2,671 research outputs found
Observations of cosmic ray induced phosphenes
Phosphene observations by astronauts on flights near and far from earth atmosphere are discussed. It was concluded that phosphenes could be observed by the naked eye. Further investigation is proposed to determine realistic human tolerance levels for extended missions and to evaluate the need to provide special spacecraft shielding
(1+1)-Dimensional Yang-Mills Theory Coupled to Adjoint Fermions on the Light Front
We consider SU(2) Yang-Mills theory in 1+1 dimensions coupled to massless
adjoint fermions. With all fields in the adjoint representation the gauge group
is actually SU(2)/Z_2, which possesses nontrivial topology. In particular,
there are two distinct topological sectors and the physical vacuum state has a
structure analogous to a \theta vacuum. We show how this feature is realized in
light-front quantization, with periodicity conditions used to regulate the
infrared and treating the gauge field zero mode as a dynamical quantity. We
find expressions for the degenerate vacuum states and construct the analog of
the \theta vacuum. We then calculate the bilinear condensate in the model. We
argue that the condensate does not affect the spectrum of the theory, although
it is related to the string tension that characterizes the potential between
fundamental test charges when the dynamical fermions are given a mass. We also
argue that this result is fundamentally different from calculations that use
periodicity conditions in x^1 as an infrared regulator.Comment: 20 pages, Revte
Simulation of Dimensionally Reduced SYM-Chern-Simons Theory
A supersymmetric formulation of a three-dimensional SYM-Chern-Simons theory
using light-cone quantization is presented, and the supercharges are calculated
in light-cone gauge. The theory is dimensionally reduced by requiring all
fields to be independent of the transverse dimension. The result is a
non-trivial two-dimensional supersymmetric theory with an adjoint scalar and an
adjoint fermion. We perform a numerical simulation of this SYM-Chern-Simons
theory in 1+1 dimensions using SDLCQ (Supersymmetric Discrete Light-Cone
Quantization). We find that the character of the bound states of this theory is
very different from previously considered two-dimensional supersymmetric gauge
theories. The low-energy bound states of this theory are very ``QCD-like.'' The
wave functions of some of the low mass states have a striking valence
structure. We present the valence and sea parton structure functions of these
states. In addition, we identify BPS-like states which are almost independent
of the coupling. Their masses are proportional to their parton number in the
large-coupling limit.Comment: 18pp. 7 figures, uses REVTe
Numerical Simulations of N=(1,1) SYM{1+1} with Large Supersymmetry Breaking
We consider the SYM theory that is obtained by dimensionally
reducing SYM theory in 2+1 dimensions to 1+1 dimensions and discuss soft
supersymmetry breaking. We discuss the numerical simulation of this theory
using SDLCQ when either the boson or the fermion has a large mass. We compare
our result to the pure adjoint fermion theory and pure adjoint boson DLCQ
calculations of Klebanov, Demeterfi, and Bhanot and of Kutasov. With a large
boson mass we find that it is necessary to add additional operators to the
theory to obtain sensible results. When a large fermion mass is added to the
theory we find that it is not necessary to add operators to obtain a sensible
theory. The theory of the adjoint boson is a theory that has stringy bound
states similar to the full SYM theory. We also discuss another theory of
adjoint bosons with a spectrum similar to that obtained by Klebanov, Demeterfi,
and Bhanot.Comment: 12 pages, 4 figure
Quantum Mechanics of Dynamical Zero Mode in on the Light-Cone
Motivated by the work of Kalloniatis, Pauli and Pinsky, we consider the
theory of light-cone quantized on a spatial circle with periodic
and anti-periodic boundary conditions on the gluon and quark fields
respectively. This approach is based on Discretized Light-Cone Quantization
(DLCQ). We investigate the canonical structures of the theory. We show that the
traditional light-cone gauge is not available and the zero mode (ZM)
is a dynamical field, which might contribute to the vacuum structure
nontrivially. We construct the full ground state of the system and obtain the
Schr\"{o}dinger equation for ZM in a certain approximation. The results
obtained here are compared to those of Kalloniatis et al. in a specific
coupling region.Comment: 19 pages, LaTeX file, no figure
Biofluid modeling of the coupled eye-brain system and insights into simulated microgravity conditions
This work aims at investigating the interactions between the flow of fluids in the eyes and the brain and their potential implications in structural and functional changes in the eyes of astronauts, a condition also known as spaceflight associated neuro-ocular syndrome (SANS). To this end, we propose a reduced (0-dimensional) mathematical model of fluid flow in the eyes and brain, which is embedded into a simplified whole-body circulation model. In particular, the model accounts for: (i) the flows of blood and aqueous humor in the eyes; (ii) the flows of blood, cerebrospinal fluid and interstitial fluid in the brain; and (iii) their interactions. The model is used to simulate variations in intraocular pressure, intracranial pressure and blood flow due to microgravity conditions, which are thought to be critical factors in SANS. Specifically, the model predicts that both intracranial and intraocular pressures increase in microgravity, even though their respective trends may be different. In such conditions, ocular blood flow is predicted to decrease in the choroid and ciliary body circulations, whereas retinal circulation is found to be less susceptible to microgravity-induced alterations, owing to a purely mechanical component in perfusion control associated with the venous segments. These findings indicate that the particular anatomical architecture of venous drainage in the retina may be one of the reasons why most of the SANS alterations are not observed in the retina but, rather, in other vascular beds, particularly the choroid. Thus, clinical assessment of ocular venous function may be considered as a determinant SANS factor, for which astronauts could be screened on earth and in-flight
Vacuum Structure of Two-Dimensional Gauge Theories on the Light Front
We discuss the problem of vacuum structure in light-front field theory in the
context of (1+1)-dimensional gauge theories. We begin by reviewing the known
light-front solution of the Schwinger model, highlighting the issues that are
relevant for reproducing the -structure of the vacuum. The most
important of these are the need to introduce degrees of freedom initialized on
two different null planes, the proper incorporation of gauge field zero modes
when periodicity conditions are used to regulate the infrared, and the
importance of carefully regulating singular operator products in a
gauge-invariant way. We then consider SU(2) Yang-Mills theory in 1+1 dimensions
coupled to massless adjoint fermions. With all fields in the adjoint
representation the gauge group is actually SU(2), which possesses
nontrivial topology. In particular, there are two topological sectors and the
physical vacuum state has a structure analogous to a vacuum. We
formulate the model using periodicity conditions in for infrared
regulation, and consider a solution in which the gauge field zero mode is
treated as a constrained operator. We obtain the expected vacuum
structure, and verify that the discrete vacuum angle which enters has no effect
on the spectrum of the theory. We then calculate the chiral condensate, which
is sensitive to the vacuum structure. The result is nonzero, but inversely
proportional to the periodicity length, a situation which is familiar from the
Schwinger model. The origin of this behavior is discussed.Comment: 29 pages, uses RevTeX. Improved discussion of the physical subspace
generally and the vacuum states in particular. Basic conclusions are
unchanged, but some specific results are modifie
On Zero Modes and the Vacuum Problem -- A Study of Scalar Adjoint Matter in Two-Dimensional Yang-Mills Theory via Light-Cone Quantisation
SU(2) Yang-Mills Theory coupled to massive adjoint scalar matter is studied
in (1+1) dimensions using Discretised Light-Cone Quantisation. This theory can
be obtained from pure Yang-Mills in 2+1 dimensions via dimensional reduction.
On the light-cone, the vacuum structure of this theory is encoded in the
dynamical zero mode of a gluon and a constrained mode of the scalar field. The
latter satisfies a linear constraint, suggesting no nontrivial vacua in the
present paradigm for symmetry breaking on the light-cone. I develop a
diagrammatic method to solve the constraint equation. In the adiabatic
approximation I compute the quantum mechanical potential governing the
dynamical gauge mode. Due to a condensation of the lowest omentum modes of the
dynamical gluons, a centrifugal barrier is generated in the adiabatic
potential. In the present theory however, the barrier height appears too small
to make any impact in this odel. Although the theory is superrenormalisable on
naive powercounting grounds, the removal of ultraviolet divergences is
nontrivial when the constrained mode is taken into account. The open aspects of
this problem are discussed in detail.Comment: LaTeX file, 26 pages. 14 postscript figure
Wave functions and properties of massive states in three-dimensional supersymmetric Yang-Mills theory
We apply supersymmetric discrete light-cone quantization (SDLCQ) to the study
of supersymmetric Yang-Mills theory on R x S^1 x S^1. One of the compact
directions is chosen to be light-like and the other to be space-like. Since the
SDLCQ regularization explicitly preserves supersymmetry, this theory is totally
finite, and thus we can solve for bound-state wave functions and masses
numerically without renormalizing. We present an overview of all the massive
states of this theory, and we see that the spectrum divides into two distinct
and disjoint sectors. In one sector the SDLCQ approximation is only valid up to
intermediate coupling. There we find a well defined and well behaved set of
states, and we present a detailed analysis of these states and their
properties. In the other sector, which contains a completely different set of
states, we present a much more limited analysis for strong coupling only. We
find that, while these state have a well defined spectrum, their masses grow
with the transverse momentum cutoff. We present an overview of these states and
their properties.Comment: RevTeX, 25 pages, 16 figure
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