558 research outputs found
Recommended from our members
Acute silencing of hippocampal CA3 reveals a dominant role in place field responses.
Neurons in hippocampal output area CA1 are thought to exhibit redundancy across cortical and hippocampal inputs. Here we show instead that acute silencing of CA3 terminals drastically reduces place field responses for many CA1 neurons, while a smaller number are unaffected or have increased responses. These results imply that CA3 is the predominant driver of CA1 place cells under normal conditions, while also revealing heterogeneity in input dominance across cells
Constraints on the Universe as a Numerical Simulation
Observable consequences of the hypothesis that the observed universe is a numerical simulation performed on a cubic space-time lattice or grid are explored. The simulation scenario is first motivated by extrapolating current trends in computational resource requirements for lattice QCD into the future. Using the historical development of lattice gauge theory technology as a guide, we assume that our universe is an early numerical simulation with unimproved Wilson fermion discretization and investigate potentially-observable consequences. Among the observables that are considered are the muon g-2 and the current differences between determinations of alpha, but the most stringent bound on the inverse lattice spacing of the universe, b−1 \u3e ~ 10^11 GeV, is derived from the high-energy cut off of the cosmic ray spectrum. The numerical simulation scenario could reveal itself in the distributions of the highest energy cosmic rays exhibiting a degree of rotational symmetry breaking that reflects the structure of the underlying lattice
Two-Nucleon Systems in a Finite Volume: (II) 3S1-3D1 Coupled Channels and the Deuteron
The energy spectra of two nucleons in a cubic volume provide access to the
two phase shifts and one mixing angle that define the S-matrix in the 3S1-3D1
coupled channels containing the deuteron. With the aid of recently derived
energy quantization conditions for such systems, and the known scattering
parameters, these spectra are predicted for a range of volumes. It is found
that extractions of the infinite-volume deuteron binding energy and leading
scattering parameters, including the S-D mixing angle at the deuteron pole, are
possible from Lattice QCD calculations of two-nucleon systems with boosts of
|P| <= 2pi sqrt{3}/L in volumes with 10 fm <~ L <~ 14 fm. The viability of
extracting the asymptotic D/S ratio of the deuteron wavefunction from Lattice
QCD calculations is discussed.Comment: 31 pages, 17 figure
Two-Baryon Systems with Twisted Boundary Conditions
We explore the use of twisted boundary conditions in extracting the nucleon
mass and the binding energy of two-baryon systems, such as the deuteron, from
Lattice QCD calculations. Averaging the results of calculations performed with
periodic and anti-periodic boundary conditions imposed upon the light-quark
fields, or other pair-wise averages, improves the volume dependence of the
deuteron binding energy from ~exp(-kappa*L)/L to ~exp(-sqrt(2)kappa*L)/L.
However, a twist angle of pi/2 in each of the spatial directions improves the
volume dependence from ~exp(-kappa*L)/L to ~exp(-2kappa*L)/L. Twist averaging
the binding energy with a random sampling of twist angles improves the volume
dependence from ~exp^(-kappa*L)/L to ~exp(-2kappa*L)/L, but with a standard
deviation of ~exp(-kappa*L)/L, introducing a signal-to-noise issue in modest
lattice volumes. Using the experimentally determined phase shifts and mixing
angles, we determine the expected energies of the deuteron states over a range
of cubic lattice volumes for a selection of twisted boundary conditions.Comment: 20 pages, 3 figure
Theoretical aspects of quantum electrodynamics in a finite volume with periodic boundary conditions
First-principles studies of strongly-interacting hadronic systems using
lattice quantum chromodynamics (QCD) have been complemented in recent years
with the inclusion of quantum electrodynamics (QED). The aim is to confront
experimental results with more precise theoretical determinations, e.g. for the
anomalous magnetic moment of the muon and the CP-violating parameters in the
decay of mesons. Quantifying the effects arising from enclosing QED in a finite
volume remains a primary target of investigations. To this end, finite-volume
corrections to hadron masses in the presence of QED have been carefully studied
in recent years. This paper extends such studies to the self-energy of moving
charged hadrons, both on and away from their mass shell. In particular, we
present analytical results for leading finite-volume corrections to the
self-energy of spin-0 and spin- particles in the presence of QED
on a periodic hypercubic lattice, once the spatial zero mode of the photon is
removed, a framework that is called . By altering
modes beyond the zero mode, an improvement scheme is introduced to eliminate
the leading finite-volume corrections to masses, with potential applications to
other hadronic quantities. Our analytical results are verified by a dedicated
numerical study of a lattice scalar field theory coupled to
. Further, this paper offers new perspectives on the
subtleties involved in applying low-energy effective field theories in the
presence of , a theory that is rendered non-local
with the exclusion of the spatial zero mode of the photon, clarifying recent
discussions on this matter.Comment: 57 pages, 10 figures, version accepted for publication in Phys. Rev.
Multifractal clustering of passive tracers on a surface flow
We study the anomalous scaling of the mass density measure of Lagrangian
tracers in a compressible flow realized on the free surface on top of a three
dimensional flow. The full two dimensional probability distribution of local
stretching rates is measured. The intermittency exponents which quantify the
fluctuations of the mass measure of tracers at small scales are calculated from
the large deviation form of stretching rate fluctuations. The results indicate
the existence of a critical exponent above which exponents
saturate, in agreement with what has been predicted by an analytically solvable
model. Direct evaluation of the multi-fractal dimensions by reconstructing the
coarse-grained particle density supports the results for low order moments.Comment: 7 pages, 4 figures, submitted to EP
- …