40 research outputs found
Supersymmetric solutions on SU(4)-structure deformed Stenzel space
The Stenzel space fourfold is a non-compact Calabi-Yau which is a higher
dimensional analogue of the deformed conifold. We consider N = (1,1) type IIA,
N = 1 M-theory and N = (2,0) type IIB compactifications on this Stenzel space,
thus examining the gravity side of potentially higher dimensional analogues of
Klebanov-Strassler-like compactifications. We construct families of
SU(4)-structures and solve associated moduli spaces, of complex and symplectic
structures amongst others. By making use of these, we can construct IIA
compactifications on manifolds homeomorphic to the Stenzel space fourfold, but
with complex non-CY SU(4)-structures. Such compactifications are sourced by a
distribution of NS5-branes. The external metric is asymptotically conformal
AdS_3 and should thus be suitable for holography applications.Comment: 55 pages, 2 figures. v3: minor clarifications added, published
versio
3d N=1 effective supergravity and F-theory from M-theory on fourfolds
We consider 3d N=1 M-theory compactifications on Calabi-Yau fourfolds, and
the effective 3d theory of light modes obtained by reduction from eleven
dimensions. We study in detail the mass spectrum at the vacuum and, by
decoupling the massive multiplets, we derive the effective 3d N=1 theory in the
large-volume limit up to quartic fermion terms. We show that in general it is
an ungauged N=1 supergravity of the form expected from 3d supersymmetry. In
particular the massless bosonic fields consist of the volume modulus and the
axions originating from the eleven-dimensional three-form, while the
moduli-space metric is locally isometric to hyperbolic space. We consider the
F-theory interpretation of the 3d N=1 M-theory vacua in the light of the
F-theory effective action approach. We show that these vacua generally have
F-theory duals with circle fluxes, thus breaking 4d Poincar\'e invariance.Comment: 37 pages. Published version, minor change
IIB supergravity on manifolds with SU(4) structure and generalized geometry
We consider N=(2,0) backgrounds of IIB supergravity on eight-manifolds M_8
with strict SU(4) structure. We give the explicit solution to the Killing
spinor equations as a set of algebraic relations between irreducible su(4)
modules of the fluxes and the torsion classes of M_8. One consequence of
supersymmetry is that M_8 must be complex. We show that the conjecture of
arxiv:1010.5789 concerning the correspondence between background supersymmetry
equations in terms of generalized pure spinors and generalized calibrations for
admissible static, magnetic D-branes, does not capture the full set of
supersymmetry equations. We identify the missing constraints and express them
in the form of a single pure-spinor equation which is well defined for generic
SU(4)\times SU(4) backgrounds. This additional equation is given in terms of a
certain analytic continuation of the generalized calibration form for
codimension-2 static, magnetic D-branes.Comment: 23 pages. V2: added references, including to spinorial geometr
Mirror symmetry & supersymmetry on SU(4)-structure backgrounds
We revisit the backgrounds of type IIB on manifolds with -structure
and discuss two sets of solutions arising from internal geometries that are
complex and symplectic respectively. Both can be realized in terms of
generalized complex geometry. We identify a map which relates the complex and
symplectic supersymmetric systems. In the semi-flat torus bundle setting this
map corresponds to T-duality and suggest a way of extending the mirror
transform to non-K\"ahler geometries.Comment: 40 page
IIA supergravity and M-theory on manifolds with SU(4) structure
We give the general form of supersymmetric backgrounds with two real
supercharges of M-theory and type IIA supergravity (with non-zero Romans mass
in general) of the form \mathbb{R}^{1,d} \times \M_8, d=1,2, on
eight-dimensional manifolds with SU(4) structure. We point out a subtlety in
the integrability theorems for low-dimensional supersymmetric
compactifications. As a special case we examine Calabi-Yau flux vacua and we
show that unbroken supersymmetry does not in general require the four-form flux
to be (2,2) or primitive. Our results could be used to construct novel
higher-dimensional analogues of the Klebanov-Strassler geometry. In the case of
M-theory large-volume Calabi-Yau flux vacua our results are in agreement with
partial supersymmetry breaking in three-dimensional N=2 supergravity.
Alternatively, the conditions for supersymmetry can be expressed in terms of a
real `superpotential' in accordance with three-dimensional N=1 supergravity. We
present explicit examples of M-theory flux vacua on K3 \times K3, which however
do not appear to possess F-theory duals with four-dimensional Poincar\'e
invariance.Comment: 41 pages. V2: the K3xK3 examples of section 3.2.2 have been
generalized to manifestly admit a large-volume limit. Published versio
Generalized complex geometry of pure backgrounds in ten and eleven dimensions
Pure backgrounds are a natural generalization of supersymmetric Calabi-Yau
compactifications in the presence of flux. They are described in the language
of generalized SU(d) x SU(d) structures and generalized complex geometry, and
they exhibit some interesting general patterns: the internal manifold is
generalized Calabi-Yau, while the Ramond-Ramond flux is exact in a precise
sense discussed in this paper. We have shown that although these two
characteristics do persist in the case of generic ten-dimensional Euclidean
type II pure backgrounds, they do not capture the full content of
supersymmetry. We also discuss the uplift of real Euclidean type IIA pure
backgrounds to supersymmetric backgrounds of Lorentzian eleven-dimensional
supergravity.Comment: 26 pages. Typos fixed, references adde
Application of ultrasound to monitor in vivo residual bone movement within transtibial prosthetic sockets
Transtibial prosthetic users do often struggle to achieve an optimal prosthetic fit, leading to residual limb pain and stump-socket instability. Prosthetists face challenges in objectively assessing the impact of prosthetic adjustments on residual limb loading. Understanding the mechanical behaviour of the pseudo-joint formed by the residual bone and prosthesis may facilitate prosthetic adjustments and achieving optimal fit. This study aimed to assess the feasibility of using B-mode ultrasound to monitor in vivo residual bone movement within a transtibial prosthetic socket during different stepping tasks. Five transtibial prosthesis users participated, and ultrasound images were captured using a Samsung HM70A system during five dynamic conditions. Bone movement relative to the socket was quantified by tracking the bone contour using Adobe After-Effect. During the study a methodological adjustment was made to improve data quality, and the first two participants were excluded from analysis. The remaining three participants exhibited consistent range of motion, with a signal to noise ratio ranging from 1.12 to 2.59. Medial–lateral and anterior–posterior absolute range of motion varied between 0.03 to 0.88 cm and 0.14 to 0.87 cm, respectively. This study demonstrated that it is feasible to use B-mode ultrasound to monitor in vivo residual bone movement inside an intact prosthetic socket during stepping tasks