79,029 research outputs found
Higher-spin Realisations of the Bosonic String
It has been shown that certain algebras can be linearised by the
inclusion of a spin--1 current. This provides a way of obtaining new
realisations of the algebras. Recently such new realisations of were
used in order to embed the bosonic string in the critical and non-critical
strings. In this paper, we consider similar embeddings in and
strings. The linearisation of is already known, and can be
achieved for all values of central charge. We use this to embed the bosonic
string in critical and non-critical strings. We then derive the
linearisation of using a spin--1 current, which turns out to be
possible only at central charge . We use this to embed the bosonic
string in a non-critical string.Comment: 8 pages. CTP TAMU-10/95
Liouville and Toda Solitons in M-theory
We study the general form of the equations for isotropic single-scalar,
multi-scalar and dyonic -branes in superstring theory and M-theory, and show
that they can be cast into the form of Liouville, Toda (or Toda-like)
equations. The general solutions describe non-extremal isotropic -branes,
reducing to the previously-known extremal solutions in limiting cases. In the
non-extremal case, the dilatonic scalar fields are finite at the outer event
horizon.Comment: Latex, 10 pages. Minor corrections to text and titl
Collective flow of open and hidden charm in Au+Au collisions at = 200 GeV
We study the collective flow of open charm mesons and charmonia in Au+Au
collisions at = 200 GeV within the hadron-string-dynamics (HSD)
transport approach. The detailed studies show that the coupling of
mesons to the light hadrons leads to comparable directed and elliptic flow as
for the light mesons. This also holds approximately for mesons since
more than 50% of the final charmonia for central and mid-central collisions
stem from induced reactions in the transport calculations. The
transverse momentum spectra of mesons and 's are only very
moderately changed by the (pre-)hadronic interactions in HSD which can be
traced back to the collective flow generated by elastic interactions with the
light hadrons.Comment: 9 pages, 8 figures, Phys. Rev. C, in pres
Structure and decays of nuclear three-body systems: the Gamow coupled-channel method in Jacobi coordinates
Weakly bound and unbound nuclear states appearing around
particle thresholds are prototypical open quantum systems. Theories of such
states must take into account configuration mixing effects in the presence of
strong coupling to the particle continuum space.
To describe structure and decays of three-body systems, we
developed a Gamow coupled-channel (GCC) approach in Jacobi coordinates by
employing the complex-momentum formalism. We benchmarked the new framework
against the complex-energy Gamow Shell Model (GSM).
The GCC formalism is expressed in Jacobi coordinates, so
that the center-of-mass motion is automatically eliminated. To solve the
coupled-channel equations, we use hyperspherical harmonics to describe the
angular wave functions while the radial wave functions are expanded in the
Berggren ensemble, which includes bound, scattering and Gamow states.
We show that the GCC method is both accurate and robust. Its
results for energies, decay widths, and nucleon-nucleon angular correlations
are in good agreement with the GSM results.
We have demonstrated that a three-body GSM formalism
explicitly constructed in cluster-orbital shell model coordinates provides
similar results to a GCC framework expressed in Jacobi coordinates, provided
that a large configuration space is employed. Our calculations for
systems and O show that nucleon-nucleon angular correlations are
sensitive to the valence-neutron interaction. The new GCC technique has many
attractive features when applied to bound and unbound states of three-body
systems: it is precise, efficient, and can be extended by introducing a
microscopic model of the core.Comment: 10 pages, 8 figure
Odd-even mass staggering with Skyrme-Hartree-Fock-Bogoliubov theory
We have studied odd-even nuclear mass staggering with the
Skyrme-Hartree-Fock-Bogoliubov theory by employing isoscalar and isovector
contact pairing interactions. By reproducing the empirical odd-even mass
differences of the Sn isotopic chain, the strengths of pairing interactions are
determined. The optimal strengths adjusted in this work can give better
description of odd-even mass differences than that fitted by reproducing the
experimental neutron pairing gap of Sn.Comment: 9 pages, 3 figures, submitted to PRC Brief Repor
Breaking of the overall permutation symmetry in nonlinear optical susceptibilities of one-dimensional periodic dimerized Huckel model
Based on infinite one-dimensional single-electron periodic models of
trans-polyacetylene, we show analytically that the overall permutation symmetry
of nonlinear optical susceptibilities is, albeit preserved in the molecular
systems with only bound states, no longer generally held for the periodic
systems. The overall permutation symmetry breakdown provides a fairly natural
explanation to the widely observed large deviations of Kleinman symmetry for
periodic systems in off-resonant regions. Physical conditions to experimentally
test the overall permutation symmetry break are discussed.Comment: 7 pages, 1 figur
Constraining and Dark Energy with Gamma-Ray Bursts
An relationship with a small
scatter for current -ray burst (GRB) data was recently reported, where
is the beaming-corrected -ray energy and
is the peak energy in the local observer frame. By considering this
relationship for a sample of 12 GRBs with known redshift, peak energy, and
break time of afterglow light curves, we constrain the mass density of the
universe and the nature of dark energy. We find that the mass density
(at the confident level) for a flat
universe with a cosmological constant, and the parameter of an assumed
static dark-energy equation of state ().
Our results are consistent with those from type Ia supernovae. A larger sample
established by the upcoming {\em Swift} satellite is expected to provide
further constraints.Comment: 8 pages including 4 figures, to appear in ApJ Letters, typos
correcte
Quantising Higher-spin String Theories
In this paper, we examine the conditions under which a higher-spin string
theory can be quantised. The quantisability is crucially dependent on the way
in which the matter currents are realised at the classical level. In
particular, we construct classical realisations for the algebra,
which is generated by a primary spin- current in addition to the
energy-momentum tensor, and discuss the quantisation for . From these
examples we see that quantum BRST operators can exist even when there is no
quantum generalisation of the classical algebra. Moreover, we find
that there can be several inequivalent ways of quantising a given classical
theory, leading to different BRST operators with inequivalent cohomologies. We
discuss their relation to certain minimal models. We also consider the
hierarchical embeddings of string theories proposed recently by Berkovits and
Vafa, and show how the already-known strings provide examples of this
phenomenon. Attempts to find higher-spin fermionic generalisations lead us to
examine the whether classical BRST operators for ( odd)
algebras can exist. We find that even though such fermionic algebras close up
to null fields, one cannot build nilpotent BRST operators, at least of the
standard form.Comment: CTP TAMU-24/94, KUL-TF-94/11, SISSA-135/94/E
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