7559852
A renormalization group study of asymmetrically coupled minimal models
Abstract We investigate the renormalization group flows and fixed point structure of many coupled minimal models. The models are coupled two by two by energy-energy couplings. We take the general approach where the bare couplings are all taken to be independent. New fixed points are found for N models ( N ≥3). At these fixed points, the coupling constants all have the same magnitude, but some are positive while others are negative. By analogy with spin lattices, these can be interpreted as non-frustrated configurations with a maximal number of antiferromagnetic links. The stability of the different fixed points is studied. We compute the critical exponents and spin-spin correlation functions between different models. Our classification is shown to be complete.
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.
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.
16157496
Universal amplitude ratios of the renormalization group: two-dimensional tricritical Ising model.
The scaling form of the free energy near a critical point allows for the definition of various thermodynamical amplitudes and the determination of their dependence on the microscopic nonuniversal scales. Universal quantities can be obtained by considering special combinations of the amplitudes. Together with the critical exponents they characterize the universality classes and may be useful quantities for their experimental identification. We compute the universal amplitude ratios for the tricritical Ising model in two dimensions by using several theoretical methods from perturbed conformal field theory and scattering integrable quantum field theory. The theoretical approaches are further supported and integrated by results coming from a numerical determination of the energy eigenvalues and eigenvectors of off-critical systems in an infinite cylinder.
117969814
Mutation of Andreev into Majorana bound states in long superconductor-normal and superconductor-normal-superconductor junctions
We study one-dimensional topological SN and SNS long junctions obtained by placing a topological insulating nanowire in the proximity of either one or two SC finite-size leads. Using the Majorana Polarization order parameter (MP) introduced in Phys. Rev. Lett. 108, 096802 (2012)(arxiv:1109.5697) we find that the extended Andreev bound states (ABS) of the normal part of the wire acquire a finite MP: for a finite-size SN junction the ABS spectrum exhibits a zero-energy extended state which carries a full Majorana fermion, while the ABS of long SNS junctions with phase difference $\pi$ transform into two zero-energy states carrying two Majorana fermions with the same MP. Given their extended character inside the whole normal link, and not only close to an interface, these Majorana-Andreev states can be directly detected in tunneling spectroscopy experiments.
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.
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.
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.
1663219
CARS: the CFHTLS-Archive-Research Survey II. Weighing dark matter halos of Lyman-break galaxies at z = 3-5
Aims. We measure the clustering properties for a large samples of u- (z ~ 3), g- (z ~ 4), and r- (z ~ 5) dropouts from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep fields. 
 
Methods. Photometric redshift distributions along with simulations allow us to de-project the angular correlation measurements and estimate physical quantities such as the correlation length, halo mass, galaxy bias, and halo occupation as a function of UV luminosity. 
 
Results. For the first time we detect a significant one-halo term in the correlation function at z ~ 5 . The comoving correlation lengths and halo masses of LBGs are found to decrease with decreasing rest-frame UV-luminosity. No significant redshift evolution is found in either quantity. The typical halo mass hosting an LBG is M ≳ 10^(12)h^(-1) M⊙ and the halos are typically occupied by less than one galaxy. Clustering segregation with UV luminosity is clearly observed in the dropout samples, however redshift evolution cannot clearly be disentangled from systematic uncertainties introduced by the redshift distributions. We study a range of possible redshift distributions to illustrate the effect of this choice. Spectroscopy of representative subsamples is required to make high-accuracy absolute measurements of high-z halo masses.
119192831
Towards an understanding of third-order galaxy-galaxy lensing
Context. Third-order galaxy-galaxy lensing (G3L) is a next generation galaxy-galaxy lensing (GGL) technique that either measures the excess shear about lens pairs or the excess shear-shear correlations about lenses. From their definition it is clear that these statistics assess the three-point correlations between galaxy positions and projected matter density. Aims. For future applications of these novel statistics, we aim at a more intuitive understanding of G3L to isolate the main features that possibly can be measured. Methods. We construct a toy model (“isolated lens model”; ILM) for the distribution of galaxies and associated matter to determine the measured quantities of the two G3L correlation functions and traditional GGL in a simplified context. The ILM presumes single lens galaxies to be embedded inside arbitrary matter haloes that, however, are statistically independent (“isolated”) from any other halo or lens position. Clusters of galaxies and their common cluster matter haloes are a consequence of clustering smaller haloes. In particular, the average mass-to-galaxy number ratio of clusters of any size cannot change in the ILM. Results. GGL and galaxy clustering alone cannot distinguish an ILM from any more complex scenario. The lens-lens-shear correlator in combination with second-order statistics enables us to detect deviations from a ILM, though. This can be quantified by a difference signal defined in the paper. We demonstrate with the ILM that this correlator picks up the excess matter distribution about galaxy pairs inside clusters, whereas pairs with lenses well separated in redshift only suppress the overall amplitude of the correlator. The amplitude suppression can be normalised. The lens-lens-shear correlator is sensitive to variations among matter haloes. In principle, it could be devised to constrain the ellipticities of haloes, without the need for luminous tracers, or maybe even random halo substructure.
5127951
Time evolution of the stochastic linear bias of interacting galaxies on linear scales
We extend the time dependent bias model of Tegmark & Peebles (1998) to predict the large-scale evolution of the stochastic linear bias of different galaxy populations with respect to both the dark matter and each other. The resulting model equations contain a general expression, coined the "interaction term", accounting for the destruction or production of galaxies. This term may be used to model couplings between different populations that lead to an increase or decrease of the number of a galaxies belonging to a population, e.g. passive evolution or merging processes. This is explored in detail using a toy model. In particular, it is shown that the presence of such a coupling may change the evolution of the bias parameter compared to an interaction-free evolution. We argue that the observation of the evolution of the large-scale bias and galaxy number density with wide-field surveys may be used to infer fundamental interaction parameters between galaxy populations, possibly giving an insight in their formation and evolution.