645 research outputs found
Relativistic Spin-Flavor States in Light Front Dynamics
Orthonormal spin-flavor wave functions of Lorentz covariant quark models of
the Bakamjian-Thomas type are constructed for nucleon resonances. Three
different bases are presented. The manifestly Lorentz covariant Dirac-Melosh
basis is related to the Pauli-Melosh basis and the symmetrized Bargmann-Wigner
basis that are manifestly orthogonal.Comment: 30 pages, 8 tables, no figs; submitted to Ann.Phys.(NY
From Tetraquark to Hexaquark: A Systematic Study of Heavy Exotics in the Large Limit
A systematic study of multiquark exotics with one or heavy quarks in
the large limit is presented. By binding a chiral soliton to a heavy
meson, either a normal -quark baryon or an exotic -quark baryon
is obtained. By replacing the heavy quark with heavy antiquarks, exotic
-quark and -quark mesons are obtained. When , they are
just the normal triquark baryon , the exotic pentaquark baryon , tetraquark di-meson and the hexaquark
di-baryon respectively. Their
stabilities and decays are also discussed. In particular, it is shown that the
``heavy to heavy'' semileptonic decays are described by the Isgur--Wise form
factors of the normal baryons.Comment: 14 pages in REVTeX, no Figure
Role of Sterile Neutrino Warm Dark Matter in Rhenium and Tritium Beta Decays
Sterile neutrinos with mass in the range of one to a few keV are important as
extensions of the Standard Model of particle physics and are serious dark
matter (DM) candidates. This DM mass scale (warm DM) is in agreement with both
cosmological and galactic observations. We study the role of a keV sterile
neutrino through its mixing with a light active neutrino in Rhenium 187 and
Tritium beta decays. We pinpoint the energy spectrum of the beta particle, 0 <
T_e < (Q_{beta} - m_s), as the region where a sterile neutrino could be
detected and where its mass m_s could be measured. This energy region is at
least 1 keV away rom the region suitable to measure the mass of the light
active neutrino, located near the endpoint Q_{beta} . The emission of a keV
sterile neutrino in a beta decay could show up as a small kink in the spectrum
of the emitted beta particle. With this in view, we perform a careful
calculation of the Rhenium and Tritium beta spectra and estimate the size of
this perturbation by means of the dimensionless ratio R of the sterile neutrino
to the active neutrino contributions. We comment on the possibility of
searching for sterile neutrino signatures in two experiments which are
currently running at present, MARE and KATRIN, focused on the Rhenium 187 and
Tritium beta decays respectively.Comment: 16 pages, 10 figures. Version to appear in Nucl. Phys. B. Results and
conclusions unchange
Heavy quarkonium 2S states in light-front quark model
We study the charmonium 2S states and , and the bottomonium
2S states and , using the light-front quark model and the
2S state wave function of harmonic oscillator as the approximation of the 2S
quarkonium wave function. The decay constants, transition form factors and
masses of these mesons are calculated and compared with experimental data.
Predictions of quantities such as Br are made. The
2S wave function may help us learn more about the structure of these heavy
quarkonia.Comment: 5 latex pages, final version for journal publicatio
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
All-optical switching and strong coupling using tunable whispering-gallery-mode microresonators
We review our recent work on tunable, ultrahigh quality factor
whispering-gallery-mode bottle microresonators and highlight their applications
in nonlinear optics and in quantum optics experiments. Our resonators combine
ultra-high quality factors of up to Q = 3.6 \times 10^8, a small mode volume,
and near-lossless fiber coupling, with a simple and customizable mode structure
enabling full tunability. We study, theoretically and experimentally, nonlinear
all-optical switching via the Kerr effect when the resonator is operated in an
add-drop configuration. This allows us to optically route a single-wavelength
cw optical signal between two fiber ports with high efficiency. Finally, we
report on progress towards strong coupling of single rubidium atoms to an
ultra-high Q mode of an actively stabilized bottle microresonator.Comment: 20 pages, 24 figures. Accepted for publication in Applied Physics B.
Changes according to referee suggestions: minor corrections to some figures
and captions, clarification of some points in the text, added references,
added new paragraph with results on atom-resonator interactio
Wind modelling of very massive stars up to 300 solar masses
Some studies have claimed a universal stellar upper-mass limit of 150 Msun. A
factor that is often overlooked is that there might be a difference between the
current and initial masses of the most massive stars, as a result of mass loss.
We present Monte Carlo mass-loss predictions for very massive stars in the
range 40-300 Msun, with large luminosities and Eddington factors Gamma. Using
our new dynamical approach, we find an upturn in the mass-loss vs. Gamma
dependence, at the point where the winds become optically thick. This coincides
with the location where wind efficiency numbers surpass the single-scattering
limit of Eta = 1, reaching values up to Eta = 2.5. Our modelling suggests a
transition from common O-type winds to Wolf-Rayet characteristics at the point
where the winds become optically thick. This transitional behaviour is also
revealed with respect to the wind acceleration parameter beta, which starts at
values below 1 for the optically thin O-stars, and naturally reaches values as
high as 1.5-2 for the optically thick Wolf-Rayet models. An additional finding
concerns the transition in spectral morphology of the Of and WN characteristic
He II line at 4686 Angstrom. When we express our mass-loss predictions as a
function of the electron scattering Gamma_e (=L/M) only, we obtain a mass-loss
Gamma dependence that is consistent with a previously reported power-law Mdot
propto Gamma^5 (Vink 2006) that was based on our semi-empirical modelling
approach. When we express Mdot in terms of both Gamma and stellar mass, we find
Mdot propto M^0.8 Gamma^4.8 for our high Gamma models. Finally, we confirm that
the Gamma-effect on the mass-loss predictions is much stronger than that of an
increased helium abundance, calling for a fundamental revision in the way mass
loss is incorporated in evolutionary models of the most massive stars.Comment: minor language changes (Astronomy & Astrophysics in press - 11 pages,
10 figures
Optimal measurements for simultaneous quantum estimation of multiple phases
A quantum theory of multiphase estimation is crucial for quantum-enhanced
sensing and imaging and may link quantum metrology to more complex quantum
computation and communication protocols. In this letter we tackle one of the
key difficulties of multiphase estimation: obtaining a measurement which
saturates the fundamental sensitivity bounds. We derive necessary and
sufficient conditions for projective measurements acting on pure states to
saturate the maximal theoretical bound on precision given by the quantum Fisher
information matrix. We apply our theory to the specific example of
interferometric phase estimation using photon number measurements, a convenient
choice in the laboratory. Our results thus introduce concepts and methods
relevant to the future theoretical and experimental development of
multiparameter estimation.Comment: 4 pages + appendix, 2 figure
Non-identical particle correlations in 130 and 200 AGeV collisions at STAR
STAR has performed a correlation analyses of pion-kaon and pion-proton pairs
for sqrt(s_NN)=130 AGeV and sqrt(s_NN)=200 AGeV and kaon-proton, proton-Lambda
and pion-Cascade pairs for AuAu collisions sqrt(s_NN)=200 AGeV. They show that
average emission space-time points of pions, kaons and protons are not the
same. These asymmetries are interpreted as a consequence of transverse radial
expansion of the system; emission time differences explain only part of the
asymmetry. Therefore our measurements independently confirm the existence of
transverse radial flow. Furthermore, correlations of strange hyperons is
investigated by performing proton-Lambda and pion-Cascade analyses, giving
estimates of source size at high m_{T}. The strong interaction potential
between (anti-)proton and lambda as well as kaon and proton is investigated.Comment: 5 pages, 3 figures, Quark Matter 04 proceedings, submitted to J.
Phys. G: Nucl. Phy
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