Minimal dark matter in type III seesaw

We explore the possibility of a new dark matter candidate in the supersymmetric type III seesaw mechanism where a neutral scalar component of the Y=0 triplet can be the lightest supersymmetric particle. Its thermal abundance can be in the right range if non-standard cosmology such as kination domination is assumed. The enhanced cross-section of the dark matter annihilation to W+W- can leave detectable astrophysical and cosmological signals whose current observational data puts a lower bound on the dark matter mass. The model predicts the existence of a charged scalar almost degenerate with the dark matter scalar and its lifetime lies between 5.5 cm and 6.3 m. It provides a novel opportunity of the dark mater mass measurement by identifying slowly-moving and highly-ionizing tracks in the LHC experiments. If the ordinary lightest supersymmetric particle is the usual Bino, its decay leads to clean signatures of same-sign di-lepton and di-charged-scalar associated with observable displaced vertices which are essentially background-free and can be fully reconstructed.Comment: 3 figures, 12 pages; An error in the antiproton limit corrected; the lower bound on the dark matter mass strengthened; references added; typos correcte

Catalog Extraction in SZ Cluster Surveys: a matched filter approach

We present a method based on matched multifrequency filters for extracting cluster catalogs from Sunyaev-Zel'dovich (SZ) surveys. We evaluate its performance in terms of completeness, contamination rate and photometric recovery for three representative types of SZ survey: a high resolution single frequency radio survey (AMI), a high resolution ground-based multiband survey (SPT), and the Planck all-sky survey. These surveys are not purely flux limited, and they loose completeness significantly before their point-source detection thresholds. Contamination remains relatively low at <5% (less than 30%) for a detection threshold set at S/N=5 (S/N=3). We identify photometric recovery as an important source of catalog uncertainty: dispersion in recovered flux from multiband surveys is larger than the intrinsic scatter in the Y-M relation predicted from hydrodynamical simulations, while photometry in the single frequency survey is seriously compromised by confusion with primary cosmic microwave background anisotropy. The latter effect implies that follow-up observations in other wavebands (e.g., 90 GHz, X-ray) of single frequency surveys will be required. Cluster morphology can cause a bias in the recovered Y-M relation, but has little effect on the scatter; the bias would be removed during calibration of the relation. Point source confusion only slightly decreases multiband survey completeness; single frequency survey completeness could be significantly reduced by radio point source confusion, but this remains highly uncertain because we do not know the radio counts at the relevant flux levels.Comment: 14 pages, 13 figures, replaced to match version accepted for publication in A&

The kk-essence scalar field in the context of Supernova Ia Observations

A $k$-essence scalar field model having (non canonical) Lagrangian of the form $L=-V(\phi)F(X)$ where $X=1/2g^{\mu\nu}\nabla_{\mu}\phi\nabla_{\nu}\phi$ with constant $V(\phi)$ is shown to be consistent with luminosity distance-redshift data observed for type Ia Supernova. For constant $V(\phi)$, $F(X)$ satisfies a scaling relation which is used to set up a differential equation involving the Hubble parameter $H$, the scale factor $a$ and the $k$-essence field $\phi$. $H$ and $a$ are extracted from SNe Ia data and using the differential equation the time dependence of the field $\phi$ is found to be: $\phi(t) \sim \lambda_0 + \lambda_1 t + \lambda_2 t^2$. The constants $\lambda_i$ have been determined. The time dependence is similar to that of the quintessence scalar field (having canonical kinetic energy) responsible for homogeneous inflation. Furthermore, the scaling relation and the obtained time dependence of the field $\phi$ is used to determine the $X$-dependence of the function $F(X)$.Comment: 8 pages, 5 figures, Late

Baryon Acoustic Oscillations in the Sloan Digital Sky Survey Data Release 7 Galaxy Sample

The spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) galaxy sample represents the final set of galaxies observed using the original SDSS target selection criteria. We analyse the clustering of galaxies within this sample, including both the Luminous Red Galaxy (LRG) and Main samples, and also include the 2-degree Field Galaxy Redshift Survey (2dFGRS) data. Baryon Acoustic Oscillations are observed in power spectra measured for different slices in redshift; this allows us to constrain the distance--redshift relation at multiple epochs. We achieve a distance measure at redshift z=0.275, of r_s(z_d)/D_V(0.275)=0.1390+/-0.0037 (2.7% accuracy), where r_s(z_d) is the comoving sound horizon at the baryon drag epoch, D_V(z)=[(1+z)^2D_A^2cz/H(z)]^(1/3), D_A(z) is the angular diameter distance and H(z) is the Hubble parameter. We find an almost independent constraint on the ratio of distances D_V(0.35)/D_V(0.2)=1.736+/-0.065, which is consistent at the 1.1sigma level with the best fit Lambda-CDM model obtained when combining our z=0.275 distance constraint with the WMAP 5-year data. The offset is similar to that found in previous analyses of the SDSS DR5 sample, but the discrepancy is now of lower significance, a change caused by a revised error analysis and a change in the methodology adopted, as well as the addition of more data. Using WMAP5 constraints on Omega_bh^2 and Omega_ch^2, and combining our BAO distance measurements with those from the Union Supernova sample, places a tight constraint on Omega_m=0.286+/-0.018 and H_0 = 68.2+/-2.2km/s/Mpc that is robust to allowing curvature and non-Lambda dark energy. This result is independent of the behaviour of dark energy at redshifts greater than those probed by the BAO and supernova measurements. (abridged)Comment: 22 pages, 16 figures, minor changes to match version published in MNRA

Superclusters of galaxies from the 2df redshift survey. 1. the catalogue

We use the 2dF Galaxy Redshift Survey data to compile catalogues of superclusters for the Northern and Southern regions of the 2dFGRS, altogether 543 superclusters at redshifts 0.009 {le} z {le} 0.2. We analyze methods of compiling supercluster catalogues and use results of the Millennium Simulation to investigate possible selection effects and errors. We find that the most effective method is the density field method using smoothing with an Epanechnikov kernel of radius 8 h{sup -1} Mpc. We derive positions of the highest luminosity density peaks and find the most luminous cluster in the vicinity of the peak, this cluster is considered as the main cluster and its brightest galaxy the main galaxy of the supercluster. In catalogues we give equatorial coordinates and distances of superclusters as determined by positions of their main clusters. We also calculate the expected total luminosities of the superclusters

Empirical Hα emitter count predictions for dark energy surveys

Future galaxy redshift surveys aim to measure cosmological quantities from the galaxy power spectrum. A prime example is the detection of baryonic acoustic oscillations, providing a standard ruler to measure the dark energy equation of state, w(z), to high precision. The strongest practical limitation for these experiments is how quickly accurate redshifts can be measured for sufficient galaxies to map the large-scale structure. A promising strategy is to target emission-line (i.e. star-forming) galaxies at high redshift (z∼ 0.5–2); not only is the space density of this population increasing out to z∼ 2, but also emission lines provide an efficient method of redshift determination. Motivated by the prospect of future dark energy surveys targeting Hα emitters at near-infrared wavelengths (i.e. z > 0.5), we use the latest empirical data to model the evolution of the Hα luminosity function out to z∼ 2 and thus provide predictions for the abundance of Hα emitters for practical limiting fluxes. We caution that the estimates presented in this work must be tempered by an efficiency factor, ε, giving the redshift success rate from these potential targets. For a range of practical efficiencies and limiting fluxes, we provide an estimate of Graphic, where Graphic is the 3D galaxy number density and P0.2 is the galaxy power spectrum evaluated at k= 0.2 h Mpc−1. Ideal surveys must provide Graphic in order to balance shot-noise and cosmic variance errors. We show that a realistic emission-line survey (ε= 0.5) could achieve Graphic out to z∼ 1.5 with a limiting flux of 10−16 erg s−1 cm−2. If the limiting flux is a factor of 5 brighter, then this goal can only be achieved out to z∼ 0.5, highlighting the importance of survey depth and efficiency in cosmological redshift surveys