101,863 research outputs found
A Classification and Analysis of Higgs-flavor Models
A classification is given of Higgs-flavor models. In these models, there are
several Higgs doublets in an irreducible multiplet R_{Phi} of a non-abelian
symmetry G_{Phi}, under which the quarks and leptons do not transform (thus
giving minimal flavor-changing for the fermions). It is found that different
G_{Phi} and R_{Phi} lead to very distinctive spectra of the extra Higgs
doublets, including different numbers of "sequential Higgs" and of "inert
Higgs" that could play the role of dark matter, different mass relations, and
different patterns of SU(2)_L-breaking splittings within the Higgs doublets.Comment: 35 page
Interplay of Spin and Orbital Angular Momentum in the Proton
We derive the consequences of the Myhrer-Thomas explanation of the proton
spin problem for the distribution of orbital angular momentum on the valence
and sea quarks. After QCD evolution these results are found to be in very good
agreement with both recent lattice QCD calculations and the experimental
constraints from Hermes and JLab
Preliminary results of noble metal thermocouple research program, 1000 - 2000 C
Noble metal thermocouple research involving combustion gase
Numerical calculations of a high brilliance synchrotron source and on issues with characterizing strong radiation damping effects in non-linear Thomson/Compton backscattering experiments
A number of theoretical calculations have studied the effect of radiation
reaction forces on radiation distributions in strong field counter-propagating
electron beam-laser interactions, but could these effects - including quantum
corrections - be observed in interactions with realistic bunches and focusing
fields, as is hoped in a number of soon to be proposed experiments? We present
numerical calculations of the angularly resolved radiation spectrum from an
electron bunch with parameters similar to those produced in laser wakefield
acceleration experiments, interacting with an intense, ultrashort laser pulse.
For our parameters, the effects of radiation damping on the angular
distribution and energy distribution of \emph{photons} is not easily
discernible for a "realistic" moderate emittance electron beam. However,
experiments using such a counter-propagating beam-laser geometry should be able
to measure such effects using current laser systems through measurement of the
\emph{electron beam} properties. In addition, the brilliance of this source is
very high, with peak spectral brilliance exceeding
photonssmmmrad% bandwidth with
approximately 2% efficiency and with a peak energy of 10 MeV.Comment: 11 figures, 11 page
Decoherence of spin echoes
We define a quantity, the so-called purity fidelity, which measures the rate
of dynamical irreversibility due to decoherence, observed e.g in echo
experiments, in the presence of an arbitrary small perturbation of the total
(system + environment) Hamiltonian. We derive a linear response formula for the
purity fidelity in terms of integrated time correlation functions of the
perturbation. Our relation predicts, similarly to the case of fidelity decay,
faster decay of purity fidelity the slower decay of time correlations is. In
particular, we find exponential decay in quantum mixing regime and faster,
initially quadratic and later typically gaussian decay in the regime of
non-ergodic, e.g. integrable quantum dynamics. We illustrate our approach by an
analytical calculation and numerical experiments in the Ising spin 1/2 chain
kicked with tilted homogeneous magnetic field where part of the chain is
interpreted as a system under observation and part as an environment.Comment: 22 pages, 10 figure
Flow field predictions for a slab delta wing at incidence
Theoretical results are presented for the structure of the hypersonic flow field of a blunt slab delta wing at moderately high angle of attack. Special attention is devoted to the interaction between the boundary layer and the inviscid entropy layer. The results are compared with experimental data. The three-dimensional inviscid flow is computed numerically by a marching finite difference method. Attention is concentrated on the windward side of the delta wing, where detailed comparisons are made with the data for shock shape and surface pressure distributions. Surface streamlines are generated, and used in the boundary layer analysis. The three-dimensional laminar boundary layer is computed numerically using a specially-developed technique based on small cross-flow in streamline coordinates. In the rear sections of the wing the boundary layer decreases drastically in the spanwise direction, so that it is still submerged in the entropy layer at the centerline, but surpasses it near the leading edge. Predicted heat transfer distributions are compared with experimental data
Radio-frequency dressing of multiple Feshbach resonances
We demonstrate and theoretically analyze the dressing of several proximate
Feshbach resonances in Rb-87 using radio-frequency (rf) radiation. We present
accurate measurements and characterizations of the resonances, and the dramatic
changes in scattering properties that can arise through the rf dressing. Our
scattering theory analysis yields quantitative agreement with the experimental
data. We also present a simple interpretation of our results in terms of
rf-coupled bound states interacting with the collision threshold.Comment: 4+ pages, 3 figures, 1 table; revised introduction & references to
reflect published versio
Gravitational Instantons and Fluxes from M/F-theory on Calabi-Yau fourfolds
We compactify four-dimensional N=1 gauged supergravity theories on a circle
including fluxes for shift-symmetric scalars. Four-dimensional Taub-NUT
gravitational instantons universally correct the three-dimensional
superpotential in the absence of fluxes. In the presence of fluxes these
Taub-NUT instanton contributions are no longer gauge-invariant. Invariance can
be restored by gauge instantons on top of Taub-NUT instantons. We establish the
embedding of this scenario into M-theory. Circle fluxes and gaugings arise from
a restricted class of M-theory four-form fluxes on a resolved Calabi-Yau
fourfold. The M5-brane on the base of the elliptic fourfold dualizes into the
universal Taub-NUT instanton. In the presence of fluxes this M5-brane is
anomalous. We argue that anomaly free contributions arise from involved
M5-brane geometries dual to gauge-instantons on top of Taub-NUT instantons.
Adding a four-dimensional superpotential to the gravitational instanton
corrections leads to three-dimensional Anti-de Sitter vacua at stabilized
compactification radius. We comment on the possibility to uplift these M-theory
vacua, and to tunnel to four-dimensional F-theory vacua.Comment: 47 pages, 2 figure
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