15,392 research outputs found

### Canonical bases arising from quantum symmetric pairs

We develop a general theory of canonical bases for quantum symmetric pairs
(\mathbf{U}, \mathbf{U}^\imath) with parameters of arbitrary finite type. We
construct new canonical bases for the simple integrable $\mathbf{U}$-modules
and their tensor products regarded as \mathbf{U}^\imath-modules. We also
construct a canonical basis for the modified form of the $\imath$quantum group
\mathbf{U}^\imath. To that end, we establish several new structural results
on quantum symmetric pairs, such as bilinear forms, braid group actions,
integral forms, Levi subalgebras (of real rank one), and integrality of the
intertwiners.Comment: v1, 76 pages. v2, 62 pages, much shortened appendix, modified
introduction and other corrections, to appear in Invent. Mat

### Block Spin Ground State and 3-Dimensionality of (K,Tl)Fe$_{1.6}$Se$_2$

The magnetic properties and electronic structure of (K,Tl)y Fe1.6 Se2 is
studied using first-principles calculations. The ground state is checkerboard
antiferromagnetically coupled blocks of the minimal Fe4 squares, with a large
block spin moment ~11.2{\mu}B . The magnetic interactions could be modelled
with a simple spin model involving both the inter- and intra-block, as well as
the n.n. and n.n.n. couplings. The calculations also suggest a metallic ground
state except for y = 0.8 where a band gap ~400 - 550 meV opens, showing an
antiferromagnetic insulator ground state for (K,Tl)0.8 Fe1.6 Se2 . The
electronic structure of the metallic (K,Tl)y Fe1.6 Se2 is highly 3-dimensional
with unique Fermi surface structure and topology. These features indicate that
the Fe-vacancy ordering is crucial to the physical properties of (K,Tl)y Fe2-x
Se2 .Comment: Magnetic coupling constants double checked, journal ref. adde

### Isospin Diffusion in Heavy-Ion Collisions and the Neutron Skin Thickness of Lead

The correlation between the thickness of the neutron skin in Pb-208, and the
degree of isospin diffusion in heavy-ion collisions is examined. The same
equation of state is used to compute the degree of isospin diffusion in an
isospin-depedent transport model and the neutron skin thickness in the
Hartree-Fock approximation. We find that skin thicknesses less than 0.15 fm are
excluded by the isospin diffusion data.Comment: 5 pages, 4 figures; few minor corrections and updates; version to
appear in PR

### Triton-3He relative and differential flows and the high density behavior of nuclear symmetry energy

Using a transport model coupled with a phase-space coalescence after-burner
we study the triton-3He relative and differential transverse flows in
semi-central 132Sn+124Sn reactions at a beam energy of 400 MeV/nucleon. We find
that the triton-3He pairs carry interesting information about the density
dependence of the nuclear symmetry energy. The t-3He relative flow can be used
as a particularly powerful probe of the high-density behavior of the nuclear
symmetry energy.Comment: 6 pages, 2 figures, Proceeding of The International Workshop on
Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energ

### Constraining the Skyrme effective interactions and the neutron skin thickness of nuclei using isospin diffusion data from heavy ion collisions

Recent analysis of the isospin diffusion data from heavy-ion collisions based
on an isospin- and momentum-dependent transport model with in-medium
nucleon-nucleon cross sections has led to the extraction of a value of $L=88\pm
25$ MeV for the slope of the nuclear symmetry energy at saturation density.
This imposes stringent constraints on both the parameters in the Skyrme
effective interactions and the neutron skin thickness of heavy nuclei. Among
the 21 sets of Skyrme interactions commonly used in nuclear structure studies,
the 4 sets SIV, SV, G$_\sigma$, and R$_\sigma$ are found to give $L$ values
that are consistent with the extracted one. Further study on the correlations
between the thickness of the neutron skin in finite nuclei and the nuclear
matter symmetry energy in the Skyrme Hartree-Fock approach leads to predicted
thickness of the neutron skin of $0.22\pm 0.04$ fm for $^{208}$Pb, $0.29\pm
0.04$ fm for $^{132}$Sn, and $0.22\pm 0.04$ fm for $^{124}$Sn.Comment: 10 pages, 4 figures, 1 Table, Talk given at 1) International
Conference on Nuclear Structure Physics, Shanghai, 12-17 June, 2006; 2) 11th
China National Nuclear Structure Physics Conference, Changchun, Jilin, 13-18
July, 200

### A Note on Topological M5-branes and String-Fivebrane Duality

We derive the stability conditions for the M5-brane in topological M-theory
using kappa-symmetry. The non-linearly self-dual 3-form on the world-volume is
necessarily non-vanishing, as is the case also for the 2-form field strengths
on coisotropic branes in topological string theory. It is demonstrated that the
self-duality is consistent with the stability conditions, which are solved
locally in terms of a tensor in the representation 6 of SU(3) in G_2. The
double dimensional reduction of the M5-brane is the D4-brane, and its direct
reduction is an NS5-brane. We show that the equation of motion for the 3-form
on the NS5-brane wrapping a Calabi-Yau space is exactly the Kodaira-Spencer
equation, providing support for a string-fivebrane duality in topological
string theory.Comment: 11 pp, plain te

### Laboratory studies of photodissociation processes relevant to the formation of cometary radicals

The strength of the C2(d 3 Pi g yields a 3 Pi u) Swan band emission in the spectra of cometary comae identifies this species as a prominent constituent of the coma gas. It was previously suggested that the formation of cometary C2 proceeds via the secondary photolysis of the C2H radical. The detection of C2H in the interstellar medium and the recent analysis of the radial variation in C2(delta V=O) surface brightness of Comet Halley support the postulate that C2 is a third-generation molecule. Measurement of the C2 and C2H translational energy distributions produced from the multiphoton dissociation (MPD) of acetylene at 193 nm are identified . Time-resolved FTIR emission studies of the nascent C2H radical formed in the C2H2 yields C2H + H reaction verify that this species is produced both vibrationally and electronically excited. A survey of the internal energy distributions of the C2 fragments produced from the MPD of acetylene using a high intensity ArF laser is currently in progress in the laboratory. Recent experiments have focused on the measurement of rotational energy distribution for the C2(A 1 Pi u, a 3 Pi u) fragments. The C2(a 3 Pi u) detection capability is currently being improved by performing this experiment in a molecular beam, thus allowing for discrimination between initial emission and laser-induced fluorescence (LIF). Although the experiments performed to date provide considerable evidence in support of C2H yields C2 + H reaction, there is an important distinction to be made when comparing the laboratory conditions to those typically found in comets. The C2H radicals generated in the laboratory experiments are formed vibrationally and/or electronically excited. Any rotationally/vibrationally excited C2H present in cometary comae will quickly undergo radiative relaxation in the infrared to their lowest rotational and vibrational state. Experiments are currently under way to confirm the cometary formation of C2 via the VUV dissociation of cold C2H

### Efficacy of crustal superfluid neutrons in pulsar glitch models

In order to assess the ability of purely crust-driven glitch models to match
the observed glitch activity in the Vela pulsar, we conduct a systematic
analysis of the dependence of the fractional moment of inertia of the inner
crustal neutrons on the stiffness of the nuclear symmetry energy at saturation
density $L$. We take into account both crustal entrainment and the fact that
only a fraction $Y_{\rm g}$ of the core neutrons may couple to the crust on the
glitch-rise timescale. We use a set of consistently-generated crust and core
compositions and equations-of-state which are fit to results of low-density
pure neutron matter calculations. When entrainment is included at the level
suggested by recent microscopic calculations and the core is fully coupled to
the crust, the model is only able to account for the Vela glitch activity for a
1.4$M_{\odot}$ star if the equation of state is particularly stiff $L>100$ MeV.
However, an uncertainty of about 10\% in the crust-core transition density and
pressure allows for the Vela glitch activity to be marginally accounted for in
the range $L\approx30-60$MeV consistent with a range of experimental results.
Alternatively, only a small amount of core neutrons need be involved. If less
than 50\% of the core neutrons are coupled to the crust during the glitch, we
can also account for the Vela glitch activity using crustal neutrons alone for
EOSs consistent with the inferred range of $L$. We also explore the possibility
of Vela being a high-mass neutron star, and of crustal entrainment being
reduced or enhanced relative to its currently predicted values.Comment: 10 pages, 6 figure

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