412 research outputs found
De Rham Cohomology of the Supermanifolds and Superstring BRST Cohomology
We show that the BRST operator of Neveu-Schwarz-Ramond superstring is closely
related to de Rham differential on the moduli space of decorated super-Riemann
surfaces P. We develop formalism where superstring amplitudes are computed via
integration of some differential forms over a section of P over the super
moduli space M. We show that the result of integration does not depend on the
choice of section when all the states are BRST physical. Our approach is based
on the geometrical theory of integration on supermanifolds of which we give a
short review.Comment: 6 page
Effective Tachyonic Potential in Closed String Field Theory
We calculate the effective tachyonic potential in closed string field theory
up to the quartic term in the tree approximation. This involves an elementary
four-tachyon vertex and a sum over the infinite number of Feynman graphs with
an intermediate massive state. We show that both the elementary term and the
sum can be evaluated as integrals of some measure over different regions in the
moduli space of four-punctured spheres. We show that both elementary and
effective coupling give negative contributions to the quartic term in the
tachyon potential. Numerical calculations show that the fourth order term is
big enough to destroy a local minimum which exists in the third order
approximation.Comment: 41 pages, LaTeX + psfig macro package, 15 uuencoded tar-compressed
postscript figures include
Cech and de Rham Cohomology of Integral Forms
We present a study on the integral forms and their Cech/de Rham cohomology.
We analyze the problem from a general perspective of sheaf theory and we
explore examples in superprojective manifolds. Integral forms are fundamental
in the theory of integration in supermanifolds. One can define the integral
forms introducing a new sheaf containing, among other objects, the new basic
forms delta(dtheta) where the symbol delta has the usual formal properties of
Dirac's delta distribution and acts on functions and forms as a Dirac measure.
They satisfy in addition some new relations on the sheaf. It turns out that the
enlarged sheaf of integral and "ordinary" superforms contains also forms of
"negative degree" and, moreover, due to the additional relations introduced,
its cohomology is, in a non trivial way, different from the usual superform
cohomology.Comment: 20 pages, LaTeX, we expanded the introduction, we add a complete
analysis of the cohomology and we derive a new duality between cohomology
group
Inhibition of saccadic eye movements to locations in spatial working memory
Inhibition of return (IOR) refers to a bias against overt and covert attentional orienting toward previously attended locations. According to the reorienting hypothesis, IOR is generated when attention is withdrawn from the attended location and is prevented from "returning" to it. The present study investigated whether maintenance of attention at the cued location could affect the inhibition of oculomotor orienting to it. To preclude dis-engagement of attention, we asked participants to maintain the cued location in working memory. Maintenance of visuospatial information in memory has been shown to be accomplished through a sustained shift of spatial attention to a memorized location. Our results show that oculomotor IOR occurs at a particular location even when that location is kept in working memory (Experiment 1). Furthermore, we demonstrate that the mere act of maintenance of a location in working memory produces oculomotor inhibition similar to IOR (Experiments 2 and 3). We conclude that the oculomotor system is used for coding and maintaining locations in spatial working memory. In addition, we demonstrate that endogenous attention associated with maintenance of a location in working memory can be dissociated from the attention needed for execution of a saccadic eye movement. © 2009 The Psychonomic Society, Inc
Angry faces hold the eyes
peer reviewedEfficient processing of complex social and biological stimuli associated with threat is crucial for survival. Previous studies have suggested that threatening stimuli such as angry faces not only capture visual attention, but also delay the disengagement of attention from their location. However, in the previous studies disengagement of attention was measured indirectly and was inferred on the basis of delayed manual responses. The present study employed a novel paradigm that allows to directly examine the delayed disengagement hypothesis by measuring the time it takes to disengage the eyes from threatening stimuli. The results showed that participants were indeed slower to make an eye movement away from an angry face presented at fixation than from either a neutral or a happy face. This finding provides converging support that the delay in disengagement of attention is an important component of processing threatening information
Transfer of information into working memory during attentional capture
Previous research has shown that task-irrelevant onsets can capture spatial attention even when attending to the onset is inconsistent with our intentions. The present study investigated whether information acquired during attentional capture is transferred into working memory. To measure whether this is the case, 25% of visual search trials were followed by a distractor recognition task. The results showed that the onset letter was recognized more often than a nononset letter. In addition, the magnitude of attentional capture was positively correlated with the onset letter recognition advantage. The results suggest that attentional capture results in transfer of information into working memory
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