2,308 research outputs found
Electroweak Constraints on Warped Geometry in Five Dimensions and Beyond
Here we consider the tree level corrections to electroweak (EW) observables
from standard model (SM) particles propagating in generic warped extra
dimensions. The scale of these corrections is found to be dominated by three
parameters, the Kaluza-Klein (KK) mass scale, the relative coupling of the KK
gauge fields to the Higgs and the relative coupling of the KK gauge fields to
fermion zero modes. It is found that 5D spaces that resolve the hierarchy
problem through warping typically have large gauge-Higgs coupling. It is also
found in where the additional dimensions are warped the relative
gauge-Higgs coupling scales as a function of the warp factor. If the warp
factor of the additional spaces is contracting towards the IR brane, both the
relative gauge-Higgs coupling and resulting EW corrections will be large.
Conversely EW constraints could be reduced by finding a space where the
additional dimension's warp factor is increasing towards the IR brane. We
demonstrate that the Klebanov Strassler solution belongs to the former of these
possibilities.Comment: 18 pages, 3 figures (references added) version to appear in JHE
Reducing Constraints in a Higher Dimensional Extension of the Randall and Sundrum Model
In order to investigate the phenomenological implications of warped spaces in
more than five dimensions, we consider a dimensional extension to
the Randall and Sundrum model in which the space is warped with respect to a
single direction by the presence of an anisotropic bulk cosmological constant.
The Einstein equations are solved, giving rise to a range of possible spaces in
which the additional spaces are warped. Here we consider models in
which the gauge fields are free to propagate into such spaces. After carrying
out the Kaluza Klein (KK) decomposition of such fields it is found that the KK
mass spectrum changes significantly depending on how the additional
dimensions are warped. We proceed to compute the lower bound on the KK mass
scale from electroweak observables for models with a bulk
gauge symmetry and models with a bulk gauge
symmetry. It is found that in both cases the most favourable bounds are
approximately TeV, corresponding to a mass of the first gauge
boson excitation of about 4-6 TeV. Hence additional warped dimensions offer a
new way of reducing the constraints on the KK scale.Comment: 27 pages, 15 figures, v3: Additional comments in sections 1, 2 and 4.
New appendix added. Five additional figures. References adde
Additive Manufacturing of Biomechanically Tailored Meshes for Compliant Wearable and Implantable Devices
Additive manufacturing (AM) of medical devices such as orthopedic implants and hearing aids is highly attractive because of AM’s potential to match the complex form and mechanics of individual human bodies. Externally worn and implantable tissue-support devices, such as ankle or knee braces, and hernia repair mesh, offer a new opportunity for AM to mimic tissue-like mechanics and improve both patient outcomes and comfort. Here, it is demonstrated how explicit programming of the toolpath in an extrusion AM process can enable new, flexible mesh materials having digitally tailored mechanical properties and geometry. Meshes are fabricated by extrusion of thermoplastics, optionally with continuous fiber reinforcement, using a continuous toolpath that tailors the elasticity of unit cells of the mesh via incorporation of slack and modulation of filament-filament bonding. It is shown how the tensile mesh mechanics can be engineered to match the nonlinear response of muscle, incorporate printed mesh into an ankle brace with directionally specific inversion stiffness, and present further concepts for tailoring their 3D geometry for medical applications.Financial support was provided by a National Science Foundation Science, Engineering, and Education for Sustainability postdoctoral fellowship (Award number: 1415129) to S.W.P.; a Samsung Scholarship to J.L; the School of Engineering and Sciences from Tecnologico de Monterrey to R.R.; the Manufacturing Demonstration Facility, Oak Ridge National Laboratory, the Department of Energy, UT-Batelle, Oak Ridge Associated Universities, the DOE’s Advanced Manufacturing Office to G.D.; the German Academic Exchange Service (DAAD) to C.M.; and the Eric P. and Evelyn E. Newman Fund and NSF-CRCNS-1724135 to N.H
Suppressing Electroweak Precision Observables in 5D Warped Models
We elaborate on a recently proposed mechanism to suppress large contributions
to the electroweak precision observables in five dimensional (5D) warped
models, without the need for an extended 5D gauge sector. The main ingredient
is a modification of the AdS metric in the vicinity of the infrared (IR) brane
corresponding to a strong deviation from conformality in the IR of the 4D
holographic dual. We compute the general low energy effective theory of the 5D
warped Standard Model, emphasizing additional IR contributions to the wave
function renormalization of the light Higgs mode. We also derive expressions
for the S and T parameters as a function of a generic 5D metric and zero-mode
wave functions. We give an approximate formula for the mass of the radion that
works even for strong deviation from the AdS background. We proceed to work out
the details of an explicit model and derive bounds for the first KK masses of
the various bulk fields. The radion is the lightest new particle although its
mass is already at about 1/3 of the mass of the lightest resonances, the KK
states of the gauge bosons. We examine carefully various issues that can arise
for extreme choices of parameters such as the possible reintroduction of the
hierarchy problem, the onset of nonperturbative physics due to strong IR
curvature or the creation of new hierarchies near the Planck scale. We conclude
that a KK scale of 1 TeV is compatible with all these constraints.Comment: 44 pages, 11 figures, references adde
The effect of lysergic acid diethylamide (LSD) on whole-brain functional and effective connectivity
Psychedelics have emerged as promising candidate treatments for various psychiatric conditions, and given their clinical potential, there is a need to identify biomarkers that underlie their effects. Here, we investigate the neural mechanisms of lysergic acid diethylamide (LSD) using regression dynamic causal modelling (rDCM), a novel technique that assesses whole-brain effective connectivity (EC) during resting-state functional magnetic resonance imaging (fMRI). We modelled data from two randomised, placebo-controlled, double-blind, cross-over trials, in which 45 participants were administered 100 μg LSD and placebo in two resting-state fMRI sessions. We compared EC against whole-brain functional connectivity (FC) using classical statistics and machine learning methods. Multivariate analyses of EC parameters revealed predominantly stronger interregional connectivity and reduced self-inhibition under LSD compared to placebo, with the notable exception of weakened interregional connectivity and increased self-inhibition in occipital brain regions as well as subcortical regions. Together, these findings suggests that LSD perturbs the Excitation/Inhibition balance of the brain. Notably, whole-brain EC did not only provide additional mechanistic insight into the effects of LSD on the Excitation/Inhibition balance of the brain, but EC also correlated with global subjective effects of LSD and discriminated experimental conditions in a machine learning-based analysis with high accuracy (91.11%), highlighting the potential of using whole-brain EC to decode or predict subjective effects of LSD in the future
Ultrasoft NLL Running of the Nonrelativistic O(v) QCD Quark Potential
Using the nonrelativistic effective field theory vNRQCD, we determine the
contribution to the next-to-leading logarithmic (NLL) running of the effective
quark-antiquark potential at order v (1/mk) from diagrams with one potential
and two ultrasoft loops, v being the velocity of the quarks in the c.m. frame.
The results are numerically important and complete the description of ultrasoft
next-to-next-to-leading logarithmic (NNLL) order effects in heavy quark pair
production and annihilation close to threshold.Comment: 25 pages, 7 figures, 3 tables; minor modifications, typos corrected,
references added, footnote adde
Optical Trapping of an Ion
For several decades, ions have been trapped by radio frequency (RF) and
neutral particles by optical fields. We implement the experimental
proof-of-principle for trapping an ion in an optical dipole trap. While
loading, initialization and final detection are performed in a RF trap, in
between, this RF trap is completely disabled and substituted by the optical
trap. The measured lifetime of milliseconds allows for hundreds of oscillations
within the optical potential. It is mainly limited by heating due to photon
scattering. In future experiments the lifetime may be increased by further
detuning the laser and cooling the ion. We demonstrate the prerequisite to
merge both trapping techniques in hybrid setups to the point of trapping ions
and atoms in the same optical potential.Comment: 5 pages, 3 figure
The Custodial Randall-Sundrum Model: From Precision Tests to Higgs Physics
We reexamine the Randall-Sundrum (RS) model with enlarged gauge symmetry
SU(2)_L x SU(2)_R x U(1)_X x P_LR in the presence of a brane-localized Higgs
sector. In contrast to the existing literature, we perform the Kaluza-Klein
(KK) decomposition within the mass basis, which avoids the truncation of the KK
towers. Expanding the low-energy spectrum as well as the gauge couplings in
powers of the Higgs vacuum expectation value, we obtain analytic formulas which
allow for a deep understanding of the model-specific protection mechanisms of
the T parameter and the left-handed Z-boson couplings. In particular, in the
latter case we explain which contributions escape protection and identify them
with the irreducible sources of P_LR symmetry breaking. We furthermore show
explicitly that no protection mechanism is present in the charged-current
sector confirming existing model-independent findings. The main focus of the
phenomenological part of our work is a detailed discussion of Higgs-boson
couplings and their impact on physics at the CERN Large Hadron Collider. For
the first time, a complete one-loop calculation of all relevant Higgs-boson
production and decay channels is presented, incorporating the effects stemming
from the extended electroweak gauge-boson and fermion sectors.Comment: 74 pages, 13 figures, 3 tables. v2: Matches version published in JHE
Flavor Phenomenology in General 5D Warped Spaces
We have considered a general 5D warped model with SM fields propagating in
the bulk and computed explicit expressions for oblique and non-oblique
electroweak observables as well as for flavor and CP violating effective
four-fermion operators. We have compared the resulting lower bounds on the
Kaluza-Klein (KK) scale in the RS model and a recently proposed model with a
metric modified towards the IR brane, which is consistent with oblique
parameters without the need for a custodial symmetry. We have randomly
generated 40,000 sets of O(1) 5D Yukawa couplings and made a fit of the quark
masses and CKM matrix elements in both models. This method allows to identify
the percentage of points consistent with a given KK mass, which in turn
provides us with a measure for the required fine-tuning. Comparison with
current experimental data on Rb, FCNC and CP violating operators exhibits an
improved behavior of our model with respect to the RS model. In particular,
allowing 10% fine-tuning the combined results point towards upper bounds on the
KK gauge boson masses around 3.3 TeV in our model as compared with 13 TeV in
the RS model. One reason for this improvement is that fermions in our model are
shifted, with respect to fermions in the RS model, towards the UV brane thus
decreasing the strength of the modifications of electroweak observables.Comment: 28 pages, 7 figures, 4 table
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