1,120 research outputs found
Spontaneous chiral symmetry breaking in the linked cluster expansion
We investigate dynamical chiral symmetry breaking in the Coulomb gauge
Hamiltonian QCD. Within the framework of the linked cluster expansion we extend
the BCS ansatz for the vacuum and include correlation beyond the
quark-antiquark paring. In particular we study the effects of the three-body
correlations involving quark-antiquark and transverse gluons. The high momentum
behavior of the resulting gap equation is discussed and numerical computation
of the chiral symmetry breaking is presented.Comment: 13 pages, 9 figure
Heat-kernel expansion and counterterms of the Faddeev-Popov determinant in Coulomb and Landau gauge
The Faddeev-Popov determinant of Landau gauge in d dimensions and Coulomb
gauge in d+1 dimensions is calculated in the heat-kernel expansion up to
next-to-leading order. The UV-divergent parts in d=3,4 are isolated and the
counterterms required for a non-perturbative treatment of the Faddeev-Popov
determinant are determined.Comment: 7 page
A Quantum Hall Fluid of Vortices
In this note we demonstrate that vortices in a non-relativistic Chern-Simons
theory form a quantum Hall fluid. We show that the vortex dynamics is
controlled by the matrix mechanics previously proposed by Polychronakos as a
description of the quantum Hall droplet. As the number of vortices becomes
large, they fill the plane and a hydrodynamic treatment becomes possible,
resulting in the non-commutative theory of Susskind. Key to the story is the
recent D-brane realisation of vortices and their moduli spaces.Comment: 10 pages. v2(3): (More) References adde
Truncating first-order Dyson-Schwinger equations in Coulomb-Gauge Yang-Mills theory
The non-perturbative domain of QCD contains confinement, chiral symmetry
breaking, and the bound state spectrum. For the calculation of the latter, the
Coulomb gauge is particularly well-suited. Access to these non-perturbative
properties should be possible by means of the Green's functions. However,
Coulomb gauge is also very involved, and thus hard to tackle. We introduce a
novel BRST-type operator r, and show that the left-hand side of Gauss' law is
r-exact.
We investigate a possible truncation scheme of the Dyson-Schwinger equations
in first-order formalism for the propagators based on an instantaneous
approximation. We demonstrate that this is insufficient to obtain solutions
with the expected property of a linear-rising Coulomb potential. We also show
systematically that a class of possible vertex dressings does not change this
result.Comment: 22 pages, 4 figures, 1 tabl
Instability of vortex array and transitions to turbulent states in rotating helium II
We consider superfluid helium inside a container which rotates at constant
angular velocity and investigate numerically the stability of the array of
quantized vortices in the presence of an imposed axial counterflow. This
problem was studied experimentally by Swanson {\it et al.}, who reported
evidence of instabilities at increasing axial flow but were not able to explain
their nature. We find that Kelvin waves on individual vortices become unstable
and grow in amplitude, until the amplitude of the waves becomes large enough
that vortex reconnections take place and the vortex array is destabilized. The
eventual nonlinear saturation of the instability consists of a turbulent tangle
of quantized vortices which is strongly polarized. The computed results compare
well with the experiments. Finally we suggest a theoretical explanation for the
second instability which was observed at higher values of the axial flow
Topological Superfluid in one-dimensional Ultracold Atomic System with Spin-Orbit Coupling
We propose a one-dimensional Hamiltonian which supports Majorana
fermions when -wave superfluid appears in the ultracold atomic
system and obtain the phase-separation diagrams both for the
time-reversal-invariant case and time-reversal-symmetry-breaking case. From the
phase-separation diagrams, we find that the single Majorana fermions exist in
the topological superfluid region, and we can reach this region by tuning the
chemical potential and spin-orbit coupling . Importantly, the
spin-orbit coupling has realized in ultracold atoms by the recent experimental
achievement of synthetic gauge field, therefore, our one-dimensional ultra-cold
atomic system described by is a promising platform to find the
mysterious Majorana fermions.Comment: 5 papers, 2 figure
The Infrared Behaviour of the Pure Yang-Mills Green Functions
We review the infrared properties of the pure Yang-Mills correlators and
discuss recent results concerning the two classes of low-momentum solutions for
them reported in literature; i.e. decoupling and scaling solutions. We will
mainly focuss on the Landau gauge and pay special attention to the results
inferred from the analysis of the Dyson-Schwinger equations of the theory and
from "{\it quenched}" lattice QCD. The results obtained from properly
interplaying both approaches are strongly emphasized.Comment: Final version to be published in FBS (54 pgs., 11 figs., 4 tabs
From Gapped Excitons to Gapless Triplons in One Dimension
Often, exotic phases appear in the phase diagrams between conventional
phases. Their elementary excitations are of particular interest. Here, we
consider the example of the ionic Hubbard model in one dimension. This model is
a band insulator (BI) for weak interaction and a Mott insulator (MI) for strong
interaction. Inbetween, a spontaneously dimerized insulator (SDI) occurs which
is governed by energetically low-lying charge and spin degrees of freedom.
Applying a systematically controlled version of the continuous unitary
transformations (CUTs) we are able to determine the dispersions of the
elementary charge and spin excitations and of their most relevant bound states
on equal footing. The key idea is to start from an externally dimerized system
using the relative weak interdimer coupling as small expansion parameter which
finally is set to unity to recover the original model.Comment: 18 pages, 10 figure
Weak lensing, dark matter and dark energy
Weak gravitational lensing is rapidly becoming one of the principal probes of
dark matter and dark energy in the universe. In this brief review we outline
how weak lensing helps determine the structure of dark matter halos, measure
the expansion rate of the universe, and distinguish between modified gravity
and dark energy explanations for the acceleration of the universe. We also
discuss requirements on the control of systematic errors so that the
systematics do not appreciably degrade the power of weak lensing as a
cosmological probe.Comment: Invited review article for the GRG special issue on gravitational
lensing (P. Jetzer, Y. Mellier and V. Perlick Eds.). V3: subsection on
three-point function and some references added. Matches the published versio
Critical exponents and equation of state of the three-dimensional Heisenberg universality class
We improve the theoretical estimates of the critical exponents for the
three-dimensional Heisenberg universality class. We find gamma=1.3960(9),
nu=0.7112(5), eta=0.0375(5), alpha=-0.1336(15), beta=0.3689(3), and
delta=4.783(3). We consider an improved lattice phi^4 Hamiltonian with
suppressed leading scaling corrections. Our results are obtained by combining
Monte Carlo simulations based on finite-size scaling methods and
high-temperature expansions. The critical exponents are computed from
high-temperature expansions specialized to the phi^4 improved model. By the
same technique we determine the coefficients of the small-magnetization
expansion of the equation of state. This expansion is extended analytically by
means of approximate parametric representations, obtaining the equation of
state in the whole critical region. We also determine a number of universal
amplitude ratios.Comment: 40 pages, final version. In publication in Phys. Rev.
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