Galactic conformity measured in semi-analytic models

We study the correlation between the specific star formation rate of central galaxies and neighbour galaxies, also known as 'galactic conformity', out to 20 Mpc/h using three semi-analytic models (SAMs, one from L-GALAXIES and other two from GALFORM). The aim is to establish whether SAMs are able to show galactic conformity using different models and selection criteria. In all the models, when the selection of primary galaxies is based on an isolation criterion in real space, the mean fraction of quenched galaxies around quenched primary galaxies is higher than that around star-forming primary galaxies of the same stellar mass. The overall signal of conformity decreases when we remove satellites selected as primary galaxies, but the effect is much stronger in GALFORM models compared with the L-GALAXIES model. We find this difference is partially explained by the fact that in GALFORM once a galaxy becomes a satellite remains as such, whereas satellites can become centrals at a later time in L-GALAXIES. The signal of conformity decreases down to 60% in the L-GALAXIES model after removing central galaxies that were ejected from their host halo in the past. Galactic conformity is also influenced by primary galaxies at fixed stellar mass that reside in dark matter haloes of different masses. Finally, we explore a proxy of conformity between distinct haloes. In this case the conformity is weak beyond ~ 3 Mpc/h (<3% in L-GALAXIES, <1-2% in GALFORM models). Therefore, it seems difficult that conformity is directly related with a long-range effect.Comment: 15 pages, 7 figures. Accepted for publication in MNRA

Magnon valley Hall effect in CrI3-based vdW heterostructures

Magnonic excitations in the two-dimensional (2D) van der Waals (vdW) ferromagnet CrI3 are studied. We find that bulk magnons exhibit a non-trivial topological band structure without the need for Dzyaloshinskii-Moriya (DM) interaction. This is shown in vdW heterostructures, consisting of single-layer CrI3 on top of different 2D materials as MoTe2, HfS2 and WSe2. We find numerically that the proposed substrates modify substantially the out-of-plane magnetic anisotropy on each sublattice of the CrI3 subsystem. The induced staggered anisotropy, combined with a proper band inversion, leads to the opening of a topological gap of the magnon spectrum. Since the gap is opened non-symmetrically at the K+ and K- points of the Brillouin zone, an imbalance in the magnon population between these two valleys can be created under a driving force. This phenomenon is in close analogy to the so-called valley Hall effect (VHE), and thus termed as magnon valley Hall effect (MVHE). In linear response to a temperature gradient we quantify this effect by the evaluation of the temperature-dependence of the magnon thermal Hall effect. These findings open a different avenue by adding the valley degrees of freedom besides the spin, in the study of magnons

The relative efficacy of price announcements and express communication for collusion: experimental findings

This study conducts experiments to determine the modes of communication that are able to produce and sustain collusion and how the efficacy of communication depends on market structure. Two communication treatments are considered: non-binding price announcements and unrestricted written communication. We find that price announcements are conducive to coordinating on a high price but only under duopoly and when firms are symmetric. The standard experimental finding that collusion without communication is rare when there are more than two firms is shown to be robust to allowing firms to make price announcements. When firms are asymmetric, price announcements do result in higher prices but there is little evidence that firms are coordinating their behavior. When firms are allowed to engage in unrestricted written communication, coordination on high prices occurs for all market structures. We find that the incremental value to express communication (compared to price announcements) is greater when firms are asymmetric and there are more firms

The Relative Efficacy of Price Announcements and Express Communication for Collusion: Experimental Findings

Collusion is when firms coordinate on suppressing competition, and coordination typically requires that firms communicate in some manner. This study conducts experiments to determine what modes of communications are able to produce and sustain collusion and how the efficacy of communication depends on firm heterogeneity and the number of firms. We consider two different communication treatments: non-binding price announcements and unrestricted written communication. Our main findings are that price announcements allow subjects to coordinate on a high price but only under duopoly and when firms are symmetric. While price announcements do result in higher prices when subjects are asymmetric, there is little evidence that they are coordinating their behavior. When subjects are allowed to engage in unrestricted communication, coordination on high prices occurs whether they are symmetric or asymmetric. We find that the incremental value to express communication (compared to price announcements) is greater when firms are asymmetric and there are more firms