24,522 research outputs found
A Fat Higgs with a Fat Top
A new variant of the supersymmetric Fat Higgs model is presented in which the
MSSM Higgses as well as the top quark are composite. The underlying theory is
an s-confining SU(3) gauge theory with the MSSM gauge groups realized as gauged
sub-groups of the chiral flavor symmetries. This motivates the large Yukawas
necessary for the large top mass and SM-like Higgs of mass>>M_Z in a natural
way as the residual of the strong dynamics responsible for the composites. This
removes fine-tuning associated with these couplings present in the original Fat
Higgs and New Fat Higgs models, respectively.Comment: 17 pages, 4 figures, Latex2e, uses JHEP3.cls and youngtab.sty, new
references adde
USHER: an algorithm for particle insertion in dense fluids
The insertion of solvent particles in molecular dynamics simulations of
complex fluids is required in many situations involving open systems, but this
challenging task has been scarcely explored in the literature. We propose a
simple and fast algorithm (USHER) that inserts the new solvent particles at
locations where the potential energy has the desired prespecified value. For
instance, this value may be set equal to the system's excess energy per
particle, in such way that the inserted particles are energetically
indistinguishable from the other particles present. During the search for the
insertion site, the USHER algorithm uses a steepest descent iterator with a
displacement whose magnitude is adapted to the local features of the energy
landscape. The only adjustable parameter in the algorithm is the maximum
displacement and we show that its optimal value can be extracted from an
analysis of the structure of the potential energy landscape. We present
insertion tests in periodic and non-periodic systems filled with a
Lennard-Jones fluid whose density ranges from moderate values to high values.Comment: 10 pages (Latex), 8 figures (postscript); J. Chem. Phys. (in press)
200
Radiatively Generated Isospin Violations in the Nucleon and the NuTeV Anomaly
Predictions of isospin asymmetries of valence and sea distributions are
presented which are generated by QED leading photon
bremsstrahlung effects. Together with isospin violations arising from
nonperturbative hadronic sources (such as quark and target mass differences) as
well as with even a conservative contribution from a strangeness asymmetry
(), the discrepancy between the large NuTeV `anomaly' result for
and the world average of other measurements is removed.Comment: 10 pages, 2 figure
Constraints on spin-dependent parton distributions at large x from global QCD analysis
We investigate the behavior of spin-dependent parton distribution functions
(PDFs) at large parton momentum fractions x in the context of global QCD
analysis. We explore the constraints from existing deep-inelastic scattering
data, and from theoretical expectations for the leading x -> 1 behavior based
on hard gluon exchange in perturbative QCD. Systematic uncertainties from the
dependence of the PDFs on the choice of parametrization are studied by
considering functional forms motivated by orbital angular momentum arguments.
Finally, we quantify the reduction in the PDF uncertainties that may be
expected from future high-x data from Jefferson Lab at 12 GeV.Comment: 14 pages, 3 figures, 1 tabl
Effective mean-field equations for cigar-shaped and disk-shaped Bose-Einstein condensates
By applying the standard adiabatic approximation and using the accurate
analytical expression for the corresponding local chemical potential obtained
in our previous work [Phys. Rev. A \textbf{75}, 063610 (2007)] we derive an
effective 1D equation that governs the axial dynamics of mean-field
cigar-shaped condensates with repulsive interatomic interactions, accounting
accurately for the contribution from the transverse degrees of freedom. This
equation, which is more simple than previous proposals, is also more accurate.
Moreover, it allows treating condensates containing an axisymmetric vortex with
no additional cost. Our effective equation also has the correct limit in both
the quasi-1D mean-field regime and the Thomas-Fermi regime and permits one to
derive fully analytical expressions for ground-state properties such as the
chemical potential, axial length, axial density profile, and local sound
velocity. These analytical expressions remain valid and accurate in between the
above two extreme regimes. Following the same procedure we also derive an
effective 2D equation that governs the transverse dynamics of mean-field
disk-shaped condensates. This equation, which also has the correct limit in
both the quasi-2D and the Thomas-Fermi regime, is again more simple and
accurate than previous proposals. We have checked the validity of our equations
by numerically solving the full 3D Gross-Pitaevskii equation.Comment: 11 pages, 7 figures; Final version published in Phys. Rev. A;
Manuscript put in the archive and submitted to Phys. Rev. A on 17 July 200
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