3,960 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
Thermal phase transitions in rotating QCD with dynamical quarks
Relativistic rotation causes a change of QCD critical temperatures. Various
phenomenological and effective models predict a decrease of the critical
temperatures in rotating QCD. Nevertheless, lattice simulations showed that the
critical temperature in gluodynamics increases due to rotation. We extend the
lattice study to the theory with dynamical fermions. We present the first
lattice results for rotating QCD with dynamical clover-improved Wilson
quarks. We also study separately the effect of rotation on gluonic and
fermionic degrees of freedom. It is shown that separate rotations of gluons and
fermions have opposite effects on the critical temperatures. In aggregate, the
pseudo-critical temperatures in QCD increase with angular velocity. Dependence
of the results on the pion mass is also discussed.Comment: 10 pages, 5 figures, Proceedings of the 39th International Symposium
on Lattice Field Theory, 8th-13th August, 2022, Bonn, German
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
Progress in crystal extraction and collimation
Recent IHEP Protvino experiments show efficiencies of crystal-assisted slow
extraction and collimation of 85.3+-2.8%, at the intensities of the channeled
beam on the order of 10^12 proton per spill of 2 s duration. The obtained
experimental data well follows the theory predictions. We compare the
measurements against theory and outline the theoretical potential for further
improvement in the efficiency of the technique. This success is important for
the efficient use of IHEP accelerator and for implementation of
crystal-assisted collimation at RHIC and slow extraction from AGS onto E952,
now in preparation. Future applications, spanning in the energy from order of 1
GeV (scraping in SNS, slow extraction from COSY and medical accelerators) to
order of 1 TeV and beyond (scraping in Tevatron, LHC, VLHC), can benefit from
these studies.Comment: 7pp. Presented at HEACC 2001 (Tsukuba, March 25-30
Crystal experiments on efficient beam extraction
Silicon crystal was channeling and extracting 70-GeV protons from the U-70
accelerator with efficiency of 85.3+-2.8% as measured for a beam of 10^12
protons directed towards crystals of 2 mm length in spills of 1-2 s duration.
The experimental data follow very well the prediction of Monte Carlo
simulations. This success is important to devise a more efficient use of the
U-70 accelerator in Protvino and provides a crucial support for implementation
of crystal-assisted collimation of gold ion beam in RHIC and slow extraction
from AGS onto E952, now in preparation at Brookhaven Nat'l Lab. Future
applications, spanning in the energy from sub-GeV (medical) to order of 1 GeV
(scraping in the SNS, extraction from COSY) to order of 1 TeV and beyond
(scraping in the Tevatron, LHC, VLHC), can benefit from these studies.Comment: 12pp. Presented at 19-th Intern. Conference on Atomic Collisions in
Solids (ICACS-19: Paris, July 29 - August 3, 2001
Highly efficient crystal deflector for channeling extraction of a proton beam from accelerators
The design and performance of a novel crystal deflector for proton beams are
reported. A silicon crystal was used to channel and extract 70 GeV protons from
the U-70 accelerator in Protvino with an efficiency of 85%, as measured for a
beam of ~1e12 protons directed towards crystals of ~2 mm length in spills of ~2
s duration. Experimental data agree with the theoretically predicted Monte
Carlo results for channeling. The technique allows one to manufacture a very
short deflector along the beam direction (2 mm). Consequently, multiple
encounters of circulating particles with the crystal are possible with little
probability of multiple scattering and nuclear interactions per encounter.
Thus, drastic increase in efficiency for particle extraction out of the
accelerator was attained. We show the characteristics of the crystal- deflector
and the technology behind it. Such an achievement is important in devising a
more efficient use of the U-70 accelerator and provides crucial support for
implementing crystal-assisted slow extraction and collimation in other
machines, such as the Tevatron, RHIC, the AGS, the SNS, COSY, and the LHC.Comment: Presented at PAC 2003 (Portland, May 12-16
- …