48 research outputs found
Lattice Quantum Monte Carlo Study of Chiral Magnetic Effect in Dirac Semimetals
In this paper Chiral Magnetic Effect (CME) in Dirac semimetals is studied by
means of lattice Monte Carlo simulation. We measure conductivity of Dirac
semimetals as a function of external magnetic field in parallel
and perpendicular to the external field
directions. The simulations are carried out in three regimes: semimetal phase,
onset of the insulator phase and deep in the insulator phase. In the semimetal
phase grows whereas drops with magnetic
field. Similar behaviour was observed in the onset of the insulator phase but
conductivity is smaller and its dependence on magnetic field is weaker. Finally
in the insulator phase conductivities are close to
zero and do not depend on magnetic field. In other words, we observe
manifestation of the CME current in the semimetal phase, weaker manifestation
of the CME in the onset of the insulator phase. We do not observe signatures of
CME in the insulator phase. We believe that the suppression of the CME current
in the insulator phase is connected to chiral symmetry breaking and generation
of dynamical fermion mass which take place in this phase.Comment: 6 pages, 4 figure
Estimating Herbaceous Biomass of Grassland Vegetation Using the Reference Unit Method
Aboveground net primary production provides valuable information on wildlife habitat, fire fuel loads, and forage availability. Aboveground net primary production in herbaceous plant communities is typically measured by clipping aboveground biomass. However, the high costs associated with physically harvesting plant biomass may prevent collecting sufficient data to account for natural spatial and temporal variability of vegetation at a landscape scale. Various double-sampling techniques have been developed to increase sample size while reducing cost. We applied a biomass estimation technique previously developed for estimating shrub biomass using representative samples or “reference units” to estimate herbaceous grassland biomass. Our reference units consisted of major grass species and functional groups that involved combining species with similar origin (native vs. introduced) and life-form characteristics. This study was conducted in 2010 on and around prairie dog colonies on the Buffalo Gap National Grassland in southwestern South Dakota, which provided a range of plant communities for testing the method. Results of the study demonstrate that reference units can provide accurate and precise estimates of herbaceous plant biomass on grasslands, including multi-species functional groups. Twenty-five of 26 double sampling calibrations were validated by time with no changes in observer estimation trends over the sampling season. Use of the reference unit method was consistent among observers and is a viable option for estimating and monitoring herbaceous grassland aboveground biomass
Closed Geodesics on Godel-type Backgrounds
We consider radial oscillations of supertube probes in the Godel-type
background which is U-dual to the compactified pp-wave obtained from the
Penrose limit of the NS five-brane near horizon geometry. The supertube probe
computation can be carried over directly to a string probe calculation on the
U-dual background. The classical equations of motion are solved explicitly. In
general, the probe is not restricted to travel unidirectionally through any
global time coordinate. In particular, we find geodesics that close.Comment: latex, 15 pages, 1 figure. v3: reference added, clarifications added
and some discussions expande
Childhood maltreatment and psychotic experiences: exploring the specificity of early maladaptive schemas.
Objective: One potential mechanism that has received limited attention within psychosis research, is early maladaptive schemas (EMS). Our aim was to examine if EMS acts as a potential mediating pathway between early trauma and psychotic symptomology. Methods: A quantitative survey was hosted online. N=302 participants took part. The analysis employed a multiple mediation framework. Results: Analysis demonstrated significant specificity effects. Different forms of child maltreatment were significantly associated with psychosis experiences through specific dimensions of maladaptive schemas. Conclusions: Results indicated specificity effects in that specific types of maltreatment are associated with specific maladaptive schemas. From a practitioner’s perspective, these findings offer credence to cognitive theories of psychopathology, and support the validity of EMS identification and modification among clients with psychotic symptomology; both as a fundamental component of traditional CBT and within specialised schema focused therapy
Study of lattice QCD at finite baryon density using the canonical approach
At finite baryon density lattice QCD first-principle calculations can not be
performed due to the sign problem. In order to circumvent this problem, we use
the canonical approach, which provides reliable analytical continuation from
the imaginary chemical potential region to the real chemical potential region.
We briefly present the canonical partition function method, describe our
formulation, and show the results, obtained for two temperatures: and in lattice QCD with two flavors of improved Wilson
fermions.Comment: 8 pages, 4 figures, Contribution to XIIth Quark Confinement and the
Hadron Spectru
Phase diagram and Chiral Magnetic Effect in Dirac Semimetals from Lattice Simulation
Dirac Semimetals Na 3 Bi and Cd 3 As 2 are recently discovered materials, which low energy electronic spectrum is described by two flavours of massless 3+1D fermions. In order to study electronic properties of these materials we formulated lattice field theory with rooted staggered fermions on anisotropic lattice. It is shown that in the limit of zero temporal lattice spacing this theory reproduces effective theory of Dirac semimetals. Using the lattice field theory we study the phase diagram of Dirac semimetals in the plane effective coupling constant - Fermi velocity anisotropy. We also measure conductivity of Dirac Semimetals within lattice field theory in external magnetic field. Our results confirm the existence of Chiral Magnetic Effect in Dirac Semimetals. © The Authors, published by EDP Sciences, 2018.Acknowdedgements. The work supported by the RSF grant under contract 16-12-10059. Numerical simulations were carried out on GPU cluster of NRC Kurchatov Institute and at MSU supercomputer "Lomonosov".Consejo Superior de Investigaciones Cient�ficas;et al.;Institute of Cosmos Sciences (ICCUB);Universidad Aut�noma de Madrid (UAM);Universidad de Granada;Universidad Valenci
Lattice QCD at finite baryon density using analytic continuation
We simulate lattice QCD with two flavors of Wilson fermions at imaginary
baryon chemical potential. Results for the baryon number density computed in
the confining and deconfining phases at imaginary baryon chemical potential are
used to determine the baryon number density and higher cumulants at the real
chemical potential via analytical continuation.Comment: 8 pages, 8 figures, Contribution to ICNFP2017, to be published in EPJ
Web of Conference
Chronology protection in stationary three-dimensional spacetimes
We study chronology protection in stationary, rotationally symmetric
spacetimes in 2+1 dimensional gravity, focusing especially on the case of
negative cosmological constant. We show that in such spacetimes closed timelike
curves must either exist all the way to the boundary or, alternatively, the
matter stress tensor must violate the null energy condition in the bulk. We
also show that the matter in the closed timelike curve region gives a negative
contribution to the conformal weight from the point of view of the dual
conformal field theory. We illustrate these properties in a class of examples
involving rotating dust in anti-de Sitter space, and comment on the use of the
AdS/CFT correspondence to study chronology protection.Comment: 20 pages. V2: minor corrections, Outlook expanded, references added,
published versio