237 research outputs found
Brane Effects on Extra Dimensional Scenarios: A Tale of Two Gravitons
We analyze the propagation of a scalar field in multidimensional theories
which include kinetic corrections in the brane, as a prototype for
gravitational interactions in a four dimensional brane located in a (nearly)
flat extra dimensional bulk. We regularize the theory by introducing an
infrared cutoff given by the size of the extra dimensions and a physical
ultraviolet cutoff of the order of the fundamental Planck scale in the higher
dimensional theory. We show that, contrary to recent suggestions, the radius of
the extra dimensions cannot be arbitrarily large. Moreover, for finite radii,
the gravitational effects localized on the brane can substantially alter the
phenomenology of collider and/or table-top gravitational experiments. This
phenomenology is dictated by the presence of a massless graviton, with standard
couplings to the matter fields, and a massive graviton which couples to matter
in a much stronger way. While graviton KK modes lighter than the massive
graviton couple to matter in a standard way, the couplings to matter of the
heavier KK modes are strongly suppressed.Comment: 21 pages, latex2e, axodraw.sty, 2 figure
Upper Bounds on Lepton-number Violating Processes
We consider four lepton-number violating (\lv) processes: (a) neutrinoless
double-beta decay (0\nu\beta\beta), (b) Delta L = 2 tau decays, (c) Delta L = 2
rare meson decays and (d) nuclear muon-positron conversion. In the absence of
exotic \lv interactions, the rates for these processes are determined by
effective neutrino masses _{\ell_1\ell_2}, which can be related to the sum
of light neutrino masses, the neutrino mass-squared differences, the neutrino
mixing angles, a Dirac phase and two Majorana phases. We sample the
experimentally allowed ranges of _{\ell_1\ell_2} based on neutrino
oscillation experiments as well as cosmological observations, and obtain a
stringent upper bound _{\ell_1\ell_2} \lsim 0.14 eV. We then calculate the
allowed ranges for _{\ell_1\ell_2} from the experimental rates of direct
searches for the above Delta L = 2 processes. Comparing our calculated rates
with the currently or soon available data, we find that only the
experiment may be able to probe _{ee} with a sensitivity
comparable to the current bound. Muon-positron conversion is next in
sensitivity, while the limits of direct searches for the other Delta L = 2
processes are several orders of magnitude weaker than the current bounds on
_{\ell_1\ell_2}. Any positive signal in those direct searches would indicate
new contributions to the \lv interactions beyond those from three light
Majorana neutrinos.Comment: 20 pages, revtex4, 2 figures (5 files), Version published in Physical
Review
The Nerve/Tunnel Index: A New Diagnostic Standard for Carpal Tunnel Syndrome Using Sonography
Objectives—To define the relationship between body indices of healthy adults and cross-sectional areas of the carpal tunnel and median nerve and to obtain the nerve/tunnel index, which represents a new standard for diagnosing carpal tunnel syndrome using sonography. Methods—Body indices (height, weight, and body mass index) were analyzed in 60 healthy adults, and electromyography and sonography were also performed. The crosssectional areas of the proximal and distal median nerve and carpal tunnel were obtained by sonography. The proximal and distal nerve/tunnel indices were obtained by calculating the ratio between the proximal and distal cross-sectional areas of the median nerve to those of the carpal tunnel and multiplying the value by 100. Results—Although the proximal cross-sectional areas of the median nerve and body indices showed statistically significant relationships with weak positive correlations, the proximal and distal areas of the carpal tunnel showed relatively stronger correlations with body indices. Between sexes, there were significant differences in the proximal median nerve cross-sectional area (mean ± SD: male, 10.48 ± 3.21 mm2; female, 8.81 ± 3.21 mm2; P < .05) and proximal carpal tunnel area (male, 182.50 ± 21.15 mm2; female, 151.23 ± 21.14 mm2; P < .05). There was no difference in the proximal nerve/tunnel index (male, 5.80% ± 1.72%; female, 5.91% ± 1.63%). There was a statistically significant difference in the distal carpal tunnel cross-sectional area (male, 138.90 ± 20.95 mm2; female, 121.50 ± 18.99 mm2; P < .05) between sexes, but the distal median area (male, 9.99 ± 3.42 mm2; female, 8.46 ± 1.84 mm2) and distal nerve/tunnel index (male, 7.15% ± 2.00%; female, 7.01% ± 1.38%) showed no significant differences. The proximal index was significantly higher than the distal index (proximal, 5.85% ± 1.66%; distal, 7.08% ± 1.71%). Conclusions—The nerve/tunnel index is unaffected by body indices or sex and thus may be a useful and objective standard for diagnosing carpal tunnel syndrome
Constructing a counterexample to the black hole complementarity
We propose a regular black hole whose inside generates a de Sitter space and
then is finally frustrated into a singularity. It is a modified model which was
suggested originally by Frolov, Markov, and Mukhanov. In our model, we could
adjust a regular black hole so that its period before going into the extreme
state is much longer than the information retention time. During this period an
observer could exist who observes the information of the Hawking radiation,
falls freely into the regular center of the black hole, and finally meets the
free-falling information again. The existence of such an observer implies that
the complementary view may not be consistent with a regular black hole, and
therefore, is not appropriate as a generic principle of black hole physics.Comment: 8 pages, 5 figure
Charge and current oscillations in Fractional quantum Hall systems with edges
Stationary solutions of the Chern-Simons effective field theory for the
fractional quantum Hall systems with edges are presented for Hall bar, disk and
annulus. In the infinitely long Hall bar geometry (non compact case), the
charge density is shown to be monotonic inside the sample. In sharp contrast,
spatial oscillatory modes of charge density are found for the two circular
geometries, which indicate that in systems with compact geometry, charge and
current exist also far from the edges.Comment: 16 pages, 6 figures Revte
Friedmann Equation and Stability of Inflationary Higher Derivative Gravity
Stability analysis on the De Sitter universe in pure gravity theory is known
to be useful in many aspects. We first show how to complete the proof of an
earlier argument based on a redundant field equation. It is shown further that
the stability condition applies to Friedmann-Robertson-Walker spaces
based on the non-redundant Friedmann equation derived from a simple effective
Lagrangian. We show how to derive this expression for the Friedmann equation of
pure gravity theory. This expression is also generalized to include scalar
field interactions.Comment: Revtex, 6 pages, Add two more references, some typos correcte
New physics searches at near detectors of neutrino oscillation experiments
We systematically investigate the prospects of testing new physics with tau
sensitive near detectors at neutrino oscillation facilities. For neutrino beams
from pion decay, from the decay of radiative ions, as well as from the decays
of muons in a storage ring at a neutrino factory, we discuss which effective
operators can lead to new physics effects. Furthermore, we discuss the present
bounds on such operators set by other experimental data currently available.
For operators with two leptons and two quarks we present the first complete
analysis including all relevant operators simultaneously and performing a
Markov Chain Monte Carlo fit to the data. We find that these effects can induce
tau neutrino appearance probabilities as large as O(10^{-4}), which are within
reach of forthcoming experiments. We highlight to which kind of new physics a
tau sensitive near detector would be most sensitive.Comment: 20 pages, 2 figures, REVTeX
Euclidean three-point function in loop and perturbative gravity
We compute the leading order of the three-point function in loop quantum
gravity, using the vertex expansion of the Euclidean version of the new spin
foam dynamics, in the region of gamma<1. We find results consistent with Regge
calculus in the limit gamma->0 and j->infinity. We also compute the tree-level
three-point function of perturbative quantum general relativity in position
space, and discuss the possibility of directly comparing the two results.Comment: 16 page
Inflationary Universe in Higher Derivative Induced Gravity
In an induced-gravity model, the stability condition of an inflationary
slow-rollover solution is shown to be . The presence of higher derivative terms
will, however, act against the stability of this expanding solution unless
further constraints on the field parameters are imposed. We find that these
models will acquire a non-vanishing cosmological constant at the end of
inflation. Some models are analyzed for their implication to the early
universe.Comment: 6 pages, two typos correcte
The interactive role of predation, competition and habitat conditions in structuring an intertidal bivalve population
Habitat characteristics, predation and competition are known to interactively drive population dynamics. Highly complex habitats, for example, may reduce predation and competition, allowing more individuals living together in a certain area. However, the strength and direction of such interactions can differ strongly and are context dependent. Furthermore, as habitat characteristics are rapidly changing due to anthropogenic impacts, it becomes increasingly important to understand such interactions. Here, we studied the interactive effects of predation and competition on common cockle (Cerastoderma edule) recruitment, growth and survival under different habitat characteristics in the Wadden Sea, one of the world's largest intertidal ecosystems. In a predator-exclosure experiment, we manipulated cockle densities (100 vs. 1000 individuals m-2) and shorebird predation at two sites differing in habitat characteristics, namely at the wake of a blue mussel bed (Mytilus edulis) and at an adjacent sandy site. We found that recruitment was higher in the mussel-modified habitat, most likely due to reduction of hydrodynamic stress. Although bird predation strongly reduced recruit density, the combined effects still yielded more recruitment at the vicinity of the mussel bed compared to the sandy area. Furthermore, we found that high cockle densities combined with high densities of other potential prey (i.e. mussels) at the mussel-modified site, mitigated predation effects for adult cockles. Apart from these positive effects on adults, mussel-modified habitat reduced cockle growth, most likely by reducing hydrodynamics in the wake of the mussel bed and by increasing inter-specific competition for food. Our study experimentally underpins the importance of habitat characteristics, competition and predation in interactively structuring intertidal communities
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