sol se traduisent par des profils salins et hydriques relativement simples à établir, mais qui ne permettent pas de quantifier directement la salinité et la pression osmotique des solutions, car toute l’eau présente dans le sol n’est pas disponible pour la solubilisation des sels et tous les sels présents ne sont pas toujours à l’état dissous, surtout dans les horizons proches de la surface du sol où se manifestent en été des accumulations de NaCl (salant blanc et salant pulvérulent), de CaC12 (salant humide) et de gypse souvent associé au calcaire. Pour accéder aux solutions du sol, deux méthodes ont été employées suivant les valeurs du pF. Pour les pF bas (période hivernale), l’extraction des solutions en place par des batteries de bougies poreuses, a permis de connaître les variations saisonnières de salinité (tableau 3.11) et d’établir un modèle du processus de dessalement au cours de la période automne-hiver. Pour les fortes valeurs du pF, une méthode indirecte a consisté à essayer de reconstituer les solutions du sol à partir des profils hydriques et salins et des lois réglant la composition ionique des solutions salines en voie de concentration. La faible profondeur de la nappe aquifère et la texture fine du matériau, favorables à l’ascension capillaire des solutions du sol assurent, dans la plupart des cas, une bonne alimentation en eau des zones rhizosphériques même en été, malgré la forte sol licitation vers le haut (E et ET). Les contraintes hydriques qu’ont à subir les halophytes résultent plus du potentiel osmotique des solutions salines (50 à 100 bars) que du potentiel capillaire. D’autre part, les différences de salinité des premiers décimètres des sols en été ne sont pas assez nettes sous les différentes espèces de salicornes pour expliquer leur répartition spatiale. Par contre, les différences de salinité des eaux souterraines sont bien marquées (35 à 70 g.l- 1 sous Salicornia fruticosa, 80 à 110 g.l-1 sous Arthrocnemum glaucum) et l’exploitation de la nappe aqui fère par un réseau racinaire profond, associée à la résistance plus ou moins grande à la submersion hivernale, peut expliquer cette répartition spatiale.The spatial distribution of different species of Salicornia in the Camargue depends upon 1) variations in the chemical composition and the seasonal dynamics of the soil solutions in the aerated layer of halomorphic soils, 2) the salinity and dynamics of ground water, and 3) the length of time that the soil is flooded during the rainy season. These conditions are in turn controlled by certain local factors : morphology of the sub horizontal low littoral plain (water table shallow and saline), a sediment of Holocene origin (composed of fine particles), and climate (evaporation > precipitation). Vertical movements of soil solutions are determined by saline and hydric profiles which are relatively simple to establish. They do not however, permit the direct quantification of the salinity and osmotic pressure of these solutions, as not all of the water present in the soil is available for the dissolution of salts and all the salts present are not always in a dissolved state. This is especially true for the layers near the surface where, during the summer, accumulations of NaCl (white and pulverulent “salant”), CaCl2 (moist “salant”) and of gypsum often mixed with calcium can be observed. In order to obtain samples of soil solutions, two methods were employed, depending on pF values. For low pF (winter period) the solutions were extracted by means of porous ceramic cups which permitted the observation of seasonal changes in salinity (table 3-11) as well as the establishment of a desalinization process during the autumn-winter period. For high pF values, an indirect method was employed to reconstitute the soil solutions on the basis of hydric and saline profiles and establish the laws governing the ionic composition of saline solutions undergoing concentration. Since the shallow water table and fine soils particles favor the capillary ascension of soil solutions, the rhizospheric zones receive, in most cases, a good supply of water even during the summer, despite a strong tendency to rise (E and ET). The hydric constraints on halophytes are due more to the osmotic potential of soil solutions (50 to 100 bars) than to capillary potential. Moreover, differences in the salinity of the first decimetres of the soil during summer are not large enough under different species of Salicornia to explain their spatial distribution. But the important differences in the salinity of ground water (35 to 70 g I-1 under Salicornia fruticosa, 80 to 110 g 1— 1 under Arthroc- nemum glaiicum) and the utilization of the water table by a deep root system, associated with a fairly strong resistance to winter flooding, can explain this distribution

Elastic Scattering and Direct Detection of Kaluza-Klein Dark Matter

Recently a new dark matter candidate has been proposed as a consequence of universal compact extra dimensions. It was found that to account for cosmological observations, the masses of the first Kaluza-Klein modes (and thus the approximate size of the extra dimension) should be in the range 600-1200 GeV when the lightest Kaluza-Klein particle (LKP) corresponds to the hypercharge boson and in the range 1 - 1.8 TeV when it corresponds to a neutrino. In this article, we compute the elastic scattering cross sections between Kaluza-Klein dark matter and nuclei both when the lightest Kaluza-Klein particle is a KK mode of a weak gauge boson, and when it is a neutrino. We include nuclear form factor effects which are important to take into account due to the large LKP masses favored by estimates of the relic density. We present both differential and integrated rates for present and proposed Germanium, NaI and Xenon detectors. Observable rates at current detectors are typically less than one event per year, but the next generation of detectors can probe a significant fraction of the relevant parameter space.Comment: 23 pages, 11 figures; v2,v3: Ref. added, discussion improved, conclusions unchanged. v4: Introduction was expanded to be more appropriate for non experts. Various clarifications added in the text. Version to be published in New Journal of Physic