3,386 research outputs found
Random matrix theory of unquenched two-colour QCD with nonzero chemical potential
We solve a random two-matrix model with two real asymmetric matrices whose
primary purpose is to describe certain aspects of quantum chromodynamics with
two colours and dynamical fermions at nonzero quark chemical potential mu. In
this symmetry class the determinant of the Dirac operator is real but not
necessarily positive. Despite this sign problem the unquenched matrix model
remains completely solvable and provides detailed predictions for the Dirac
operator spectrum in two different physical scenarios/limits: (i) the
epsilon-regime of chiral perturbation theory at small mu, where mu^2 multiplied
by the volume remains fixed in the infinite-volume limit and (ii) the
high-density regime where a BCS gap is formed and mu is unscaled. We give
explicit examples for the complex, real, and imaginary eigenvalue densities
including Nf=2 non-degenerate flavours. Whilst the limit of two degenerate
masses has no sign problem and can be tested with standard lattice techniques,
we analyse the severity of the sign problem for non-degenerate masses as a
function of the mass split and of mu.
On the mathematical side our new results include an analytical formula for
the spectral density of real Wishart eigenvalues in the limit (i) of weak
non-Hermiticity, thus completing the previous solution of the corresponding
quenched model of two real asymmetric Wishart matrices.Comment: 45 pages, 31 figures; references added, as published in JHE
End-to-end Recovery of Human Shape and Pose
We describe Human Mesh Recovery (HMR), an end-to-end framework for
reconstructing a full 3D mesh of a human body from a single RGB image. In
contrast to most current methods that compute 2D or 3D joint locations, we
produce a richer and more useful mesh representation that is parameterized by
shape and 3D joint angles. The main objective is to minimize the reprojection
loss of keypoints, which allow our model to be trained using images in-the-wild
that only have ground truth 2D annotations. However, the reprojection loss
alone leaves the model highly under constrained. In this work we address this
problem by introducing an adversary trained to tell whether a human body
parameter is real or not using a large database of 3D human meshes. We show
that HMR can be trained with and without using any paired 2D-to-3D supervision.
We do not rely on intermediate 2D keypoint detections and infer 3D pose and
shape parameters directly from image pixels. Our model runs in real-time given
a bounding box containing the person. We demonstrate our approach on various
images in-the-wild and out-perform previous optimization based methods that
output 3D meshes and show competitive results on tasks such as 3D joint
location estimation and part segmentation.Comment: CVPR 2018, Project page with code: https://akanazawa.github.io/hmr
Polarization in Hadronic \Lambda Hyperon Production and Chiral-Odd Twist-3 Distribution
Polarization of the \Lambda hyperon produced with a large transverse momentum
in the unpolarized nucleon-nucleon collision is analyzed in the framework of
QCD factorization. We focus on the mechanism in which the soft-gluon component
of the chiral-odd spin-independent twist-3 quark distribution E_F(x,x) becomes
a source of the polarized quark fragmenting into the polarized \Lambda. Our
simple model estimate for this contribution indicates that it gives rise to a
significant \Lambda polarization at large x_F. This is in parallel with the
observation that the soft gluon pole mechanism gives rise to a large single
transverse spin asymmetry in the pion production at x_F\to 1.Comment: 10 pages in LaTex + 5 figures in PS files. Phys. Rev. D in press.
Title changed and some discussions adde
Local dynamics of topological magnetic defects in the itinerant helimagnet FeGe
Chiral magnetic interactions induce complex spin textures including helical
and conical spin waves, as well as particle-like objects such as magnetic
skyrmions and merons. These spin textures are the basis for innovative device
paradigms and give rise to exotic topological phenomena, thus being of interest
for both applied and fundamental sciences. Present key questions address the
dynamics of the spin system and emergent topological defects. Here we analyze
the micromagnetic dynamics in the helimagnetic phase of FeGe. By combining
magnetic force microscopy, single-spin magnetometry, and
Landau-Lifschitz-Gilbert simulations we show that the nanoscale dynamics are
governed by the depinning and subsequent motion of magnetic edge dislocations.
The motion of these topologically stable objects triggers perturbations that
can propagate over mesoscopic length scales. The observation of stochastic
instabilities in the micromagnetic structure provides new insight to the
spatio-temporal dynamics of itinerant helimagnets and topological defects, and
discloses novel challenges regarding their technological usage
Do we understand the single-spin asymmetry for inclusive production in pp collisions?
The cross section data for inclusive production in collisions is
considered in a rather broad kinematic region in energy , Feynman
variable and transverse momentum . The analysis of these data is
done in the perturbative QCD framework at the next-to-leading order. We find
that they cannot be correctly described in the entire kinematic domain and this
leads us to conclude that the single-spin asymmetry, for this process,
observed several years ago at FNAL by the experiment E704 and the recent result
obtained at BNL-RHIC by STAR, are two different phenomena. This suggests that
STAR data probes a genuine leading-twist QCD single-spin asymmetry for the
first time and finds a large effect.Comment: text modified, version to be published in Eur. Phys. J. C, 6 pages, 5
figure
Topological phase separation in 2D quantum lattice Bose-Hubbard system away from half-filling
We suppose that the doping of the 2D hard-core boson system away from
half-filling may result in the formation of multi-center topological
inhomogeneity (defect) such as charge order (CO) bubble domain(s) with Bose
superfluid (BS) and extra bosons both localized in domain wall(s), or a {\it
topological} CO+BS {\it phase separation}, rather than an uniform mixed CO+BS
supersolid phase. Starting from the classical model we predict the properties
of the respective quantum system. The long-wavelength behavior of the system is
believed to remind that of granular superconductors, CDW materials, Wigner
crystals, and multi-skyrmion system akin in a quantum Hall ferromagnetic state
of a 2D electron gas. To elucidate the role played by quantum effects and that
of the lattice discreteness we have addressed the simplest nanoscopic
counterpart of the bubble domain in a checkerboard CO phase of 2D hc-BH square
lattice. It is shown that the relative magnitude and symmetry of
multi-component order parameter are mainly determined by the sign of the
and transfer integrals. In general, the topologically inhomogeneous phase
of the hc-BH system away from the half-filling can exhibit the signatures both
of , and symmetry of the off-diagonal order.Comment: 12 pages, 6 figure
Transverse Double-Spin Asymmetries for Muon Pair Production in pp-Collisions
We calculate the rapidity dependence of the transverse double-spin asymmetry
for the Drell-Yan process to next-to-leading order in the strong coupling.
Input transversity distributions are obtained by saturating the Soffer
inequality at a low hadronic mass scale. Results for the polarized BNL-RHIC
proton-proton collider and the proposed HERA-N fixed-target experiment are
presented, and the influence of the limited muon acceptance of the detectors on
measurements of the asymmetry is studied in detail.Comment: 7 pages including 5 figures; significantly shortened, to be published
in Phys. Rev.
- …