6,562 research outputs found
Light-cone Gauge Superstring Field Theory and Dimensional Regularization II
We propose a dimensional regularization scheme to deal with the divergences
caused by colliding supercurrents inserted at the interaction points, in the
light-cone gauge NSR superstring field theory. We formulate the theory in
dimensions and define the amplitudes as analytic functions of . With an
appropriately chosen three-string interaction term and large negative , the
tree level amplitudes for the (NS,NS) closed strings can be recast into a BRST
invariant form, using the superconformal field theory proposed in
Ref.[arXiv:0911.3704]. We show that in the limit they coincide with
the results of the first quantized theory. Therefore we obtain the desired
results without adding any contact interaction terms to the action.Comment: 23 pages; v2: minor modifications; v3: revised argument in section 3,
added appendix C, results unchanged; v4: added clarifications, two figures
and a footnote; v5: minor modification
Post-traumatic stress disorders, depression, and anxiety in unaccompanied refugee minors exposed to war-related trauma: a systematic review
This systematic review gathers data from the existing literature on the prevalence and course of psychiatric disorders among unaccompanied refugee minors (URMs). The databases PsychINFO, PubMed, Scopus and Web of Science were searched and reference lists of papers were also manually examined to identify relevant articles. Peer-reviewed journal articles included focused on the mental health of URMs, who were forced to leave their place of residence because of threats of wars. A narrative synthesis was done to analyse the data presented in the studies. Results from the fifteen studies included in the review highlighted the high prevalence of post-traumatic stress disorders (PTSD), depression, and anxiety among URMs. The association between internalizing disorders and exposure to trauma, and time since displacement were examined. Separation from family members, death of parents and close relatives, level of exposure to armed conflicts, and threats to a person were the most frequent stressful life events (SLE) among URMs before migration. Although the number of research done on this vulnerable population is increasing overtime, the review highlights the need for further examination of refugee mental health and the factors affecting symptoms of PTSD, depression, and anxiety
Light-cone Gauge NSR Strings in Noncritical Dimensions II -- Ramond Sector
Light-cone gauge superstring theory in noncritical dimensions corresponds to
a worldsheet theory with nonstandard longitudinal part in the conformal gauge.
The longitudinal part of the worldsheet theory is a superconformal field theory
called X^{\pm} CFT. We show that the X^{\pm} CFT combined with the
super-reparametrization ghost system can be described by free variables. It is
possible to express the correlation functions in terms of these free variables.
Bosonizing the free variables, we construct the spin fields and BRST invariant
vertex operators for the Ramond sector in the conformal gauge formulation. By
using these vertex operators, we can rewrite the tree amplitudes of the
noncritical light-cone gauge string field theory, with external lines in the
(R,R) sector as well as those in the (NS,NS) sector, in a BRST invariant way.Comment: 33 pages; v2: minor modification
Spacetime Fermions in Light-cone Gauge Superstring Field Theory and Dimensional Regularization
We consider the dimensional regularization of the light-cone gauge type II
superstring field theories in the NSR formalism. In the previous work, we have
calculated the tree-level amplitudes with external lines in the (NS,NS) sector
using the regularization and shown that the desired results are obtained
without introducing contact term interactions. In this work, we study the
tree-level amplitudes with external lines in the Ramond sector. In order to
deal with them, we propose a worldsheet theory to be used instead of that for
the naive dimensional regularization. With the worldsheet theory, we regularize
and define the tree-level amplitudes by analytic continuation. We show that the
results coincide with those of the first quantized formulation.Comment: 28 pages, 5 figures; v2: more details of our manipulations in
subsection 3.2 added, figures and references added; v3: clarifications adde
The dynamics of spiral arms in pure stellar disks
It has been believed that spirals in pure stellar disks, especially the ones
spontaneously formed, decay in several galactic rotations due to the increase
of stellar velocity dispersions. Therefore, some cooling mechanism, for example
dissipational effects of the interstellar medium, was assumed to be necessary
to keep the spiral arms. Here we show that stellar disks can maintain spiral
features for several tens of rotations without the help of cooling, using a
series of high-resolution three-dimensional -body simulations of pure
stellar disks. We found that if the number of particles is sufficiently large,
e.g., , multi-arm spirals developed in an isolated disk can
survive for more than 10 Gyrs. We confirmed that there is a self-regulating
mechanism that maintains the amplitude of the spiral arms. Spiral arms increase
Toomre's of the disk, and the heating rate correlates with the squared
amplitude of the spirals. Since the amplitude itself is limited by the value of
, this makes the dynamical heating less effective in the later phase of
evolution. A simple analytical argument suggests that the heating is caused by
gravitational scattering of stars by spiral arms, and that the self-regulating
mechanism in pure-stellar disks can effectively maintain spiral arms on a
cosmological timescale. In the case of a smaller number of particles, e.g.,
, spiral arms grow faster in the beginning of the simulation
(while is small) and they cause a rapid increase of . As a result, the
spiral arms become faint in several Gyrs.Comment: 18 pages, 19 figures, accepted for Ap
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