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  • We study interaction effects, including both long-ranged Coulomb and short-range interactions, in three-dimensional topological triple-Weyl semimetals whose triple-Weyl points are protected by crystal symmetries. By performing Wilsonian renormalization group analysis of the low-energy effective field theory of the minimal model with triple-Weyl nodes, we find that the fixed point of noninteracting triple-Weyl fermions is unstable against Coulomb interactions and flows to a nontrivial stable fixed point with anisotropic screening effects. We further discuss relevant unusual physical consequences due to the novel behavior of correlation effects in this system. Read More
  • In this paper we introduce the phylogenetic Dirichlet-multinomial (PhyloDM) model for investigating cross-group differences in microbiome compositions. Traditional Dirichlet-Multinomial (DM) models ignore species relatedness, leading to loss in efficiency and to results that are difficult to interpret. PhyloDM solves these issues by replacing the global model with a cascade of independent local DMs on the internal nodes of the phylogenetic tree. Each of the local DMs captures the count distributions of a certain number of operational taxonomic units (OTU) at a given resolution. Since distributional differences tend to occur in clusters along evolutionary lineages, we design a scan statistic over the phylogenetic tree to allow nodes to borrow signal strength from their parents and children. We also derive a formula to bound the tail probability of the scan statistic, and verify its accuracy through simulations. The PhyloDM model is applied to the American Gut dataset to identify taxa associated with diet habits. Empirical studies performed on this dataset show that PhyloDM achieves a significantly better fit, and has higher testing power than DM. Read More
  • We here theoretically study the global phase diagram of a three-dimensional dirty Weyl system. The generalized Harris criterion, augmented by a perturbative renormalization-group (RG) analysis shows that weak disorder is an irrelevant perturbation at the Weyl semimetal(WSM)-insulator quantum critical point (QCP). But, a metallic phase sets in through a quantum phase transition (QPT) at strong disorder across a multicritical point, characterized by the correlation length exponent $\nu=2$ and dynamic scaling exponent (DSE) $z=5/4$. Deep inside the WSM phase, generic disorder is also an irrelevant perturbation, while a metallic phase appears at strong disorder through a QPT. We here demonstrate that in the presence of generic, but chiral symmetric disorder (e.g., chemical potential, axial potential, etc.) the WSM-metal QPT is always characterized by the exponents $\nu=1$ and $z=3/2$ to one-loop order. We here anchor such emergent \emph{chiral superuniversality} through complimentary RG calculations, controlled via $\epsilon$-expansions, and numerical analysis of average density of states across WSM-metal QPT. Even though in the presence of chiral symmetry breaking disorder, as for instance random spin-orbit coupling, the exact value of DSE across such QPT depends on the RG scheme, we always find $z>d$, with $d$ as dimensionality of the WSM, and $\nu=1$. We also discuss scaling behavior of various physical observables, such as residue of quasiparticle pole, dynamic conductivity, specific heat, Gr$\ddot{\mbox{u}}$neisen ratio, across the WSM-metal QPTs. Read More
  • The accelerating expansion of the universe is one of the most profound discoveries in modern cosmology, pointing to a universe in which 70% of the mass-energy density has an unknown form spread uniformly across the universe. This result has been well established using a combination of cosmological probes (e.g., Planck Collaboration et al. 2016), resulting in a "standard model" of modern cosmology that is a combination of a cosmological constant with cold dark matter and baryons. The first compelling evidence for this acceleration came in the late 1990's, when two independent teams studying type Ia supernovae discovered that distant SNe Ia were dimmer than expected. The combined analysis of modern cosmology experiments, including SNe Ia (Betoule et al. 2014), the cosmic microwave background (Planck Collaboration et al. 2016), and baryon acoustic oscillations (Alam et al. 2016), indicate ~ 75 sigma evidence for positive Omega_Lambda. A recent study has claimed that the evidence for acceleration from SNe Ia is marginal. Here we demonstrate errors in that analysis which reduce the significance from SNe Ia, and show that constraints on the flatness or matter density of the universe greatly increase the significance of acceleration. Analyzing the Joint Light-curve Analysis supernova sample, we find 4.2 sigma evidence for acceleration with SNe Ia alone, and 11.2 sigma in a flat universe. With the correct supernova analysis and by not rejecting all other cosmological constraints, we find that acceleration is quite secure. Read More
  • Galactic outflows are ubiquitously observed in star-forming disk galaxies and are critical for galaxy formation. Supernovae (SNe) play the key role in driving the outflows, but there is no consensus as to how much energy, mass and metal they can launch out of the disk. We perform 3D, high-resolution hydrodynamic simulations to study SNe-driven outflows from stratified media. Assuming SN rate scales with gas surface density $\Sigma_{\rm{gas}}$ as in the Kennicutt-Schmidt (KS) relation, we find the mass loading factor, defined as the mass outflow flux divided by the star formation surface density, decreases with increasing $\Sigma_{\rm{gas}}$ as $\propto \Sigma^{-0.61}_{\rm{gas}}$. Approximately $\Sigma_{\rm{gas}} \lesssim$ 50 $M_\odot/pc^2$ marks when the mass loading factor $\gtrsim$1. About 10-50\% of the energy and 40-80\% of the metals produced by SNe end up in the outflows. The tenuous hot phase ($T>3\times 10^5$ K) carries the majority of the energy and metals in outflows. We discuss how various physical processes, including vertical distribution of SNe, photoelectric heating, external gravitational field and SN rate, affect the loading efficiencies. The relative scale height of gas and SNe is a very important factor in determining the loading efficiencies. Read More
  • The boundary Weyl anomalies live on a codimension-1 boundary, $\partial {\cal M}$. The entanglement entropy originates from infinite correlations on both sides of a codimension-2 surface, $\Sigma$. Motivated to have a further understanding of the boundary effects, we introduce a notion of reduction entropy, which, guided by thermodynamics, is a combination of the boundary effective action and the boundary stress tensor defined by allowing the metric on $\partial {\cal M}$ to fluctuate. We discuss how a reduction might be performed so that the reduction entropy reproduces the entanglement structure. Read More