257 research outputs found
Restrictions on infinite sequences of type IIB vacua
Ashok and Douglas have shown that infinite sequences of type IIB flux vacua
with imaginary self-dual flux can only occur in so-called D-limits,
corresponding to singular points in complex structure moduli space. In this
work we refine this no-go result by demonstrating that there are no infinite
sequences accumulating to the large complex structure point of a certain class
of one-parameter Calabi-Yau manifolds. We perform a similar analysis for
conifold points and for the decoupling limit, obtaining identical results.
Furthermore, we establish the absence of infinite sequences in a D-limit
corresponding to the large complex structure limit of a two-parameter
Calabi-Yau. In particular, our results demonstrate analytically that the series
of vacua recently discovered by Ahlqvist et al., seemingly accumulating to the
large complex structure point, are finite. We perform a numerical study of
these series close to the large complex structure point using appropriate
approximations for the period functions. This analysis reveals that the series
bounce out from the large complex structure point, and that the flux eventually
ceases to be imaginary self-dual. Finally, we study D-limits for F-theory
compactifications on K3\times K3 for which the finiteness of supersymmetric
vacua is already established. We do find infinite sequences of flux vacua which
are, however, identified by automorphisms of K3.Comment: 35 pages. v2. Typos corrected, ref. added. Matches published versio
PALP - a User Manual
This article provides a complete user's guide to version 2.1 of the toric
geometry package PALP by Maximilian Kreuzer and others. In particular,
previously undocumented applications such as the program nef.x are discussed in
detail. New features of PALP 2.1 include an extension of the program mori.x
which can now compute Mori cones and intersection rings of arbitrary dimension
and can also take specific triangulations of reflexive polytopes as input.
Furthermore, the program nef.x is enhanced by an option that allows the user to
enter reflexive Gorenstein cones as input. The present documentation is
complemented by a Wiki which is available online.Comment: 71 pages, to appear in "Strings, Gauge Fields, and the Geometry
Behind - The Legacy of Maximilian Kreuzer". PALP Wiki available at
http://palp.itp.tuwien.ac.at/wiki/index.php/Main_Pag
Bag Formation in Quantum Hall Ferromagnets
Charged skyrmions or spin-textures in the quantum Hall ferromagnet at filling
factor nu=1 are reinvestigated using the Hartree-Fock method in the lowest
Landau level approximation. It is shown that the single Slater determinant with
the minimum energy in the unit charge sector is always of the hedgehog form. It
is observed that the magnetization vector's length deviates locally from unity,
i.e. a bag is formed which accommodates the excess charge. In terms of a
gradient expansion for extended spin-textures a novel O(3) type of effective
action is presented, which takes bag formation into account.Comment: 13 pages, 3 figure
The Casimir energy of skyrmions in the 2+1-dimensional O(3)-model
One-loop quantum corrections to the classical vortices in 2+1 dimensional
O(3)-models are evaluated. Skyrme and Zeeman potential terms are used to
stabilize the size of topological solitons. Contributions from zero modes,
bound-states and scattering phase-shifts are calculated for vortices with
winding index n=1 and n=2. For both cases the S-matrix shows a pronounced
series of resonances for magnon-vortex scattering in analogy to the
well-established baryon resonances in hadron physics, while vortices with n>2
are already classically unstable against decay. The quantum corrections
destabilize the classically bound n=2 configuration. Approximate independence
of the results with respect to changes in the renormalization scale is
demonstrated.Comment: 24 pages LaTeX, 14 figure
Hot Nucleons in Chiral Soliton Models
Chiral lagrangians as effective field theories of QCD are most suitable for
the study of nucleons in a hot pion gas because they contain pions and also
baryons as solitons of the same action. The semiclassical treatment of the
soliton solutions must be augmented by pionic fluctuations which requires
renormalisation to 1-loop, and finite temperatures do not introduce new
ultraviolet divergencies and may easily be considered. Alternatively, a
renormalisation scheme based on the renormalisation group equation at finite
temperature comprises and extends the rigorous results of chiral perturbation
theory and renders the low energy constants temperature-dependent which allows
the construction of temperature-dependent solitons below the critical
temperature. The temperature-dependence of the baryon energy and the
pion-nucleon coupling is studied. There is no simple scaling law for the
temperature-dependence of these quantities.Comment: 17 pages (RevTeX), 5 figure
A possible explanation why the Theta+ is seen in some experiments and not in others
To understand the whole set of positive and null data on the
Theta+(1530)-production, we suggest the hypothesis that multiquark hadrons are
mainly generated from many-quark states, which emerge either as short-term
hadron fluctuations, or as hadron remnants in hard processes. This approach
allows us to describe both non-observation of the Theta+ in current null
experiments and peculiar features of its production in positive experiments.
Further, we are able to propose new experiments that might be decisive for the
problem of the Theta+ existence. Distributions of the Theta+ in such
experiments can give important information both on higher Fock components of
conventional hadrons and about structure and hadronization properties of hadron
remnants produced in hard processes. We also explain that description of
multiquark hadrons may require a modified form of the constituent quark model,
with quark masses and couplings being intermediate between their values for the
familiar constituent quarks and the current ones.Comment: 18 pages. Some changes in the text; experimental suggestions
collected in a special subsection, references added and refreshe
Strangeness, charm and bottom in a chiral quark-meson model
In this paper we investigate an SU(3) extension of the chiral quark-meson
model. The spectra of baryons with strangeness, charm and bottom are considered
within a "rigid oscillator" version of this model. The similarity between the
quark part of the Lagrangian in the model and the Wess-Zumino term in the
Skyrme model is noted. The binding energies of baryonic systems with baryon
number B=2 and 3 possessing strangeness or heavy flavor are estimated. The
results obtained are in good qualitative agreement with those obtained
previously in the topological soliton (Skyrme) model.Comment: 12 pages, no figures. Journal ref: submitted to Nucl.Phys.
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