465 research outputs found
On the pion-nucleon coupling constant
In view of persisting misunderstanding about the determination of the
pion-nucleon coupling constants in the Nijmegen multienergy partial-wave
analyses of pp, np, and pbar-p scattering data, we present additional
information which may clarify several points of discussion. We comment on
several recent papers addressing the issue of the pion-nucleon coupling
constant and criticizing the Nijmegen analyses.Comment: 19 pages, Nijmegen preprint THEF-NYM-92-0
Superfluid transition temperature in a trapped gas of Fermi atoms with a Feshbach resonance
We investigate strong coupling effects on the superfluid phase transition in
a gas of Fermi atoms with a Feshbach resonance. The Feshbach resonance
describes a composite quasi-Boson, which can give rise to an additional pairing
interaction between the Fermi atoms. This attractive interaction becomes
stronger as the threshold energy of the Feshbach resonance two-particle bound
state is lowered. In a recent paper, we showed that in the uniform Fermi gas,
this tunable pairing interaction naturally leads to a BCS-BEC crossover of the
Nozi`eres and Schmitt-Rink kind, in which the BCS-type superfluid phase
transition continuously changes into the BEC-type as the threshold energy is
decreased. In this paper, we extend our previous work by including the effect
of a harmonic trap potential, treated within the local density approximation
(LDA). We also give results for both weak and strong coupling to the Feshbach
resonance. We show that the BCS-BEC crossover phenomenon strongly modifies the
shape of the atomic density profile at the superfluid phase transition
temperature Tc, reflecting the change of the dominant particles going from
Fermi atoms to composite Bosons. In the BEC regime, these composite Bosons are
shown to first appear well above Tc. We also discuss the "phase diagram" above
Tc as a function of the tunable threshold energy. We introduce a characteristic
temperature T* describing the effective crossover in the normal phase from a
Fermi gas of atoms to a gas of stable molecules.Comment: 43 pages, 13 figures (submitted to PRA
Dynamics of quantum quenching for BCS-BEC systems in the shallow BEC regime
The problem of coupled Fermi-Bose mixtures of an ultracold gas near a narrow
Feshbach resonance is approached through the time-dependent and complex
Ginzburg-Landau (TDGL) theory. The dynamical system is constructed using
Ginzburg-Landau-Abrikosov-Gor'kov (GLAG) path integral methods with the single
mode approximation for the composite Bosons, and the equilibrium states are
obtained in the BEC regime for adiabatic variations of the Feshbach detuning
along the stationary solutions of the dynamical system. Investigations into the
rich superfluid dynamics of this system in the shallow BEC regime yields the
onset of multiple interference patterns in the dynamics as the system is
quenched from the deep-BEC regime. This results in a partial collapse and
revival of the coherent matter wave field of the BEC, whose temporal profile is
reported.Comment: 24 pages, 7 figures. Submitted to European Journal of Physics Plu
Resonance effects on the crossover of bosonic to fermionic superfluidity
Feshbach scattering resonances are being utilized in atomic gases to explore
the entire crossover region from a Bose-Einstein Condensation (BEC) of
composite bosons to a Bardeen-Cooper-Schrieffer (BCS) of Cooper pairs. Several
theoretical descriptions of the crossover have been developed based on an
assumption that the fermionic interactions are dependent only on the value of a
single microscopic parameter, the scattering length for the interaction of
fermion particles. Such a picture is not universal, however, and is only
applicable to describe a system with an energetically broad Feshbach resonance.
In the more general case in which narrow Feshbach resonances are included in
the discussion, one must consider how the energy dependence of the scattering
phase shift affects the physical properties of the system. We develop a
theoretical framework which allows for a tuning of the scattering phase shift
and its energy dependence, whose parameters can be fixed from realistic
scattering solutions of the atomic physics. We show that BCS-like nonlocal
solutions may build up in conditions of resonance scattering, depending on the
effective range of the interactions.Comment: 8 pages,7 figure
Resonance Superfluidity: Renormalization of Resonance Scattering Theory
We derive a theory of superfluidity for a dilute Fermi gas that is valid when
scattering resonances are present. The treatment of a resonance in many-body
atomic physics requires a novel mean-field approach starting from an
unconventional microscopic Hamiltonian. The mean-field equations incorporate
the microscopic scattering physics, and the solutions to these equations
reproduce the energy-dependent scattering properties. This theory describes the
high- behavior of the system, and predicts a value of which is a
significant fraction of the Fermi temperature. It is shown that this novel
mean-field approach does not break down for typical experimental circumstances,
even at detunings close to resonance. As an example of the application of our
theory we investigate the feasibility for achieving superfluidity in an
ultracold gas of fermionic Li.Comment: 15 pages, 10 figure
The Origins of Bagan: The archaeological landscape of Upper Burma to AD 1300.
The archaeological landscape of Upper Burma from the middle of the first millennium BC to the Bagan period in the 13th-14th century AD is a landscape of continuity. Finds of polished stone and bronze artifacts suggest the existence of early metal-using cultures in the Chindwin and Samon River Valleys, and along parts of the Ayeyarwady plain. Increasing technological and settlement complexity in the Samon Valley suggests that a distinctive culture whose agricultural and trade success can be read in the archaeological record of the Late Prehistoric period developed there. The appearance of the early urban "Pyu" system of walled central places during the early first millennium AD seems to have involved a spread of agricultural and management skills and population from the Samon. The leaders of the urban centres adopted Indic symbols and Sanskrit modes of kingship to enhance and extend their authority. The early urban system was subject over time to a range of stresses including siltation of water systems, external disruption and social changes as Buddhist notions of leadership eclipsed Brahmanical ones. The archaeological evidence indicates that a settlement was forming at Bagan during the last centuries of the first millennium AD. By the mid 11th century Bagan began to dominate Upper Burma, and the region began a transition from a system of largely autonomous city states to a centralised kingdom. Inscriptions of the 11th to 13th centuries indicate that as the Bagan Empire expanded it subsumed the agricultural lands that had been developed by the Pyu
Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton
Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using
data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000.
The corresponding integrated luminosity is 650 pb^{-1}. The values of the
cross-section obtained are found to be in agreement with QED predictions.
Limits on the anomalous magnetic and electric dipole moments of the tau lepton
are deduced.Comment: 20 pages, 9 figures, Accepted by Eur. Phys. J.
CP asymmetry in in a general two-Higgs-doublet model with fourth-generation quarks
We discuss the time-dependent CP asymmetry of decay in an
extension of the Standard Model with both two Higgs doublets and additional
fourth-generation quarks. We show that although the Standard Model with
two-Higgs-doublet and the Standard model with fourth generation quarks alone
are not likely to largely change the effective from the decay of
, the model with both additional Higgs doublet and
fourth-generation quarks can easily account for the possible large negative
value of without conflicting with other experimental
constraints. In this model, additional large CP violating effects may arise
from the flavor changing Yukawa interactions between neutral Higgs bosons and
the heavy fourth generation down type quark, which can modify the QCD penguin
contributions. With the constraints obtained from processes
such as and , this model can lead to the
effective to be as large as in the CP asymmetry of .Comment: 13 pages, 5 figures, references added, to appear in Eur.Phys.J.
Energy dependence of Cronin momentum in saturation model for and collisions
We calculate dependence of Cronin momentum for and
collisions in saturation model. We show that this dependence is consistent with
expectation from formula which was obtained using simple dimentional
consideration. This can be used to test validity of saturation model (and
distinguish among its variants) and measure dependence of saturation
momentum from experimental data.Comment: LaTeX2e, 12 pages, 8 figure
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
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