14198652
Bosonic-type S -matrix, vacuum instability and CDD ambiguities
Abstract We consider the simplest bosonic-type S -matrix which is usually regarded as unphysical due to the complex values of the finite volume ground state energy. While a standard quantum field theory interpretation of such a scattering theory is precluded, we argue that the physical situation described by this S -matrix is of a massive Ising model perturbed by a particular set of irrelevant operators. The presence of these operators drastically affects the stability of the original vacuum of the massive Ising model and its ultraviolet properties.
119500460
Coupled critical models: application to Ising-Potts models
Abstract We discuss the critical behaviour of 2 D Ising and q -states Potts models coupled by their energy density. We found new tricritical points. The procedure employed is the renormalisation approach of the perturbations series around conformal field theories representing pure models as already used for disordered spins models. This analysis could be useful to understand the physics of coupled critical models like the fully frustrated XY model.
119273967
Josephson effect in superconducting wires supporting multiple Majorana edge states
We study superconducting-normal-superconducting (SNS) Josephson junctions in one-dimensional topological superconductors which support more than one Majorana end mode. The variation of the energy spectrum with the superconducting phase is investigated by combining numerical diagonalizations of tight-binding models describing the SNS junction together with an analysis of appropriate low-energy effective Hamiltonians. We show that the four pi-periodicity characteristic of the fractional dc Josephson effect is preserved. Additionally, the ideal conductance of a NS junction with a topological supraconductor, hosting two Majorana modes at its ends, is doubled compared to the single Majorana case. Last, we illustrate how a nonzero superconducting phase gradient can potentially destroy the phases supporting multiple Majorana end states.
17068714
Signatures in a Giant Radio Galaxy of a Cosmological Shock Wave at Intersecting Filaments of Galaxies
Sensitive images of low-level, megaparsec-sized radio cocoons offer new opportunities to probe large-scale intergalactic gas flows outside clusters of galaxies. New radio images of high surface brightness sensitivity at strategically chosen wavelengths of the giant radio galaxy NGC 315 reveal significant asymmetries and particularities in the morphology, radio spectrum, and polarization of the ejected radio plasma. We argue that the combination of these signatures provides a sensitive probe of an environmental shock wave. Analysis of optical redshifts in NGC 315's vicinity confirms its location to be near, or at, a site of large-scale flow collisions in the 100 Mpc sized Pisces-Perseus supercluster region. NGC 315 resides at the intersection of several galaxy filaments, and its radio plasma serves there as a "weather station," probing the flow of the elusive and previously invisible intergalactic medium gas. If our interpretation is correct, this is the first indication for a shock wave in flows caused by the cosmological large-scale structure formation, which is located in a filament of galaxies. The possibility that the putative shock wave is a source of gamma rays and ultrahigh-energy cosmic rays is briefly discussed.
44434714
CFHTLenS: higher order galaxy–mass correlations probed by galaxy–galaxy–galaxy lensing
We present the first direct measurement of the galaxy–matter bispectrum as a function of galaxy luminosity, stellar mass and type of spectral energy distribution (SED). Our analysis uses a galaxy–galaxy–galaxy lensing technique (G3L), on angular scales between 9 arcsec and 50 arcmin, to quantify (i) the excess surface mass density around galaxy pairs (excess mass hereafter) and (ii) the excess shear–shear correlations around single galaxies, both of which yield a measure of two types of galaxy–matter bispectra. We apply our method to the state-of-the-art Canada–France–Hawaii Telescope Lensing Survey (CFHTLenS), spanning 154 square degrees. This survey allows us to detect a significant change of the bispectra with lens properties. Measurements for lens populations with distinct redshift distributions become comparable by a newly devised normalization technique. That will also aid future comparisons to other surveys or simulations. A significant dependence of the normalized G3L statistics on luminosity within −23 ≤ Mr ≤ −18 and stellar mass within 5 × 10^9 M_⊙ ≤ M* ≤ 2 × 10^(11) M_⊙ is found (h = 0.73). Both bispectra exhibit a stronger signal for more luminous lenses or those with higher stellar mass (up to a factor of 2–3). This is accompanied by a steeper equilateral bispectrum for more luminous or higher stellar mass lenses for the excess mass. Importantly, we find the excess mass to be very sensitive to galaxy type as recently predicted with semi-analytic galaxy models: luminous (M_r < −21) late-type galaxies show no detectable signal, while all excess mass detected for luminous galaxies seems to be associated with early-type galaxies. We also present the first observational constraints on third-order stochastic galaxy biasing parameters.
8253626
The non-Gaussianity of the cosmic shear likelihood or How odd is the Chandra Deep Field South?
Aims. We study the validity of the approximation of a Gaussian cosmic shear likelihood. We estimate the true likelihood for a fiducial cosmological model from a large set of ray-tracing simulations and investigate the impact of non-Gaussianity on cosmological parameter estimation. We investigate how odd the recently reported very low value of σ8 really is as derived from the Chandra Deep Field South (CDFS) using cosmic shear by taking the non-Gaussianity of the likelihood into account, as well as the possibility of biases coming from the way the CDFS was selected. Methods. A brute force approach to estimating the likelihood from simulations must fail because of the high dimensionality of the problem. We therefore use independent component analysis to transform the cosmic shear correlation functions to a new basis, in which the likelihood approximately factorises into a product of one-dimensional distributions. Results. We find that the cosmic shear likelihood is significantly non-Gaussian. This leads to both a shift of the maximum of the posterior distribution and a significantly smaller credible region compared to the Gaussian case. We re-analyse the CDFS cosmic shear data using the non-Gaussian likelihood in combination with conservative galaxy selection criteria that minimise calibration uncertainties. Assuming that the CDFS is a random pointing, we find σ8 = 0.68 +0.09 −0.16 for fixed Ωm = 0.25. In a WMAP5-like cosmology, a value equal to or lower than this would be expected in ≈5% of the times. Taking biases into account arising from the way the CDFS was selected, which we model as being dependent on the number of haloes in the CDFS, we obtain σ8 = 0.71 +0.10 −0.15 . Combining the CDFS data with the parameter constraints from WMAP5 yields Ωm = 0.26 +0.03 −0.02 and σ8 = 0.79 +0.04 −0.03 for a flat universe.
119206013
Galaxy-galaxy(-galaxy) lensing as a sensitive probe of galaxy evolution
Context. The gravitational lensing effect provides various ways to study the mass environment of galaxies. Aims. We investigate how galaxy-galaxy(-galaxy) lensing can be used to test models of galaxy formation and evolution. Methods. We consider two semi-analytic galaxy formation models based on the Millennium Run N-body simulation: the Durham model by Bower et al. (2006, MNRAS, 370, 645) and the Garching model by Guo et al. (2011, MNRAS, 413, 101). We generate mock lensing observations for the two models, and then employ Fast Fourier Transform methods to compute second- and third-order aperture statistics in the simulated fields for various galaxy samples. Results. We find that both models predict qualitatively similar aperture signals, but there are large quantitative differences. The Durham model predicts larger amplitudes in general. In both models, red galaxies exhibit stronger aperture signals than blue galaxies. Using these aperture measurements and assuming a linear deterministic bias model, we measure relative bias ratios of red and blue galaxy samples. We find that a linear deterministic bias is insufficient to describe the relative clustering of model galaxies below ten arcmin angular scales. Dividing galaxies into luminosity bins, the aperture signals decrease with decreasing luminosity for brighter galaxies, but increase again for fainter galaxies. This increase is likely an artifact due to too many faint satellite galaxies in massive group and cluster halos predicted by the models. Conclusions. Our study shows that galaxy-galaxy(-galaxy) lensing is a sensitive probe of galaxy evolution.
17142858
GaBoDS: The Garching-Bonn Deep Survey: VI. Cosmic shear analysis
Aims. We present a cosmic shear analysis and data validation of 15 square degree high-quality R-band data of the Garching-Bonn Deep Survey obtained with the Wide Field Imager of the MPG/ESO 2.2m telescope. Methods. We measure the two-point shear correlation functions to calculate the aperture mass dispersion. Both statistics are used to perform the data quality control. Combining the cosmic shear signal with a photometric redshift distribution of a galaxy sub-sample obtained from two square degree of UBVRI-band observations of the Deep Public Survey we determine constraints for the matter density Omega_m, the mass power spectrum normalisation sigma_8 and the dark energy density Omega_Lambda in the magnitude interval R in [21.5,24.5]. In this magnitude interval the effective number density of source galaxies is n=12.5/sq. arcmin, and their mean redshift is z_m=0.78. To estimate the posterior likelihood we employ the Monte Carlo Markov Chain method. Results. Using the aperture mass dispersion we obtain for the mass power spectrum normalisation sigma_8=0.80 +- 0.10 (1 sigma statistical error) at a fixed matter density Omega_m=0.30 assuming a flat universe with negligible baryon content and marginalising over the Hubble parameter and the uncertainties in the fitted redshift distribution.