987 research outputs found
Quark-Hadron Duality and Parity Violating Asymmetry of Electroweak Reactions in the Delta Region
A dynamical model of electroweak pion production reactions in the Delta(1232)
region has been extended to include the neutral current contributions for
examining the local Quark-Hadron Duality in neutrino-induced reactions and for
investigating how the axial N-Delta form factor can be determined by the parity
violating asymmetry of N(\vec{e},e') reactions. We first show that the recent
data of (e,e') structure functions F_1 and F_2, which exhibit the Quark-Hadron
Duality, are in good agreement with our predictions. For possible future
experimental tests, we then predict that the structure functions F_1, F_2, and
F_3 for (\nu,e) and (\nu,\nu') processes also show the similar Quark-Hadron
Duality. The spin dependent structure functions g_1 and g_2 of (e,e') have also
been calculated from our model. It is found that the local Quark-Hadron Duality
is not seen in the calculated g_1 and g_2, while our results for g_1 and some
polarization observables associated with the exclusive p(\vec{e},e' pi) and
\vec{p}(\vec{e},e' pi) reactions are in reasonably good agreement with the
recent data. In the investigation of parity violating asymmetry A of
N(\vec{e},e') reactions, it is found that the non-resonant contribution is
small at the Delta peak and a measurement of A can be used to distinguish two
previously determined axial N-Delta transition form factors. The predicted
asymmetry A are also compared with the Parton Model predictions for future
experimental investigations of Quark-Hadron Duality.Comment: 28 pages, 19 figures v2; figures and references adde
M-Theory of Matrix Models
Small M-theories unify various models of a given family in the same way as
the M-theory unifies a variety of superstring models. We consider this idea in
application to the family of eigenvalue matrix models: their M-theory unifies
various branches of Hermitean matrix model (including Dijkgraaf-Vafa partition
functions) with Kontsevich tau-function. Moreover, the corresponding duality
relations look like direct analogues of instanton and meron decompositions,
familiar from Yang-Mills theory.Comment: 12 pages, contribution to the Proceedings of the Workshop "Classical
and Quantum Integrable Systems", Protvino, Russia, January, 200
Electroproduction, photoproduction, and inverse electroproduction of pions in the first resonance region
Methods are set forth for determining the hadron electromagnetic structure in
the sub--threshold timelike region of the virtual-photon ``mass'' and
for investigating the nucleon weak structure in the spacelike region from
experimental data on the process at low energies. These
methods are formulated using the unified description of photoproduction,
electroproduction, and inverse electroproduction of pions in the first
resonance region in the framework of the dispersion-relation model and on the
basis of the model-independent properties of inverse electroproduction.
Applications of these methods are also shown.Comment: The revised published version; Revtex4, 18 pages, 6 figure
Brane Decay and Death of Open Strings
We show how open strings cease to propagate when unstable D-branes decay. The
information on the propagation is encoded in BSFT two-point functions for
arbitrary profiles of open string excitations. We evaluate them in tachyon
condensation backgrounds corresponding to (i) static spatial tachyon kink (=
lower dimensional BPS D-brane) and (ii) homogeneous rolling tachyon. For (i)
the propagation is restricted to the directions along the tachyon kink, while
for (ii) all the open string excitations cease to propagate at late time and
are subject to a collapsed light cone characterized by Carrollian contraction
of Lorentz group.Comment: 19 pages, published version (typos corrected, a reference added
Challenges of Matrix Models
Brief review of concepts and unsolved problems in the theory of matrix
models.Comment: Contribution to Proceedings of Cargese 200
The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water
Comet 81P/Wild 2 samples returned by NASA's Stardust mission provide an unequalled opportunity to study the contents of, and hence conditions and processes operating on, comets. They can potentially validate contentious interpretations of cometary infrared spectra and in situ mass spectrometry data: specifically the identification of phyllosilicates and carbonates. However, Wild 2 dust was collected via impact into capture media at ~6 km s−1, leading to uncertainty as to whether these minerals were captured intact, and, if subjected to alteration, whether they remain recognizable. We simulated Stardust Al foil capture conditions using a two‐stage light‐gas gun, and directly compared transmission electron microscope analyses of pre‐ and postimpact samples to investigate survivability of lizardite and cronstedtite (phyllosilicates) and calcite (carbonate). We find the phyllosilicates do not survive impact as intact crystalline materials but as moderately to highly vesiculated amorphous residues lining resultant impact craters, whose bulk cation to Si ratios remain close to that of the impacting grain. Closer inspection reveals variation in these elements on a submicron scale, where impact‐induced melting accompanied by reducing conditions (due to the production of oxygen scavenging molten Al from the target foils) has resulted in the production of native silicon and Fe‐ and Fe‐Si‐rich phases. In contrast, large areas of crystalline calcite are preserved within the calcite residue, with smaller regions of vesiculated, Al‐bearing calcic glass. Unambiguous identification of calcite impactors on Stardust Al foil is therefore possible, while phyllosilicate impactors may be inferred from vesiculated residues with appropriate bulk cation to Si ratios. Finally, we demonstrate that the characteristic textures and elemental distributions identifying phyllosilicates and carbonates by transmission electron microscopy can also be observed by state‐of‐the‐art scanning electron microscopy providing rapid, nondestructive initial mineral identifications in Stardust residues
Hidden sl(2,R) Symmetry in 2D CFTs and the Wave Function of 3D Quantum Gravity
We show that all two-dimensional conformal field theories possess a hidden
sl(2,R) affine symmetry. More precisely, we add appropriate ghost fields to an
arbitrary CFT, and we use them to construct the currents of sl(2,R). We then
define a BRST operator whose cohomology defines a physical subspace where the
extended theory coincides with the original CFT. We use the sl(2,R) algebra to
construct candidate wave functions for 3-d quantum gravity coupled to matter,
and we discuss their viability.Comment: Minor misprints corrected.Eight references added. To appear in
JHEP.34 pages, LaTe
An Improved Brane Anti-Brane Action from Boundary Superstring Field Theory and Multi-Vortex Solutions
We present an improved effective action for the D-brane-anti-D-brane system
obtained from boundary superstring field theory. Although the action looks
highly non-trivial, it has simple explicit multi-vortex (i.e. codimension-2
multi-BPS D-brane) multi-anti-vortex solutions. The solutions have a curious
degeneracy corresponding to different ``magnetic'' fluxes at the core of each
vortex. We also generalize the brane anti-brane effective action that is
suitable for the study of the inflationary scenario and the production of
defects in the early universe. We show that when a brane and anti-brane are
distantly separated, although the system is classically stable it can decay via
quantum tunneling through the barrier.Comment: 24 pages, 1 figure, JHEP3.cls; v2: references added, tunneling rate
discussion expande
Observation of confined current ribbon in JET plasmas
we report the identification of a localised current structure inside the JET
plasma. It is a field aligned closed helical ribbon, carrying current in the
same direction as the background current profile (co-current), rotating
toroidally with the ion velocity (co-rotating). It appears to be located at a
flat spot in the plasma pressure profile, at the top of the pedestal. The
structure appears spontaneously in low density, high rotation plasmas, and can
last up to 1.4 s, a time comparable to a local resistive time. It considerably
delays the appearance of the first ELM.Comment: 10 pages, 6 figure
Small Momentum Evolution of the Extended Drell--Hearn--Gerasimov Sum Rule
We investigate the momentum dependence of the extended Drell-Hearn-Gerasimov
sum rule. An economical formalism is developed which allows to express the
extended DHG sum rule in terms of a single virtual Compton amplitude in forward
direction. Rigorous results for the small momentum evolution are derived from
chiral perturbation theory within the one-loop approximation. Furthermore, we
evaluate some higher order contributions arising from
intermediate states and relativistic corrections. (2 figures available upon
request).Comment: 12 pages, TeX, BUTP-92/51 and CRN-92-5
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