779 research outputs found
Three Dimensional N=2 Supersymmetry on the Lattice
We show how 3-dimensional, N=2 supersymmetric theories, including super QCD
with matter fields, can be put on the lattice with existing techniques, in a
way which will recover supersymmetry in the small lattice spacing limit.
Residual supersymmetry breaking effects are suppressed in the small lattice
spacing limit by at least one power of the lattice spacing a.Comment: 21 pages, 2 figures, typo corrected, reference adde
3D N = 1 SYM Chern-Simons theory on the Lattice
We present a method to implement 3-dimensional N = 1 SUSY Yang-Mills theory
(a theory with two real supercharges containing gauge fields and an adjoint
Majorana fermion) on the lattice, including a way to implement the Chern-Simons
term present in this theory. At nonzero Chern-Simons number our implementation
suffers from a sign problem which will make the numerical effort grow
exponentially with volume. We also show that the theory with vanishing
Chern-Simons number is anomalous; its partition function identically vanishes.Comment: v2, minor changes: expanded discussion in section III c, typos
corrected, 17 pages, 9 figure
Surface Normal Deconvolution: Photometric Stereo for Optically Thick Translucent Objects
Computer Vision â ECCV 2014
13th European Conference, Zurich, Switzerland, September 6-12, 2014,This paper presents a photometric stereo method that works for optically thick translucent objects exhibiting subsurface scattering. Our method is built upon the previous studies showing that subsurface scattering is approximated as convolution with a blurring kernel. We extend this observation and show that the original surface normal convolved with the scattering kernel corresponds to the blurred surface normal that can be obtained by a conventional photometric stereo technique. Based on this observation, we cast the photometric stereo problem for optically thick translucent objects as a deconvolution problem, and develop a method to recover accurate surface normals. Experimental results of both synthetic and real-world scenes show the effectiveness of the proposed method
A lower limit on the dark particle mass from dSphs
We use dwarf spheroidal galaxies as a tool to attempt to put precise lower
limits on the mass of the dark matter particle, assuming it is a sterile
neutrino. We begin by making cored dark halo fits to the line of sight velocity
dispersions as a function of projected radius (taken from Walker et al. 2007)
for six of the Milky Way's dwarf spheroidal galaxies. We test Osipkov-Merritt
velocity anisotropy profiles, but find that no benefit is gained over constant
velocity anisotropy. In contrast to previous attempts, we do not assume any
relation between the stellar velocity dispersions and the dark matter ones, but
instead we solve directly for the sterile neutrino velocity dispersion at all
radii by using the equation of state for a partially degenerate neutrino gas
(which ensures hydrostatic equilibrium of the sterile neutrino halo). This
yields a 1:1 relation between the sterile neutrino density and velocity
dispersion, and therefore gives us an accurate estimate of the Tremaine-Gunn
limit at all radii. By varying the sterile neutrino particle mass, we locate
the minimum mass for all six dwarf spheroidals such that the Tremaine-Gunn
limit is not exceeded at any radius (in particular at the centre). We find
sizeable differences between the ranges of feasible sterile neutrino particle
mass for each dwarf, but interestingly there exists a small range 270-280eV
which is consistent with all dSphs at the 1- level.Comment: 13 pages, 2 figures, 1 tabl
Critical points in edge tunneling between generic FQH states
A general description of weak and strong tunneling fixed points is developed
in the chiral-Luttinger-liquid model of quantum Hall edge states. Tunneling
fixed points are a subset of `termination' fixed points, which describe
boundary conditions on a multicomponent edge. The requirement of unitary time
evolution at the boundary gives a nontrivial consistency condition for possible
low-energy boundary conditions. The effect of interactions and random hopping
on fixed points is studied through a perturbative RG approach which generalizes
the Giamarchi-Schulz RG for disordered Luttinger liquids to broken left-right
symmetry and multiple modes. The allowed termination points of a multicomponent
edge are classified by a B-matrix with rational matrix elements. We apply our
approach to a number of examples, such as tunneling between a quantum Hall edge
and a superconductor and tunneling between two quantum Hall edges in the
presence of interactions. Interactions are shown to induce a continuous
renormalization of effective tunneling charge for the integrable case of
tunneling between two Laughlin states. The correlation functions of
electronlike operators across a junction are found from the B matrix using a
simple image-charge description, along with the induced lattice of boundary
operators. Many of the results obtained are also relevant to ordinary Luttinger
liquids.Comment: 23 pages, 6 figures. Xiao-Gang Wen: http://dao.mit.edu/~we
Pumping current of a Luttinger liquid with finite length
We study transport properties in a Tomonaga-Luttinger liquid in the presence
of two time-dependent point like weak impurities, taking into account
finite-length effects. By employing analytical methods and performing a
perturbation theory, we compute the backscattering pumping current (I_bs) in
different regimes which can be established in relation to the oscillatory
frequency of the impurities and to the frequency related to the length and the
renormalized velocity (by the electron-electron interactions) of the charge
density modes. We investigate the role played by the spatial position of the
impurity potentials. We also show how the previous infinite length results for
I_bs are modified by the finite size of the system.Comment: 9 pages, 7 figure
Dark Matter Direct Detection with Non-Maxwellian Velocity Structure
The velocity distribution function of dark matter particles is expected to
show significant departures from a Maxwell-Boltzmann distribution. This can
have profound effects on the predicted dark matter - nucleon scattering rates
in direct detection experiments, especially for dark matter models in which the
scattering is sensitive to the high velocity tail of the distribution, such as
inelastic dark matter (iDM) or light (few GeV) dark matter (LDM), and for
experiments that require high energy recoil events, such as many directionally
sensitive experiments. Here we determine the velocity distribution functions
from two of the highest resolution numerical simulations of Galactic dark
matter structure (Via Lactea II and GHALO), and study the effects for these
scenarios. For directional detection, we find that the observed departures from
Maxwell-Boltzmann increase the contrast of the signal and change the typical
direction of incoming DM particles. For iDM, the expected signals at direct
detection experiments are changed dramatically: the annual modulation can be
enhanced by more than a factor two, and the relative rates of DAMA compared to
CDMS can change by an order of magnitude, while those compared to CRESST can
change by a factor of two. The spectrum of the signal can also change
dramatically, with many features arising due to substructure. For LDM the
spectral effects are smaller, but changes do arise that improve the
compatibility with existing experiments. We find that the phase of the
modulation can depend upon energy, which would help discriminate against
background should it be found.Comment: 34 pages, 16 figures, submitted to JCAP. Tables of g(v_min), the
integral of f(v)/v from v_min to infinity, derived from our simulations, are
available for download at http://astro.berkeley.edu/~mqk/dmdd
Lowest-Landau-level theory of the quantum Hall effect: the Fermi-liquid-like state
A theory for a Fermi-liquid-like state in a system of charged bosons at
filling factor one is developed, working in the lowest Landau level. The
approach is based on a representation of the problem as fermions with a system
of constraints, introduced by Pasquier and Haldane (unpublished). This makes
the system a gauge theory with gauge algebra W_infty. The low-energy theory is
analyzed based on Hartree-Fock and a corresponding conserving approximation.
This is shown to be equivalent to introducing a gauge field, which at long
wavelengths gives an infinite-coupling U(1) gauge theory, without a
Chern-Simons term. The system is compressible, and the Fermi-liquid properties
are similar, but not identical, to those in the previous U(1) Chern-Simons
fermion theory. The fermions in the theory are effectively neutral but carry a
dipole moment. The density-density response, longitudinal conductivity, and the
current density are considered explicitly.Comment: 32 pages, revtex multicol
Counting BPS states on the Enriques Calabi-Yau
We study topological string amplitudes for the FHSV model using various
techniques. This model has a type II realization involving a Calabi-Yau
threefold with Enriques fibres, which we call the Enriques Calabi-Yau. By
applying heterotic/type IIA duality, we compute the topological amplitudes in
the fibre to all genera. It turns out that there are two different ways to do
the computation that lead to topological couplings with different BPS content.
One of them leads to the standard D0-D2 counting amplitudes, and from the other
one we obtain information about bound states of D0-D4-D2 branes on the Enriques
fibre. We also study the model using mirror symmetry and the holomorphic
anomaly equations. We verify in this way the heterotic results for the D0-D2
generating functional for low genera and find closed expressions for the
topological amplitudes on the total space in terms of modular forms, and up to
genus four. This model turns out to be much simpler than the generic B-model
and might be exactly solvable.Comment: 62 pages, v3: some results at genus 3 corrected, more typos correcte
Lectures on conformal field theory and Kac-Moody algebras
This is an introduction to the basic ideas and to a few further selected
topics in conformal quantum field theory and in the theory of Kac-Moody
algebras.Comment: 59 pages, LaTeX2e, extended version of lectures given at the Graduate
Course on Conformal Field Theory and Integrable Models (Budapest, August
1996), to appear in Springer Lecture Notes in Physic
- âŠ