671 research outputs found
Electroweak Precision Constraints on the Littlest Higgs Model with T Parity
We compute the leading corrections to the properties of W and Z bosons
induced at the one-loop level in the SU(5)/SO(5) Littlest Higgs model with T
parity, and perform a global fit to precision electroweak data to determine the
constraints on the model parameters. We find that a large part of the model
parameter space is consistent with data. Values of the symmetry breaking scale
as low as 500 GeV are allowed, indicating that no significant fine tuning in
the Higgs potential is required. We identify a region within the allowed
parameter space in which the lightest T-odd particle, the partner of the
hypercharge gauge boson, has the correct relic abundance to play the role of
dark matter. In addition, we find that a consistent fit to data can be obtained
for large values of the Higgs mass, up to 800 GeV, due to the possibility of a
partial cancellation between the contributions to the T parameter from Higgs
loops and new physics.Comment: 23 pages, 9 figures. Minor correction
Polarization Transfer in Inelastic Proton Scattering from 12-C and 16-O
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
The Intermediate Higgs
Two paradigms for the origin of electroweak superconductivity are a weakly
coupled scalar condensate, and a strongly coupled fermion condensate. The
former suffers from a finetuning problem unless there are cancelations to
radiative corrections, while the latter presents potential discrepancies with
precision electroweak physics. Here we present a framework for electroweak
symmetry breaking which interpolates between these two paradigms, and mitigates
their faults. As in Little Higgs theories, the Higgs is a pseudo-Nambu
Goldstone boson, potentially composite. The cutoff sensitivity of the one loop
top quark contribution to the effective potential is canceled by contributions
from additional vector-like quarks, and the cutoff can naturally be higher than
in the minimal Standard Model. Unlike the Little Higgs models, the cutoff
sensitivity from one loop gauge contributions is not canceled. However, such
gauge contributions are naturally small as long as the cutoff is below 6 TeV.
Precision electroweak corrections are suppressed relative to those of
Technicolor or generic Little Higgs theories. In some versions of the
intermediate scenario, the Higgs mass is computable in terms of the masses of
these additional fermions and the Nambu-Goldstone Boson decay constant. In
addition to the Higgs, new scalar and pseudoscalar particles are typically
present at the weak scale
A Nonlinear Force-Free Magnetic Field Approximation Suitable for Fast Forward-Fitting to Coronal Loops. I. Theory
We derive an analytical approximation of nonlinear force-free magnetic field
solutions (NLFFF) that can efficiently be used for fast forward-fitting to
solar magnetic data, constrained either by observed line-of-sight magnetograms
and stereoscopically triangulated coronal loops, or by 3D vector-magnetograph
data. The derived NLFFF solutions provide the magnetic field components
, , , the force-free parameter
, the electric current density , and are
accurate to second-order (of the nonlinear force-free -parameter). The
explicit expressions of a force-free field can easily be applied to modeling or
forward-fitting of many coronal phenomena.Comment: Solar Physics (in press), 26 pages, 11 figure
Spin structure of the nucleon at low energies
The spin structure of the nucleon is analyzed in the framework of a
Lorentz-invariant formulation of baryon chiral perturbation theory. The
structure functions of doubly virtual Compton scattering are calculated to
one-loop accuracy (fourth order in the chiral expansion). We discuss the
generalization of the Gerasimov-Drell-Hearn sum rule, the Burkhardt-Cottingham
sum rule and moments of these. We give predictions for the forward and the
longitudinal-transverse spin polarizabilities of the proton and the neutron at
zero and finite photon virtuality. A detailed comparison to results obtained in
heavy baryon chiral perturbation theory is also given.Comment: 29 pp, 14 fig
A Test of the Coplanar and Far-side Features of Intermediate Energy (d,p) Reactions
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
The flavor-changing bottom-strange quark production in the littlest Higgs model with T parity at the ILC
In the littlest Higgs model with T-parity (LHT) the mirror quarks induce the
special flavor structures and some new flavor-changing (FC) couplings which
could greatly enhance the production rates of the FC processes. We in this
paper study some bottom and anti-strange production processes in the LHT model
at the International Linear Collider (ILC), i.e.,
and . The results show that the production
rates of these processes are sizeable for the favorable values of the
parameters. Therefore, it is quite possible to test the LHT model or make some
constrains on the relevant parameters of the LHT through the detection of these
processes at the ILC.Comment: 12 pages, 8 figure
Two photons into \pi^0\pi^0
We perform a theoretical study based on dispersion relations of the reaction
\gamma\gamma\to \pi^0\pi^0 emphasizing the low energy region. We discuss how
the f_0(980) signal emerges in \gamma\gamma\to \pi\pi within the dispersive
approach and how this fixes to a large extent the phase of the isoscalar S-wave
\gamma\gamma\to \pi\pi amplitude above the K\bar{K} threshold. This allows us
to make sharper predictions for the cross section at lower energies and our
results could then be used to distinguish between different \pi\pi isoscalar
S-wave parameterizations with the advent of new precise data on
\gamma\gamma\to\pi^0\pi^0. We compare our dispersive approach with an updated
calculation employing Unitary Chiral Perturbation Theory (U\chiPT). We also pay
special attention to the role played by the \sigma resonance in
\gamma\gamma\to\pi\pi and calculate its coupling and width to gamma\gamma, for
which we obtain \Gamma(\sigma\to\gamma\gamma)=(1.68\pm 0.15) KeV.Comment: 31 pages, 9 figure
Enhancement of the Near-Side Component in Quasi-Adiabatic Calculations of the 66-Zn(d,p)67-Zn Reaction
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Significant Biochemical, Biophysical and Metabolic Diversity in Circulating Human Cord Blood Reticulocytes
10.1371/journal.pone.0076062PLoS ONE810-POLN
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