186 research outputs found
Zeta Functions in Brane World Cosmology
We present a calculation of the zeta function and of the functional
determinant for a Laplace-type differential operator, corresponding to a scalar
field in a higher dimensional de Sitter brane background, which consists of a
higher dimensional anti-de Sitter bulk spacetime bounded by a de Sitter
section, representing a brane. Contrary to the existing examples, which all
make use of conformal transformations, we evaluate the zeta function working
directly with the higher dimensional wave operator. We also consider a generic
mass term and coupling to curvature, generalizing previous results. The
massless, conformally coupled case is obtained as a limit of the general result
and compared with known calculations. In the limit of large anti-de Sitter
radius, the zeta determinant for the ball is recovered in perfect agreement
with known expressions, providing an interesting check of our result and an
alternative way of obtaining the ball determinant.Comment: 14 pages, 1 figur
Massless scalar fields and infrared divergences in the inflationary brane world
We study the quantum effects induced by bulk scalar fields in a model with a
de Sitter (dS) brane in a flat bulk (the Vilenkin-Ipser-Sikivie model) in more
than four dimensions. In ordinary dS space, it is well known that the stress
tensor in the dS invariant vacuum for an effectively massless scalar
(m_\eff^2=m^2+\xi {\cal R}=0 with the Ricci scalar) is infrared
divergent except for the minimally coupled case. The usual procedure to tame
this divergence is to replace the dS invariant vacuum by the Allen Follaci (AF)
vacuum. The resulting stress tensor breaks dS symmetry but is regular.
Similarly, in the brane world context, we find that the dS invariant vacuum
generates \tmn divergent everywhere when the lowest lying mode becomes
massless except for massless minimal coupling case. A simple extension of the
AF vacuum to the present case avoids this global divergence, but \tmn remains
to be divergent along a timelike axis in the bulk. In this case, singularities
also appear along the light cone emanating from the origin in the bulk,
although they are so mild that \tmn stays finite except for non-minimal
coupling cases in four or six dimensions. We discuss implications of these
results for bulk inflaton models. We also study the evolution of the field
perturbations in dS brane world. We find that perturbations grow linearly with
time on the brane, as in the case of ordinary dS space. In the bulk, they are
asymptotically bounded.Comment: 20 pages. References adde
Stress-energy tensor for a quantised bulk scalar field in the Randall-Sundrum brane model
We calculate the vacuum expectation value of the stress-energy tensor for a
quantised bulk scalar field in the Randall-Sundrum model, and discuss the
consequences of its local behaviour for the self-consistency of the model. We
find that, in general, the stress-energy tensor diverges in the vicinity of the
branes. Our main conclusion is that the stress-energy tensor is sufficiently
complicated that it has implications for the effective potential, or radion
stabilisation, methods that have so far been used.Comment: 16 pages, 3 figures. Minor changes made and references added. To
appear in Phys. Rev.
The effect of elastic therapeutic taping on lumbar extensor isokinetic performance
Objective: To investigate the effects of elastic therapeutic tape when applied overlaying the lumbar extensors on different measures of muscle performance, compared to a placebo taping technique and a no-tape control.
Relevance: Elastic therapeutic tape is frequently used as an adjunct to enhance athletic performance amongst athletes. However, limited research exists supporting its application on isokinetic performance of the lumbar extensor muscles.
Methods: A cross-sectional experimental study. 21 participants received three taping conditions in a randomised order: elastic therapeutic tape, a placebo tape and a no-tape control. Peak torque, the time taken to reach peak torque and peak velocity were measured using an isokinetic dynamometer.
Analysis: Friedman’s test and post-hoc Wilcoxon signed-rank test were used to determine the statistical differences between the three taping conditions. Level of significance was set at 0.05.
Results: A statistically significant improvement in peak lumbar extensor torque was observed when comparing elastic therapeutic tape with the no-tape control (p 0.05).
Conclusions: Results demonstrate that the application of elastic therapeutic tape overlaying the primary lumbar extensors significantly improves the maximal lumbar extension peak torque in healthy, asymptomatic adults
Dendritic morphology of hippocampal and amygdalar neurons in adolescent mice is resilient to genetic differences in stress reactivity.
The psychosocial impact of prostate cancer on patients and their partners
The document attached has been archived with permission from the editor of the Medical Journal of Australia. An external link to the publisher’s copy is included.See page 5 of PDF for this item.James A Smith, Shaun M Filiault, Murray J Drummond and Robert J Knapma
The role of salt bridges, charge density, and subunit flexibility in determining disassembly routes of protein complexes
Mass spectrometry can be used to characterize multiprotein complexes, defining their subunit stoichiometry and composition following solution disruption and collision-induced dissociation (CID). While CID of protein complexes in the gas phase typically results in the dissociation of unfolded subunits, a second atypical route is possible wherein compact subunits or subcomplexes are ejected without unfolding. Because tertiary structure and subunit interactions may be retained, this is the preferred route for structural investigations. How can we influence which pathway is adopted? By studying properties of a series of homomeric and heteromeric protein complexes and varying their overall charge in solution, we found that low subunit flexibility, higher charge densities, fewer salt bridges, and smaller interfaces are likely to be involved in promoting dissociation routes without unfolding. Manipulating the charge on a protein complex therefore enables us to direct dissociation through structurally informative pathways that mimic those followed in solution
Casimir effect between anti-de Sitter braneworlds
We calculate the one-loop effective action of a scalar field with general
mass and coupling to the curvature in the detuned Randall-Sundrum brane world
scenario, where the four-dimensional branes are anti-de Sitter. We make use of
conformal transformations to map the problem to one on the direct product of
the hyperbolic space H^4 and the interval. We also include the cocycle function
for this transformation. This Casimir potential is shown to give a sizable
correction to the classical radion potential for small values of brane
separation.Comment: 14 pages, 3 figures, revtex. Typos corrected and references added.
Minor mistakes in Eq. 48 and Eq. A10 correcte
Monitoring postmatch fatigue during a competitive season in elite youth soccer players
Context: Countermovement jump (CMJ) and perceived wellness measures are useful for monitoring fatigue. Fatigue indicators should simultaneously show sensitivity to previous load and demonstrate influence on subsequent physical output; however, these factors have not been examined. Objective: To explore the efficacy of CMJ and wellness measures to both detect postmatch fatigue and predict subsequent physical match output in elite youth soccer players. Design: Cross-sectional study. Patients or Other Participants: Sixteen soccer players (18 ± 1 years) from 36 English Football League Youth Alliance League fixtures. Main Outcome Measure(s): Physical match outputs (total distance, high-speed running, very high-speed running, and accelerations and decelerations [AD]) were recorded using a 10-Hz global positioning system and 200-Hz accelerometer device during competitive match play. The CMJ height and perceived wellness were assessed weekly and daily, respectively, as indirect indicators of fatigue. Four subunits of wellness (perceived soreness, energy, general stress, and sleep) were measured using customized psychometric questionnaires. Results: Simple linear regression showed that match AD predicted energy (R 2 = 0.08, P =.001), stress (R 2 = 0.09, P<.001), and total wellness (R 2 = 0.06, P =.002) at 2 days postmatch. The CMJ (R 2 = 0.05, P =.002), stress (R 2 = 0.08, P<.001), sleep (R 2 = 0.03, P =.034), and total wellness (R 2 = 0.05, P =.006) measures at 5 days prematch predicted AD during the subsequent match. Conclusions: The CMJ and wellness measures may be useful for detecting postmatch fatigue. Wellness scores, but not CMJ, at 5 days prematch influenced subsequent match output and therefore may be used to plan and periodize training for the upcoming microcycle
Wightman function and Casimir densities on AdS bulk with application to the Randall-Sundrum braneworld
Positive frequency Wightman function and vacuum expectation value of the
energy-momentum tensor are computed for a massive scalar field with general
curvature coupling parameter subject to Robin boundary conditions on two
parallel plates located on - dimensional AdS background. The general case
of different Robin coefficients on separate plates is considered. The mode
summation method is used with a combination of a variant of the generalized
Abel-Plana formula for the series over zeros of combinations of cylinder
functions. This allows us to extract manifestly the parts due to the AdS
spacetime without boundaries and boundary induced parts. The asymptotic
behavior of the vacuum densities near the plates and at large distances is
investigated. The vacuum forces acting on the boundaries are presented as a sum
of the self-action and interaction forces. The first one contains well-known
surface divergences and needs further regularization. The interaction forces
between the plates are attractive for Dirichlet scalar. We show that threre is
a region in the space of parameters defining the boundary conditions in which
the interaction forces are repulsive for small distances and attractive for
large distances. An application to the Randall-Sundrum braneworld with
arbitrary mass terms on the branes is discussed.Comment: 26 pages, 6 figures, discussions and figure labels added, accepted
for publication in Nuclear Physics
- …