92 research outputs found
A model realisation of the Jaffe-Wilczek correlation for pentaquarks
We discuss a realisation of the pentaquark structure proposed by Jaffe and
Wilczek within a simple quark model with colour-spin contact interactions and
coloured harmonic confinement, which accurately describes the
splitting. In this model spatially compact diquarks are formed in the
pentaquark but no such compact object exists in the nucleon. The colour-spin
attraction brings the Jaffe-Wilczek-like state down to a low mass, compatible
with the experimental observation and below that of the naive ground state with
all -waves. We find, however, that although these trends are maintained, the
extreme effects observed do not survive the required ``smearing'' of the delta
function contact interaction. We also demonstrate the weakness of the
``schematic'' approximation when applied to a system containing a -wave. An
estimate of the anti-charmed pentaquark mass is made which is in line with the
Jaffe-Wilczek prediction and significantly less than the value reported by the
H1 collaboration.Comment: 10 pages, uses psfra
Supersymmetric AdS(4) compactifications of IIA supergravity
We derive necessary and sufficient conditions for N=1 compactifications of
(massive) IIA supergravity to AdS(4) in the language of SU(3) structures. We
find new solutions characterized by constant dilaton and nonzero fluxes for all
form fields. All fluxes are given in terms of the geometrical data of the
internal compact space. The latter is constrained to belong to a special class
of half-flat manifolds.Comment: 24 pages, references adde
Type IIB Flows with N=1 Supersymmetry
We write general and explicit equations which solve the supersymmetry
transformations with two arbitrary complex-proportional Weyl spinors on
supersymmetric type IIB strings backgrounds with all R-R ,
, and NS-NS fluxes turned on using SU(3) structures. The
equations are generalizations of the ones found for specific relations between
the two spinors by Grana, Minasian, Petrini and Tomasiello in [1] and by Butti,
Grana, Minasian, Petrini and Zaffaroni in [2]. The general equations allow to
study systematically generic type IIB backgrounds with
supersymmetry. We then explore some specific classes of flows with constant
axion, flows with constant dilaton, flows on conformally Calabi-Yau
backgrounds, flows with imaginary self-dual 3-form flux, flows with constant
ratio of the two spinors, the corresponding equations are written down and some
of their features and relations are discussed.Comment: 28 page
New G2 holonomy metrics, D6 branes with inherent U(1)xU(1) isometry and gamma-deformations
It is found the most general local form of the 11-dimensional supergravity
backgrounds which, by reduction along one isometry, give rise to IIA
supergravity solutions with a RR field and a non trivial dilaton, and for which
the condition holds. This condition is stronger than the usual
condition , required by supersymmetry. It is shown that these
D6 wrapped backgrounds arise from the direct sum of the flat Minkowski metric
with certain G2 holonomy metrics admitting an U(1) action, with a local form
found by Apostolov and Salamon. Indeed, the strong supersymmetry condition is
equivalent to the statement that there is a new isometry on the G2 manifold,
which commutes with the old one; therefore these metrics are inherently toric.
An example that is asymptotically Calabi-Yau is presented. There are found
another G2 metrics which give rise to half-flat SU(3) structures. All this
examples possess an U(1)x U(1)x U(1) isometry subgroup. Supergravity solutions
without fluxes corresponding to these G2 metrics are constructed. The presence
of a subgroup of isometries permits to apply the \gamma-deformation
technique in order to generate new supergravity solutions with fluxes.Comment: 29 pages, no figures. References added and corrected. The discussion
is minimaly changed and a subtle notational problem was correcte
The Geometry of D=11 Killing Spinors
We propose a way to classify all supersymmetric configurations of D=11
supergravity using the G-structures defined by the Killing spinors. We show
that the most general bosonic geometries admitting a Killing spinor have at
least a local SU(5) or an (Spin(7)\ltimes R^8)x R structure, depending on
whether the Killing vector constructed from the Killing spinor is timelike or
null, respectively. In the former case we determine what kind of local SU(5)
structure is present and show that almost all of the form of the geometry is
determined by the structure. We also deduce what further conditions must be
imposed in order that the equations of motion are satisfied. We illustrate the
formalism with some known solutions and also present some new solutions
including a rotating generalisation of the resolved membrane solutions and
generalisations of the recently constructed D=11 Godel solution.Comment: 36 pages. Typos corrected and discussion on G-structures improved.
Final version to appear in JHE
AdS Vacua, Attractor Mechanism and Generalized Geometries
We consider flux vacua attractor equations in type IIA string theory
compactified on generalized geometries with orientifold projections. The
four-dimensional N=1 superpotential in this compactification can be written as
the sum of the Ramond-Ramond superpotential and a term described by
(non)geometric flux charges. We exhibit a simple model in which supersymmetric
AdS and Minkowski solutions are classified by means of discriminants of the two
superpotentials. We further study various configurations without Ramond-Ramond
flux charges. In this case we find supersymmetric AdS vacua both in the case of
compactifications on generalized geometries with SU(3) x SU(3) structures and
on manifolds with an SU(3)-structure without nongeometric flux charges. In the
latter case, we have to introduce correction terms into the prepotential in
order to realize consistent vacua.Comment: 35 pages, accepted version in JHE
Scherk-Schwarz reduction of M-theory on G2-manifolds with fluxes
We analyse the 4-dimensional effective supergravity theories obtained from
the Scherk--Schwarz reduction of M-theory on twisted 7-tori in the presence of
4-form fluxes. We implement the appropriate orbifold projection that preserves
a G2-structure on the internal 7-manifold and truncates the effective field
theory to an N=1, D=4 supergravity. We provide a detailed account of the
effective supergravity with explicit expressions for the Kaehler potential and
the superpotential in terms of the fluxes and of the geometrical data of the
internal manifold. Subsequently, we explore the landscape of vacua of M-theory
compactifications on twisted tori, where we emphasize the role of geometric
fluxes and discuss the validity of the bottom-up approach. Finally, by reducing
along isometries of the internal 7-manifold, we obtain superpotentials for the
corresponding type IIA backgrounds.Comment: 43 pages, Latex; v3 typos corrected, one reference added, JHEP
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