2,755 research outputs found
Electroweak Symmetry Breaking and Large Extra Dimensions
If spacetime contains large compact extra dimensions, the fundamental mass
scale of nature, , may be close to the weak scale, allowing
gravitational physics to significantly modify electroweak symmetry breaking.
Operators of the form and , where and are the SU(2) and U(1) field strengths and is
the Higgs field, remove the precision electroweak bound on the Higgs boson mass
for values of in a wide range: . Within this
framework, there is no preference between a light Higgs boson, a heavy Higgs
boson, or a non-linearly realized SU(2)xU(1) symmetry beneath . If
there is a Higgs doublet, then operators of the form , where and are the QCD and electromagnetic field strengths,
modify the production of the Higgs boson by gluon-gluon fusion, and the decay
of the Higgs boson to 2 photons, respectively. At Run II of the Tevatron
collider, a 2-photon signal for extra dimensions will be discovered if
is below 2.5 (1) TeV for a Higgs boson of mass 100 (300) GeV. Furthermore, such
a signal would point to gravitational physics, rather than to new conventional
gauge theories at . The discovery potential of the LHC depends
sensitively on whether the gravitational amplitudes interfere constructively or
destructively with the standard model amplitudes, and ranges from = 3
- 10 (2 - 4) TeV for a light (heavy) Higgs boson.Comment: 14 pages LaTeX, 3 figure
CFD Modeling Of Very High Air Flow In A Residential Clothes Dryer To Investigate Pressure Loss And Flow Through The Air Flow Path
A New Perspective on Cosmic Coincidence Problems
Cosmological data suggest that we live in an interesting period in the
history of the universe when \rho_\Lambda \sim \rho_M \sim \rho_R. The
occurence of any epoch with such a "triple coincidence" is puzzling, while the
question of why we happen to live during this special epoch is the "Why now?"
problem. We introduce a framework which makes the triple coincidence
inevitable; furthermore, the ``Why now?'' problem is transformed and greatly
ameliorated. The framework assumes that the only relevant mass scales are the
electroweak scale, M_{EW}, and the Planck scale, M_{Pl}, and requires
\rho_\Lambda^{1/4} \sim M_{EW}^2/M_{Pl} parametrically. Assuming that the true
vacuum energy vanishes, we present a simple model where a false vacuum energy
yields a cosmological constant of this form.Comment: 5 pages, 1 figure, uses psfig. Refs added, slightly enhance
New Mechanism of Flavor Symmetry Breaking from Supersymmetric Strong Dynamics
We present a class of supersymmetric models in which flavor symmetries are
broken dynamically, by a set of composite flavon fields. The strong dynamics
that is responsible for confinement in the flavor sector also drives flavor
symmetry breaking vacuum expectation values, as a consequence of a
quantum-deformed moduli space. Yukawa couplings result as a power series in the
ratio of the confinement to Planck scale, and the fermion mass hierarchy
depends on the differing number of preons in different flavor symmetry-breaking
operators. We present viable non-Abelian and Abelian flavor models that
incorporate this mechanism.Comment: 24 pp. LaTe
A Supersymmetric Theory of Flavor and R Parity
We construct a renormalizable, supersymmetric theory of flavor and parity
based on the discrete flavor group . The model can account for all the
masses and mixing angles of the Standard Model, while maintaining sufficient
squark degeneracy to circumvent the supersymmetric flavor problem. By starting
with a simpler set of flavor symmetry breaking fields than we have suggested
previously, we construct an economical Froggatt-Nielsen sector that generates
the desired elements of the fermion Yukawa matrices. With the particle content
above the flavor scale completely specified, we show that all renormalizable
-parity-violating interactions involving the ordinary matter fields are
forbidden by the flavor symmetry. Thus, parity arises as an accidental
symmetry in our model. Planck-suppressed operators that violate parity, if
present, can be rendered harmless by taking the flavor scale to be GeV.Comment: 28 pp. LaTeX, 1 Postscript Figur
SUSY, the Third Generation and the LHC
We develop a bottom-up approach to studying SUSY with light stops and
sbottoms, but with other squarks and sleptons heavy and beyond reach of the
LHC. We discuss the range of squark, gaugino and Higgsino masses for which the
electroweak scale is radiatively stable over the "little hierarchy" below ~ 10
TeV. We review and expand on indirect constraints on this scenario, in
particular from flavor and CP tests. We emphasize that in this context,
R-parity violation is very well motivated. The phenomenological differences
between Majorana and Dirac gauginos are also discussed. Finally, we focus on
the light subsystem of stops, sbottom and neutralino with R-parity, in order to
probe the current collider bounds. We find that 1/fb LHC bounds are mild and
large parts of the motivated parameter space remain open, while the 10/fb data
can be much more decisive.Comment: 42 pages, 8 figures, 1 table. V2: minor corrections, references adde
nnResting state fMRI scanner instabilities revealed by longitud inal phantom scans in a multi-center study
Quality assurance (QA) is crucial in longitudinal and/or multi-site studies, which involve the collection of data from a group of subjects over time and/or at different locations. It is important to regularly monitor the performance of the scanners over time and at different locations to detect and control for intrinsic differences (e.g., due to manufacturers) and changes in scanner performance (e.g., due to gradual component aging, software and/or hardware upgrades, etc.). As part of the Ontario Neurodegenerative Disease Research Initiative (ONDRI) and the Canadian Biomarker Integration Network in Depression (CAN-BIND), QA phantom scans were conducted approximately monthly for three to four years at 13 sites across Canada with 3T research MRI scanners. QA parameters were calculated for each scan using the functional Biomarker Imaging Research Network\u27s (fBIRN) QA phantom and pipeline to capture between- and within-scanner variability. We also describe a QA protocol to measure the full-width-at-half-maximum (FWHM) of slice-wise point spread functions (PSF), used in conjunction with the fBIRN QA parameters. Variations in image resolution measured by the FWHM are a primary source of variance over time for many sites, as well as between sites and between manufacturers. We also identify an unexpected range of instabilities affecting individual slices in a number of scanners, which may amount to a substantial contribution of unexplained signal variance to their data. Finally, we identify a preliminary preprocessing approach to reduce this variance and/or alleviate the slice anomalies, and in a small human data set show that this change in preprocessing can have a significant impact on seed-based connectivity measurements for some individual subjects. We expect that other fMRI centres will find this approach to identifying and controlling scanner instabilities useful in similar studies
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