481 research outputs found
5-dimensional contact SO(3)-manifolds and Dehn twists
In this paper the 5-dimensional contact SO(3)-manifolds are classified up to
equivariant contactomorphisms. The construction of such manifolds with singular
orbits requires the use of generalized Dehn twists.
We show as an application that all simply connected 5-manifoldswith singular
orbits are realized by a Brieskorn manifold with exponents (k,2,2,2). The
standard contact structure on such a manifold gives right-handed Dehn twists,
and a second contact structure defined in the article gives left-handed twists.Comment: 16 pages, 1 figure; simplification of arguments by restricting
classification to coorientation preserving contactomorphism
Antiflow of kaons in relativistic heavy ion collisions
We compare relativistic transport model calculations to recent data on the
sideward flow of neutral strange K^0_s mesons for Au+Au collisions at 6 AGeV. A
soft nuclear equation of state is found to describe very well the positive
proton flow data measured in the same experiment. In the absence of kaon
potential, the K^0 flow pattern is similar to that of protons. The kaon flow
becomes negative if a repulsive kaon potential determined from the impulse
approximation is introduced. However, this potential underestimates the data
which exhibits larger antiflow. An excellent agreement with the data is
obtained when a relativistic scalar-vector kaon potential, that has stronger
density dependence, is used. We further find that the transverse momentum
dependence of directed and elliptic flow is quite sensitive to the kaon
potential in dense matter.Comment: 5 pages, Revtex, 4 figure
Nucleon Resonance Transition Couplings to Vector Mesons
Recent heavy ion experiments indicate modifications of the meson mass
in medium. In the CERES experiments mesons are produced at normal
nuclear matter density, where hadrons are more appropriate constituents than
quarks. A collective "nuclear ", in which every nucleon is excited to the
N(1520) state, with equal amplitude, enters in this description. At the higher
densities reached by future experiments constituent quarks become the
appropriate variables. Here the and transition couplings to the
nucleon resonances up to 1700 MeV, including the N(1520), are derived by means
of the chiral quark model. The relevant coupling constants are expressed in
terms of the corresponding vector coupling constants to nucleons. The quality
of the model relations is tested by a calculation of the corresponding
pion-resonance coupling constants, which are known from the empirical pion
decay widths.Comment: 30 pages, Late
Negative Kaons in Dense Baryonic Matter
Kaon polarization operator in dense baryonic matter of arbitrary isotopic
composition is calculated including s- and p-wave kaon-baryon interactions. The
regular part of the polarization operator is extracted from the realistic
kaon-nucleon interaction based on the chiral and 1/N_c expansion. Contributions
of the Lambda(1116), Sigma(1195), Sigma*(1385) resonances are taken explicitly
into account in the pole and regular terms with inclusion of mean-field
potentials. The baryon-baryon correlations are incorporated and fluctuation
contributions are estimated. Results are applied for K- in neutron star matter.
Within our model a second-order phase transition to the s-wave K- condensate
state occurs at rho_c \gsim 4 \rho_0 once the baryon-baryon correlations are
included. We show that the second-order phase transition to the p-wave
condensate state may occur at densities in
dependence on the parameter choice. We demonstrate that a first-order phase
transition to a proton-enriched (approximately isospin-symmetric) nucleon
matter with a p-wave K- condensate can occur at smaller densities, \rho\lsim 2
\rho_0. The transition is accompanied by the suppression of hyperon
concentrations.Comment: 41 pages, 24 figures, revtex4 styl
Applying precision methods to treatment selection for moderate/severe depression in person-centered experiential therapy or cognitive behavioral therapy
Objective:
To develop two prediction algorithms recommending person-centered experiential therapy (PCET) or cognitiveâbehavioral therapy (CBT) for patients with depression: (1) a full data model using multiple trial-based and routine variables, and (2) a routine data model using only variables available in the English NHS Talking Therapies program.
Method:
Data was used from the PRaCTICED trial comparing PCET vs. CBT for 255 patients meeting a diagnosis of moderate or severe depression. Separate full and routine data models were derived and the latter tested in an external data sample.
Results:
The full data model provided the better prediction, yielding a significant difference in outcome between patients receiving their optimal vs. non-optimal treatment at 6- (Cohenâs d =.65 [.40,.91]) and 12 months (d =.85 [.59, 1.10]) post-randomization. The routine data model performed similarly in the training and test samples with non-significant effect sizes, d =.19 [â.05,.44] and d =.21 [â.00,.43], respectively. For patients with the strongest treatment matching (d â„ 0.3), the resulting effect size was significant, d =.38 [.11, 64].
Conclusion:
A treatment selection algorithm might be used to recommend PCET or CBT. Although the overall effects were small, targeted matching yielded somewhat larger effects
K^+ versus \Lambda flow in relativistic heavy-ion collisions
We study and flow in heavy-ion collisions at beam energies of
about 2A GeV. We present our results in both the `traditional' (i.e., in terms
of the average transverse momentum in the reaction plane) as well as `modern'
(i.e., in terms of coefficients of the Fourier analysis of azimuthal
distributions) methods of flow analysis. We find significant differences
between the and the flow: while the flow is basically
similar to that of nucleons, the flow almost disappears. This difference
is attributed chiefly to their different mean field potentials in dense matter.
The comparisons with the experimental data, as well as theoretical results from
independent calculations, indicate clearly the pivotal roles of both and
medium effects. We emphasize that similar experimental data from
independent collaborations are essential for the eventual verification of these
medium effects.Comment: RevTeX, 11 pages, including 18 postscript figures, to be published in
Nuclear Physics
Simultaneous Softening of sigma and rho Mesons associated with Chiral Restoration
Complex poles of the unitarized pi-pi scattering amplitude in nuclear matter
are studied. Partial restoration of chiral symmetry is modeled by the decrease
of in-medium pion decay constant f*_{pi}.
For large chiral restoration (f*_{pi}/f_{pi} << 1),
2nd sheet poles in the scalar (sigma) and the vector (rho) mesons are both
dictated by the Lambert W function and show universal softening as f*_{pi}
decreases.
In-medium pi-pi cross section receives substantial contribution from the soft
mode and exhibits a large enhancement in low-energy region.
Fate of this universality for small chiral restoration (f*_{pi}/f_{pi} ~ 1)
is also discussed.Comment: 5 pages, 4-eps figures, version accepted by Phys. Rev. C (R) with
minor modification
Antikaon condensation and the metastability of protoneutron stars
We investigate the condensation of meson along with
condensation in the neutrino trapped matter with and without hyperons.
Calculations are performed in the relativistic mean field models in which both
the baryon-baryon and (anti)kaon-baryon interactions are mediated by meson
exchange. In the neutrino trapped matter relevant to protoneutron stars, the
critical density of condensation is shifted considerably to higher
density whereas that of condensation is shifted slightly to higher
density with respect to that of the neutrino free case. The onset of
condensation always occurs earlier than that of condensation. A
significant region of maximum mass protoneutron stars is found to contain condensate for larger values of the antikaon potential. With the
appearance of condensation, there is a region of symmetric nuclear
matter in the inner core of a protoneutron star. It is found that the maximum
mass of a protoneutron star containing and condensate is
greater than that of the corresponding neutron star. We revisit the implication
of this scenario in the context of the metastability of protoneutron stars and
their evolution to low mass black holes.Comment: 26 pages; Revtex; 8 figures include
Hadronic properties of the S_{11}(1535) studied by electroproduction off the deuteron
Properties of excited baryonic states are investigated in the context of
electroproduction of baryon resonances off the deuteron. In particular, the
hadronic radii and the compositeness of baryon resonances are studied for
kinematic situations in which their hadronic reinteraction is the dominant
contribution. Specifically, we study the reaction at for kinematics in which the produced hadronic state reinteracts
predominantly with the spectator nucleon. A comparison of constituent quark
model and effective chiral Lagrangian calculations of the shows
substantial sensitivity to the structure of the produced resonance.Comment: 24 pages, 5 figure
Dilepton production in heavy ion collisions at intermediate energies
We present a unified description of the vector meson and dilepton production
in elementary and in heavy ion reactions. The production of vector mesons
() is described via the excitation of nuclear resonances ().
The theoretical framework is an extended vector meson dominance model (eVMD).
The treatment of the resonance decays with arbitrary spin is
covariant and kinematically complete. The eVMD includes thereby excited vector
meson states in the transition form factors. This ensures correct asymptotics
and provides a unified description of photonic and mesonic decays. The
resonance model is successfully applied to the production in
reactions. The same model is applied to the dilepton production in elementary
reactions (). Corresponding data are well reproduced. However, when
the model is applied to heavy ion reactions in the BEVALAC/SIS energy range the
experimental dilepton spectra measured by the DLS Collaboration are
significantly underestimated at small invariant masses. As a possible solution
of this problem the destruction of quantum interference in a dense medium is
discussed. A decoherent emission through vector mesons decays enhances the
corresponding dilepton yield in heavy ion reactions. In the vicinity of the
-peak the reproduction of the data requires further a substantial
collisional broadening of the and in particular of the meson.Comment: 32 pages revtex, 19 figures, to appear in PR
- âŠ