344 research outputs found
Magnetic Charge Can Locally Stabilize Kaluza-Klein Bubbles
We construct a new 2-parameter family of static topological solitons in 5D
minimal supergravity which are endowed with magnetic charge and mass. The
solitons are asymptotically , where the radius of the
has a lower bound . Setting up initial data on a Cauchy
slice at a moment of time symmetry, we demonstrate that if these
solitons correspond to a perturbatively stable "small" static bubble as well as
an unstable "large" static bubble, whereas if there are no static
bubbles. The energetics and thermodynamics of the magnetic black string are
then discussed and it is shown that the locally stable bubble is the end point
of a phase transition for an appropriate range of black string parameters.Comment: 5 pages, 1 figure. v3: references and stringy discussion added, v4:
introduction expanded. Minor comments throughout. Accepted for publication in
PL
Binary Cosmic Strings
The properties of cosmic strings have been investigated in detail for their
implications in early-universe cosmology. Although many variations of the basic
structure have been discovered, with implications for both the microscopic and
macroscopic properties of cosmic strings, the cylindrical symmetry of the
short-distance structure of the string is generally unaffected. In this paper
we describe some mechanisms leading to an asymmetric structure of the string
core, giving the defects a quasi-two-dimensional character. We also begin to
investigate the consequences of this internal structure for the microscopic and
macroscopic physics.Comment: 19 pages; uses harvmac (not included
Supersymmetric Electroweak Cosmic Strings
We study the connection between supersymmetry and a topological bound
in a two-Higgs-doublet system with an gauge group. We derive the Bogomol'nyi equations from
supersymmetry considerations showing that they hold provided certain conditions
on the coupling constants, which are a consequence of the huge symmetry of the
theory, are satisfied. Their solutions, which can be interpreted as electroweak
cosmic strings breaking one half of the supersymmetries of the theory, are
studied. Certain interesting limiting cases of our model which have recently
been considered in the literature are finally analyzed.Comment: 20 pages, RevTe
In vivo activity of a mixture of two human monoclonal antibodies (anti-HBs) in a chronic hepatitis B virus carrier chimpanzee
A 35-year-old female hepatitis B virus carrier chimpanzee was infused with
one dose of a mixture of human monoclonal antibodies 9H9 and 4-7B
(antibodies against hepatitis B virus surface antigen; HBsAg). Blood
samples were taken before and up to 3 weeks after infusion. HBsAg and
antibodies against HBsAg (anti-HBs) were quantified by radioimmunoassay
and enzyme immunoassay. Free anti-HBs was never detected. Thirty min after
the start of the infusion the HBsAg level was minimal with maximum loading
of the chimpanzee HBsAg with human immunoglobulin. HBsAg complexes could
be dissociated by acid treatment. The HBsAg level was completely restored
on day 7. Similar results were obtained for the preS1-containing particles
that may represent the infectious viral particles in the chimpanzee serum.
A mouse monoclonal anti-HBs (HBs.OT40) was found to compete with 9H9 in
artificial immune complexes with the pre-treatment HBsAg from the
chimpanzee. Used as a conjugate, HBs.OT40 yielded a maximum decrease in
the signal in the 30 min sample compared to non-competing anti-HBs
conjugates. This indicates binding of HBsAg with 9H9 in the circulation of
the chimpanzee. Immune-complexed 4-7B could not be detected by its
corresponding 4-7B peptide conjugate, probably due to its low
concentration in the complexes. It is concluded that human monoclonal
anti-HBs can effectively reduce the level of HBsAg in serum from this
chronic carrier. Monoclonals 9H9 and 4-7B may complement each other due to
their different mechanisms of inactivation, probably with higher
efficiency than that monitored by our HBsAg screening assays
Gaugino Condensation in M-theory on S^1/Z_2
In the low energy limit of for M-theory on S^1/Z_2, we calculate the gaugino
condensate potential in four dimensions using the background solutions due to
Horava. We show that this potential is free of delta-function singularities and
has the same form as the potential in the weakly coupled heterotic string. A
general flux quantization rule for the three-form field of M-theory on S^1/Z_2
is given and checked in certain limiting cases. This rule is used to fix the
free parameter in the potential originating from a zero mode of the form field.
Finally, we calculate soft supersymmetry breaking terms. We find that
corrections to the Kahler potential and the gauge kinetic function, which can
be large in the strongly coupled region, contribute significantly to certain
soft terms. In particular, for supersymmetry breaking in the T-modulus
direction, the small values of gaugino masses and trilinear couplings that
occur in the weakly coupled, large radius regime are enhanced to order m_3/2 in
M-theory. The scalar soft masses remain small even, in the strong coupling
M-theory limit.Comment: 20 pages, LATE
Dynamical Cobordisms in General Relativity and String Theory
We describe a class of time-dependent solutions in string- or M-theory that
are exact with respect to alpha-prime and curvature corrections and interpolate
in physical space between regions in which the low energy physics is
well-approximated by different string theories and string compactifications.
The regions are connected by expanding "domain walls" but are not separated by
causal horizons, and physical excitations can propagate between them. As
specific examples we construct solutions that interpolate between oriented and
unoriented string theories, and also between type II and heterotic theories.
Our solutions can be weakly curved and under perturbative control everywhere
and can asymptote to supersymmetric at late times.Comment: 35 pages, 5 figures, LaTeX v2: reference adde
Moduli potentials in string compactifications with fluxes: mapping the Discretuum
We find de Sitter and flat space solutions with all moduli stabilized in four
dimensional supergravity theories derived from the heterotic and type II string
theories, and explain how all the previously known obstacles to finding such
solutions can be removed. Further, we argue that if the compact manifold allows
a large enough space of discrete topological choices then it is possible to
tune the parameters of the four dimensional supergravity such that a hierarchy
is created and the solutions lie in the outer region of moduli space in which
the compact volume is large in string units, the string coupling is weak, and
string perturbation theory is valid. We show that at least two light chiral
superfields are required for this scenario to work, however, one field is
sufficient to obtain a minimum with an acceptably small and negative
cosmological constant. We discuss cosmological issues of the scenario and the
possible role of anthropic considerations in choosing the vacuum of the theory.
We conclude that the most likely stable vacuua are in or near the central
region of moduli space where string perturbation theory is not strictly valid,
and that anthropic considerations cannot help much in choosing a vacuum.Comment: 34 pages, no figure
String Universality
If there is a single underlying "theory of everything" which in some limits
of its "moduli space" reduces to the five weakly coupled string theories in
10D, and 11D SUGRA, then it is possible that all six of them have some common
domain of validity and that they are in the same universality class, in the
sense that the 4D low energy physics of the different theories is the same. We
call this notion String Universality. This suggests that the true vacuum of
string theory is in a region of moduli space equally far (in some sense) from
all perturbative theories, most likely around the self-dual point with respect
to duality symmetries connecting them. We estimate stringy non-perturbative
effects from wrapped brane instantons in each perturbative theory, show how
they are related by dualities, and argue that they are likely to lead to moduli
stabilization only around the self-dual point. We argue that moduli
stabilization should occur near the string scale, and SUSY breaking should
occur at a much lower intermediate scale, and that it originates from different
sources. We discuss the problems of moduli stabilization and SUSY breaking in
currently popular scenarios, explain why these problems are generic, and
discuss how our scenario can evade them. We show that String Universality is
not inconsistent with phenomenology but that it is in conflict with some
popular versions of brane world scenarios.Comment: 48 pages, 1 figure; one reference adde
Promoting Physical Activity in Middle School Girls: Trial of Activity for Adolescent Girls
Background - Physical activity is important for weight control and good health; however, activity levels decline in the adolescent years, particularly in girls.
Design - Group randomized controlled trial.
Setting/participants - Middle school girls with English-speaking skills and no conditions to prevent participation in physical activity in 36 schools in six geographically diverse areas of the United States. Random, cross-sectional samples were drawn within schools: 6th graders in 2003 (n=1721) and 8th graders in 2005 (n=3504) and 2006 (n=3502).
Intervention - A 2-year study-directed intervention (fall 2003 to spring 2005) targeted schools, community agencies, and girls to increase opportunities, support, and incentives for increased physical activity. Components included programs linking schools and community agencies, physical education, health education, and social marketing. A third-year intervention used school and community personnel to direct intervention activities.
Main outcome measures - The primary outcome, daily MET-weighted minutes of moderate-to-vigorous physical activity (MET-weighted MVPA), was assessed using accelerometry. Percent body fat was assessed using anthropometry.
Results - After the staff-directed intervention (pre-stated primary outcome), there were no differences (mean=-0.4, 95% CI=-8.2 to 7.4) in adjusted MET-weighted MVPA between 8th-grade girls in schools assigned to intervention or control. Following the Program Champion-directed intervention, girls in intervention schools were more physically active than girls in control schools (mean difference 10.9 MET-weighted minutes of MVPA, 95% CI=0.52-21.2). This difference is about 1.6 minutes of daily MVPA or 80 kcal per week. There were no differences in fitness or percent body fat at either 8th-grade timepoint.
Conclusion - A school-based, community-linked intervention modestly improved physical activity in girls
Moduli Stabilisation in Heterotic Models with Standard Embedding
In this note we analyse the issue of moduli stabilisation in 4d models
obtained from heterotic string compactifications on manifolds with SU(3)
structure with standard embedding. In order to deal with tractable models we
first integrate out the massive fields. We argue that one can not only
integrate out the moduli fields, but along the way one has to truncate also the
corresponding matter fields. We show that the effective models obtained in this
way do not have satisfactory solutions. We also look for stabilised vacua which
take into account the presence of the matter fields. We argue that this also
fails due to a no-go theorem for Minkowski vacua in the moduli sector which we
prove in the end. The main ingredient for this no-go theorem is the constraint
on the fluxes which comes from the Bianchi identity.Comment: 20 pages, LaTeX; references adde
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