18,171 research outputs found
Competing Nematic, Anti-ferromagnetic and Spin-flux orders in the Ground State of Bilayer Graphene
We analyze the phase diagram of the Bilayer graphene (BLG) at zero
temperature and doping. Assuming that at the high energies the electronic
system of BLG can be described within a weak coupling theory (consistent with
the experimental evidence), we systematically study the evolution of the
couplings with going from high to low energies. The divergences of the
couplings at some energies indicates the tendency towards certain symmetry
breakings. Carrying out this program, we found that the phase diagram is
determined by microscopic couplings defined on the short distances (initial
conditions). We explored all plausible space of these initial conditions and
found that the three states have the largest phase volume of the initial
couplings: nematic, antiferromagnetic and spin flux (a.k.a quantum spin Hall).
In addition, ferroelectric and two superconducting phases and appear only near
the very limits of the applicability of the weak coupling approach.
The paper also contains the derivation and analysis of the renormalization
group equations and the group theory classification of all the possible phases
which might arise from the symmetry breakings of the lattice, spin rotation,
and gauge symmetries of graphene.Comment: 19 pages, 16 figure
Spatially-averaged oscillatory flow over a rough bed
Peer reviewedPublisher PD
Identifying Unclear Questions in Community Question Answering Websites
Thousands of complex natural language questions are submitted to community
question answering websites on a daily basis, rendering them as one of the most
important information sources these days. However, oftentimes submitted
questions are unclear and cannot be answered without further clarification
questions by expert community members. This study is the first to investigate
the complex task of classifying a question as clear or unclear, i.e., if it
requires further clarification. We construct a novel dataset and propose a
classification approach that is based on the notion of similar questions. This
approach is compared to state-of-the-art text classification baselines. Our
main finding is that the similar questions approach is a viable alternative
that can be used as a stepping stone towards the development of supportive user
interfaces for question formulation.Comment: Proceedings of the 41th European Conference on Information Retrieval
(ECIR '19), 201
Inversion of polarimetric data from eclipsing binaries
We describe a method for determining the limb polarization and limb darkening
of stars in eclipsing binary systems, by inverting photometric and polarimetric
light curves.
Because of the ill-conditioning of the problem, we use the Backus-Gilbert
method to control the resolution and stability of the recovered solution, and
to make quantitative estimates of the maximum accuracy possible. Using this
method we confirm that the limb polarization can indeed be recovered, and
demonstrate this with simulated data, thus determining the level of
observational accuracy required to achieve a given accuracy of reconstruction.
This allows us to set out an optimal observational strategy, and to critcally
assess the claimed detection of limb polarization in the Algol system.
The use of polarization in stars has been proposed as a diagnostic tool in
microlensing surveys by Simmons et al. (1995), and we discuss the extension of
this work to the case of microlensing of extended sources.Comment: 10pp, 5 figures. To appear in A&
Double-averaged velocity and stress distributions for hydraulically-smooth and transitionally-rough turbulent flows
Peer reviewedPreprin
Scaling tests with dynamical overlap and rooted staggered fermions
We present a scaling analysis in the 1-flavor Schwinger model with the full
overlap and the rooted staggered determinant. In the latter case the chiral and
continuum limit of the scalar condensate do not commute, while for overlap
fermions they do. For the topological susceptibility a universal continuum
limit is suggested, as is for the partition function and the Leutwyler-Smilga
sum rule. In the heavy-quark force no difference is visible even at finite
coupling. Finally, a direct comparison between the complete overlap and the
rooted staggered determinant yields evidence that their ratio is constant up to
effects.Comment: 28 pages, 20 figures containg 37 graphs. v2: 6 new references, 2 new
footnotes (to match published version
Double-averaged velocity profiles over fixed dune shapes
Peer reviewedPublisher PD
On First-Order Generalized Maxwell Equations
The generalized Maxwell equations including an additional scalar field are
considered in the first-order formalism. The gauge invariance of the Lagrangian
and equations is broken resulting the appearance of a scalar field. We find the
canonical and symmetrical Belinfante energy-momentum tensors. It is shown that
the traces of the energy-momentum tensors are not equal to zero and the
dilatation symmetry is broken in the theory considered. The matrix Hamiltonian
form of equations is obtained after the exclusion of the nondynamical
components. The canonical quantization is performed and the propagator of the
fields is found in the first-order formalism.Comment: 14 pages, corrections in Eq.(38),(39),(59
Spontaneous interlayer coherence in bilayer Kondo systems
Bilayer Kondo systems present interesting models to illustrate the
competition between the Kondo effect and intermoment exchange. Such bilayers
can exhibit two sharply distinct Fermi liquid phases which are distinguished by
whether or not the local moments participate in the Fermi sea. We study these
phases and the evolution from one to the other upon changing Kondo coupling. We
argue that an ordered state with spontaneous interlayer phase coherence
generically intervenes between the two Fermi liquids. Such a condensate phase
breaks a U(1) symmetry and is bounded by a finite-temperature
Kosterlitz-Thouless transition. Based on general arguments and mean-field
calculations we investigate the phase diagram and associated quantum phase
transitions.Comment: 4 pages, 3 figs, (v2) misprints in eqs corrected, final version as
publishe
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